… you are now in a position where you need to decide on specific target sizes for swipe gestures. They are an important issue, as they will determine if your users will, or not, be able to complete many actions and tasks throughout the flow of your UI.
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Selecting a range of target sizes that are most adequate for a given group of users requires a thorough understanding of their particular characteristics, expectations and preferences. Official smartphone OS guidelines such as, Windows Phone’s “User Experience Design Guidelines”, Google’s “Android Design”, and Apple’s “iOS Human Interface Guidelines”, do not provide guidance in designing swipe targets for specific groups of users such as older adults.
These official guidelines recommend target sizes that are smaller than the average human finger (10 to 14 mm) (Dandekar, Raju, & Srinivasan, 2003), raising issues such as target occlusion while performing a gesture and/or accidentally touching neighbouring targets.
It is well accepted that visual acuity (Fisk, Rogers, Charness, Czaja, & Sharit, 2009), movement control, hand-eye coordination, 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 during the ageing process. Thus making it harder to see small targets, and to perform the necessary movements in order to accurately acquire them.
Additionally, vision and psychomotor capabilities can be further compromised by common diseases among older adults such as Age-related Macular Degeneration, cataracts, presbyopia glaucoma — relative to visual abilities; and multiple sclerosis, arthritis, osteoporosis, stroke and Parkinson’s disease — related to psychomotor issues. 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).
Inevitably, accurately acquiring small targets becomes increasingly difficult as age progresses. Providing targets that are too small makes a UI more difficult to use and could result in frustration and anxiety among older adults (Czaja & Sharit, 1998; Laguna & Babcock, 1997; Turner, Turner, & Van De Walle, 2007) and should therefore be avoided.
Target sizes should be adjusted to meet the specific needs of older adults, in order to provide a more comfortable and enjoyable user experience.
Accordingly, our own work revealed that participants were quicker, and more accurate with swipe targets larger than 17.5 mm square. For this target size participants’ mean accuracy level was 97.24%, and mean task completion times were 2.8 seconds. Revealing that the end intention of a movement — whether to finalise in a tap or swipe — influences older adults’ accuracy and speed in acquiring targets. Where swipe targets need to be larger than tap targets.
In cases where available screen space for swipe targets is not an issue and the task requires high performance measures, use target sizes for swipe gestures that are at least 17.5 mm square. Otherwise, when screen real estate is limited and smaller swipe targets cannot be avoided see RECOMMENDED SWIPE 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
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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.
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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.
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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