Abstract
When holding a tablet computer with two hands, the touch keyboard configuration imposes postural constraints on the user because of the need to simultaneously hold the device and type with the thumbs. Designers have provided users with several possible keyboard configurations (device orientation, keyboard layout and location). However, potential differences in performance, usability and postures among these configurations have not been explored. We hypothesize that (1) the narrower standard keyboard layout in the portrait orientation leads to lower self-reported discomfort and less reach than the landscape orientation; (2) a split keyboard layout results in better overall outcomes compared to the standard layout; and (3) the conventional bottom keyboard location leads to the best outcomes overall compared to other locations. A repeated measures laboratory experiment of 12 tablet owners measured typing speed, discomfort, task difficulty, and thumb/wrist joint postures using an active marker system during typing tasks for different combinations of device orientation (portrait and landscape), keyboard layout (standard and split), and keyboard location (bottom, middle, top). The narrower standard keyboard with the device in the portrait orientation was associated with less discomfort (least squares mean (and S.E.) 2.9±0.6) than the landscape orientation (4.5±0.7). Additionally, the split keyboard decreased the amount of reaching required by the thumb in the landscape orientation as defined by a reduced range of motion and less MCP extension, which may have led to reduced discomfort (2.7±0.6) compared to the standard layout (4.5±0.7). However, typing speed was greater for the standard layout (127±5 char./min.) compared to the split layout (113±4 char./min.) regardless of device orientation and keyboard location. Usage guidelines and designers can incorporate these findings to optimize keyboard design parameters and form factors that promote user performance and usability for thumb interaction.
Highlights
Tablets were first introduced as an alternative to smartphones and laptop computers to improve the user experience for certain tasks such as browsing the web, email, and playing games [1]
There was a significant interaction effect between device orientation and keyboard layout for self-reported discomfort (F = 5.8, p = 0.018) (Table 1), indicating that discomfort was reduced for the split keyboard layout compared with the standard layout only when the device was in the landscape orientation (2.760.6 for the split layout vs. 4.560.7 for the standard layout), but not in the portrait orientation (2.860.6 for the split layout vs. 2.960.6 for the standard layout) (Figure 3a)
There were significant interactions between device orientation and keyboard layout for three postural measures as well: wrist adduction (F = 10.4, p = 0.002) (Figure 3b), IP flexion (F = 26.6, p,0.001) (Figure 3c), and wrist range of motion about the flexion/extension axis (F = 4.5, p = 0.037) (Figure 3d). These postural measures were similar across device orientations for the split layout, but they all differed significantly with the keyboard in the standard layout, with the landscape orientation being associated with more wrist adduction, less IP flexion, and more wrist range of motion along the flexion/extension axis
Summary
Tablets were first introduced as an alternative to smartphones and laptop computers to improve the user experience for certain tasks such as browsing the web, email, and playing games [1]. Because of their mobility, ease of use, and low cost compared to desktop and laptop personal computers, tablets are being used for accomplishing the same tasks as computers, with the most frequent task accomplished on tablets being email [2]. Because the tablet affords a mobile computing experience, users often hold it with both hands while sitting, standing, or walking. This interaction technique requires a very different posture than interacting with a computer workstation. Current tablet keyboard designs may not be appropriate for the postures required by thumb interaction [3], [4]
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