Designing High Quality ICT for Altered Environmental Conditions Daryoush Daniel Vaziri, Dirk Schreiber, Andreas Gadatsch Bonn-Rhine-Sieg University of Applied Science, Sankt Augustin, Germany
[email protected] [email protected] [email protected] Abstract: This article concerns the design and development of Information- and Communication Technology, in particular computer systems in regard to the demographic transition which will influence user capabilities. It is questionable if current applied computer systems are able to meet the requirements of altered user groups with diversified capabilities. Such an enquiry is necessary based on actual forecasts leading to the assumption that the average age of employees in enterprises will increase significantly within the next 50-60 years, while the percentage of computer aided business tasks, operated by human individuals, rises from year to year. This progress will precipitate specific consequences for enterprises regarding the design and application of computer systems. If computer systems are not adapted to altered user requirements, efficient and productive utilisation could be negatively influenced. These consequences constitute the motivation to extend traditional design methodologies and thereby ensure the application of computer systems that are usable, independent of user capabilities. In theory as well as in practice several design and development concepts described are respectively applied. However, in most cases these concepts are considered as solitary independent solutions. Generally, theories contrast usability and accessibility as two different concepts. While the first provides possibilities for specific user groups to accomplish tasks efficiently, effectively and satisfactorily, the latter provides solutions taking into consideration people with a wide range of capabilities, such as disabled people or people with an enduring health problem. Both concepts are quite extensive. Therefore developers tend to decide between these concepts, which always leads to failures. This article seeks to provide a universal design and development approach for computer systems, by combining these individually considered concepts into one common approach. This approach will not distinguish between user groups, but instead, will provide procedures and solutions to design computer systems, which consider all relevant user capabilities. The results of this article provide a theoretical approach for design and development cycles. Enterprises will be sensitised for the identification of relevant user requirements and the design of human-centred computer systems. Keywords: Universal design, usability, accessibility, Information and Communication Technology, computer system, demographic transition
1. Introduction The effective and productive application of computer systems is highly dependent on the user’s capabilities. Therefore it is crucial to analyse the user’s behaviour when interacting with computer systems. Figure 1 defines the authors’ comprehension of computer systems in the context of this article.
Figure 1: Computer system
However, in many cases the requirement analysis concentrates on specific stakeholders that are currently employed or involved with the system and as such does not consider requirements of potential users with
divergent capabilities. Such a combination of system functionalities and new user capabilities will eventually result in a mismatch that might reduce efficiency and productivity.
2. Background Figure 2 schematically visualises the mismatch of user requirements and system functionalities. Diversity of user capabilities
Mismatch of user requirements and system functionalities
Computer system lifecycle
Figure 2: Coherence of user capabilities and system lifecycle
The trigger for this development is the demographic transition of industrialised nations. In most industrialised countries the population declines and grows old (Lutz et al, 2011). Figure 3 provides an overview of the latest population data and estimations up to the year 2050 for the nations France, Germany and United States of America (United Nations, 2010).
Figure 3: Demographic transition of industrialised countries
While the percentage of people aged 15-24 declines and respectively stagnates, the percentage of people aged 60-65 or over increases significantly. As fewer young people join the labour market, enterprises need to compensate by employing older personnel for the required human resources. In addition, the intergenerational contract demands that employees retire at a later date (Sanderson et al, 2010), as life expectancy rates increase (Leon, 2011). The authors identified three consequences, which will affect the development of computer systems. Consequence 1: The age distribution in enterprises will rise; therefore capabilities of older user groups might differ significantly from younger user groups. Susceptibility to disorders or injuries related to computer work tendentially has to be classified higher than for younger employees. A survey from the year 2001 examined upper extremity disorders of 485 people. The mean age of that group was 38.5 years. Seventy per cent were computer users. Significant findings of that survey included postural misalignment with protracted shoulders
(78%), head forward position (71%), neurogenic thoracic outlet syndrome (70%) and many more (Pascarelli et al, 2001). Consequence 2: Enterprises will lack young qualified personnel that cannot be compensated for by elder employees. To sustain capability to compete on the global market, enterprises need a specific number of young employees, who may have just completed academic and/or vocational training to integrate modern, unprejudiced and open minds. Enterprises thereby benefit from radical, innovative ideas and therefore need to look out for additional sources of human capital. One source could be found in people with disabilities or people who mainly have an enduring health problem. Europe is inhabited by approx. 502 million people (Marcu, 2011). In 2010 approx. 67 per cent respectively 336.4 million of Europe inhabitants were declared as working age population (European Comission Eurostat, 2011). About 45 million people of the declared working age population either had a disability or an enduring health problem (European Comission Eurostat, 2003). Worldwide the number of disabled people aged 15 and older is estimated as 720 million (World Health Organization, 2011). However, current computer systems do not meet the requirements of this user group. Consequence 3: Susceptibility to mental disorders induced by computer-related stress factors increases. In the latest report, Wittchen et al. learned that almost 165 million Europeans suffer from brain disorders like depression, anxiety, insomnia or dementia every year (Wittchen et al, 2010). This is an increase of about 100 million people compared to a similar major European study of brain disorders conducted in the year 2005 (Walker, 2011). Current HCI research does not sufficiently deal with these developments. In the professional context, most human-computer-interactions are still executed with keyboard or mouse devices. Graphical User Interfaces (GUI) become more complex and require the user to apply more cognitive resources. With regard to the demographic transition, the authors identified the need to provide a universal design approach for computer systems that takes environmental alterations into account.
3. Universal approach to the design of computer systems The following paragraphs will introduce the reader to a universal design approach. Consideration of recommendations and thoughts given in these paragraphs will improve the long-term usability of computer systems.
3.1 Human-centred design of interactions When it comes to defining interaction design, three major schools of thought can be distinguished (Saffer, 2010): • A technology centred view • A behaviourist view • A social Interaction Design view Human-centred design can be classified in the behaviourist view. The behaviour of people using products is the central focus of interest. Rather than centred on the restrictions of end user capabilities, the majority of professional system development is constrained to specific software packages or technologies and the capabilities associated with them (Poslad, 2009; Kolko, 2011). In most cases, this leads to company cultures that are strongly computing centred (Kolko, 2011). However, research studies showed that comprehension and consideration of human behaviour and human capabilities, for the purposes of system development, result in more usable and accessible products (Kolko, 2011; Wickens et al, 2000). A cyclic process of perceiving, thinking, recognising, acting and evaluating actions can be observed, when users interact with computer systems (Monk, 1998). Figure 4 shows how main elements of cognition interact with one another and in the wider context of cognitive processing (Persad et al, 2007).
Long-term Memory
1
6
Input
Output
3
Low-level senses
Action
2 Perception
Working memory Executive function Attentional resources
4
Similarity matching
5
Environment and product Figure 4: Simplified model of cognition processing
Step 1: The user gets in contact with external stimuli, for example a GUI. Step 2: The perception component analyses and processes the incoming sensory information. Step 3: The working memory retrieves long-term memories and decides to act on the selected stimuli. The attention resources are directed to focus on the most informative parts of the stimuli and initiate actions and reasoning (Mieczakowski et al, 2010). Step 4: For matching the selected stimuli with objects of similar physical properties and functional attributes and for grouping them into categories in memory, working memory frequently has to refer to long-term memory (Miller, 1956). Step 5: If the user has experienced the stimuli before and is familiar with the GUI or computer system, information about them will probably affect the speed and efficiency of cognitive processing. Step 6: The user executes an action based upon the previous cognitive processing. Studies that ageing and certain impairments or disabilities can have significant effects on the elements of cognition are depicted in figure 6 (Rabbitt 1993; Freudenthal, 1999).
3.1.1 Design of graphical user interfaces The successful design of GUIs follows principles of usability engineering. Usability is defined as: “The extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency, and satisfaction in a specified context of use” (ISO, 1998). To provide an overview of the huge extent of usability engineering, figure 5 will illustrate major usability categories (Bailey et al, 2003).
Usability engineering Hardware and Software Search Lists
Writing Web Content Homepage Content organisation
Page Layout
Scrolling and paging
Graphics, Images and Multimedia
Accessibility
Navigation
Screenbased controls
Text appearance
Headings, Titles and Labels
Figure 5: Usability engineering
Usability guidelines often consider accessibility as a detached usability category that exists alongside the extensive amount of remaining categories. Developers are partially overwhelmed by the mass of usability principles, so that they tend to avoid the application of accessibility principles. This perspective leaves the impression that accessibility only provides benefits for specific user minorities. In fact, accessibility can be considered as a distinct engineering discipline that, upon application, provides significant benefits for every system user. The definition for accessibility given by the ISO is as follows. “The usability of a product, service, environment or facility by people with the widest range of capabilities” (ISO, 2008). This definition implies that true usability can only be achieved by applying accessibility principles within each usability category. The World Wide Web Consortium (W3C) already provides an extensive guideline on Web content accessibility. The following paragraphs will shortly explain each accessibility category. Perceptibility: Perceptibility implies that content presented on a website or within an application is perceivable for every user regardless of his capability (Pühretmair et al, 2005). To fulfil this principle, developers can integrate additional functionalities like scalability or the two-channel principle. The latter is used to provide multiple opportunities for the user to succeed in a specific task (Wegge et al, 2007). Furthermore the content can be enriched by alternative tags, which furnish non-textual content with descriptions. Another crucial, often underestimated, criterion is the colour contrast of content. Depending on the combination of colours, viewing content on the computer screen can be more than exhausting for users. Additionally visually-impaired users are not able to perceive specific colour combinations; therefore conveyance of information should not be solely executed by colour changes. There are approximately 200 million people afflicted with dyschromatopsia worldwide and such people are not able to differentiate between red and green content. An example would be to imagine high level executives, afflicted with dyschromatopsia, reviewing operating numbers that are represented in a usual traffic light-system. Understandability: This criterion intends to make text content readable and understandable as well as to make the application processes appear predictable and operable. Therefore developers can for example programmatically determine the default language of the application or label unusual words and abbreviations. A Screen-Reader, used by many disabled people to read the content presented on a website or within an application, can only help the user when text or text parts are labelled correctly. To render application processes predictable to the user it is an advantage to highlight any focused components. Furthermore navigational mechanisms that are repeated on multiple web pages or application screens should be consistent if possible and components that share the same functionality should use a similar identifier like a symbol or name (W3C, 2008).
Operability: To make applications operable for people with disabilities or restrictions, all functionalities should be triggerable through a keyboard. Some people afflicted by physical movement disabilities are not able to use a computer mouse and the only way for them to navigate through the content of a web site or application is to use the tabulator-key of the keyboard. Focus order and focus visibility are important and have to be considered. Hence, developers should avoid keyboard traps, which would kill the operability at a stroke. Generally the user should be provided with enough time to use, read and process the content. Seizure disorders also have to be taken into account when developing a website or application. So, rapidly flashing content should be avoided (W3C, 2008). Technical robustness and technical openness: Website or application content must be robust enough, so that a variety of assisting technologies can interpret the content reliably. Assisting technologies help users with restricted capabilities to perceive, understand and operate the content. Screen readers or screen magnifiers are examples of assisting technologies; however, compatibility of current and future technologies has to be ensured. In addition, fulfilling this principle prohibits redundant data and multiple versions. Special features of robust content are listed below (W3C, 2008): • Elements have complete start and end tags • Elements are nested according to their specifications • Elements do not contain duplicate attributes • Any IDs are unique (specific exceptions allowed) The four-level structure elaborated by the W3C provides a robust categorisation to integrate usability and accessibility principles. Therefore, the authors recommend the complete and equivalent transformation of accessibility and usability principles into a corporate framework for the human-centred design of GUIs, as depicted in figure 6. Within each category the developers will find accepted criteria to ensure the accessibility and usability of GUIs.
Human-centred Design Effectiveness Perceptibility Hardware and Software Search Lists Homepage
Operability
Content organisation
Page Layout
Graphics, Images and Multimedia
Scrolling and paging
Text appearance
Screen-based controls
Understandability
Writing Web Content
Headings, Titles and Labels
Navigation
Technical robustness and openness
Efficiency
Satisfaction
Figure 6: Universal Design approach to the development of GUIs
3.1.2 Design of computer control systems As mentioned in section 1, studies revealed that current computer control systems are mainly responsible for several injuries, induced by computer-aided work and therefore future environmental changes will call for innovative control systems, which take alterations of human capabilities into account. The last decade has already introduced an innovative computer control system. With the release of Apple’s iPhone, the first touchscreen control system became famous and affordable for the broad majority allowing visually impaired people especially to benefit from this control system. In combination with the integrated screen reader “VoiceOver”, these minorities were able to experience a new standard of living. Automatic speech recognition (ASR) is another promising computer control system, which is less disseminated. ASR systems
provide new opportunities for the human-centred design of interactions, especially in the context of environmental changes, which were described in section 1. Theory defines specific requirements that must be fulfilled by the ASR system, in order to work properly (Marine et al, 2011). The system needs to support a framework, managing the interaction between human and machine which includes processing of inputs and outputs that enable the user an individualized interaction that is most natural to him and fit the skills and physical needs of the user. Rule-based systems are able to realize this requirement, as they describe the behaviour of the user in a way that the system can understand and save it. Furthermore, the user can edit and parameterize the described behaviour to fit it to his needs (Marine et al, 2011). As the intended system behaviour depends on the current system state and the context of the user, the system needs to permit saving, reading and changing of the current context (Marine et al, 2011). In practice, ASR systems are not widely disseminated among enterprises and this is presumably due to the fact that the accuracy rate of these systems is not 100 per cent (Freitas, 2009). The average accuracy rate lies between 90-98 per cent, depending on software and testing environment (Karpov et al, 2008; Blanc et al, 2009; Yuschik, 2010). This means that out of a hundred words spoken, 2 to 10 words would not be recognized correctly by the ASR system and according to the context of use, this failure rate would be unacceptable. The following example shown in figure 7 illustrates the authors assuming the application of an ASR system within a SAP GUI.
Figure 7: SAP GUI
A major problem in using ASR technology in SAP will be the accurate execution of specific functions. If the user wants to select the tab “vendor” via speech command, the system will be confronted with two identically named objects. The failure probability would be 50 per cent in this case. The more identically or similarly named objects a GUI comprises, the higher will be the failure probability. To improve voice recognition accuracy rate, the ASR system functionalities could be extended by human-eye capabilities. The human-eye is able to precisely focus a desired object on a GUI. Around a focused area an acceptance radius could be defined. The user’s speech command will be matched with the objects within this radius. This might significantly diminish failure probability and allow accuracy rates between 99 and 100 per cent. Available technologies like eye tracking systems can be applied to identify the human-eye and to determine the eye focus. Figure 8 illustrates the SAP GUI from figure 9 with the conceptual idea of combining ASR and eye tracking technology.
Figure 8: SAP Navigation with ASR and Eye Tracking
In the demonstrated SAP GUI, the reader also finds objects and functions that are either abbreviations or icons. These objects require an alternative tag, as proposed in section 3.1.1 to be executed by speech commands. If the user focuses on such an object, the defined alternative tag should appear, so the user is able to execute an accurate speech command.
3.2 Quantifying user experiences The adaptation of legacy systems in accordance with design approaches as introduced in sections 3.1.1 and 3.1.2 will burden enterprises with additional expenditures and risks. Responsible actors need to be convinced of benefits that will arise with the implementation of computer systems following a human-centred design philosophy, as mentioned in this article. To convince economic operators, quantifiable and monetary key performance indicators are inevitable. Clarity must exist on how the benefits of human-centred computer systems will exceed implementation expenditures. A well-known methodology to quantify human-computerinteraction is usability testing. When referring to usability testing, the authors align with the definition of Carol M. Barnum: Usability testing: “The activity that focuses on observing users working with a product, performing tasks that are real and meaningful to them” (Barnum, 2011). The proposed approach to planning the usability test and quantifying user experiences is composed of six steps.
Figure 9: Usability Testing approach
3.2.1 Select strategic objectives Strategic objectives are necessary to define goals that should be achieved by the computer system. They allow an evaluation of results and findings gained during the usability test. To identify and quantify need for improvement they are an inevitable artefact. Possible strategic objectives are, for example, value creation of the system, long-term system stability and efficient support of business processes. At this stage the determination of target groups is crucial as well. To receive valuable results, it is important to know the systems end user. End users could be paying customers or employees, for example. The false determination of target groups will lead to an inferior selection of test users.
3.2.2 Identify test users Based on the determined target groups from step one, test users need to be identified and in order to achieve meaningful results, the test users should be identical with stakeholders, who have been interviewed during the requirements analysis phase. If that scenario is not possible, the characteristics of selected test users should equal the characteristics of these stakeholders. It is necessary to create user profiles for each test user, to compare user characteristics and to make potential test-user-group classifications. Important data for elicitation are age, profession, experience with the system, disabilities and impairments, satisfaction with current system, etc. The higher the diversity of capabilities of the test users, the more valuable test results can be expected. For detailed information on how to identify test users and structure user profiles, the authors refer to Salvendy (2012) and Rubin et al. (2008).
3.2.3 Derive key metrics Key metrics or key performance indicators (KPI) represent the most important figure for quantification of user experiences. They make test results tangible and comparable. They allow the deduction of recommendations for the adaptation of the computer system. In practice there is a variety of different metrics for the purpose of usability testing. The authors, however, suggest focusing on a few key metrics to reduce complexity. In order to achieve the goals defined in step 1 it is necessary that the computer system meets the users’ requirements. Therefore, key metrics should base on end user requirements. Possible key metrics could be, for example, task time, error rate, user satisfaction, clicks per task, understandability of content, user stress-level, cognitive load, degree of attention, etc.
3.2.4 Determine test instruments and tasks To measure the KPIs, corresponding instruments have to be applied during the usability test. Some KPIs can be measured by traditional observation methodologies; however, KPIs referring to the cognitive processing of the user require special equipment and know-how. To measure cognitive processing electroencephalograms (EEG) can be applied. These instruments are able to record electrical activities along the scalp. As output, the EEG
generates a pattern of waves, which represent brain activity. The analysis of these waves allows identifying, for example, states of stress, fatigue or concentration (Sharma et al, 2010). The installation of eye tracking technology will help to measure the degree of attention. Eye tracking is a widely disseminated technology for usability testing. Results can be visualised in heat diagrams for example, showing sections of the GUI the user paid most attention to. The definition of real and meaningful tasks is an important activity in this step. The test tasks should be a part of the user behaviour. For example, a paying customer should test order processes or community functionalities whereas an employee should be confronted with test tasks that refer to his profession and knowledge base. After test instruments are identified and test tasks are defined, the testing environment must be prepared and the operational plan, including size of test-user groups, responsibilities for conduction, time for each usability test, etc., has to be created.
3.2.5 Conduct usability testing For test preparation it would be beneficial to introduce the test users to special technologies like EEG or eye tracking. The test tasks should be explained in detail. This avoids confusion of the users during the usability test, which would distort any results. The test users should be as undisturbed as possible, meaning that there is enough room between test systems. This ensures that test users are influenced by each other.
3.2.6 Evaluate results The findings and results acquired from the usability test need to be analysed and evaluated to derive appropriate actions. Particularly EEG and Eye Tracking results require special know-how from the analysts. EEG results can provide important information about the cognitive load of the user while working with the computer system. Figure 10 shows how EEG results can be interpreted (Sharma et al, 2010; Mulert et al, 2010; Hammond, 2006). Feature
Delta
Theta
Frequency
1.5-4 Hz
4-8 Hz
Occurrance
Deeper stages of sleep without dreams
Stage of relaxation and meditation
Brain is not actively engaged in mental processes
Brain is actively engaged in mental processes
Interpretation
User is sleeping
User is in a state of deep relaxation. He is not concentrating on a specific task
User is calm and lucid. However, he is not thinking and therefore not concentrating on a specific task
The user is completely awake and concentrated on a specific task
Inattentiveness
Alpha 1
Alpha 2
Alpha 3
Beta 1
9-13 Hz
Beta 2
Beta 3
Beta 4
14-30 Hz
Good cognitive load
Stress
Figure 10: Interpretation of EEG results
Oscillations of alpha 3 and beta 1 would represent a state of positive cognitive load, while oscillations above beta 1 would be an indicator for negative cognitive load. Oscillations of beta 3 and 4 would indicate that the user is stressed, overworked or the given task is too difficult for him. Oscillations below alpha 3 would indicate that the user is inattentive. Waves in the range of alpha 2 and alpha 1 could be an indicator that the user’s attention is distracted by an element of the GUI. To collect more accurate data material, it is possible to combine EEG and eye tracking instruments.
4. Conclusion This article discussed the alterations of environmental conditions. The authors identified consequences that might influence the efficiency and productivity of current computer systems and proposed a universal design approach, which takes divergent user capabilities into account. The application of human-centred design perspectives was highlighted as a critical success factor. In section 3.1.1 the authors introduced the reader to a universal design approach for GUIs. Afterwards, section 3.1.2 dealt with computer control systems that would be appropriate for a universal design approach. A combination of ASR and eye tracking technology was introduced to the reader. Finally the article closed with an approach to quantifying the benefits of human-centred computer systems.
References Bailey, R. W.; Barnum, C.; Bosley, J.; Chaparro, B.; Dumas, J.; Ivory, M. Y.; John, B.; Miller-Jacobs, H.; Koyani, S. J. (2003) Research-Based Web Design & Usability Guidelines, published by U.S. Government, available: http://www.usability.gov/guidelines/guidelines_book.pdf. Barnum, C. M. (2011) Usability Testing Essentials, published by Elsevier Inc., p. 13. Blanc, I., Vento, C. (2009) Performing with Microsoft Office 2007: Introductory, USA, p. 13. European Commission Eurostat (2003) Employment of Disabled People in Europe in 2002, ISBN 1024-4352, catalogue number: KS-NK-03-026-EN-N, cited in: Buhalis, D., V.; Eichhorn, E.; Michopoulou& G. Miller. October (2005) Accessibility Market and Stakeholder analysis – One stop shop for accessible tourism in Europe, University of Surrey, UK, available: http://www.accessibletourism.org/resources/ossate_market_analysis_public_final.pdf, p. 33. European Commission Eurostat (2011) Population structure and ageing, available: http://epp.eurostat.ec.europa.eu/statistics_explained/index.php/Population_structure_and_ageing. Freitas, J., Calado, A., Barros, M. J., Dias, M. S. (2009) Spoken language interface for mobile devices, published in: Vetulani, Z., Uszkoreit, H. (2009) Human language technology-challenges of the information society, Third language and technology conference, LTD 2007, Poland, p. 34. Freudenthal, A. (1999) The Design of Home Appliances for Young and Old Consumers. Series Ageing and Ergonomics, part 2, PhD Thesis. Delft University Press, The Netherlands ISBN 90-407-1755-9. Hammond, D. C. (2006) What is Neurofeedback?, published in: International society for Neurofeedback and Research, pp. 1-11. ISO, International Organization for Standardization. (1998) ISO 9241-11, Ergonomic requirements for office work with visual display terminals (VDTs) - Part 11: Guidance on usability. ISO, International Organization for Standardization. (2008) ISO 9241-171, Ergonomics of human-system interaction -- Part 171: Guidance on software accessibility. Karpov, A., Carbini, S., Ronzhin, A., Viallet, J. E. (2008) Two similar different speech and gestures multimodal interfaces, published in: Tzovaras, D. (2008) Multimodal user interfaces-from signals to interactions, Berlin Heidelberg, p. 169. Kolko, J. (2011) Thoughts on Interaction Design, published by Elsevier Inc., pp. 13-24. Leon, D. A. March (2011) Trends in European life expectancy: A salutary view, published in: International journal of epidemiology 2011, pp. 1-7. Lutz. W. et al. (2011) Demographic challenges for sustainable Development, published in: International Institute for applied systems analysis (IIASA), September 30 – October 1st 2011, available: http://www.iiasa.ac.at/Research/POP/Laxenburg%20Declaration%20on%20Population%20and%20Developmen t.html. Marcu, M. (2011) Population grows in twenty EU Member States - Population change in Europe in 2010: first results, published in: Eurostat - statistics in focus, Vol. 38, available: http://epp.eurostat.ec.europa.eu/cache/ITY_OFFPUB/KS-SF-11-038/EN/KS-SF-11-038-EN.PDF, pp. 1-4. Marine, A., Stocklöw, C., Braun, A., Limberger, C., Hofmann, C., Kuijper, A. (2011) Interactive Personalization of ambient assisted living environments, published in: Smith, M. J., Salvendy, G. (2011) Human Interface, Part I, HCII, LNCS 6771, Berlin / Heidelberg, p. 573. Mieczakowski, A; Langdon, P. M.; Clarkson, P. J. (2010) Investigating Designers’ Cognitive Representations for Inclusive Interaction Between Products and Users, published in: Langdon, P. M.; Clarkson, P. J.; Robinson, P. (2010) Designing inclusive interactions, published by Springer London, pp. 133-144. Miller, G. A. (1956) The magical number seven, plus or minus two: some limits on our capacity for processing information, published in: Psychological review, 63, pp. 81-97. Monk, A. (1998) Cyclic interaction: a unitary approach to intention, action and the environment,published in: Cognition, 68, pp. 95-110. Mulert, C.; Lemieux, L. (2010) EEG- FMRI: Physiology, Technique and Applications, published by Springer Berlin / London.. Pascarelli, E. F.; Hsu, Y. P. (2001) Understanding Work-Related Upper Extremity Disorders: Clinical Findings in 485 Computer Users, Musicians, and Others, published in: Journal of Occupational Rehabilitation, Vol. 11, No. 1, 2001, pp. 1-21. Persad, U.; Langdon, P.; Clarkson, P. J. (2007) Characterising user capabilities to support inclusive design evaluation.Published in: Universal access in the information society.Special Issue on Designing Accessible Technology, 6, pp. 119-135. Poslad, S. (2009) Ubiquitous Computing-Smart devices, environments and interactions, published by John Wiley & Sons Ltd.
Pühretmair, F., Miesenberger, K. (2005) Making sense of accessibility in IT Design - usable accessibility vs. accessible usability, published in: IEEE Computer society, Proceedings of the 16th international Workshop on Database and Expert Systems Applications (DEXA'05), 1529-4188/05, p. 2. Rabbitt, P. (1993) Does it all go together when it goes? The nineteenth Bartlett memorial lecture. The Quarterly Journal of Experimental Psychology, 46A, pp. 385-434. Rubin, J. B.; Rubin, J.; Chisnell, D. (2008) Handbook of usability testing - How to plan, design, and conduct effective tests, 2nd Edition, published by Wiley publishing Inc. Saffer, D. (2010) Designing for Interaction: Creating Innovative Applications and Devices, pp. 4-15. Salvendy, G. (2012) Human Factors and Ergonomics, 4th Edition, published by John Wiley & Sons Inc., pp. 1276-1283. Sanderson, W.; Scherbov, S. (2010) Remeasuring Aging, published in: Science, September 2010, vol. 329, No. 5997, pp. 1278-1288. Sharma, J. K.; Singh, D.; Deepak, K. K.; Agrawal, D. P. (2010) Neuromarketing-A peep into customers’ minds, published by PHI learning private limited, p. 126. United Nations, population Division of the Department of Economic and Social Affairs of the United Nations Secretariat (2010) world population prospects, the 2010 revision, available: http://esa.un.org/unpd/wpp/unpp/Panel_profiles.htm. W3C. December 11, (2008) Web Content Accessibility Guidelines (WCAG) 2.0, available: http://www.w3.org/TR/2008/REC-WCAG20-20081211/. Walker, C. (2011) Europe plagued with mental health problems, published by: Mental Healthy, available: http://www.mentalhealthy.co.uk/news/841-europe-plagued-with-mental-health-problems.html. Wegge, K. P., Zimmermann, D. (2007) Accessibility, Usability, Safety, Ergonomics, Concepts, Models and Differences, published in: Stephanidis, C., Universal Access in HCI, Part I, HCII 2007, LNCS 4554, Berlin / Heidelberg: Springer, p. 297. Wickens, C. D.; Hollands, J. G. (2000) Engineering psychology and human performance, 3rdedn.Prentice Hall, Upper Saddle River, NJ, US. Wittchen, H. U., et al. (2010) The size and burden of mental disorders and other disorders of the brain in Europe 2010, ECNP/EBC REPORT 2011, published in: European Neuropsychopharmacology, (2011) vol. 21, pp. 655– 679. World Health Organization. (2011) World report on disability, ISBN 978 92 4 068521 5, available: http://whqlibdoc.who.int/publications/2011/9789240685215_eng.pdf, p. 27. Yuschik, M. (2010) Leveraging multimodality to improve call center productivity, published in: Neustein, A. 2010, Advances in speech recognition-Mobile environments, call centers and clinics, New York, p. 143.
