Comparing the User Experience of Touchscreen Technologies in an Automotive Application Matthew J. Pitts1 Lee Skrypchuk2 1 WMG, University of Warwick Coventry CV4 7AL, United Kingdom +44 (0) 24 7657 5936 {m.pitts; a.attridge; m.a.williams.1} @warwick.ac.uk ABSTRACT
Touchscreen interfaces are increasingly used on a daily basis in both mobile devices and in cars. The majority of vehicles use resistive touchscreens which, while reliable and inexpensive, may not perform as well as alternative touchscreen technologies. A simulator-based user-centred study was conducted to compare the User Experience of resistive touchscreens against capacitive and infra-red variants in a range of automotive use cases. This paper details an initial treatment of the data focusing on touchscreen task performance and subjective usability measures. Findings identified that the resistive display was clearly least preferred, with capacitive offering the best overall performance. Author Keywords
Touchscreen; HMI; Automotive ACM Classification Keywords
H.5.2. User Interfaces - Input devices and strategies (e.g., mouse, touchscreen) INTRODUCTION
The touchscreen interface has become part of our daily technology experience, driven largely by the prevalence of the technology in smartphone and tablet devices. It is estimated that 97% of all smartphones will feature touchscreen interfaces by 2016 [1], with annual smartphone sales now topping one billion units per annum [2]. Touchscreen interfaces offer a number potential usability benefits [3]. Firstly, the flexibility of the interface allows multiple functions to be controlled with a single physical configuration. Input is direct as the display and input Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for components of this work owned by others than ACM must be honored. Abstracting with credit is permitted. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. Request permissions from
[email protected]. AutomotiveUI '14, September 17 - 19 2014, Seattle, WA, USA Copyright 2014 ACM 978-1-4503-3212-5/14/09…$15.00 http://dx.doi.org/10.1145/2667317.2667418
Alex Attridge1 Mark A. Williams1 2 Jaguar Land Rover Abbey Road Whitley Coventry CV3 4LF, United Kingdom
[email protected] elements of the interface are co-located, enabling an intuitive mode of interaction that is easy to learn even for novice users [4]. Touchscreen interfaces also provide the opportunity for vehicle designers to reduce the number of physical controls visible in the vehicle interior, creating a cleaner and less cluttered design (see Volvo’s 2014 Concept Estate as a recent example [5]). The Handbook of Visual Display Technology [6] details four basic types of touchscreen technology which are applicable to mobile and automotive applications: resistive, capacitive, surface acoustic wave (SAW) and infra-red (IR). The key features of each are discussed below. Resistive – Touch sensing is based on electrical conduction between a flexible front layer and a stiff back layer. This allows use with non-conductive objects (e.g. a gloved finger), but generally requires a higher input force than other designs. The technology is mature and relatively inexpensive, but commonly-used designs only support single-touch inputs. Resistive screens currently account for nearly all of the automotive market, although it is predicted they will be replaced by capacitive devices over the next few years [7]. Capacitive – This type of touchscreen features a transparent conductive layer that senses the change in capacitance that occurs when a conductive object, such as a finger or stylus, is brought into proximity. Projected Capacitive (PCAP) touchscreens, as widely used in mobile phones, support multi-touch inputs and offer greater visual clarity than resistive, albeit at a higher cost. Surface Acoustic Wave – SAW touchscreens utilise acoustic transducers at the edges of the screen that create a field of ultrasonic waves. The field is disturbed when the user touches the screen, allowing input to be sensed. As the screen has no additional sensing overlay, it offers improved visual clarity compared to resistive and capacitive types. However, this type of screen can be difficult to environmentally seal and screen contamination can cause sensing errors. Infra-Red – IR touchscreens use a grid of transmitters and receivers around the edge of the display; when a user touches the screen the IR beams are broken and the
location of the touch can be derived. As such, the display effectively requires zero input force and can be inputs can be made with any object. As with SAW, there is no sensing overlay to limit visual clarity. The spatial sensing resolution of IR touchscreens is however limited by the pitch of the transmitter/receiver array, and sensitivity may be affected by ambient light levels. Automotive applications for touchscreens present specific issues relating to visual workload and ergonomics. As touchscreens utilise visual output to relay information, the driver is required to divert their attention away from the forward roadway. Early research into CRT touch panels in cars [8] found that drivers were more prone to driving and secondary task errors when using touchscreens, due to their inherent visual workload demand. Tsimhoni et al [9] evaluated speech-based methods of destination entry versus a touchscreen keyboard and found that touchscreen interaction resulted in longer task times and increased lateral lane variation, although degradation in driving performance was also observed for speech-based interactions. Bach et al. [10] compared touchscreen interaction to traditional tactile push buttons and gesture inputs, and found that while touchscreens allowed the fastest task times, they also required the highest number of long (>2 second) eye glances. In a study of input and output modalities, Christiansen et al [11] found gesture input required fewer eye glances than touch input, but caused greater degradation in driving performance. Fuller et al. studied the effect of different touchscreen positions, concluding that increasing the visual or physical distance of the display to the driver increased task completion times [12] and glance count [13]. Examples of comparisons between touchscreen technologies for automotive applications are limited. Burnett et al. [14] compared capacitive and resistive touchscreens in a driving simulator-based study using a number of different input and manipulation tasks. Their findings identified a reduction in task times for the capacitive display, with a higher number of long glances (>2 seconds duration) made when using the resistive screen. Their work does not however include any other touchscreen types, nor investigate users’ affective responses to the technologies. Study outline
The increased prevalence of touchscreen devices raises questions relating to the use of touchscreens in automotive applications, where the market is largely dominated by an incumbent but arguably outdated technology. A study was therefore proposed to investigate the relative benefits of resistive, capacitive and infra-red touchscreens in terms of their user experience. This paper details an initial treatment of the data gathered; as such, the driving performance data is not discussed, instead focusing on objective task performance along with subjective measures of workload, usability and affective response.
Research questions and hypotheses
The study aimed to address the following research questions: Can drivers differentiate between different types of touchscreen technology in use? Do drivers display a preference for touchscreen technology types? Is the performance of touchscreen tasks influenced by interface technology? What are the key aspects of user experience for touchscreens in an automotive context? The hypothesis was formed that drivers would be able to identify a difference between the capacitive display (as commonly used on smartphones and tablets) and the resistive display. As the tasks performed in the study were identical for all devices under test (see ‘Experiment design’), no major differences in objective measures of task performance were expected. However, subjective evaluations of task performance were expected to reflect users’ expectations, highlighting differences in the relative user experience of the devices. METHODOLOGY Participants
A total of 20 participants were recruited for the study, 17 male and 3 female. Two male participants withdrew from the study due to the effects of simulator sickness. For the remaining 18, age ranged from 21 to 60 years (mean = 39.4 years, SD = 13.6 years). All participants were UK drivers with a minimum of 1 year experience; all had experience of using touchscreen devices and owned touchscreen-based smartphones, with 8 being regular users of factory-installed in-car touchscreen systems. Equipment
The study was conducted using the WMG driving simulator, a medium-fidelity, fixed-base system based on the cabin of a 2009 Jaguar XJ premium saloon car, shown in Figure 1. The simulator provides a context-rich environment to facilitate the evaluation of in-vehicle technologies, retaining the interior features of the original vehicle. The vehicle controls are instrumented and the steering is fitted with a force-feedback system. The virtual environment is generated using Oktal SCANeR Studio software. Visualisation consists of three forward projection screens encompassing a 135° viewing angle, using three SXGA+ resolution projectors. A 5.1 channel surround sound system provides immersive audio from both traffic vehicles and the driver’s vehicle, including engine, road and wind noise.
Figure 1 - WMG driving simulator
Figure 3 - GUI menu screen
The simulation scenario employed featured a three-lane motorway, with lane widths and road markings based on UK road specifications. The roadway featured constantradius curvature in alternating clockwise and counterclockwise directions, requiring constant lane tracking input in order to maintain lateral position. Participants were required instructed to follow a lead vehicle that was travelling at a constant speed, at what they perceived to be a safe distance. Additional automated vehicles were included for context but the scenario did not require negotiation of traffic. A screenshot from the simulator is shown in Figure 2.
The devices were designed to be visually identical, each with the same bezel and running the same user interface, with display brightness levels normalised. The display units were mounted in the centre console of the simulator vehicle cabin in the horizontal and vertical position of the original touchscreen; due to the size of the display bezel and the mounting arrangement, the touchscreen protruded slightly when fitted, as shown in Figure 4.
Figure 4 - Touchscreen installed in simulator cabin Figure 2 - Simulator screen shot
The study utilised three technology evaluator touchscreen devices developed by Continental AG. The devices consisted of a screen unit mounted in a common bezel, connected to a display controller driven by an embedded Linux device running a custom GUI application. This was designed to emulate a typical automotive user interface and featured a range of functionality commonly found in modern vehicles, including navigation, audio, telephone and text message functions; the tasks are discussed further below. The menu screen for the interface is shown in Figure 3.
Experiment design
The study utilised a 3x10 within-subjects experiment design, with display type and task type as the independent variables. Participants completed a baseline drive with no secondary tasks, followed by three evaluation drives using one of the displays per drive. The experiment design was counterbalanced for display presentation order. The average duration of each drive was approximately 10 minutes. Participants completed a total of ten touchscreen tasks per drive, representing a range of automotive use cases and requiring different levels of menu navigation, described below. Tasks were initiated by the experimenter via verbal instruction. Tasks were varied slightly across the three displays to avoid repetition but retaining the same number of inputs to complete (e.g. button presses).
Audio Tasks
Radio Preset – select specified radio station from preset stations Seek radio station – adjust radio tuning to specified frequency Select track from playlist – select and play the specified audio track from the USB playlist using list scrolling Navigation tasks
Destination Entry – Input a 7 character UK post code using the QWERTY keyboard and initiate route guidance Map scroll – Scroll the map to the programmed navigation destination Map rotate – Rotate the navigation map through 180° using a gesture or soft keys Messaging tasks
SMS reply, QWERTY entry – Reply to an existing SMS with a specified three-word, 13-character phrase (e.g. ‘be right back’). Participants were instructed to complete the phrase in full and avoid abbreviations (‘txt speak’) SMS reply, handwriting entry – The interface was programmed with a ‘spoofed’ handwriting entry function, whereby inputs to the screen would emulate the sequential input of characters from a pre-determined phrase. By using this approach with the message task above, a convincing handwriting recognition effect was achieved Phone tasks
Call from contact list – select and call a specified contact from the contact list, using list scrolling Dial number and call – Enter a UK phone number using a numeric keypad and initiate the call. Participants were instructed to use a number that was familiar to them Task presentation order was determined by using a 10x10 latin square to balance for first-order repetition effects. User interface training was provided using the capacitive display on-bench in a static condition prior to the commencement of the dual-task drives. Dependent variables
A range of objective and subjective data were collected. Firstly, user inputs to the touchscreen were logged by the interface software, enabling the calculation of task completion time. Participants completed a questionnaire after each drive to provide subjective rating data across a number of measures. Overall liking was assessed using the 9-point hedonic rating scale [15] with semantic anchors at each point. Workload was assessed using the NASA-RTLX method [16] and usability of the touchscreen system was assessed using the System Usability Scale [17, 18]. Finally, a semi-structured interview was conducted on completion of all drives to gain qualitative insights into the relative User Experiences of the three display technologies. This
included a record of participants’ most and least preferred displays. RESULTS
Due to a technical failure of the resistive display part way through the study, the data are effectively split into two sets, with twelve participants having experienced all three displays and six participants having experienced the capacitive and infra-red (IR) displays only. While this split must be enforced for all subjective data, it is legitimate to consider objective task completion time data across all 18 participants when comparing the capacitive and IR displays, as it is assumed that task performance using one device does not influence subsequent performance using another. The findings are therefore presented below with this structure in place. Task completion time
Figure 5 shows the mean task completion time per task for the three displays experienced by twelve participants. Mean task time ranged from 9.1s (radio preset task, resistive display) to 60.9s (handwriting text entry task, IR display). A two-way within-subjects ANOVA showed that while interaction was significant (F(18,198) = 1.93, p
