…you are now in a phase of the project where decisions need to be made regarding adequate target sizes for tap gestures. Choosing target sizes for a particular gestures is an important decision as it will determine whether your intended users will, or not, be able to complete necessary actions and tasks throughout the flow of your UI.
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As a result of the ageing process, sensory and psychomotor capabilities undergo several declines and these alterations may render conventional tap target sizes as inadequate for older adults. Furthermore, existing smartphone OS guidelines do not provide guidance concerning specific audiences, such as older adults.
Previous research has explored adequate target sizes for tap gestures on large touch-surfaces (Colle & Hiszem, 2004), PDAs (Parhi, Karlson, & Bederson, 2006; Park, Han, Park, & Cho, 2008; Perry & Hourcade, 2008; Sears & Zha, 2003), or more recently on tablets (Jin, Plocher, & Kiff, 2007) and smartphones (Henze, Rukzio, & Boll, 2011), but very few have explored target sizes for older adults on smartphones (Kobayashi et al., 2011).
Consequently, most guidelines that are currently available (Apple's iOS Human Interface Guidelines, Google's Android Design, and Microsoft's User Experience Guidelines) do not aid designers in creating a smartphone UIs that adequately respond to older adults’ specific characteristics.
It is commonly accepted that visual acuity, visual search capabilities (Fisk, Rogers, Charness, Czaja, & Sharit, 2009), fine-motor skills, hand dexterity (Carmeli, Patish, & Coleman, 2003) and touch sensitivity (Carmeli et al., 2003; Fisk et al., 2009; Nusbaum, 1999; Wickremaratchi & Llewelyn, 2006) suffer considerable losses with age. Additionally, natural age-related declines of the sensory and psychomotor systems can be further aggravated by diseases such as Age-related Macular Degeneration, cataracts, presbyopia and glaucoma — relative to visual abilities, and multiple sclerosis, arthritis, osteoporosis, stroke and Parkinson’s disease — related to psychomotor issues (Kurniawan, 2008). Movement can be severely affected by these diseases, causing symptoms such as weakness, numbness, loss of muscle coordination, pain, stiffness, tremors, rigidity and slow movement (Kurniawan, 2008). Therefore, one cannot safely assume that target sizes that have been found to be adequate for younger adults will also provide a comfortable user experience for the elderly.
It is clear that special considerations need to be taken into account when designing UIs for older adults. Targets for all gestures should be resized to fit the elderly population’s particular characteristics. Tap target sizes are no exception.
Accordingly, our own research revealed that older adults were most accurate, and took less time to correctly acquire tap targets larger than 14 mm. Where registered mean completion times for this target size were 1.7 seconds, and the mean accuracy rates were 97.94%.
If screen real estate is not an issue and the task requires high performance levels, use targets for tap gestures that are at least 14 mm square. Otherwise, in cases where screen real estate is very limited and smaller tap targets cannot be avoided see RECOMMENDED TAP TARGET SIZES FOR LIMITED SCREEN REAL ESTATE.
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Carmeli, E., Patish, H., & Coleman, R. (2003).The Aging Hand. The Journals of Gerontology Series A: Biological Sciences and Medical Sciences, 58, M146-M152. doi: 10.1093/gerona/58.2.M146
Colle, H. A., & Hiszem, K. J. (2004). Standing at a kiosk: Effects of key size and spacing on touch screen numeric keypad performance and user preference. Ergonomics, 47(13), 1406-1423. doi: 10.1080/00140130410001724228
Fisk, A. D., Rogers, W. A., Charness, N., Czaja, S. J., & Sharit, J. (2009) Designing for Older Adults: Principles and Creative Human Factors Approaches, Second Edition (Human Factors & Aging): CRC Press.
Henze, N., Rukzio, E., & Boll, S. (2011). 100,000,000 taps: analysis and improvement of touch performance in the large. Proceedings of the 13th International Conference on Human Computer Interaction with Mobile Devices and Services - MobileHCI '11. New York, New York, USA: ACM Press.
Jin, Z. X., Plocher, T., & Kiff, L. (2007). Touch screen user interfaces for older adults: button size and spacing. Universal Acess in Human Computer Interaction Coping with Diversity, 4554, 933-941.
Kobayashi, M., Hiyama, A., Miura, T., Asakawa, C., Hirose, M., & Ifukube, T. (2011). Elderly user evaluation of mobile touchscreen interactions. Ifip International Federation For Information Processing, 83-99.
Kurniawan, S. H. (2008). Web Accessibility: A Foundation for Research. In S.-V. London (Ed.), Human-Computer Interaction Series (pp. 47-58).
Nusbaum, N. (1999). Aging and sensory senescence. Southern medical journal.
Parhi, P., Karlson, A. K., & Bederson, B. B. (2006). Target size study for one-handed thumb use on small touchscreen devices. Proceedings of the 8th conference on Human-computer interaction with mobile devices and services - MobileHCI '06. New York, New York, USA: ACM Press.
Park, Y. S., Han, S. H., Park, J., & Cho, Y. (2008). Touch key design for target selection on a mobile phone. Proceedings of the 10th international conference on Human computer interaction with mobile devices and services - MobileHCI '08. New York, New York, USA: ACM Press.
Perry, K., & Hourcade, J. P. (2008). Evaluating one handed thumb tapping on mobile touchscreen devices. Proceedings of graphics interface 2008, 57-64.
Sears, A., & Zha, Y. (2003). Data entry for mobile devices using soft keyboards: Understanding the effects of keyboard size and user tasks. International Journal of Human-Computer, 16, 163-184. doi: 10.1207/S15327590IJHC1602_03
Wickremaratchi, M. M., & Llewelyn, J. G. (2006). Effects of ageing on touch. Postgraduate medical journal, 82, 301-304. doi: 10.1136/pgmj.2005.039651