Target size study for one-handed thumb use on small touchscreen devices

Abstract

This paper describes a two-phase study conducted to determine optimal target sizes for one-handed thumb use of mobile handheld devices equipped with a touch-sensitive screen. Similar studies have provided recommendations for target sizes when using a mobile device with two hands plus a stylus, and interacting with a desktop-sized display with an index finger, but never for thumbs when holding a small device in a single hand. The first phase explored the required target size for single-target (discrete) pointing tasks, such as activating buttons, radio buttons or checkboxes. The second phase investigated optimal sizes for widgets used for tasks that involve a sequence of taps (serial), such as text entry. Since holding a device in one hand constrains thumb movement, we varied target positions to determine if performance depended on screen location. The results showed that while speed generally improved as targets grew, there were no significant differences in error rate between target sizes ≥ 9.6 mm in discrete tasks and targets ≥ 7.7 mm in serial tasks. Along with subjective ratings and the findings on hit response variability, we found that target size of 9.2 mm for discrete tasks and targets of 9.6 mm for serial tasks should be sufficiently large for one-handed thumb use on touchscreen-based handhelds without degrading performance and preference.

F4-4 The effects of smartphone width on touch performance

“…In particular, the success rate of 67mm device was higher than that of other devices and the results of rest devices were similar. This result is in line with findings of previous works (Colle and Hiszem, 2004;Hwangbo et al, 2013;Parhi et al, 2006, September) We expected that the results of task completion time were similar with those of success rate. However, the task completion time of 67mm devices was poor regardless of task difficulties.…”

User interface design guidelines for smartphone applications for people with Parkinson’s disease

“…However, their study setup included a fixed tablet in a specific angle, which is quite different from the normal usage of a smartphone. These target sizes contrast with the 9-10mm suggested by other studies [40,41]. A more recent study [26] reported that older adults have the best accuracy when tap targets on the smartphone have between 14 and 17.5mm, with 10mm being acceptable when screen space is restricted.…”

Touch the 3rd Dimension! Understanding Stereoscopic 3D Touchscreen Interaction

“…From the press point error distribution we calculated the 98 percentile points in positive and negative directions for both x and y. Taking the approach described by [39], this defines the bounding rectangle that captures 95% of user presses. As the distributions are slightly skewed to either positive or negative sides, and in practice it is not possible to position a touch target at the exactly the correct offset from the center, thus we take double the larger absolute value, which may be considered as the minimum size for targets in the UI.…”

“…It should be noted that these values are based on index finger usage, as in the test protocol. For thumb usage sizes will be somewhat larger (see [39]). The minimum target sizes are shown in Table 2. and diagrammatically in Fig.…”

“…Holtz and Baudisch [26] and Parhi et al [39]. Holtz's summary, that inaccuracy is largely due to a "parallax" artifact between user control based on the top of the finger and sensing based on the bottom side of the finger, is particularly relevant, as in the S3D case another on-screen parallax effect is introduced.…”