Understanding Users' Perceived Difficulty of Multi-Touch Gesture Articulation

We show that users are consistent in their assessments of the articulation difficulty of multi-touch gestures, even under the many degrees of freedom afforded by multi-touch input, such as (1) various number of fingers touching the surface, (2) various number of strokes that structure the gesture shape, and (3) single-handed and bimanual input. To understand more about perceived difficulty, we characterize gesture articulations captured under these conditions with geometric and kinematic descriptors computed on a dataset of 7,200 samples of 30 distinct gesture types collected from 18 participants. We correlate the values of the objective descriptors with users' subjective assessments of articulation difficulty and report path length, production time, and gesture size as the highest correlators (max Pearson's r=.95). We also report new findings about multi-touch gesture input, e.g., gestures produced with more fingers are larger in size and take more time to produce than single-touch gestures; bimanual articulations are not only faster than single-handed input, but they are also longer in path length, present more strokes, and result in gesture shapes that are deformed horizontally by 35% in average. We use our findings to outline a number of 14 guidelines to assist multi-touch gesture set design, recognizer development, and inform gesture-to-function mappings through the prism of the user-perceived difficulty of gesture articulation.