Mid-air haptics for shape recognition of virtual objects.

This paper presents an experiment in which participants had to discriminate three mid-air haptic shapes (circle, square, point) by reporting whether the haptic stimulus (e.g. circle on the palm of the hand) was compatible with an image (e.g. a circle) or a word (e.g. 'circle') displayed on a screen. Results indicate that only the 'point' stimulus was appreciably recognised and discriminated in terms of accuracy and time needed for the identification. Accuracy increased with repetition, and response time decreased, suggesting a learning effect. The comparison between visual and textual labels shows that for the haptic point stimulus there is no significant difference but a tendency to have greater accuracy with images than with texts, while the opposite result is found for the circle stimulus. This outcome suggests the need for new experiments focussed of the effect of visual/textual labels to make the recognition/discrimination tasks of haptic stimuli easier. Three haptic shapes were presented with images or texts, matching or not the stimuli. The point was easy to recognise, while the circle and the square were difficult to discriminate against each other. Visual/textual labels bring contradictory results for different shapes. 1D: one-dimensional; 2D: two-dimensional; 3D: three-dimensional; API: application programming interface; cm: centimeter; GLMM: generalised linear mixed-effect model; HCI: human-computer interaction; Hz: hertz; LMM: linear mixed-effect model; MCC: Matthews' correlation coefficient; mm: millimeter; ms: millisecond; QQ-plot: Quantile-Quantile plot; SD: standard deviation.