Effect of Sitting Orientation on Touchscreen Performance, Touch Characteristics, User Preference, and Workload

OCCUPATIONAL APPLICATIONS Sitting in a parallel orientation in front of a touch screen (requiring twisting of the torso) was found to cause a decrement in touchscreen performance (36%–48%). However, the adverse effect of sitting orientation on performance could be ameliorated by interface design, most notably by using button sizes greater than 20×20 mm. Larger button sizes also benefit individuals with upper extremity motor control disabilities, and this information could be used to incorporate universal design in touchscreen interfaces. Larger button sizes also help in reducing the force-time integral during button activation. Touchscreens are widely used in occupational settings, such as retail, restaurants, and health care. The touchscreen performance findings from this study are applicable to touchscreen interface design for users with and without upper extremity motor control disabilities, and the touch characteristics findings are useful for ergonomists quantifying forces involved in touchscreen operation. TECHNICAL ABSTRACT Background: Touchscreens can be used in stand-alone kiosks, embedded in larger structures, such as walls, or arranged in multi-display configurations (e.g., a control station). As a result, users may not always be positioned in front of the screen and may instead operate it in a variety of orientations. Previous touchscreen research has not considered the effect of user sitting orientation on touchscreen performance, such as in terms of the number of errors (incorrect button activation), misses (touch that does not result in button activation), task completion time, and touch characteristics (e.g., force, dwell time [the time the button was pressed], and force-time integral). Purpose: This study evaluates the effect of sitting orientation on performance and touch characteristics during a digit entry task among individuals with and without motor control disabilities, including wheelchair users and non-users. Methods: Participants with (n = 21) and without (n = 21) upper extremity motor control disabilities (+MCD and −MCD, respectively) completed a four-digit entry task on a touchscreen in both front and parallel orientations to the touchscreen. Button sizes of 10×10 to 30×30 mm (5-mm increments) and two button gaps (3 or 5 mm) were used. Results: Accuracy was adversely affected, with errors (36%) and misses (48%) greater in the parallel orientation. Dwell time (12%) and force-time integral (21%) were also greater in the parallel orientation than in the front orientation. Larger button sizes (≥20 mm) lowered misses, errors, force-time integrals, and dwell times for both orientations. The +MCD group had a greater percentage of trials with misses (150%) and longer dwell times (66%) than the −MCD group, but in general, similar trends in performance and touch characteristics were observed for both groups across button sizes, button gaps, and sitting orientation. Conclusions: Decrements in touchscreen performance occurred in the parallel orientation compared to the front orientation. In addition, greater forces were exerted and greater workload was reported in the parallel orientation than in the front orientation. However, performance may be improved by using larger button sizes (≥20×20 mm). This may be especially important in critical touchscreen activities.