A Data-Driven Design Evaluation Tool for Handheld Device Soft Keyboards

Abstract

Thumb interaction is a primary technique used to operate small handheld devices such as smartphones. Despite the different techniques involved in operating a handheld device compared to a personal computer, the keyboard layouts for both devices are similar. A handheld device keyboard that considers the physical capabilities of the thumb may improve user experience. We developed and applied a design evaluation tool for different geometries of the QWERTY keyboard using a performance evaluation model. The model utilizes previously collected data on thumb motor performance and posture for different tap locations and thumb movement directions. We calculated a performance index (PITOT, 0 is worst and 2 is best) for 663 designs consisting in different combinations of three variables: the keyboard's radius of curvature (R) (mm), orientation (O) (°), and vertical location on the screen (L). The current standard keyboard performed poorly (PITOT = 0.28) compared to other designs considered. Keyboard location (L) contributed to the greatest variability in performance out of the three design variables, suggesting that designers should modify this variable first. Performance was greatest for designs in the middle keyboard location. In addition, having a slightly upward curve (R = −20 mm) and orientated perpendicular to the thumb's long axis (O = −20°) improved performance to PITOT = 1.97. Poorest performances were associated with placement of the keyboard's spacebar in the bottom right corner of the screen (e.g., the worst was for R = 20 mm, O = 40°, L = Bottom (PITOT = 0.09)). While this evaluation tool can be used in the design process as an ergonomic reference to promote user motor performance, other design variables such as visual access and usability still remain unexplored.

Thumb performance of elderly users on smartphone touchscreen

“…In order to retain the consistent reliability of study results for elderly participants, the present study adopted the identical method retrieved from the previous study. In addition, the task settings of both two studies referred to those in previous studies reported by Trudeau et al ( 2012a , b , 2014 ), and hence some similarities in the experimental task settings among these studies can be found in the present study.…”

Two-handed grip on a mobile phone affords greater thumb motor performance, decreased variability, and a more extended thumb posture than a one-handed grip

“…Second, tapping constitutes a subtask of typing, and thus performance for taps at specific locations on the screen can be used to predict the performance for more complex tasks. A predictive evaluation model can thus be developed for small mobile device keyboard designs to determine which design may lead to better performance, as shown by Trudeau et al (2014). Third, simple tapping tasks are important as they are commonly used in gaming, selecting applications or dialing on a number pad.…”

The Effects of Keyboard Layout and Size on Smartphone Typing Performance

“…Future studies should evaluate the usability and user experience with curved keyboards in more robust mobility scenarios (i.e., standing, walking). Additionally, keyboard configurations aligned with the middle of the screen should also be explored per the findings of Trudeau (2014).…”

“…The authors found that the curved QWERTY yielded the least input efficiency when evaluating the accuracy and reaction time during typing of randomly paired characters. Although several of the aforementioned studies show evidence against curved layouts (Chang et al, 2017;Trudeau et al, 2014), screen size has yet to be thoroughly investigated in relation to objective and subjective performance metrics with a curved keyboard. While previous studies have identified various issues related to current mobile keyboard design, none have evaluated the effect of one versus two-handed use as it relates to varying screen sizes and keyboard layouts using representative user typing tasks.…”

“…In addition to poor performance, layouts that bring keys closer to the bottom right of the screen have been shown to cause discomfort and muscle fatigue in user's thumbs due to an increase in flexion and abduction frequency (Chang, Choi, Tjolleng, & Jung, 2017). For these reasons, numerous studies recommend avoiding layouts that bring keys closer to the bottom right of the screen, especially for right-handed users typing with one thumb (Chang et al, 2017;Trudeau et al, 2014). However, these conclusions are based on predictive models which represent a simplified version of human performance, and do not evaluate how actual users perform during representative typing tasks, or consider user satisfaction metrics, which are paramount to the marketplace success of a design.…”