design and assessment of informative auditory warning signals for adas

DESIGN AND ASSESSMENT OF INFORMATIVE AUDITORY WARNING SIGNALS FOR ADAS

PHILIPP JORDAN STUDENT ID: 2168364 CAND.DIPL.-ING. MECHANICAL ENGINEERING

TUTOR: FREDERIK DIEDERICHS

University of Stuttgart Fraunhofer Institute for Industrial Engineering

Abstract The design of acoustic in-vehicle warning signals for advanced driver assistance systems remains a challenging task: Although methods how to manipulate perceived criticality and urgency have been investigated, there is still no clear guideline how to best convey information about the type of hazard without sacrificing user acceptance. Although representational sounds (also known as auditory icons) have been shown to increase response speed and accuracy there is a risk that drivers do not accept such generated sounds in a car environment. On the other hand, abstract sounds (such as earcons) are usually better accepted but difficult to learn or to distinguish. The present study is based on the idea to fuse abstract and representational sounds into one single warning signal with the aim to increase comprehensibility while maintaining user acceptance. A range of hybrid sound signals (from now on defined as hybricons) have been created that comprise an abstract component to code the urgency of the warning event (cautionary, imminent) and a natural sound component to indicate the type of hazard (vehicle, bicycle, pedestrian). 26 subjects took part in a study to compare nine hybricons against their five abstract equivalents in terms of comprehensibility, perceived urgency and discomfort. In order to provide the appropriate driving context a video clip has been prepared that shows a car (from the driver’s perspective) climbing a hill. Just before reaching the top of the hill the acoustic warning signal is activated and the video freezes. Immediately thereafter, the subjects were asked to assess the warning sound and the situation. Based on this method the following results were obtained: • All hybricons conveyed more information about the type of hazard (compared to their abstract components). • The perceived urgency of the hybricons can be manipulated by modifying the abstract sound component. Also the natural component itself can increase perceived urgency. • The hybricons used in this study were not perceived as less comfortable than their abstract components.

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Although the size of the effects is dependent on the type of auditory icon and the design of the abstract warning component, the obtained results generally confirm the potential of hybricons as auspicious warnings for in-vehicle ADAS and therefore should be researched and evaluated furthermore.

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Declaration of Authorship I certify that the work presented here is, to the best of my knowledge and belief, original and the result of my own investigations. I ensure to have used no other resources than quoted. Erklärung Ich bestätige hiermit, dass die hier präsentierte Arbeit eine Urschrift und das Resultat meiner eigenen Untersuchungen und Recherchen ist und versichere zudem, dass ich keine anderen als die angegebenen Hilfsmittel zur Erstellung dieser Arbeit verwendet habe.

Signature

______________________________

Student´s name

Philipp Jordan

Student ID

2168364

Date

______________________________

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Contents

Abstract ............................................................................................................. 2 List of Abbreviations ............................................................................................ 8 List of Figures...................................................................................................... 9 List of Tables ..................................................................................................... 11 Part I: Introduction to auditory warnings / Literature review 1 Introduction to SAFESPOT and ADAS ....................................................... 12 1.1 SAFESPOT ............................................................................................. 12 1.2 ADAS ...................................................................................................... 14 1.3 Warning concept ..................................................................................... 16 2 In-vehicle acoustic warnings – Literature analysis ................................... 17 2.1 Sound as warning modality for ADAS ..................................................... 17 2.1.1 Advantages .................................................................................... 18 2.1.2 Disadvantages ............................................................................... 19 2.1.3 Comparison and relation to the visual modality ............................. 20 2.2 Classification of auditory warnings .......................................................... 23 2.2.1 Type of the warning ....................................................................... 23 2.2.2 Urgency of the warning .................................................................. 24 2.2.3 Place of application........................................................................ 24 2.2.4 Auditory Icons ................................................................................ 26 2.2.5 Earcons ......................................................................................... 30 2.2.6 Speech warnings ........................................................................... 33 2.3 Human factors in auditory warnings ........................................................ 34 2.4 Multimodal displays ................................................................................. 35 2.5 Resume .................................................................................................. 36 3 Hybricons: A new type of emergency warning.......................................... 37 3.1 Sound as a medium ................................................................................ 37 3.2 Requirements.......................................................................................... 41 3.3 Hybricons ................................................................................................ 43

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Contents

Part II: The study 4 Experiment.................................................................................................... 47 4.1 Scope ...................................................................................................... 47 4.2 Hypothesis .............................................................................................. 49 4.3 Experimental design ............................................................................... 50 4.3.1 Scenario ........................................................................................ 50 4.3.2 Loudness of the sounds................................................................. 52 4.3.3 Interactive questionnaire................................................................ 53 4.3.4 Questions ...................................................................................... 56 4.4 Participants ............................................................................................. 58 5 Results .......................................................................................................... 59 5.1 Descriptive statistics ............................................................................... 60 5.1.1 Comprehensibility .......................................................................... 62 5.1.2 Urgency ......................................................................................... 65 5.1.3 Agreement ..................................................................................... 71 5.2 Interference statistics .............................................................................. 72 5.2.1 Comprehensibility .......................................................................... 72 5.2.2 Urgency ......................................................................................... 73 6 Discussion and conclusions ....................................................................... 77 6.1 Comprehensibility ................................................................................... 77 6.2 Urgency .................................................................................................. 80 6.3 Agreement .............................................................................................. 85 6.4 General conclusions ............................................................................... 86 6.5 Specific suggestions for the warning concept ......................................... 87 6.5.1 Suggestions for the hybricons without a redesign ......................... 87 6.5.2 Suggestions for the hybricons in the case of a redesign................ 88 6.6 Suggestions for further research ............................................................. 91 Bibliography ...................................................................................................... 93 Appendix A - Technical sound description ........................................................ 97

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Contents

Appendix B – Interactive questionnaire ........................................................... 106 Appendix C – Obtained data ........................................................................... 115 Appendix D – Quantitative analysis................................................................. 126

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List of Abbreviations Table 1: List of Abbreviations.

ADAS

Advanced Driver Assistance System

BRT

Brake Reaction Time

CAS

Collision Avoidance System

DB

Decibel

DBFS

Decibel full scale

DIN

Deutsches Institut für Normung – German Institute for Standardisation

ESC

Electronic Stability Control

FRAPS

Frames per second

HCI

Human Computer Interaction

HMI

Human Machine Interface

HZ

Hertz

ITS

Intelligent Transportation Systems

MB

Megabyte

PASW

Predictive Analytics SoftWare

R&D

Research and Development

RMS

Root Mean Square

TTC

Time to Collision

USDOT United States Department of Transportation V2I

Vehicle to Infrastructure

V2V

Vehicle to Vehicle

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List of Figures Figure 1: Autonomous intelligent .......................................................................... 13 Figure 2: SAFESPOT cooperative system ........................................................... 13 Figure 3: Four sine waveforms. ............................................................................ 38 Figure 4: Resulting complex wave form. .............................................................. 38 Figure 5: Normal equal-loudness-level contours. ................................................. 40 Figure 6: Video sequence with timestamps. ......................................................... 51 Figure 7: Typical page of the interactive questionnaire. ....................................... 55 Figure 8: Comprehensibility of the hybricons (Q1). .............................................. 62 Figure 9: Answer reliability for Q1 (Q2). ............................................................... 64 Figure 10: Mean distance of the expected road user (Q3). .................................. 65 Figure 11: Weighted mean distance of the expected road user (Q3*Q4). ............ 67 Figure 12: Urgency of the signal (Q5). ................................................................. 68 Figure 13: Reaction after hearing the signal (Q6)................................................. 69 Figure 14: Agreement to the signal (Q7). ............................................................. 71 Figure 15: Comprehensibility of the hybricons (Q1). ............................................ 78 Figure 16: Mean distance of the expected road user (Q3). .................................. 80 Figure 17: Weighted mean distance of the expected road user (Q3*Q4). ............ 81 Figure 18: Urgency of the signal (Q5). ................................................................. 82 Figure 19: Reaction after hearing the signal (Q6)................................................. 83 Figure 20: Agreement to the signal (Q7). ............................................................. 85 Figure 21: Sonar ping. .......................................................................................... 99 Figure 22: New message...................................................................................... 99 Figure 23: Two pulses. ....................................................................................... 100 Figure 24: Two pulses + Car horn. ..................................................................... 100 Figure 25: Two pulses + Bicycle bell. ................................................................. 101 Figure 26: Two pulses + Footsteps. ................................................................... 101 Figure 27: Two dissonant pulses. ....................................................................... 102

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Figure 28: Two dissonant pulses + Car horn. ..................................................... 102 Figure 29: Two dissonant pulses + Bicycle bell. ................................................. 103 Figure 30: Two dissonant pulses + Footsteps. ................................................... 103 Figure 31: Three pulses. .................................................................................... 104 Figure 32: Three pulses + Skidding tires. ........................................................... 104 Figure 33: Three pulses + Bicycle bell................................................................ 105 Figure 34: Three pulses + Footsteps. ................................................................. 105 Figure 35: Interactive questionnaire page 1. ...................................................... 106 Figure 36: Interactive questionnaire page 2. ...................................................... 107 Figure 37: Interactive questionnaire page 3. ...................................................... 108 Figure 38: Interactive questionnaire page 4. ...................................................... 109 Figure 39: Interactive questionnaire page 5. ...................................................... 110 Figure 40: Interactive questionnaire page 6. ...................................................... 111 Figure 41: Interactive questionnaire page 7. ...................................................... 112 Figure 42: Interactive questionnaire page 8. ...................................................... 113 Figure 43: Interactive questionnaire page 8. ...................................................... 114

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List of Tables Table 1: List of Abbreviations. ................................................................................ 8 Table 2: Relative advantages of the alarm display media. ................................... 21 Table 3: When to use auditory or visual presentation. .......................................... 22 Table 4: Three level urgency-response correlations for sound signals. ................ 24 Table 5: Set of auditory icons for an individual traffic participant. ......................... 44 Table 6: Set of earcons and their intended state of urgency. ............................... 44 Table 7: Selection of hybricons regarding the evaluation. .................................... 45 Table 8: Hypothesis. ............................................................................................. 49 Table 9: Loudness adjustment. ............................................................................ 52 Table 10: Structure of the questionnaire. ............................................................. 53 Table 11: Complete list of evaluated signals. ....................................................... 61 Table 12: Colour coding for the assessment of question 6. .................................. 69 Table 13: Chi2 results for question 1. ................................................................... 72 Table 14: Paired t-test results for question 3. ....................................................... 73 Table 15: Paired t-test results within the abstract signals for question 5. ............. 75 Table 16: Suggested solutions for comprehensibility improvement. ..................... 88 Table 17: Suggested solutions for urgency improvement. .................................... 90 Table 18: Selected parameters of the evaluated sounds. .................................... 97 Table 19: Subject´s personal data. ..................................................................... 115 Table 20: Scenario-Signal-Relationship. ............................................................ 116 Table 21: Scenario sequences for each subject. ................................................ 117 Table 22: Results for question 1. ........................................................................ 118 Table 23: Results for question 2 and question 3. ............................................... 120 Table 24: Results for question 4 and question 5. ............................................... 122 Table 25: Results for question 6 and question 7. ............................................... 124 Table 26: Chi2 frequencies and residuals for question 1. ................................... 126 Table 27: Chi2 results for question 1. ................................................................. 128

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1 Introduction to SAFESPOT and ADAS

1 Introduction to SAFESPOT and ADAS 1.1 SAFESPOT {This introduction mainly represents the content found on the official SAFESPOT website in August 2009 (SAFESPOT, 2009) and has been adopted for this thesis.} The growing mobility of people and goods has a very high societal cost in terms of traffic congestion, fatalities and injured people every year. In the past decade a lot of research has been dedicated to solve these problems by the development of advanced driver assistance systems (ADAS) based on autonomous sensor technologies that are able to perceive the traffic situation surrounding the vehicle and, in case of danger, to properly warn the driver. Telematic technologies are now entering on vehicles as information and support systems supported by the growing consumer market do, which offer in consequence systems and services with a high reliability at low cost. The vision of the cooperative approach is born in a view of joining the advantages of the telematic technologies and of their diffusion on the market to enable the development of reliable and extended driving support systems for road safety. The cooperative approach envisages a scenario in which the vehicles and the infrastructure cooperate to perceive potential dangerous situations extended in space and time horizon, that will only be limited by the range of the radio communications. The safety "added value" of SAFESPOT (SAFESPOT, 2009) is to look for the "combination" of the information from vehicles and from the infrastructure. The focus is on R&D activities for the identification of cooperative solutions that will firstly be applied to the critical areas, such as the so called "black spots". SAFESPOT is working to design cooperative systems for road safety based on vehicle to vehicle (V2V) and vehicle to infrastructure (V2I) communication. The primary goal of SAFESPOT is to develop a SAFETY MARGIN ASSISSTANT, which will be able to detect in advance potentially dangerous situations and extend drivers´ awareness of the surrounding environment in space and time.

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This assistant system aims to bridge the gap from today´s autonomous intelligent vehicles (Figure 1) to cooperative systems (Figure 2), providing and assessing information from every road user to every road user.

Figure 1: Autonomous intelligent vehicle (SAFESPOT, 2009).

Figure 2: SAFESPOT cooperative system (SAFESPOT, 2009).

The SAFESPOT co-operative system will be composed by the following communicating elements: • Intelligent vehicles equipped with on board co-operative systems. • Intelligent infrastructure including road side units. • Safety centre(s) and/or Traffic centre(s) which are able to centralize or forward safety information coming from the intelligent vehicle and/or the intelligent infrastructure.

SAFESPOT aims to: • Use the infrastructure and the vehicles as sources and destinations of safety-related information and develop an open, flexible and modular architecture and communication platform. • Develop the key enabling technologies: ad-hoc dynamic network, accurate relative localization, dynamic local traffic maps. • Develop and test scenario-based applications to evaluate the impacts on road safety. • Define a sustainable deployment strategy for cooperative systems for road safety, evaluating also related liability, regulations and standardization aspects.

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1.2 ADAS Advanced Driver Assistance Systems (ADAS) for autonomous driven vehicles like cars, trucks and motorcycles can be classified with reference to intervention in car control into three different groups (Rempis, 2004, p. 9): • Informative, advisory and warning ADAS • Partial controlled ADAS • Total controlled ADAS Primary tasks of informative and warning ADAS are to assist the driver with carand driving-related safety information. Their intention is to support the driver with information, e.g. to light a fuel indicator lamp in the cockpit when the estimated range of the car is below a certain value, to guide the driver, e.g. to avoid a traffic jam while providing an alternative route and to warn the driver in terms of personal safety, e.g. playing a constant signal while driving without a fastened seatbelt. In contrast, partly or total controlled ADAS do not intervene in the driver´s car control. Especially the warning based ADAS must have an efficient and effective HMI design, e.g. to transport the content of the warning clear and comprehensible, fast and accurate and last but not least considering human factors, like user acceptance and annoyance. In contrast, partial controlled ADAS usually intervene into the driver´s car control in particular situations. Listening and overseeing the current driving situation continuously is the concept behind these systems. If a defined limit or condition is exceeded or achieved, they react and therefore intervene into the driver´s manual driving control. Popular examples are the Electronic Stability Control ADAS or the anti-brake system. According to Rempis (2004) the driver is normally able to interrupt these systems, e.g. with a manual steering control manoeuvre or accelerator pedal releasement. Even when these automatic systems take over control in certain situations, the driver is still fully responsible for driving.

Total controlled ADAS are systems with the highest degree in automated car control, able to intervene in the complete driving and steering process. At the moment, these systems are in development stage. Legal issues, like identifying 14


the responsible causer of an accident with a fully controlled car involved have to be clarified before these systems can be released to the market. Nevertheless, these systems have already been applied in enclosed systems, like train test tracks for example. In this context, the previously introduced SAFESPOT MARGIN ASSISTANT is an informative, advisory and warning ADAS. It does not in intervene into the driver´s car control. The driver is fully responsible for driving, braking and steering his car. But of course, this assistant system aims to improve road security through supporting the driver with intelligent, time-dependent warnings. These warnings will make use of the human´s visual and auditory modalities. As part of the SAFESPOT ADAS the visual warning system has already been developed, assembled and evaluated (Bosler, 2008). As part of the SAFESPOT ADAS, the basic approaches for the auditory warning system have already been made: A set of specific sound signals developed by a professional sound design lab have been generated. Evaluation of these signals and in consequence, the whole warning concept is objective of this thesis.

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1.3 Warning concept For the SAFESPOT in-vehicle ADAS a warning concept has been outlined: Depending on the possible positions of a certain hazard (vehicles and vulnerable road participants) a driver may encounter or the remaining TTC 1 in very imminent situations, it defines loosely three different levels of conveying urgency via the auditory channel. Through the early stage of development, no exact values or borders between these three conditions are defined at the moment. Urgency state 1: comfort warning signal / informative signal Main characteristic of this urgency state is that no time critical reaction or immediate driver response will be necessary: The auditory signal´s intention is to inform the driver that a certain condition has changed and aims to attract his attention to an in-vehicle visual display providing further information. This state will represent the informative character of the system. Urgency state 2: safety / advisory warning signal Main characteristic of this urgency state is that the driver has to react in a certain time window, meaning that a time critical, well thought out reaction from a certain range of approximately 4-10 seconds will be necessary to avoid a potential hazard. This state will represent the advisory character of the system. Urgency state 3: critical / imminent warning signal Main characteristic of this urgency state is that the driver will have a maximum of four seconds TTC (van der Horst et al., 2006; Graham, 1999, p. 1237) to avoid an instantaneous crash after the CAS warning is displayed. The auditory signal´s aims to alert the driver and provoke an instant and intuitive reaction which will be necessary to avoid the danger. This state will represent the warning character of the system at highest priority.

1

According to Hayward (1973) Time to collision (TTC) is defined as the time required for two

vehicles to collide if they continue at their present speed and on the same path.

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2 In-vehicle acoustic warnings – Literature analysis

2 In-vehicle acoustic warnings – Literature analysis The following chapter summarizes the results of a literature study focused on auditory emergency warnings. The general potential of sound as a warning modality for in-vehicle ADAS is explained. Important classes of auditory warnings are introduced and reviewed in detail. Advantages and disadvantages within the different types of acoustic signals are presented and discussed. These include comparisons to the other human sense modalities like the visual modality which found to be the most important modality for an in-vehicle ADAS.

2.1 Sound as warning modality for ADAS Driving a car consists of a number of complex tasks, e.g. steering, monitoring speed and changing gears. Driving can be truly described as a continuously multitasking thread for the driver. Most of the information is consumed and processed via the visual channel. These competitive tasks are struggling for the driver´s limited resources. The auditory channel on the other side is only fractionally stressed and probably most used for infotainment 2 purposes, e.g. listening to the radio or playing a signal if the seatbelt is not fastened. But sound can be used for more, than entertaining the driver; in particular for active, intelligent warning sounds. Belz et al. (1999) states to the general potential of sound for in-vehicle warnings in context to the visual channel:"Driving is a visually intensive manual control tracking task, and the vast majority of in-vehicle displays are visual. As intelligent transportation systems (ITSs) are introduced, the number of in-vehicle displays will probably increase, each competing for the driver’s limited resources. Even in wellconceived integrated systems, an overload of the visual modality can easily occur. To avoid visual overload, the use of other sensory modalities must be investigated

2

In the context of in-vehicle ADAS, the term infotainment describes complex car HMI-Systems

which include e.g. the capability to automatically capture and replay a huge variety of music, as well as provide information services, such as help in finding an open parking place in the city.

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as a means of conveying critical information, and the most promising and robust of these modalities is audition." (Belz et al., 1999, p. 1) The USDOT (2004) suggests to “use the auditory modality for presenting high priority alerts and warnings; present additional contextual information visually." (USDOT, 2004, p. 6-2) Fagerlönn (2007) identifies improvement potential for auditory warnings in terms of conveying more information than only a simple alert: "A clear trend for auditory warning signals in is that they become more and more informative. Their intention is not only to alert, but also to inform users about the nature of a critical incident." (Fagerlönn, 2007, p. 1)

2.1.1 Advantages Auditory warnings or acoustic displays offer a lot of unique advantages in relation to the other human sense modalities, e.g. the visual channel, and are therefore in general suitable as CAS warnings. For example, Sanders et al. (1987) recommends that the auditory medium is preferable to the visual one when • the origin of the signal is itself a sound, • the message is simple, • the message will not be referred to later, • the message refers to events in time, • the message calls for immediate action, • continuously changing information of the same type is presented, • the visual system is overburdened, • the speech channels are fully employed, • illumination limits vision, • and the receiver moves from one play to another.

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In consequence, they are often used in emergency situations because they are omnidirectional in nature and can reach further distances than can visual warnings (Stevens et al., 2006, p. 14). An ambulance siren for example, is able to alert a driver even when the ambulance car itself is not in the driver´s field of view. Stanton (1999) confirms this profit: “An unquestionable benefit of auditory warning and display systems is that they present a means of unburdening the visual channel.” (Stanton, 1999, p. 5) Furthermore auditory displays offer an omnidirectional way of communication with the operator, resulting in successful information transfer, even when the operator is in charge with other tasks (DIN 2009a, 2009, p. 8). Especially in situations, where people are confronted with a high visual and cognitive load, auditory warnings can be very useful information carriers.

2.1.2 Disadvantages A lot of disadvantages associated with the usage of sound for emergency warnings are directly related to their design characteristics and perceived loudness. It is probably the most common and easiest way to increase the loudness of an emergency signal to deliver a higher level of urgency to the person receiving the warning. But this can obviously cause problems, like panic reactions (DIN 2000, 2000, p.1) or noise annoyance, especially when added to existing noise

causes

or

when

there

is

a

high

incidence

of

false

alarms

(Wogaltera et al., 2002, p. 224). Also the spectrum of available sounds and displays is infinite. Consequently, their number must be limited to a minimum to ensure as little as possible in interpretation efforts a user has to invest (DIN 2009a, 2009, p. 22). Additionally a high amount of acoustic warning sounds can also result in operator confusion. For cases in which too many auditory signals in are in use, the Standards (DIN 2009a, 2009, p. 21) recommend the application of speech warnings. Finally of course, the amount of appropriate and well-known signals is strongly related to the individual subject´s experience and education.

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2.1.3 Comparison and relation to the visual modality When driving car, the most important sense modality is the visual channel: Driving, steering, shifting gears, observing the mirrors, paying attention to other road users and to traffic signs and lights cause a high visual workload a driver has to process. In the context of an auditory based ADAS, it makes sense to compare the auditory channel directly to the visual channel. Directly compared to visual displays, Stanton et al. (1999, p. 6) states that in general, auditory displays require little directional search and responses tend to be faster than to visual displays. In addition, urgency mapping and prioritization are relatively easy to incorporate because they are not affected by visual noise. They are flexible in terms of user mobility and they tend to be most suited to signalling time-dependent information. Wogaltera (2002) adds that “auditory warnings offer advantages over visual warnings in certain situations and environments because of their generally omnidirectional nature and ability to attract attention." (Wogaltera et al., 2002, p. 223) In the context of CAS, according to Stanton et al. (1999), the missing blocking ability of the human´s ears compared to his eyes (by blinking or simple closing the lids) is another useful advantage: “...because we cannot "shut our ears" in the same way that we can our eyes, our hearing tends to act as a natural warning sense. It is no surprise, then, that auditory displays and alarms are commonplace.” (Stanton et al., 1999, p. 6) Graham (1999) also stresses the independence between the visual and auditory channel mentioning “that sound is both `eyes-free and `hands-free. Those warnings can be perceived while the listener is giving full attention to other visualspatial tasks." (Graham, 1999, p. 1233) Fagerlönn (2007) summarizes this advantages and classifies sound as a widelyused, appropriate information carrier for warnings and alerts in various contexts and environments

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The German Institute for Standardization (DIN 2000, 2000) also offers some useful information for the application of auditory warnings; the usage of sound as indirect signal or reference to other information channels like the visual one and attention attracting abilities in non-time critical situations is quoted (DIN 2000, 2000, p. 1). Furthermore, auditory displays must be used, when the operator is visually complete busy, when the information requires an immediate reaction or when die message is simple and short (DIN 2009a, 2009, p. 21). Moreover they are very effective for transmitting information to an operator (e.g. a driver), which require immediate replies, for simple information like indicating two different states (e.g. on/off) and for chronological events (e.g. the start/end of a certain process). Furthermore they can be used for information when a system is in change. Table 2 summarizes a lot of these findings. Table 2: Relative advantages of the alarm display media (Stanton et al., 1999, p. 6).

Auditory display

Visual display

Reception

Requires no directional search

Requires attention and selection

Speed

Fastest

Slowest

Order

Difficult to retain

Easy to retain

Urgency

Easy to incorporate

Difficult to incorporate

Noise

Not affected by visual noise

Not affected by auditory noise

Melodious, linguistic Accepted symbolism

Pictorial, linguistic

Mobility

Most flexible

Some flexibility

Suitability

Time-dependant information

Space-dependant information

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Specific suggestions when to use visual or auditory presentation can be found in Table 3 (Sanders et al., 1987 citing Deathrage, 1972). Table 3: When to use auditory or visual presentation (Sanders et al,, 1987 citing Deathrage, 1972).

Use auditory presentation if:

Use visual presentation if:

The message is simple

The message is complex

The message is short

The message is long

The message will not be referred to The message will be referred to later later The message deals with events in time The message deals with locations in space The message calls for immediate action The message does immediate action The visual system is overburdened

not

call

for

The auditory system is overburdened

The receiving location is too bright or The receiving location is too noisy dark adaptation integrity is necessary The person´s job requires moving The person´s job allows them to remain about continually in one position

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2.2 Classification of auditory warnings With respect to the relevant literature, the warning concept and the later introduced hybricons, this chapter will introduce three subclasses (type, urgency and place of application) in which auditory warnings can be ordered in. Besides of these three groups, various other classification schemes are possible.

2.2.1 Type of the warning The most common classification of auditory warnings is to distinguish between speech and non-speech warnings (Graham, 1999, p. 1233; Fagerlönn, 2007, p. 1). An advanced classification of auditory warnings (Wogaltera et al., 2002, p. 223) is to distinguish between: • simple tones, • auditory icons, also known as representational sounds, • abstract tones also known as earcons and • speech warnings Simple tones are single or grouped frequencies presented simultaneously, e.g. a pure sine wave a 1000 Hz. Earcons can described as musical tones that can be used in structured combinations to create auditory messages. These are sometimes referred to as complex tones. In contrast auditory icons are familiar environmental sounds that intuitively convey information about the object or action they represent. These are sometimes referred to as naturalistic sounds or earcons, and are intuitively recognizable. Speech message are voice messages that add information beyond pure sound (USDOT, 2004, p. 6-4).

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2.2.2 Urgency of the warning General, non-specific warning signals can also be classified within the degree of urgency of the event associated with and the appropriate operator reaction accompanied by the warning (DIN 2009b, 2009, p. 7–9). Table 4: Three level urgency-response correlations for sound signals.

Degree of Equivalent condition Appropriate operator reaction according to standard urgency High

Danger

Immediate reaction required for safety

Middle

Caution

React on demand

Low

Commandment

Officially required arrangements

Examples or use cases for this classification in the context of an in-vehicle ADAS could be the use of • a critical warning signal announcing an imminent necessary emergency brake to avoid a crash, • a safety warning signal for an upcoming dangerous situation, e.g. when approaching a bicycle with high speed and • a comfort warning signal notifying the driver, that the seatbelt is not fastened.

2.2.3 Place of application Besides the classification regarding the type and the urgency of the auditory signal there is a third option to classify auditory signals: The place of application of the system (Stanton et al., 1999): “Auditory alarm and warning displays are commonplace, and may be divided into four classes of areas of application. These are personal devices, transport, military and central control rooms.” (Stanton et al., 1999, p. 8–9) Personal devices include alarm clocks, anti-rape alarms and burglar alarms. These devices are intended for use by one individual and are not part of a wider system. Transport applications include cars, buses and civil aircraft. These are different to the personal devices in that they typically possess more than alarm, and may also be multi-person systems. Military applications include missiles,

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armoured fighting vehicles and central control rooms include hospitals and control stations in power plants. After introducing the general clusters auditory warnings can be classified in, the following chapter is a more in-depth analysis of the three different types of auditory warnings promising the most benefit for in-vehicle ADAS.

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2.2.4 Auditory Icons a) Definition The first definition to be named is Gaver´s (1986) description for auditory icons. While investigating representational earcons, he firstly introduced the term auditory icon. He defined them as “everyday sounds mapped to computer events by analogy with everyday sound producing events”. Later he added that, the recognition of auditory icons requires “everyday listening”, which is the “experience of listening to determine the source itself.” (Gaver, 1994, p. 419) Graham (1999) describes auditory icons as “natural everyday sounds (or caricatures of naturally occurring sounds) which have existing and intuitive links to the events they represent.” (Graham, 1999, p. 1234) The most recent definition to be named is Fagerlönn´s (2007), who sums up different definitions in a final one. According to him, auditory icons are “environmental sounds, non-abstract sounds, natural sounds which are common in the real world, every-day sounds, sounds that are simply associated with real events, or generally non-musical sounds that have some resemblance to the thing they are representing.” (Fagerlönn, 2007, p. 2–3) b) Classification Gaver (1986 cited in Graham, 1999, p. 1234–1235) divides auditory icons into three classes according to the type of mapping between the information to be represented and the means of representation: • symbolic • metaphorical • nomic In this classification symbolic mappings are arbitrary and rely on social conventions for their meaning; for example, the sound of an ambulance siren, whose association is well learned, may represent a medical or diagnostic emergency. Metaphoric mappings use similarities between the event and the representing system, e.g. a falling pitch might represent a reduction in the size of some quantity. Nomic mappings are based on physical causation, with the icon making the sound of the event, for example the sound of a mechanical printer 26


could be used to indicate that a computer printing function has been activated. Nomic mappings are therefore the most direct and intuitive of the three classes, with symbolic mappings the least direct. The nomic mapping between the auditory icons and the source they represent is explained by Graham (1999): "There is, however, another category of non-speech auditory signals, which maybe described by `representational sounds’. Such sounds are based on the observation that people do not respond to the sensory qualities of a sound (pitch, timbre, etc.), but rather to the object or event that causes it.” (Graham, 1999, p. 1234) A dog bark representing a dog or a steam train whistle representing a train are good examples for auditory icons as caricatures of everyday sounds. Another example for nomic mapping (a direct relation to the event being signalled) of an auditory warning can be a coughing sound to signal the presence of carbon monoxide in a civil aircraft (Stevens et al., 2006, p. 7). c) Advantages Auditory icon warnings have the advantages of being intuitive and more easily learned than abstract sounds (Graham, 1999, p. 1236–1237). Since auditory icons are based on the way people listen to the world in their everyday lives, their meanings should be easily learned and remembered (Gaver, 1986; USDOT, 2004, p. 6-5). Though their intuitive, representational nature in comparison to the later introduced earcons, they propose to be effective in time-critical situations and have the potential to convey information by non-verbal means quickly and accurately. In consequence, they should convey information about the nature of the critical event as well as alerting the operator that there is a problem (Stevens et al., 2006, p. 7). Furthermore they should be well suited for conveying dimensional data, for instance, the loudness of the icon signifying the size of the object (Graham, 1999). According to the relevant standards, car horns or police / ambulance sirens for example are well known signals and therefore suitable as emergency warnings (DIN 2000, 2000, p. 8).

27


In addition, owing to the close semantic link between the auditory icon and the event being represented, it might be expected that such a warning would prepare the driver for a correct action more efficiently than an abstract sound (Graham 1999). That goes in hand with Fagerlönn´s (2007) recommendation of the usage of very familiar auditory icons (in those cases when such sounds can be found) as a very effective way to convey critical information (Fagerlönn, 2007, p. 3). With a view to previous experiments (Fagerlönn, 2007, p. 3) they have proven to be more effective than abstract sounds both in terms of reaction time (McKeown, 2005; Graham, 1999; Stevens et al., 2006; Myra et al., 2000) and accuracy of response (McKeown, 2005; Stevens, 2006). Research also indicates that auditory icons are more easily remembered and less likely to be forgotten in comparison to conventional auditory warnings (Belz et al., 1999). In the future, there will be an increasing number of sounds coming from advanced telematic systems, such as those being developed to assist the driver with e.g. automated speed and distance maintenance when driving on highways. Auditory icons should be less confusable with these other sounds due to their inherent meaning and natural, iconic character. d) Disadvantages First of all, a lot of objects or events simply do not have a familiar or obvious representation in iconic form. In the context of an in-vehicle ADAS, consider a person sitting in a wheel chair or an inline-skater. On the other side, a lot of objects or events may have an iconic form, but also have more than one single meaning (Graham, 1999, p. 1235). The sound of a car horn may represent a car itself, but can also be interpreted as a truck or motorcycle (which actually happened in this thesis). In these instances, the designer has to create metaphors for the icons, “which can end up being just as abstract as a pure tone or earcon.” (USDOT, 2004, p. 6-5) All these issues can cause inappropriate user actions, which have verified the importance of using comprehensible auditory icons (Fagerlönn, 2007, p. 3).

28


Another issue with auditory icons and warning sounds in general is the problem of user annoyance after prolonged use (Fagerlönn, 2007, p. 3). Research also unveiled deficits in application and implementation of these auditory icons in complex systems (Graham et al., 1995; Haas et al., 1995; Belz et al. 1999). Last but not least, the inherent advantage of auditory icons as well-known representational carriers for everyday sounds can lead to misinterpretation regarding the source of the sound itself. Indeed, the human sense of hearing is a highly developed device regarding localization and perception of the source of a sound, but nevertheless, people should always be able to clearly distinguish between an auditory icon displayed via an ADAS and a “real one” from the surrounding environment.

29


2.2.5 Earcons a) Definitions Blattner et al. (1989) described how sound could be grouped or structured along principles similar to those of icons. These short sounds, which he called earcons, were defined as “non-verbal audio messages used in the user-computer interface to provide information to the user about some computer object, operation, or interaction.” (Blattner et al., 1989 cited in Fagerlönn, 2007, p. 2) Brewster et al. (1996) defined them as “abstract, synthetic tones that can be used in structured combinations to create sound messages to represent parts of an interface” (Brewster et al., 1996). Graham adds that they may have particular uses in HCI (Blattner et al., 1989), but the link between earcons and their meanings does not already exist and must be learned (Graham 1999, p. 1234). b) Classification Blattner´s (1989) classification consists of three different groups: • Representational earcons • Abstract earcons • Semi-abstract earcons In this classification, representational earcons are the equivalent of auditory icons conveying information as everyday sounds. Abstract earcons are themes and motifs that build up according to the system state, e.g. an auditory distance controlled ADAS, increasing in intervals of the signal in dependence to the remaining distance to an obstacle. Semi-abstract earcons are the combination of the first two types of earcons. With direct reference to Gaver´s introduced auditory icons Brewster (1996) confirms: “Unlike Gaver’s auditory icons, there is no intuitive link between the sound and what it represents; the link must be learned by the listener. Earcons use a more musical approach than auditory icons.”

30


c) Advantages Earcons as well as auditory icons are both language independent and have the potential to be understood more efficiently and more rapidly (Fagerlönn, 2007, p. 2). They can be better suited in environments that require other simultaneous verbal communication, or in environments with a high level of background speech and noise (Patterson, 1982; Edworthy, 1994). Furthermore extreme flexibility is also stated to be a unique advantage of this group of auditory warnings.

In cases of in-vehicle ADAS and directly compared to auditory icons, abstract earcons are more to the background noise due to their abstract, artificial nature. Also they have some potential advantages over auditory icons because they have a strong structure to link them together. This may reduce the learning time and the driver´s memory loads (Brewster, 1994). A good example of this linking ability can be found in BMW´s park distance control system (BMW, 2009): An abstract earcon is used (in optional combination with a visual display) to reduce the danger of ramming in a parked car when backing to into a parking space. A pulsing “beep” signal displays the free space to the front and back of the car to the driver. It increases in intervals (which means that the perceived urgency of the signal rises) when the distance to the obstacle decreases, finally leading into a continues signal when the free space is below the value of 30cm. The USDOT (2004) confirms this benefit: “Earcons are most effective when presenting a family of related sounds. One powerful feature associated with the use of earcons is that related information can be given related sounds and hierarchies of information can be represented.” (USDOT, 2004, p. 6-5) The advantage of urgency indication using different intervals and a hierarchical representation will be picked up in the later introduced and defined hybricons.

31


d) Disadvantages Obviously, the crucial disadvantage of any non-verbal, non-iconic auditory warning is that their meaning is not apparent and therefore must be learnt by the driver. (Wogaltera et al., 2002, p. 223–224) Because of the difficulty to make qualitative judgments they are also limited, regarding deviations from a desired state or value. Furthermore, it is also difficult to obtain accurate quantitative information for earcons (USDOT, 2004, p. 6-5). Because of these issues, the USDOT (2004) finally notices that “they are not a good choice for presenting critical, time-dependent information to the driver." (USDOT, 2004, p. 6-5) Concerning the ease of learning, Smith (2004) investigated different sound types and found that earcons were learnt and retained with far greater difficulty compared to both speech and representational sounds.

Fagerlönn (2007)

comments: "Although, given the training required and problems retaining or retrieving associations between abstract sounds and events, it has been questioned whether earcons are appropriate in very important situations, or when there is a high cognitive load.” (Fagerlönn, 2007, p.3 referring to Smith et al., 2004) Stevens et al. (2006, p. 13 quoting Begault, 1994; Momtahan et al., 1993; Patterson, 1982) summarizes a lot of problems with abstract auditory warnings. According to his investigation and research, they • are loud and repetitive, • may mask other communication, • annoy rather than inform, • do not convey the urgency of a situation, • may be too loud and elicit a startle response that interferes with the necessary reaction, • go unrecognised about 40 per cent of the time when there are more than seven or so different alarms, • and require excessive training and retraining.

32


2.2.6 Speech warnings a) Definition Speech messages are flexible and easy interpretable auditory displays. (DIN 2009a, 2009, p. 22) b) Advantages Minimal to zero learning effort for understanding a speech based signal (of course, when the human is proficient in the individual language) is the most fundamental advantage of this type of auditory signal. The use of existing knowledge, in particular, the native language of the person receiving the speech message can be seen as the best way to avoid misunderstanding or false interpretation of any information (Wogaltera et al., 2002, p. 223–224). Also they are useful for communication of complex and multidimensional information (USDOT, 2004, p. 6-5). According to Fagerlönn (2007), “Speech-based signals have advantages over non-speech based signals in situations when the information to be conveyed is very complex, when the number of warnings in a system is very large, or when the user is not required to make a particularly rapid response (Patterson, 1982)." (Fagerlönn 2007, p. 1) c) Disadvantages For a CAS application, especially when time-critical warnings are a must, Graham (1999) identifies the most important disadvantage of a speech-based signal; the time a person needs to interpret the signal: "Any spoken warning, even a single word, will require a significant period to interpret, and it is unlikely that this response time could be improved by altering the parameters of the warning." (Graham, 1999, p. 1244) Of course, altering parameters like message speed for interpretation improvement time can easily result in incomprehensible signals. Besides the mentioned problem of the interpretation time, speech messages can typically not be understood until the message is nearly complete. In consequence this can slow down response times in emergency situations (Graham, 1999, p. 1234).

33


2.3 Human factors in auditory warnings In relation to the specific differences within the three introduced groups of possible warning types (auditory icons, abstract earcons and speech messages) human factors should also be considered. Which type of sound to use may be influenced by a number of parameters (Fagerlönn, 2007, p. 4) such as • the number of potential sounds, • the information to be conveyed, • environmental conditions, • the urgency and importance of the situation, • concurrent task demands, • desired user action • and the user background.

Speed and accuracy response to a warning signal may also be influenced by modality and by task demand (Stevens et al., 2006). Ben-Yaacov et al. (2002) summarizes that "The human’s behaviour is based both on his/her own processing of the event and on the information provided by the automatic system. Some researchers found that human operators will ignore or even disable extremely faulty automatic aids (e.g. Seminara et al., 1977; Sorkin 1988; Horowitz et al., 1992), although users can be influenced by the faulty systems even if they mostly ignore them (Maltz et al., 2001)." (Ben-Yaacov, 2002, p. 3)

34


2.4 Multimodal displays In general, the use of multimodal warning displays is recommended 3. According to the USDOT (2004), almost all of the literature suggests that operator performance can be improved by combining auditory and visual messages. These channels can be used together to provide either redundant or complimentary cues to the driver: "Use the auditory modality for presenting high priority alerts and warnings; present additional contextual information visually." (USDOT, 2004, p. 6-2) The standards confirm that especially for safety-relevant or urgent tasks, the simultaneous application of visual and auditory displays (compared to the usage of only one modality) is the choice of preference (DIN 2009a, 2009, p. 21). Belz et al. (1999) examined conventional auditory warnings (tonal, non-verbal sounds) and auditory icons (representational, non-verbal sounds), alone and in combination with a dash-mounted visual display, to present information about impending collision situations to commercial motor vehicle operators. In his simulator-based study he found that the driver performance generally improved with the use of multiple-modality displays. The use of multimodal displays (auditory icons or abstract earcons and visual display) resulted in significantly faster response time to those with only the dash-mounted visual display. Belz et al. (1999) concludes that “this was expected and may be attributed to the fact that the multimodal displays contain the omnidirectional attribute of the auditory displays." (Belz et al. 1999)

3

Because of the fact, that SAFESPOT will only use the visual and auditory modality, the haptic as

the third important modality for an ADAS, as well as the remaining sense modalities are not investigated in this theses.

35


2.5 Resume The previous chapters introduced and reviewed auditory warnings. The author´s focus was to introduce the reader sententiously to the different types of possible sounds and their individual advantages and disadvantages for CAS application cases. Auditory icons, earcons and speech warnings have been identified to be the most important and appropriate auditory warnings for in-vehicle ADAS. At this point, it is important to remark, that there is uncertainty in terms of definitions and bounds of the different sounds in literature. How the sounds are described, defined, classified and used may differ between authors and type of research. Fagerlönn (2007) reminds that “commonly used terms such as earcons, every-day sounds or musical sounds, which may appear to be obvious at a first glance, can in fact span over very large spectrums of sounds. It is therefore of importance that authors who are working with sound to convey information, and use these terms, are clear about exactly what they stand for in their work.” (Fagerlönn, 2007, p. 5) The fundamental question which type of sound to use for an in-vehicle ADAS can´t be answered in general. But the advantages and disadvantages as well as the potential benefits and issues can be balanced to find appropriate, convenient warnings. The SAFESPOT warning concept will make use of these findings.

36

3 Hybricons: A new type of emergency warning

3 Hybricons: A new type of emergency warning This chapter describes the sounds used in this study, their proposed benefit and unique features as well as the general warning concept lying underneath. Appendix A includes the physical description of the acoustic parameters in terms of intensity, duration and pitch.

3.1 Sound as a medium Gaver (1994a) describes the structure of sound as a medium in six frameworks: • Acoustics • Psychoacoustics • Everyday listening • Sound localisation • Musical structures • The effects of sound processing technologies Acoustics describe the physical and perceptual parameters of sound. Physical parameters of sound contain frequency, amplitude and spectrum of the sound while the perceptual ones are pitch, loudness or timbre. Important is the distinction between acoustics and psychoacoustics: “Acoustics describe the structure of sound itself, while psychoacoustics concerns the mapping between dimensions of sound and dimensions of our perception.” (Gaver, 1994a, p.1007) The frequency of a sound is the number of repetitions or occurrences of a repeating event in time, e.g. a clear sine wave. The corresponding unit to frequency is Hertz (Hz), defined as the number of cycles per second. Amplitude is the sound wave´s degree of departure from the mean pressure level, it´s unit is the logarithmic, dimensionless decibel scale (DB) or absolute logarithmic decibel full scale (DBFS).

37


Figure 3 shows an example of four sine wave forms with the same amplitude but four different frequencies; Figure 4 the resulting complex wave form.

Figure 3: Four sine waveforms (according to Schmidt, 2009).

Figure 4: Resulting complex wave form (according to Schmidt, 2009).

Pure sine waves are very rare in nature, but virtually any complex wave can be described as a sum of different sine waves with a certain amplitude, phase and frequency. Gaver (1994a) divides these complex waves into three general groups: • Harmonic waveforms • In harmonic natural sounds • Noise

38


Psychoacoustic dimensions of sound correlate with the acoustic dimensions, e.g. amplitude is roughly related to loudness and frequency to pitch. These correlations are neither linear nor orthogonal, e.g. changing the amplitude can result in changed perceived loudness as well as in perceived pitch. Important psychoacoustic parameters (Brewster, 1994) are: • Pitch • Loudness or intensity • Timbre or quality The pitch depends upon the frequency of the waves: It´s the attribute of auditory sensation, within sounds can be ordered on a scale extending from high to low (ANSI, 1973). Pitch correspondents logarithmically to frequency and it is also affected by loudness. A sound can be so high in frequency that the waves reaching the ear cannot be heard. Likewise, some frequencies are so low that the eardrums do not convert them into sound The American National Standards Institute defines loudness as "that intensive attribute of auditory sensation in terms of which sounds may be ordered on a scale extending from soft to loud." (ANSI, 1973) Loudness is related to intensity as well as to frequency. For example, increasing intensity by 10db of amplitude doubles loudness. Figure 5 (ISO 226, 2003) shows the normal equal-loudness-contours illustrating the non-linear correlation between frequency and intensity/loudness for single tones. Loudness is also affected by bandwidth. Bandwidth is the range from the highest to the lowest frequency. And last but not least, loudness is also dependent from duration.

39


Figure 5: Normal equal-loudness-level contours 4 (ISO 226, 2003).

Timbre, also known as tone colour describes all of the aspects of a sound that do not have anything to do with the sound's pitch, loudness, or length. For example, a flute is easily discriminable from an oboe even though both are playing the same tone, with the same duration and equal loudness. Gaver (1994a) calls another approach to sound everyday listening. Everyday listening is the experience of listening to a sound to determine the source itself. This means, sounds are mapped to certain events/objects or sources. A glass breaking on the floor or a person crumpling a newspaper are popular examples for everyday listening.

4

Translation aid for Figure 5:

y-axis label: sound pressure level [db]; x-axis label: frequency [Hz]; Hörschwelle: hearing threshold level

40


3.2 Requirements According to Graham (1999, p. 1236-1237) the three most important criterions for auditory in-vehicle warnings are: • Quick and correct identification of the warning. •

Procuration of an extremely fast response from the driver.

•

Procuration of an appropriate action from the driver, e.g. an emergency brake or a steering manoeuvre.

Wogaltera et al. (2002) complements four different requirements for an effective auditory warning: "Getting noticed and attended to are the first requirements of an effective warning. A second warning component should describe the nature of the hazard present in the situation. The hazard description should be specific and complete. For example, it might involve an explanation or description of the mechanisms involved so that people will understand the nature of the hazard. At the same time, the hazard description should not be so lengthy that few people will take the time and effort to read it. Therefore, there is a need to balance completeness and brevity. Third, a warning should describe the possible consequences of noncompliance. A specific description of the mechanism of injury provides more information and informs individuals why it is important that they comply. Finally, the warning should offer directives or instructions on how to avoid the hazard.” (Wogaltera et al., 2002, p. 221) More formal and practical requirements for auditory icons can be found in the USDOT´s (2004, p. 6–12) recommendations: •

Auditory icons should be detectable 10 to 20 dB above the masked threshold.

•

No more than six auditory icons should be used in an auditory icon set.

•

Auditory icons should strive to attract the attention of the driver without generating a startle reaction.

•

Special attention should be paid to the perceived urgency associated with different candidate auditory icons.

41


Except of Wogaltera´s et al. (2002) third and fourth requirement, the design of the hybricons in this study mainly considered these requirements. A following simulator based study will evaluate response times and eye gaze in a CAS scenario to obtain objective response data.

42


3.3 Hybricons The four main types of possible auditory warnings sounds have been introduced: • Simple tones • Abstract Earcons • Representational auditory Icons • Speech messages This thesis tries now to unify the advantages and simultaneously eliminate the disadvantages of these different sound types combining them into a new signal: “A future application for abstract warning signals can be to present them concurrently with auditory icons. This may be an interesting way to make auditory warnings more redundant and decrease the risk of unexpected user actions. Whereas the auditory icon gives the driver associational information (what it is that we hear) the abstract sound carries complementary information about urgency level (how important it is). The abstract sound could further be used to help drivers distinguish warning messages from each other." (Fagerlönn, 2007, p. 4) This means in the in-vehicle warning system context in simplified words: These, from now with the term hybricons 5 designated signals, shall convey information about the road participant the driver has to expect when hearing the signal as well as tell the driver how close or far away the road user is. Furthermore these signals are proposed to be useful in complex traffic conditions where the driver is exposed to various hazard sources, e.g. a heavily trafficked intersection with crossing pedestrians, bicycles and turning cars. With the ambition to fuse the advantages of auditory icons (as carrier for the nature of the hazard) and earcons (for conveying a certain degree of urgency) a set of six different auditory icons is combined with a total of five abstract earcons.

5

For the purpose of a consistent terminology and to avoid any misunderstandings, these hybrid

sound signals or advanced, enhanced auditory icons will from now a be defined as hybricons.

43


The complete set of available auditory icons for SAFESPOT is presented in Table 5: Table 5: Set of auditory icons for an individual traffic participant.

Auditory Icon

Intended representation

Car horn

Car (alternative 1)

Skidding tyres

Car (alternative 2)

Bicycle bell

Bicycle

3 Footsteps

Pedestrian

Motorbike horn

Motorbike

Truck horn

Truck

The set of available earcons is presented in Table 6: Table 6: Set of earcons and their intended state of urgency.

Earcon

Description of the sound

Intended state of urgency

Sonar ping

Similar to a “sonar ping”, e.g. from submarines.

Comfort / informative

New message

Similar from various email software, notifying the user “you have new email”, when opening the program

Comfort / informative

Two pulses

Two non dissonant pulses

Safety

Two dissonant pulses

Two pulses, but far more dissonant.

Critical

Three pulses

Three non dissonant pulses with shortened intervals

Critical

Moreover, it was decided, that for an informative warning the representational part of the auditory warning was not important due to the fact, that the driver, is not supposed to react immediately but rather to look on a visual in-vehicle display which gives more detailed information. Because of this, only the pure earcons were used to assess the comfort state.

44


To reduce complexity and participant’s time amount exposure in the experiment, hybricons (car horn, bicycle bell, pedestrian) were used as volunteers for the whole set of available hybricons.

With this reduction in the experimental design, a total of 14 signals were used for evaluation, presented in Table 7 and marked in bold text. Table 7: Selection of hybricons regarding the evaluation.

Earcon

Auditory icon

Hybricon

Comfort signals Sonar ping

-

-

New message

-

Safety signals

Two pulses

-

-

Two pulses

Car horn

Two pulses + Car horn

Two pulses

Bicycle bell

Two pulses + Bicycle bell

Two pulses

Footsteps

Two pulses + Footsteps

Critical signals (variation one) Two dissonant pulses

-

-


Car horn



Bicycle bell



Footsteps


Critical signals (variation two) Three pulses

-

-

Three pulses

Skidding tires

Three pulses + Skidding tires

Three pulses

Bicycle bell

Three pulses + Bicycle bell

Three pulses

Footsteps


45


The group of earcons consisted of five signals; two semi-abstract signals (sonar ping, new message sound) and three abstract signals (two pulses, two dissonant pulses and three pulses). The group of hybricons consisted in total of nine signals: The three abstract signals (two pulses, two dissonant pulses and three pulses) are fused with the bicycle bell and footsteps auditory icon. Furthermore the two abstract pulses/ two dissonant abstract pulses are fused with the car horn audicon, and the three abstract pulses are fused with the skidding tires sound.

46

4 The experiment

4 Experiment This chapter describes the complete preparation and execution of this study. The following subchapters include: • Scope • Hypothesis • Participants • Experimental design • Evaluation process • Results

4.1 Scope Scope of the experiment was to evaluate the new developed hybricons and compare them to the traditional, abstract earcons in the three clusters: • Comprehensibility • Urgency • Comfort/Agreeability Quite a lot of studies investigated auditory icons as well as earcons as separate signals in the fields of comprehensibility, learnability, reaction time and in combination with/without multimodal displays. A summary of these experiments can be found in Fagerlönn´s review (Fagerlönn, 2007, p.3). For this thesis, three important studies will be briefly introduced here: Stevens et al. (2006) examined conventional auditory warnings (tonal, non-verbal sounds) and auditory icons (representational, non-verbal sounds), alone and in combination with a dash-mounted visual display, to present information about impending collision situations to commercial motor vehicle operators. A system with four signals and two attentions that signalled different levels of urgency was regarded as the optimal design. He found that iconic warnings need fewer learning time compared to abstract warnings and the use of the bimodal warnings (auditory and visual) are recognized with the greatest consistency and accuracy.

47

4 The experiment

Belz et al. (1999, p. 1) revealed significantly improved driver performance for auditory icons (brake response times) while comparing them to conventional warnings within a front-to-rear and side collision scenario. Additionally, driver performance improved when collision warning information was presented through multiple modalities. His subjective data indicated a preference for multimodal displays over single-modality displays. Graham´s (1999) experiment examined the hypothesis that auditory icons would lead to faster reaction times and more appropriate responses than conventional speech or abstract non-speech warnings in an emergency collision situation. His findings indicated that “the auditory icons have considerable potential advantages over conventional sounds in terms of response time and subjective ratings but further data must be collected before demonstrating these benefits.” (Graham, 1999, p. 1245) Graham (1999) furthermore suggests parameterizing the icons, e.g. “the loudness of the car horn could be varied to indicate the urgency of the collision situation, playing the sound from a speaker to the left or the right of the driver might give information about the direction of the target. The type of horn might indicate the nature of the target; perhaps a deep foghorn for a lorry, oral high-pitched `honk’ for a bicycle." (Graham, 1999, p. 1245) Whether objective data like BRT and eye gaze tracking will be obtained in a following simulator-based experiment, the mentioned studies support in general the idea of the introduced hybricons as well as the warning concept itself and found to be important in the context of this thesis.

48

4 The experiment

4.2 Hypothesis A total of five hypotheses (Table 8) are formulated to be investigated: Table 8: Hypothesis.

Abbreviation Hypothesis H1

Hybricons convey information about the type of hazard.

H2

Between the three groups of urgency is a difference in perceived urgency

H3_1

Signal_3_2 is more agreeable than Signal_3_1

H3_2

Between Signal_3_2 und Signal_3_1 is a difference in perceived urgency.

H3_3

Between Signal_2 and Signal_3_1 is a higher difference in perceived urgency in comparison to Signal_2 and Signal 3_2

H1 is used for evaluating the efficiency of the hybricons in terms of perceived comprehensibility. H2 is used for evaluating the difference in perceived urgency between the abstract Earcons and the hybricons. H3_1 to H3_3 is used to evaluate two abstract components alternatives within the hybricons in terms of perceived urgency and agreeability individually.

49

4 The experiment

4.3 Experimental design The following chapter describes the development of the interactive questionnaire. This includes the scenario design as well as the questions of the survey.

4.3.1 Scenario To minimize scenario influences in the subject´s assessment of the signals, it was decided to use the identical scenario for every signal: A car approaching a hill in a country side environment was found to be an ideal setting to evaluate and compare earcons and hybricons. Ideal because of the fact that the range of view for the participants was limited to the top of the hill and no visual information about what to expect behind was available. To accomplish this goal, a video sequence from the immersive driving simulator at the University of Stuttgart was recorded using FRAPS, a real-time video capturing software. The main simulator screen, from the computer-driven car approaching a hill in a country-side environment was digitally recorded and exported. The background noise, like the engine sound and tread noises, were simultaneously recorded using Audacity, an open source software for recording and editing sounds, Then the video and background noises were muxed together with one of the fourteen warnings (abstract earcon or hybricon), resulting in one small video clip (about the size of one MB). For composing the video and audio into one video clip a commercial, non-linear video-editor software (Adobe Premiere CS4) was used. Each of the fourteen videos was six seconds in total duration, playing the specific warning always at the same point (just before the car reaches the top of the peak). Immediately after the warning sound is played, the video freezes for 1 second and finally smoothly fades out. By way of illustration, the complete video sequence with time stamps is illustrated in a picture series in Figure 6 on the following page. The yellow rectangle marks the point where the sound signal is displayed; the red rectangle marks the freeze point in the video sequence.

50

4 The experiment

Figure 6: Video sequence 6 with timestamps.

6

Yellow rectangle marks the point where the auditory signal is displayed; Red rectangle marks the

point where the video freezes.

51

4 The experiment

4.3.2 Loudness of the sounds According to the USDOT ( 2004, p. 6–12) abstract earcons, hybricons and a three stage test tone were adjusted to certain levels of intensity to ensure an equal level of perceived loudness within, and a remarkable difference between the three degrees of urgency: A professional sound editor was used (Adobe Soundbooth CS4) to adjust the levels of intensity measured in DBFS the digital standard for audio editing. The RMS (root mean square) adjustment was used for calibrating the sounds and test tones to different levels of intensity. Additionally, this software offers the option of compensation the human ear´s perception of very high and very low frequencies; this option was used. Table 9: Loudness adjustment.

Level of urgency/ Signal

Mean loudness adjustment to [dbfs]

Variation in perceived loudness [dbfs]

Background noise

-29

-28,98

Comfort signals

-14

-13,86 - 14,20

Safety signals

-9

-8,96 - 9

Critical signals

-4

-3,96 - 4,41

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4 The experiment

4.3.3 Interactive questionnaire The complete study including a short description for each page can be reviewed in Appendix B. The interactive questionnaire consisted of two sections and a total of 22 pages: Table 10: Structure of the questionnaire.

First section: Introduction to the experiment (pages 1 to 7) Page 1

Welcome page

Page 2

Short introduction to SAFESPOT and ADAS with reference to in-vehicle auditory signals

Page 3

Sound check and calibration with the reference signal

Page 4

Privacy policy

Page 5

Request of the personal data (age, gender, etc.)

Page 6

Presentation of the questions including a 15 seconds video clip showing the car approaching the hill. The video smoothly fades out when the car reaches the top of the hill and no signal is played.

Page 7

Final advice for the following evaluation (page 7) including that: • The subjects will see 14 identical video clips at a single difference in the sound signal. • The video should be started first and can be replayed at will. • Afterwards Questions from 1 to 7 shall be answered in order • Commentaries are optional

Second section: Sound evaluation (pages 8 to 22) Pages from

Evaluation of the 14 signals: one page per sound/scenario

8 to 21 Page 22

Acknowledgment for participation and instructions for sending the results back to the experimenter.

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4 The experiment

The instructions as well as the videos and any additional information (privacy policy) were finally composed in an interactive PowerPoint Presentation and emailed to the subjects. Every subject received a randomized scenario sequence, to factor in learning and ordering effects. Additionally, the questionnaire included a short description of the SAFESPOT Project and the Safety margin assistant system as well as a privacy policy. Furthermore the loudness calibration was included in the introduction. People were also advised to use headphones is possible. Two test trials of the final survey under experimental conditions revealed comprehensible and understandable questions as well as analyzable data. Participant´s average handling time during the survey was about 20 minutes 7. Individual experimental conditions for each scenario varied in length from 30 seconds to 2 minutes and were presented sequentially.

7

An average handling time of 20 minutes, was the result of various trial evaluations carried out in

front of the actual experimental evaluation.

54

4 The experiment

Figure 7 shows a typical question page of the survey for one signal:

Figure 7: Typical page of the interactive questionnaire.

Subjects were told to start the video first and answer the questions afterwards. When they completed a scenario, they could progress to the next scenario with the green button in the lower right corner. A red back button was also included, if subjects accidently went on for example. The lower left corner showed the page count, to give people feedback about their progress in the survey. Additionally, a transition effect was included between each scenario, to give people additional feedback about their progress. The identical look within the fourteen scenarios caused problems in test evaluations. Subjects could not distinguish if they went on to the next page. Because of that issue, these measures have been applied to ensure comprehensibility and to avoid misunderstandings.

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4 The experiment

4.3.4 Questions For each of the fourteen videos the identical seven questions were asked: Table 8: The questions for each signal.

Number Question

Answer calibre

1

Which road user do you expect after Interactive text field, free the peak? answer calibre.

2

How confident do you feel with your Interactive slider, range from answer in Question 1? -40 to 40.

3

Here you see a side-view of the hill. Interactive slider, range from Where do you expect the road user? 0 to 1000.

4

How confident do you feel with your Interactive slider, range from answer in Question 3? -40 to 40.

5

How urgent is the signal to you?

Interactive slider, range from -40 to 40.

6

How would you react?

Multiple-choice answer calibre, three possible reactions to choose from.

7

How comfortable is the signal to you?

Interactive slider, range from -40 to 40.

8

"Question 8" was a commentary field Interactive text field, free for the individual signal. answer calibre.

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4 The experiment

Question 1 was used to validate H1: Hybricons convey information about the nature of the hazard. Answer calibre was open, which means there was an empty interactive text box where people typed in their answers.

Question 2 was used to identify guessed or random answers in Question 1. An interactive Slider with a dimensionless range from -40 to +40 was used; -40 matched unconfident and +40 matched very confident. Question 3 was used to validate H2: There is a difference in perceived urgency between the three determined states of urgency. An interactive Slider with a range from 0m to 1000m was used. Slider position 0m matched close, and slider position 1000m matched faraway. Test trials indicated problems with subject´s imagination of the distance; because of this the physical unit [m] was applied to the study. Question 4 was used to validate Question 3 and to identify guessed or random answers. An interactive Slider with a range form -40.to +40 was used. -40 matched unconfident and +40 matched very confident. Question 5 was used to validate perceived urgency in a more direct way. An interactive Slider with a range from -40 to +40 was used; -40 matched low and +40 matched high. Question 6 was used to validate perceived urgency accordingly to the three defined groups of urgency comfort, safety and critical. Subjects could choose between three options (checkboxes): • I would brake and drive slowly towards the peak. • I would step off the accelerator and roll towards the peak. • I would maintain my current speed and drive through the peak. Question 7 was used to validate agreeability to both, hybricons and abstract earcons. An interactive Slider with a range from -40 to +40 was used; -40 matched uncomfortable and +40 matched comfortable.

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4 The experiment

4.4 Participants A total 26 subjects (13 males and 13 females) with a mean age of 29.9 years (range from 18 years to 61 years) participated in this study. The complete participant´s data is can be reviewed in Appendix C. Every participant was in possession of a valid driving license for cars, trucks, or motorcycles and had no hearing damages or other auditory restrictions. Mean average years of ownership of the license was 11.2 years; mean average mileage per year was 16500km. The subjects volunteered in the study and were not paid or rewarded.

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5 Results

5 Results This chapter presents the results of this experiment as neutral and objective as possible. Discussions, interpretations and conclusions will take place in chapter 6. Results are complex and can be analysed in various options. Presentation will be focused on the comprehensibility of the hybricons, the urgency and agreeability of all signals in the corresponding degree of urgency with focus on the abstract versus the hybricons. Due to the direct dependency of questions 2, 3 and 4 (How confident do you feel with your answer in Question 1?; Where do you expect the road user?; How confident do you feel with your answer in Question 3?) to question 1 (Which road participant do you expect?) the raw data set was cleaned when people answered with • question marks (?), • minuses (-), • and nothing, don´t know or anything. To maintain consistency within the data analysis in these certain scenarios, the answers for questions 1 to 4 were not taken into account for the following analysis. After the revision of the dataset 46 from a total of 364 individual scenarios are not considered for the evaluation. Out of these 46 scenarios, 31 represent an abstract scenario (Sonar ping; New message; Two pulses; Two dissonant pulses; Three pulses). With the assumption of non direct dependence to question 1, question´s 5-7 are still evaluable: Whatever people expect while hearing the signal, they can still decide how urgent it is (question 5), how they would react (question 6) and to which degree they agree to the signal (question 7). Besides of this issue in experimental design, the dataset was complete and evaluable.

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5 Results

5.1 Descriptive statistics For the descriptive presentation and analysis of this experiment the following prescriptions are useful: Each diagram will own a written explanation, a title with a short description including an abbreviation in brackets for the investigated question; e.g. Q4 reefers to question 4. In diagrams, the signals will always be presented on the x-axis in the same order (from left to right) and an individual y-axis representing the specific individual value, category, number of subjects or unit.

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5 Results

Table 11 presents the complete list of evaluated signals within the individual stage of urgency. Table 11: Complete list of evaluated signals.

Comfort signals Sonar ping New message Safety signals Two pulses Two pulses + Car horn Two pulses + Bicycle bell Two pulses + Footsteps Critical signals (variation one) Two dissonant pulses Two dissonant pulses + Car horn Two dissonant pulses + Bicycle bell Two dissonant pulses + Footsteps Critical signals (variation two) Three pulses Three pulses + Skidding tires Three pulses + Bicycle bell Three pulses + Footsteps

Except of Figure 9, comfort signals will be marked with green, safety signals with yellow and critical signals with red colour (bright red for the critical variation set 1 and deep red for the critical variation set 2). The complete set of data can be found on Appendix C.

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5 Results

5.1.1 Comprehensibility Question 1 The descriptive analysis of question 1 is illustrated in Figure 8. Because of the assumption that the abstract earcons do not carry information about the source of the hazard, only the hybricons are evaluated 8. Two conditions are defined for evaluation of question 1: If the subject typed in the “right” keyword mapped to the specific hybricon (e.g. car or automobile for the corresponding car signals) the answer was treated as “true”. If the answer was anything else than the correct keyword (e.g. truck, tractor, or bicycle for a car signal) a, it was treated as “false”. With this strict analysis, the following results are obtained:

Figure 8: Comprehensibility of the hybricons (Q1).

88% of the subjects expected a car when hearing the skidding tires hybricon (Three pulses + Skidding tires) representing the most comprehensible hybricon. 8

Content transportation using earcons is not scope of this thesis. The results for the five abstract

signals are not presented here whether they can be found in Appendix X.

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5 Results

Representing the worst comprehensible signal, 38% of the subjects expected a car while hearing the alternative, critical car horn hybricon (Two dissonant pulses + Car horn). Actually more people assessed this signal as a truck than as a car warning signal (10 nominations for a car versus 14 for a truck). The condition, that subject´s associated the wrong meaning to a hybricon more often than the right one only happened once for this specific signal. By minor trend, the decrease of comprehensibility declines from the car (from 88%-79%; except of the anomaly two dissonant pulses + Car horn) over the bicycle (from 68%-56%) to the pedestrian (from 56%-48%) hybricons.

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5 Results

Question 2: The scores for the individual subject´s answer reliability for the expected road user are separated into the two categories “true” and “false”. This means for each hybricon, two separate average means and standard deviations are calculated for each group of subject´s which correctly identified the road participant or not (Figure 9).

Figure 9: Answer reliability for Q1 (Q2).

In seven of nine cases the mean value for the true answer lies above the mean value of the false answer. For the car horn and skidding tires hybricon (Two dissonant pulses + Car horn; Three pulses + Skidding tires) the mean value of false answers lies above the mean value of correct answers. The high variances across all signals in both answer categories (except of the false category for Three pulses + Skidding tires) which are caused by two subjects, who were very confident expecting a truck) indicate uncertainty of the subjects in answering that question.

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5 Results

5.1.2 Urgency With the presupposition that urgency is measureable by directly asking the individual´s perceived urgency of the signal and indirectly by questioning the estimated distance of the hazard and the reaction in consequence, a total of four questions are inquired for urgency assessment. Question 3 Figure 10 illustrates the results for the un-weighted estimated distance of the expected road user:

Figure 10: Mean distance of the expected road user (Q3).

Besides of high variances, by general trend, comfort signals (green) are more far away assessed than the safety (yellow) and critical (red) signals. Compared to their pure abstract component (within the corresponding state of urgency) the hybricons are fairly equal or closer assessed. When overlooking the skidding tires hybricon, the “critical variation one signals” (bright red) are by trend nearer assessed than the “critical variation two signals” (deep red).

65

5 Results

Compared to all other signals, the skidding tires hybricon (Three pulses + Ski. tires) announces the road participant the closest with little variances in the assessment.

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5 Results

Question 4 Question 4 was used to ensure subject´s responses in dependency to Question 3: To accomplish this intend, the individual answer for the estimated distance of the road user (Q3) is weighted with the individual confidence of the response in the following question (Q4). The weighted mean as well as the corresponding weightened standard deviation is presented in Figure 11:

Figure 11: Weighted mean distance of the expected road user (Q3*Q4).

The extreme variances in the subject´s responses across als signals besides of the skidding tires sound (Three pulses + Ski.tires) are evident.

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5 Results

Question 5 The results for Question 5 are illustrated in Figure 12:

Figure 12: Urgency of the signal (Q5).

By general trend, both sets of critical signals are assessed to a higher level of urgency than the safety and comfort signals. Overlooking the skidding tyres hybricon (Three pulses + Ski.tires) the “critical signals in variation one” (bright red) are located above the “critical variation two signals” (deep red).

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5 Results

Question 6 For analysis of Question 6 (How would you react after hearing the signal?), the three possible answer options are mapped to the subject´s reaction after hearing the signal representing the intended degree of urgency: Table 12: Colour coding for the assessment of question 6.

Degree of urgency

Corresponding Colour

Reaction

Comfort

Green

I would maintain my current speed and drive through the peak.

Safety

Yellow

I would step off the accelerator and roll towards the peak.

Critical

Red

I would brake and drive slowly towards the peak.

Figure 13: Reaction after hearing the signal (Q6).

For the “New message” signal e.g., 17 out of 26 subject´s would react in the “proper way”, namely to drive through the peak; 6 subjects would step off the accelerator and roll over the peak, and three would brake and drive slowly towards the peak. Answers within the comfort signals (Sonar ping; New message) are assessed the most into the corresponding, matching category (13 out 26 for the Sonar ping; 17 69

5 Results

out of 26 for New message signal). With 9 “false reactions” results for the “New message” signal are slightly better compared to the “Sonar ping” with 13 “false reactions”. Answers within the safety signals (yellow) are also assessed the most within the corresponding, matching category (52 out of 104 possible answers are located in the proper category). In between the safety signals results vary from vague (Two pulses + Bicycle bell; Two pulses + Footsteps) to more clear answers (Two pulses; Two pulses + Car horn). The “critical variation one set” (bright red) provokes in general more “appropriate” brake reactions (57 out of 104 possible answers) compared to the “critical variation two set” (deep red; 41 out of 104 possible answers). Besides of the out braking skidding tires hybricon (Three pulses + Skidding tires), the “critical variation two set” (deep red) is mainly assessed in the safety category (46 out of 77 answers).

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5 Results

5.1.3 Agreement Question 7 The analysis of question 7 is illustrated in Figure 14.

Figure 14: Agreement to the signal (Q7).

High variances across all results are evident. Across all signals, the “New message” sound represents the most comfortable signal and the skidding tires signal (Three pulses + Ski. tires) the most discomfortable signal.

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5 Results

5.2 Interference statistics For quantitative analysis, PASW Statistic 17, commercial software suite for numerical data analysis is used.

5.2.1 Comprehensibility Question 1: (Which traffic participant do you expect after the peak?) The test statistics for a nonparametric chi-square test (significance level of α=0.05) for question 1 across all hybricons are illustrated in Table 13 (The individual frequencies for each signal are listened in Appendix D). Table 13: Chi2 results for question 1.

Hybricon

Chi-Square

df Asymptotically significance


12,462a

1

,000


5,538 a

1

,019

Two diss. pulses + Car horn

1,385 a

1

,239


1,385 a

1

,239

Three pulses + Footsteps

1,385 a

1

,239


,615 a

1

,433

Two diss. pulses + Bicycle bell

,154 a

1

,695


,154 a

1

,695


,000 a

1

1,000

With the assumption of normal distribution (50% of true answers, 50% of false answers) between the answers, the result in comprehensibility for the skidding tires hybricon (Three pulses + Skidding tires; p=0,000) is found to be highly significant. Moreover, the analysis for the identification of the safety car horn hybricon (Two pulses + Car horn; p=0,019) proves statistical significance. a

0 cells (,0%) have expected frequencies less than 5. The minimum expected cell frequency is 13,0.

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5 Results

5.2.2 Urgency Question 3: (How close/far away do you expect the traffic participant?) The results for an array of paired t-tests for Question 3 including an alpha bonferroni correction are presented in Table 14. As proposed urgency carriers, only the abstract signals (Sonar ping; New message; Two pulses; Two dissonant pulses; Three pulses) are considered in this analysis: Table 14: Paired t-test results for question 3. Paired Differences 95% Confidence Interval of the Difference

Pair 1

Pair 2

Pair 3

Sonar ping -

Sig.

Mean

Std. Deviation

Std. Error Mean

Lower

Upper

t

df

(2-tailed)

-31,118

165,354

40,104

-116,135

53,899

-,776

16

,449

115,933

236,100

60,961

-14,814

246,681

1,902 14

,078

95,125

153,663

38,416

13,244

177,006

2,476 15

,026

Two pulses Sonar ping Two diss. pulses Sonar ping Three pulses

Pair 4

New message Two pulses

62,375

199,029

49,757

-43,680

168,430

1,254 15

,229

Pair 5

New message Two diss. pulses

283,733

298,676

77,118

118,332

449,135

3,679 14

,002

Pair 6

New message Three pulses

177,438

225,157

56,289

57,460

297,415

3,152 15

,007

Pair 7

Two pulses - Two diss. pulses

168,850

348,669

77,965

5,668

332,032

2,166 19

,043

Pair 8

Two pulses - Three pulses

107,200

203,420

45,486

11,996

202,404

2,357 19

,029

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5 Results

The bonferroni correction for a significance level of α=0.05 is calculated by division of the number of paired t-tests. For a row of eight t-tests, this results in a significance level of α*=0.00625. With this correction, results for Pair 5 (New message - Two diss. pulses; p=0,002) are found to be significant and results for Pair 6 (New message - Three pulses; p=0,007) are found to marginal significant. Question 4: (How confident do you feel with your answer in Question 3?) With respect to the minor differences between the weighted and unweighted results in the descriptive analysis of question 3 and 4 in chapter 6.1, as well as the overwhelming weightened variances in the descriptive results for the question 4, no statistical tests are applied for the weightened distance.

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5 Results

Question 5: (How urgent is the signal?) The results for a paired t-test for Question 5 are presented in Table 15. Again, only the abstract five earcons are considered in this analysis and the bonferroni correction (α*=0.00625 for 95% confidence; α**=0.00125 for 99% confidence) is applied to the level of significance. Table 15: Paired t-test results within the abstract signals for question 5. Paired Differences 95% Confidence Interval of the Difference

Pair 1

Pair 2

Sonar ping Two pulses

Mean

Std. Deviation

Std. Error Mean

-1,423

24,766

4,857

11,42 6

-26,000

28,945

5,677

-11,500

29,420

t

df

(2-tailed)

8,580

-,293

25

,772

37,69 1

14,30 9

-4,580

25

,000

5,770

23,38 3

,383

-1,993

25

,057

Sonar ping Two diss. pulses Sonar ping -

Lower Upper

Sig.

Pair 3

Three pulses

Pair 4

New message Two pulses

-9,500

19,127

3,751

17,22 -1,774 6

-2,533

25

,018

Pair 5

New message Two diss. pulses

-34,077

26,107

5,120

44,62 2

23,53 2

-6,656

25

,000

Pair 6

New message Three pulses

-19,577

30,636

6,008

31,95 -7,203 1

-3,258

25

,003

Pair 7

Two pulses Two diss. pulses

-24,577

21,847

4,285

33,40 1

15,75 3

-5,736

25

,000

Pair 8

Two pulses Three pulses

-10,077

27,572

5,407

21,21 4

1,060

-1,864

25

,074

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5 Results

Statistically high significant results can be proved for Pair 2 (Sonar ping - Two diss. pulses; p=0,000), Pair 5 (New message - Two diss. pulses; p=0,000) and Pair 7 (Two pulses - Two diss. pulses; p=0,000). Furthermore Pair 6 (New message - Three pulses; p=0,003) proves statistical significance in the answers.

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6 Discussion and conclusions

6 Discussion and conclusions 6.1 Comprehensibility a) Hybricons Directly compared to the abstract signals, the set of hybricons conveyed more correct information about the nature of the hazard. Except of the “Two dissonant pulses + Car horn” hybricon all remaining hybricons were nominated the most in the proper, corresponding category. The results for the “Three pulses + Skidding tires” and the “Two pulses + Car horn” sounds as the most comprehensible signals across the whole set of sounds are no surprise at all: For a regular road participant, these signals are likely the most well learnt and remembered real in-vehicle signals. The “Two dissonant pulses + Car horn” signal as a potential warning for a car fluctuates between a car and a truck warning signal (10 nominations for a car versus 14 nominations for a truck). Compared to the “Two pulses + Car horn” signal, which uses the same car horn icon as representational component, this minor variation in comprehensibility can be caused by the abstract component of the signal. A possible reason for this “little” difference in comprehensibility could be the deep-toned, dissonant and inharmonic design characteristics of the abstract part (Two dissonant pulses) of the “Two dissonant pulses + Car horn” hybricon. The “heavy”, “big” or “powerful” subject´s perception due to the abstract part of the hybricon could be responsible for this result.

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The general trend of decrease in comprehensibility from the car signals (88% Three pulses + Skidding tires; 79% Two pulses + Car horn) over the bicycle signals (68% Three pulses + Bicycle bell; 64% Two pulses + Bicycle bell; 56% Two diss. pulses + Bicycle bell) to the pedestrian signals (56% Two pulses + Footsteps; 50%; Two diss. pulses + Footsteps; 48%; Three pulses + Footsteps) is salient:

Figure 15: Comprehensibility of the hybricons (Q1).

Possible explanations for this trend are diverse and vague; first of all, it depends on the individual´s understanding of the term “road user”. As previously introduced, the only thing subject´s were aware of was that a certain signal is displayed in the same scenario fourteen times. The scenario presented in the 20 seconds introduction video a car and a truck coming in the opposite direction while climbing the hill. Within each scenario, only the last 6 seconds of the video were played and only the truck could be seen. In consequence subjects were aware of the fact, that in any case, cars and trucks are regular road participants. The bicycle bell icon, as well-known everyday sound for the auditory display of an approaching bicycle was found to be an appropriate content carrier which people already know from daily routine but are not familiar with as an in-vehicle warning sound. Maybe people had problems, to adapt this familiar sound into the concept

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of an in-vehicle warning system due to the hypothesis, that they have never heard a real bicycle bell while driving in a car. Finally the footsteps icon representing a pedestrian can be classified as a wellknown everyday sound announcing a pedestrian, but may also have different meanings besides of that. Subject´s comments like “Who´s knocking there at the end?” or “Knocking at the end of the sound makes no sense for me” emphasize this issue. Last but not least, during to their inherent design characteristics, the bicycle as well as the footsteps icons may have been more easily masked by the urgency component of hybricons than the car horn / skidding tires sounds. b) Abstract signals In contrast to the hybricons, the abstract signals are far more distributed overall categories. Besides of the noticeable amount of responses within the nothing, anything, and I don´t know categories, the car keyword was mainly nominated (probably the most likely answer if subject´s were uncertain regarding their response). This uncertainty and widespread distribution in the subject´s responses was expected due to the missing representational component of these signals, e.g. one subject associated a train to the “New message “ and another subject falling stones to the Two dissonant pulses signal.

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6.2 Urgency Under the assumption, that the estimated distance of a road participant is a measurement for the perceived urgency of the corresponding warning signal, analysis of question 3 indicates a partly success in the intended urgency implantation across all fourteen signals:

Figure 16: Mean distance of the expected road user (Q3).

The two signals for the comfort state (green) are in general placed mostly far away from the peak. The “New message” signal is placed the most far away across all signals, representing the better alternative for an informative, comfort warning. Because of minor differences and high variances within the results, the safety signals (yellow) are not interpretable compared to the comfort (green) as well as to the critical signals (red). The set of “critical variation one signals” (bright red) is placed by trend nearer to the peak owning not as much variations in the results as the other three subsets of sounds (green, yellow, deep red). They seem to incorporate high urgency more exact and strongly than the alternative “critical variation two signals” (Three pulses; Three pulses + Bicy. bell; Three pulses + Footst. without the anomaly Three pulses + Skidding tires).

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Interpretation of the skidding tires hybricon (Three pulses + Skidding tires) compared to the remaining set of “critical variation two signals” (Three pulses; Three pulses + Bicy. bell; Three pulses + Footst.) unveils a remarkable finding of this study: Besides of the abstract component, the natural component of a hybricon can drastically affect the perceived urgency of the signal as well. The “Three pulses + Skidding tires” signal is not only the signal where subjects expected the road participant the nearest; the minor variances indicate high confidence in the result. While analyzing the weighted mean distance, variances are drastically increasing across all signals (besides of the anomaly Three pulses + Skidding tires signal). Although to the not weighted distance (Question 3), the ranking of the signals is by trend the same, the enormous variances across all results annihilate any confidence in the results:

Figure 17: Weighted mean distance of the expected road user (Q3*Q4).

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To assess the perceived urgency of sound signal, a logical and direct approach is to ask the subject´s, how urgent the signal is conceived.

Figure 18: Urgency of the signal (Q5).

The “New message” signal represents again the least urgent signal across all 14 signals, proving it´s quality as an informative, not-time critical signal. The “Three pulses + Ski. Tires” signal proves the fact, that the urgency of a hybricon can also be manipulated by the natural component. The iconic skidding tires component within the hybricon seems strongly to increase it´s perceived urgency compared to the abstract “Three pulses” equivalent. The set of critical variation one signals (bright red) is assessed more urgent than the critical variation two signals (deep red). The differences between the set of comfort signals (yellow) and the than the critical variation two signals (deep red; excluding the anomaly Three pulses + Ski. tires signal) is indistinguishable.

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For question 6, the subject´s could choose an appropriate reaction in relation to the displayed signal:

Figure 19: Reaction after hearing the signal (Q6).

At first glance, the intended urgency implementation for the comfort, safety and critical variation one signals (Two diss. pulses; Two diss. pulses + Car horn; Two diss. pulses + Bicycle bell; Two diss. pulses + Footsteps) is identifiable. For the comfort signals (Sonar ping; New message), the implementation of the informative, non-urgent character can be rated as successful. With 17 appropriate reactions, the “New message” signal is superior compared to the “Sonar ping” (13 appropriate reactions) in transporting the intended meaning to the subjects. Furthermore, the “New message” signal owns only three extreme brake reaction´s compared to the six brake reactions of the “Sonar ping”. The results for the safety signals (Two pulses; Two pulses + Car horn; Two pulses + Bicycle bell; Two pulses and footsteps) are not as clear as for the comfort signals. Whether, the appropriate “roll” reaction is the most nominated for every signal in this category, differences in the individual number of nominations in between each signal are evident. Over 50% of the subjects nominated the appropriate reaction for the “Two pulses” (14 appropriate reactions) as well as for the “Two pulses + Car horn” signal (18 appropriate reactions). The nearly uniform 83


distribution of answers across all categories for the “Two pulses + Bicycle bell” and the “Two pulses + Footsteps” signal indicate a certain unease of the subjects. “Critical variation one signals” (Two diss. pulses; Two diss. pulses + Car horn; Two diss. pulses + Bicycle bell; Two diss. pulses + Footsteps) are found to be partly successful for the intended purpose of causing the appropriate brake reaction. Besides of the anomaly skidding tires sound (Three pulses + Skidding tires), the remaining “critical variation two signals” (Three pulses; Three pulses + Bicycle bell; Three pulses + Footsteps) are mainly assessed in the comfort category.

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6.3 Agreement First of all, the high variances across all signals indicate a huge uncertainty in the individual assessment of the signals:

Figure 20: Agreement to the signal (Q7).

Within the category of comfort signals (green), the “New message” signal seems to be more agreeable than the alternative “Sonar ping” signal. The differences for the agreement in between the safety (yellow) and “critical variation one signals” (bright red) are fractional to non-existent. A loose in comfort or agreement for the hybricons compared to their abstract equivalents cannot be observed. Besides of the “Three pulses + Bic. bell” signal minor differences within the “critical variation two signals” (“Three pulses”; “Three pulses + Ski. tires”; “Three pulses + Footsteps”) are measured. Especially within the safety (yellow) and critical variation one signals (bright red; partly for the critical variation two signals {deep red}), the hybricons are not assessed a lot more or less urgent compared to their abstract equivalent. Addition of the natural component to the abstract sound seems not to affect the perceived comfort of the signal.

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6.4 General conclusions The results generally confirm the potential of hybricons as combined carriers for the nature or source as well as for the urgency of the potential hazard: While the abstract component can be used to scale the representational information to a certain degree of urgency, the usage of an appropriate auditory component as information carrier is suitable for conveying representational information regarding the traffic participant to expect. However it must be admitted that this ambiguous development proposal goes along with some fundamental issues uncovered by this experiment as well: Obviously, the hybricons auditory component also carries a certain level of urgency within itself. The skidding tires sound (Three pulses + Skidding tires) compared to its abstract equivalent (Three pulses) clearly unveils this issue. Furthermore,

the

representational

hybricons component

abstract to

an

component extent,

that

can it

also can

mask even

the

cause

misunderstandings (e.g. Two dissonant pulses + Car horn). Comprehensibility and urgency can be measured and treated separately, but they also influence each other. Whether the characteristics of sound can be described in mathematical dimensions and values, the human´s individual perception of sound and his individual experience are only two of many parameters, that can´t be described in objective dimensions. For conquering the balancing act between the three investigated constructs comprehensibility, urgency and agreeability, compromises within the sound design seems to be unavoidable. Nevertheless, the potential of the hybricons is existent, a lot of research e.g. in terms of raising the comprehensibility and levelling the urgency of the auditory icons to acceptable, applicable levels needs to be made. For investigating the practical application in terms of brake reaction times, eye-gaze, user annoyance and acceptance in-vehicle or simulator-based experiments are strongly suggested.

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6.5 Specific suggestions for the warning concept 6.5.1 Suggestions for the hybricons without a redesign Under the circumstances, that the sounds in this experiment are not going to be modified, the following suggestions for choosing between the available alternatives are made: For the comfort signals (Sonar ping; New message), the “New message” signal is preferable to the “Sonar ping” signal. It has been assessed less urgent in distance as well as in urgency, it owns the higher part of appropriate driver reactions and is finally the most comfortable signal. Since no alternatives for the safety signals (Two pulses; Two pulses + Car horn; Two pulses + Bicycle bell; Two pulses and footsteps) where tested no specific selection recommendations can be made. For the two sets of critical signals, the results indicate a better urgency mapping for the “critical variation one set” (Two diss. pulses; Two diss. pulses + Car horn; Two diss. pulses + Bicycle bell; Two diss. pulses + Footsteps) but in contrast better comprehensibility for the “critical variation two set” (Three pulses; Three pulses + Skidding tires; Three pulses + Bicycle bell; Three pulses + Footsteps). Due to this, it is difficult to give a recommendation which set to prefer. Because both sets are candidates for delivering the highest possible urgency, maybe the “critical variation one set” is the one to prefer. It´s not as comprehensible as the “critical variation two set”, but is has assessed more urgent, which can be interpreted as the vital feature or requirement for the critical sounds.

87


6.5.2 Suggestions for the hybricons in the case of a redesign The results indicate the potential of the hybricons for conveying information regarding the content as well as the urgency of the source of hazard, but the results are in most cases far away from being evident. According to the analysis and interpretation of the obtained data, a redesign of the signals should be considered to improve the quality of the critical signals in terms of comprehensibility (Two diss. pulses; Two diss. pulses + Car horn; Two diss. pulses + Bicycle bell; Two diss. pulses + Footsteps) and urgency (Three pulses; Three pulses + Skidding tires; Three pulses + Bicycle bell; Three pulses + Footsteps). Within the “critical variation one set” (Two diss. pulses; Two diss. pulses + Car horn; Two diss. pulses + Bicycle bell; Two diss. pulses + Footsteps) the author suggests three options (Table 16) for comprehensibility improvement. Table 16: Suggested solutions for comprehensibility improvement.

Option

Suggested Solution

Option A

Finding and usage of better auditory icons within the hybricons.

Option B

Repetition of the iconic part within the hybricons.

Option C

Widening of categories from individual traffic participants into two groups of vulnerable and non-vulnerable traffic participants.

Option A (Finding of better auditory icons for the individual traffic participant) This obvious task is easy to identify, but in fact hard to solve. For the well-known traffic participants, like cars, bicycles and pedestrians the corresponding iconic components (car horn, skidding tires, bicycle bell, footsteps) within the hybricons were admitted to be suitable for the intended purpose. Only the skidding tires hybricon (Three pulses + Skidding tires) could give prove of that Alternative auditory icons e.g. for a pedestrian, should be investigated and evaluated to ensure a certain degree of comprehensibility before confronting the subjects with the newly developed hybricons. (This can be seen as an issue referring to this experiment)

88


Option B (Repetition of the iconic part within the hybricons) The comprehensibility of the hybricons could also be increased by repetition of the auditory component within the hybricon. For example, within the specific hybricon, the bicycle bell icon could be played more than one time or the number of footsteps within the pedestrian hybricon could be increased. Of course this would result in longer duration times, which could be in turn caught up by increasing the frequencies of the iconic components. When considering the recommended redesign, the focus should be on maintaining the comprehensibility; playing the iconic part in a faster duration can easily lead to incomprehensibly signals and also to higher perceived urgency of the hybricon. Option C {Expanding the categories into two groups} A third option for gaining better values of comprehensibility could be a category expansion into two groups, e.g. vulnerable and non-vulnerable traffic participants. This can be seen as a “relative” attempt for comprehensibility improvement: For example, when widening the category of car and truck hybricons into a category of so called non-vulnerable traffic participants (vehicles with a crushcollapsible zone), an increasement in comprehensibility might be achieved. This approach goes along with several issues, like the challenge of finding auditory icons which represent different traffic participants. Consider an auditory icon representing a pedestrian, bicycle and motorbike for example.

89


According to the analysis and interpretation of the obtained data, also a redesign of the signals considered to improve the quality of the critical signals on terms of urgency. The question how to increase the urgency of the critical variation two set is hard to answer. The anomaly skidding tires sound (Three pulses + Skidding tires) uncovered how urgency can be increased by a natural component. Since that is not hypothesis of this research and corresponding iconic sounds for bicycles and pedestrian will be surely hard to find, urgency coding using auditory icons will not be considered here. So, Table 17 offers three possible solutions for urgency improvement. Table 17: Suggested solutions for urgency improvement.

Option

Suggested Solution

Option D

Finding and usage of better abstract earcons within the hybricons.

Option E

More distinct, noticeably, intensity adjustment of the abstract component of the hybricon.

Option F

Scaling of the auditory icons to a certain level of urgency.

Option D {Finding and usage of better abstract earcons for coding the urgency} According to the same solution offered for the representational component of the hybricon in Option A, an obvious procedure for more distinct differences in perceived urgency could be the use of alternative abstract earcons. Option E {More distinct intensity/loudness adjustment of the hybricons} Another possible way for increasing the perceived urgency of the critical variation two set (Three pulses; Three pulses + Skidding tires; Three pulses + Bicycle bell; Three pulses + Footsteps) could be a more clearly intensity adjustment of the hybricons according to the three degrees of urgency. Option F {Scaling of the auditory icons to a certain level of urgency} This option aims to the anomaly “Three pulses + Skidding tires” hybricon, which found to convey high urgency with its representational part. Even when urgency mapping using the iconic part of the hybricon is not scope of this thesis, the natural

90


component obviously carries a certain degree of urgency within. To minimize influences on perceived urgency due to the iconic component of the hybricon, a scaling of the auditory icons to certain degree of urgency is recommended: Either all representational components carry the same urgency within or all representational components of the corresponding degree of urgency carry the same urgency within, in theory the differences in urgency in between the sets should be minimized. In any redesign case, iterative evaluations for validation of the results are recommended.

6.6 Suggestions for further research Research demanded examinations of new and effective emergency warnings for in-vehicle ADAS (Fagerlönn, 2007; Edworthy, 1999) so this experiment investigated the general potential of three sets of hybricons to convey driving related safety information via the auditory channel. According to the results (for this specific hybricons) it seems to be possible to code the urgency of the hazard with an abstract component as well as the source of the hazard with a representational component into one single signal. Interesting would be the question to what extent the comprehensibility and urgency of a pure iconic signal are dependant to each other: The hybricons representational component obviously carries a certain level of urgency within itself. To minimize this issue within the warning concept, the inherent urgency of auditory icons or representational sounds should be investigated. In consequence of this, a subgoal to accomplish could be the creation of representational auditory icons with a constant level of perceived urgency. After this “adjustment” and validation of the audicons, which was actually not applied to the auditory icons for this experiment, they can be fused with abstract earcons to scale them to a desired level of urgency. An alternative approach for delivering representational as well as urgency-related information could be the use of pure urgency levelled auditory icons. But this approach goes along with several obstacles, like the indistinguishability problem

91


compared to the environmental sounds and the old issue of finding appropriate auditory icons itself as well as for certain levels of urgency AND the corresponding iconic component. While a car horn sound may convey “car” and a broad range of urgency depending on the design and characteristic of the horn sound itself, a skidding tires sound will mostly convey “car” and “high urgency” to the driver. Well the problem in this approach is that an appropriate warning concept has to consider not only cars but also bicycles, pedestrians and trucks for example. Finding a comprehensible pedestrian auditory icon is quite hard, finding or creating two variations of this icon to code the urgency of the signal as well may be even harder.

92

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96

Appendix A – Technical sound description

Appendix A - Technical sound description Table 18: Selected parameters of the evaluated sounds.

Signal

Duration [sec]

Mean Mean Intensity Intensity [db]* [dbfs] Praat *Soundbooth

mean pitch [Hz]* Praat

Comfort Signals Sonar ping

1.47

-23.32

64.05

585

New message

1.65

-17.29

69,91

261

Critical Signals Two pulses

0,79

-14.13

67.52

526


0.79

-15.91

72.45

213


0.79

-19.36

66.76

453


1.32

-14.12

65.48

494

Critical signals (variation one) Two diss. pulses

0.73

-6,87

78.01

255

Two diss. pulses + Car horn

0.75

-3.64

85,9

146


0.74

-6,8

79,69

355

Two diss. pulses + Footsteps

0.73

-6.87

78.54

256

Critical signals (variation two) Three pulses Three pulses Skidding tires

+

Three pulses Bicycle bell

+

0.82

-9.13

78.93

526

0.85

-9.78

80.53

374

0.82

9.65

74

460

97


Signal

Three pulses Footsteps

Duration [sec]

+

0.75

Mean Mean Intensity Intensity [dbfs] [db]* *Soundbooth Praat -9

78.80

mean pitch [Hz]* Praat

504

98


Figure 21: Sonar ping.

Figure 22: New message.

99


Figure 23: Two pulses.

Figure 24: Two pulses + Car horn.

100


Figure 25: Two pulses + Bicycle bell.

Figure 26: Two pulses + Footsteps.

101


Figure 27: Two dissonant pulses.

Figure 28: Two dissonant pulses + Car horn.

102


Figure 29: Two dissonant pulses + Bicycle bell.

Figure 30: Two dissonant pulses + Footsteps.

103


Figure 31: Three pulses.

Figure 32: Three pulses + Skidding tires.

104


Figure 33: Three pulses + Bicycle bell.

Figure 34: Three pulses + Footsteps.

105

Appendix B – Interactive questionnaire

Appendix B – Interactive questionnaire This Appendix illustrates all pages of the study followed by a short description of each individual page. The main title of each sheet is translated (written in cursive brackets) and the salient points are explained.

Figure 35: Interactive questionnaire page 1.

Short description (Evaluation study for auditory signals) Page 1 is nothing more than a simple welcome page introducing the subjects to the study; the title says “Evaluation study for auditory signals”. The subjects are welcomed and acknowledged for participating in the experiment. At the bottom is a little hint, how to navigate between the pages: The green button in the lower right corner directs to the next page. On the lower left corner is a simple page counter giving the subjects feedback about their progress.

106



Short description (What is it all about?) This page introduces the subjects in detail to the SAFESPOT Project, the ADAS going to be developed it´s the relation to auditory signals: The official homepage is quoted as well as the foundation of the Project on C2C communication. The project handles with the improvement of existing ADAS in terms of range and detail information. Auditory signals are an integral element of the SAFESPOT warning concept. Furthermore, the subjects are informed about the handling time to expect (approximately 20 minutes) and instructed to answer the questions without hesitation and in all conscience.

107



Short description (Performance directions) This page ensures the correct functionality of the audio output. By pressing the loudspeaker icon on the lower part of the page, a three-staged test tone can be displayed to. The subject´s were advised to adjust the loudness of their personal computer/audio output to a level, where the most quiet test tone was still hearable without problems while the most unquiet tone could be comfortably heard. Furthermore the usage of headphones was recommended.

108



Short description (Hints for analysis) This page informs the subjects about the privacy policy. Personal data will not be delivered to third party and the results will be treated with confidence. Furthermore, it is expressed that the experiment aims not to assess the subject´s behaviour, but rather that the subject´s are in charge for the assessment of the signals.

109



Short description (Inquiry of the subject´s personal data) This page represents the first page where the subjects could interact within the study. The following demographic characteristics are collected: • • • • •

Age, Gender, Ownage of a valid driver´s license, Years of holding the driver´s license and Mileage per year.

110



Short description (What does the study look like?) Main intention of this page was to introduce the layout as well as the questions to the subjects. The upper text informs the subjects how to start the video and the general ability to repeat the video if required. In addition, the subjects are advised to read over the question in all conscience. The fact, that for every video the same questions will be asked is also mentioned. When clicking the play button on the upper left image, the subjects saw the 20 seconds introduction video of the car climbing the hill while passing another car and a truck. Before reaching the hill, the video smoothly fades out. The questions have already been discussed in detail (see chapter 4.4.3) and will not be listened here.

111



Short description (Final advice) The final advice page consisted of some additional information regarding the evaluation process: The subject´s are informed, that they will see 14 identical video clips, each one equipped with a different auditory signal. Each clip is 6 seconds in duration and can be repeated by will. Furthermore, the subjects are advised to answer the questions in chronological order form 1 to 7. “Question 8” is an optional commentary field.

112



Short description With this page, the actual evaluation process started. When clicking on the play button, the subject´s saw a six seconds video clip displaying an auditory warning signal and immediately freezing after. Because of the complete identical look from pages 8 to 21 and to avoid misunderstandings, from now on a transition effect between each page was applied to the study.

113



Short description (Thanks for participating!) The last page of the questionnaire gives final advice • how to save the results when clicking the red finish button in the lower right corner of the screen, • to send the Presentation back to the experimenter.

114

Appendix C – Obtained data

Appendix C – Obtained data Table 19: Subject´s personal data.

/ Driver´s license

Holding driver´s license [years]

Average mileage per year [km]

Subject

Age [years]

Male female

1

31

Male

y

13

50000

2

24

Female

y

6

30000

3

27

Female

y

9

25000

4

54

Female

y

36

8000

5

61

Male

y

41

14000

6

27

Male

y

8

800

7

34

Male

y

16

13000

8

27

Male

y

10

20000

9

26

Female

y

8

20000

10

25

Female

y

7

35000

11

24

Male

y

6

12000

12

27

Female

y

9

15000

13

27

Female

y

9

15000

14

29

Male

y

11

12000

15

29

Male

y

9

18000

16

26

Male

y

8

10000

17

29

Male

y

11

18000

18

26

Male

y

8

15000

19

21

Female

y

3

20000

20

18

Female

y

2

4000

21

24

Female

y

6

15000

22

22

Female

y

2

5000

115


/ Driver´s license

Holding driver´s license [years]

Average mileage per year [km]

Subject

Age [years]

Male female

23

61

Female

y

30

6000

24

27

Male

y

9

10000

25

28

Male

y

10

25000

26

22

Female

y

4

10000

Mean

29.9

11.2

16377

Table 20: Scenario-Signal-Relationship.

Scenario Correspond ending sound signal 1

Sonar ping

2

Two pulses

3


4


5

Two dissonant pulses + Car Horn

6


7

Two dissonant pulses + Bicycle bell

8


9

Two dissonant pulses + Footsteps

10

New message

11


12


13


14

Three pulses

116

Appendix C – Obtained data Table 21: Scenario sequences for each subject.

Scenario sequences for each subject

Subject

(chronological order from left to right)

1

7

8

11 12

9

3

4

14

6

5

2

10 13

1

2

14

7

4

1

9

11

2

6

10 12

8

5

13 14

3

1

13

2

7

8

5

6

3

4

14

9

11 10 12

4

10

7

14

3

1

4

9

6

5

13 11

2

8

12 10

5

12

7

11 10

1

13

6

4

14

3

2

9

5

8

12

6

14 12

6

5

4

11

9

13

1

3

7

10

8

2

14

7

8

1

11

5

10 13

4

2

9

7

12 14

6

3

8

8

6

13

2

11

8

1

4

7

12

3

5

10 14

9

6

9

8

12 10

9

13

1

7

14 11

4

3

6

5

2

8

10

10

8

4

14 13

2

3

6

12

5

1

7

11

9

10

11

7

6

5

13

3

14

1

4

8

2

11

9

10 12

7

12

3

6

2

4

13 11 12 14

7

5

9

10

8

1

3

13

14

1

12 11

9

5

7

10

2

6

8

4

3

13 14

14

6

13

3

4

8

5

10

1

11

2

7

12

9

6

15

2

4

11 10 12

1

5

7

9

13

8

6

3

14

2

16

1

6

2

13

9

7

3

11

5

4

12 14 10

8

1

17

4

12

5

6

8

10

9

2

3

1

7

14 11 13

4

18

1

7

8

3

12

9

6

14 13

5

4

2

10 11

1

19

12

3

8

7

10

9

6

11

4

14

2

1

5

13 12

20

2

11

7

1

3

10

9

6

14

5

4

12

8

13

2

21

14 10

9

5

1

4

3

12

6

13

2

11

7

8

14

22

6

5

9

14

3

4

11 10

2

13

7

8

1

12

6

23

5

12 13

4

7

14

8

9

1

6

11

3

10

2

5

24

13 11

3

14 10

8

1

4

9

12

6

7

2

13

5

14

3

7

1

117


Scenario sequences for each subject

Subject

(chronological order from left to right)

25

8

5

14 11 12

1

3

9

4

2

10 13

7

8

26

6

1

4

14 13 10

8

12

2

9

11

6

3

7

6

5

Table 22: Results for question 1.

Signal

Categories 9 within each signal with a nomination of at least two 10. nothing, don´t know

car

truck

bicycle

pedestrian


9

10

less than 2

3

2

New message

9

9

less than 2

2

2

Safety signals Two pulses Two pulses + Car horn Two pulses + Bicycle bell Two pulses + Footsteps

4

12

less than 2

7

less than 2

2

19

4

less than 2

less than 2

less than 2

6

less than 2

16

less than 2

less than 2

8

less than 2

2

14

less than 2

less than 2

Critical Signals (variation one) Two diss. pulses

9

5

7

9

Categories are created under the qualification that a keyword has to be named by the subjects at

least two times. 10

By way of illustration, the corresponding number of answers nominated the most within each

individual signal is written in bold letters.

118


Signal

Categories within each signal with a nomination of at least two. nothing, don´t know

Two diss. pulses + Car horn Two diss. pulses + Bicycle bell Two diss. pulses + Footsteps

car

truck

bicycle

pedestrian

less than 2

10

14

less than 2

less than 2

less than 2

5

6

14

less than 2

less than 2

5

7

less than 2

12

Critical signals (variation two) Three pulses

9

9

less than 2

2

2

Three pulses

less than 2

22

2

less than 2

less than 2

4

6

less than 2

15

less than 2

5

5

2

less than 2

10

+ Skidding tires Three pulses + Bicycle bell Three pulses + Footsteps

119

Appendix C – Obtained data Table 23: Results for question 2 and question 3.

Signal

Question 2 (Confidence in Question 1)

Question 3 (Estimated distance)

Mean value

Mean value

standard deviation

standard deviation


-10,9411765

18,8926923

380,647059

201,350112

New message

-17,1764706

19,4558323

499,352941

327,407418

Safety signals Two pulses Two pulses + Car horn Two pulses + Bicycle bell Two pulses + Footsteps

-9,04545455

22,0096889

399,136364

293,242837

3,41666667

21,9780853

311,125

200,978544

-4,16

23,5914533

345,88

267,364969

3,92

25,2403777

304,28

255,435824

Critical signals (variation one) Two diss. pulses Two diss. pulses + Car horn Two diss. pulses + Bicycle bell Two diss. pulses + Footsteps

-4,52380952

20,6920735

213,809524

173,70654

2,84615385

22,965526

215,269231

140,522043

0,8

25,7730479

166,76

94,0169666

4,42307692

24,3559817

141,230769

109,784264

Critical signals (variation two) Three pulses Three pulses + Skidding tires Three pulses + Bicycle bell

-8,22727273

18,9282651

295,045455

175,081063

4,04

21,1374076

66,96

56,9067073

-1,81818182

21,9363503

259,181818

231,453304

120


Signal


Question 2 (Confidence in Question 1)

Question 3 (Estimated distance)

Mean value

standard deviation

Mean value

standard deviation

-8,33333333

22,1773157

242,142857

180,790842

For question 2 a slider from a range of -40 to +40 could be positioned according to the response for the question: How confident do you feel with your answer in Question 1; -40 matched very uncertain, +40 matched certain.

For question 3 a slider from a range of 0 to 1000 could be positioned according to the response for the question Where do you expect the road user?; 0 matched very close, 1000 far away.

121


Signal

Question 4 (Confidence in Question 3) Mean value

standard deviation

Question 5 (Urgency of the signal) Mean value

standard deviation


32,6470588

19,1276671

-14,0769231 23,6489714

New message

41,7058824

23,0400866

-22,1538462 24,0327981

Safety Signals Two pulses Two pulses + Car horn Two pulses + Bicycle bell Two pulses + Footsteps

34,7727273

21,8107265

-12,6538462

18,3694144

32,7916667

18,6057008

-1,88461538

16,2833091

41,56

17,8514238

-9,46153846

19,0204748

37,64

20,0496883

-6

22,3606798

Critical Signals (variation one) Two diss. pulses Two diss. pulses + Car horn Two diss. pulses + Bicycle bell Two diss. pulses + Footsteps

37,952381

19,0380571

11,9230769

15,0011282

36,6538462

21,290265

17,6153846

16,9329901

38,4230769

20,3256942

14,2692308

18,5333379

37,3846154

20,6650951

20,4615385

17,0744974

Critical signals (variation two) Three pulses Three pulses + Skidding tires Three pulses + Bicycle bell

35,9090909

17,8269702

-2,57692308

22,9332476

56,48

21,5776119

33,3461538

7,96463336

34,8181818

16,4624721

0,65384615

22,9920722

122


Signal


Question 4 (Confidence in Question 3) Mean value

standard deviation

32,2857143

18,4421877

Question 5 (Urgency of the signal) Mean value 2,84

standard deviation 18,4789971

For question 4 a slider from a range of -40 to +40 could be positioned according to the response for the question: How confident do you feel with your answer in question 3; -40 matched very uncertain, +40 matched certain.

For question 4 a slider from a range of -40 to +40 could be positioned according to the response for the question How urgent is the signal to you?; -40 matched low, +40 matched high.

123


Signal

Question 6 (Subject´s Reaction ) 11 Drive

Roll

Question 7 (Agreement to the signal) Brake

Mean value

standard deviation


13

7

6

9,45833333

18,4908418

New message

17

6

3

22,8076923

18,4326216

Safety Signals Two pulses Two pulses + Car horn Two pulses + Bicycle bell Two pulses + Footsteps

9

14

3

12,7307692

19,2261441

4

18

4

9,61538462

15,0175282

9

10

7

15,9230769

15,5355671

8

10

8

11

20,6842936

Critical Signals (variation one) Two diss. pulses Two diss. pulses + Car horn Two diss. pulses + Bicycle bell Two diss. pulses + Footsteps

4

12

10

1,92307692

16,047238

1

14

11

-2,80769231

20,1375654

1

4

21

-2,61538462

18,3064512

6

14

6

0,61538462

22,1071516

Critical signals (variation two) Three pulses Three pulses + Skidding tires 11

4

16

6

2

21,6296093

2

9

15

-3

20,0599103

By way of illustration, the corresponding number of answers nominated the most within each

individual signal is written in bold letters.

124


Signal

Three pulses + Bicycle bell Three pulses + Footsteps

Question 6 (Subject´s Reaction )

Question 7 (Agreement to the signal)

Drive

Roll

Brake

Mean value

standard deviation

0

3

23

11,0769231

19,5753377

3

16

6

3

19,6022958

For question 6 a multiple choice answer regarding the columns of Table 25 could be chosen from: of -40 to +40 could be positioned according to the response for the question: How would you react?

For question 7 a slider from a range of -40 to +40 could be positioned according to the response for the Question How urgent is the signal to you?; -40 matched uncomfortable, +40 matched comfortable.

125

Appendix D – Quantitative analysis

Appendix D – Quantitative analysis Table 26: Chi2 frequencies and residuals for question 1.

Frequencies

Observed N

Expected N

Residual

Safety signals Two pulses + Car horn



False

7

13,0

-6,0

True

19

13,0

6,0

Total

26

False

10

13,0

-3,0

True

16

13,0

3,0

Total

26

False

12

13,0

-1,0

True

14

13,0

1,0

Total

26

Critical signals (variation one) Two diss. pulses + Car horn


Two diss. pulses + Footsteps

False

16

13,0

3,0

True

10

13,0

-3,0

Total

26

False

12

13,0

-1,0

True

14

13,0

1,0

Total

26

False

13

13,0

,0

True

13

13,0

,0

Total

26

126

Appendix D – Quantitative analysis

Frequencies

Observed N

Expected N

Residual

Critical signals (variation two) Three pulses + Skidding tires



False

4

13,0

-9,0

True

22

13,0

9,0

Total

26

False

11

13,0

-2,0

True

15

13,0

2,0

Total

26

False

16

13,0

3,0

True

10

13,0

-3,0

Total

26

127

Appendix D – Quantitative analysis Table 27: Chi2 results for question 1.

Signals

Chi-Square

df

asymptotically significance

Safety signals H_carhorn_2

5,538 a

1

,019

H_bb_2

1,385 a

1

,239

H_pd_2

,154 a

1

,695

Critical signals (variation one) H_carhorn_3_1

1,385 a

1

,239

H_bb_3_1

,154 a

1

,695

H_pd_3_1

,000 a

1

1,000

Critical signals (variation two)

a

H_skidding_tires_3_2

12,462a

1

,000

H_bb_3_2

,615 a

1

,433

H_pd_3_2

1,385 a

1

,239

a. 0 cells (,0%) have expected frequencies less than 5. The minimum expected cell frequency is 13,0.

128

design and assessment of informative auditory warning signals for adas

design and assessment of informative auditory warning signals for adas

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