… you have selected adequate gestures for all targets on your smartphone interface, and have decided on target sizes for tap gestures, as well as on spacing sizes between adjacent tap targets. You are now seeking information regarding the placement of tap targets on the smartphone’s display, in order to compensate for issues related to older adults’ reachability of certain screen regions.
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You have a series of tap targets that you need to distribute throughout your interface. However, not all screen regions allow for the same levels of efficiency, and accuracy in target selection. In this context, you need to place tap targets requiring higher levels on efficiency in regions that are more easily reachable and therefore allow for higher level of performance.
Activity zones are defined as the regions on the smartphone’s display that allow for better performance. Dan Saffer, in a blog article (Saffer, 2011), defined smartphone activity zones as those comprising the uppermost left corner, right and bottom edges, and centre of the display. However, these activity zones primarily consider one-handed thumb input, and as seen in our results most older adult participants used their index fingers for interaction. Several efforts have been made to define activity zones on mobile touchscreen interfaces, Parhi, Karlson and Bederson (2006) carried-out a study with twenty younger adults in order to evaluate thumb-use and the performance of both discrete and serial tap gestures. They found that participants were most accurate with targets placed toward the centre of the device, and less accurate toward the left edge, and bottom-right-corner of the device. Contrastingly, Perry and Hourcade (2008) found that participants were more accurate in acquiring targets on the edge of the screen, while being quicker and more comfortable with targets toward the centre of the screen. More recently, Henze, Rukzio and Boll (2011) found that participants were most accurate in acquiring tap targets in the centre, and toward the right and bottom edges of the display. However, these studies were conducted with younger adults, and therefore cannot provide guidance in designing for an older population.
Our own research results showed that even though older adults used their index finger and not their thumbs for interaction, that these activity zones were still similar to those outlined by (Parhi, Karlson, & Bederson, 2006) and (Henze, Rukzio, & Boll, 2011). However, contrary to the activity zones defined by Dan Saffer in the blog article, the uppermost left corner of the display was the region that registered the lowest performance measures with older adults. Still, most of our participants used their right hand for interaction, and therefore our results cannot be generalised for left-handed older adult participants. In addition, we found that offsets between the target’s centre point and participants actual touches on the screen were registered for all regions of the display. Which leads us to believe that for targets placed in more problematic regions, it might be necessary to enlarge their touchable area by the offset measures found in our research.
When placing tap targets, be sure that those requiring high levels of performance are placed toward the centre, right edge and bottom right corner of the display. However, when screen real-estate is limited and it is necessary to place targets in regions with lower performance measures, then enlarge these targets’ touchable areas by 2.68 mm to the right, and 2.97 mm to the bottom.
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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.
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.
Saffer, D. (2011). Activity Zones for Touchscreen Tablets and Phones Retrieved 05 January 2012, from http://www.kickerstudio.com/blog/2011/01/activity-zones-for-touchscreen-tablets-and-phones/