UC Berkeley

Objective: Three studies evaluated human computer interaction with alternative keyboard designs, new tablet features, and a 3D gesture-command set for their effects on biomechanics, comfort, and productivity.

Background: Keyboard key spacing, tablet designs, and the design of hand gestures for human computer interaction have been guided primarily by past practices and design convention because few studies are available that can guide design based on productivity, usability, and biomechanics.

Method: Experienced typists (N=89, 26 female) typed on keyboards which differed in horizontal and vertical key spacing while productivity, biomechanics, and subjective usability and fatigue were recorded. Thirty subjects (15 female) evaluated tablet design features (e.g., size (weight), orientation, grip shape, texture and stylus shape) on productivity, biomechanics and subjective usability and fatigue when the tablet was held with just the left hand. Thirty subjects (15 female) performed user derived gestures for 34 common computer commands. A gesture set is proposed based on user preference, match, easiness, effort, gesture popularity, and musculoskeletal postural risks.

Results: Reducing horizontal key spacing, from 19 to 17 mm, had no significant effect on productivity or usability ratings but with 16 mm horizontal spacing, the same ratings, muscle activity and postural factors were significantly worse. Reducing vertical key spacing, from 18 to 17 to 16 mm, had no significant effect on productivity or usability, but at 15.5 mm vertical spacing these measures were worse. The study evaluating table design features supported the use of smaller to mid-sized tablets, tablets with a ledge or handle shape on the back and tablets surfaced with a rubberized texture. Larger, heavier tablets had significantly worse usability and biomechanics and their use with one hand should be limited. The stylus with a tapered grip (7.5-9.5mm) or larger grip (7.6mm) had better usability and biomechanics than one with a smaller grip (5mm). For the gesture study, 34 different commands were linked to 84 different gestures with a total of 160 gesture-command combinations. A proposed gesture set using 13 gestures for the 34 commands is proposed using the six outcome measures with adjustment by expert opinion.

Conclusions: The study findings support key spacing on a computer keyboard from 17 to 19 mm in the horizontal direction and 16 to 19 mm in the vertical direction. Based on short-term tasks emulating functional tablets: smaller and medium sized tablets, portrait instead of landscape orientation, a back grip, and rubberized grip texture improved usability and security from dropping. We present a method for developing a 3D gesture language for common commands for human-computer interaction which considers subjective preference, ease of forming gesture, hand biomechanics and other factors.