Morphological Characteristics and the Location-Dependent Variations of Thumb–Touchscreen Contact Areas in Two-Thumb Mobile Interaction

This study quantitatively investigated morphological characteristics of traces occurring between thumbs and touchscreen during two-thumb touch interaction on a mobile device. Thirty-two college students were recruited, and a paper-and-ink-based touch simulation using a mockup was conducted to capture thumb touch traces. Traces were collected at 22 target points on the virtual keyboard region, encompassing flexion–extension and abduction–adduction thumb movements, and the location-dependent variations in morphology were analyzed using major axis orientation, eccentricity, and area size (elliptical features). Results exhibited that during thumb displacement from flexion to extension, the major axes of the traces rotated clockwise for the left thumb and counterclockwise for the right, while the traces themselves became more circular and increased in size. In addition, during thumb excursion from abduction to adduction, the major axes of the traces generally rotated clockwise for the left thumb and counterclockwise for the right, while the traces became more elongated and showed no statistically significant change in area.