Miika Silfverberg

Accuracy measures for evaluating computer pointing devices

In view of the difficulties in evaluating computer pointing devices across different tasks within dynamic and complex systems, new performance measures are needed. This paper proposes seven new accuracy measures to elicit (sometimes subtle) differences among devices in precision pointing tasks. The measures are target re-entry, task axis crossing, movement direction change, orthogonal direction change, movement variability, movement error, and movement offset. Unlike movement time, error rate, and throughput, which are based on a single measurement per trial, the new measures capture aspects of movement behaviour during a trial. The theoretical basis and computational techniques for the measures are described, with examples given. An evaluation with four pointing devices was conducted to validate the measures. A causal relationship to pointing device efficiency (viz. throughput) was found, as was an ability to discriminate among devices in situations where differences did not otherwise appear. Implications for pointing device research are discussed.

Making an impression: force-controlled pen input for handheld devices

The properties of force-based input on a handheld device were examined. Twenty-one participants used force input to set 10 different target levels representing consecutive force ranges (0 to 4N) with visual feedback (digits or bar graphs) or no feedback. Both accuracy and speed were greater with analog feedback (bar graph). Statistical comparisons of adjacent targets/digits indicated that subjects differentiated roughly seven input levels within the set of ten force ranges actually used. Time taken to input the target force increased significantly with the size of the target force, suggesting that smaller force ranges should be considered in future implementations of force input. The results are discussed in terms of the design of appropriate feedback for force input.

Using Mobile Keypads with Limited Visual Feedback: Implications to Handheld and Wearable Devices

Mobile devices are often used in busy contexts, where the operation takes place – at least temporarily – with limited visual information. In such ‘blind use’, the passive tactile properties of the device become crucial. Two mobile keypads with very different tactile properties were tested in an experiment with twelve experienced mobile phone users. Results highlight the importance of passive tactile feel. Most clear differences were seen in errors: while the keypad with high tactile cues could be used even in total absence of visual information, the performance with low tactility keypad collapsed. This underlines the importance of the industrial design in creating mobile devices that are accessible by anyone, in any context. Wearable keypads may also benefit from indirect visual feedback shown on the display. In this study, simple indirect feedback increased subjective ease, although only moderate effects were found in performance. Also more sophisticated feedback types need to be studied.