Fingertip behavior during tangential sliding movements

Previous studies of haptic search for object properties have shown efficient perception of various haptic features. In this study, the saliency of hardness and softness was investigated in a search task. In Experiment 1, blindfolded participants had to grasp a bundle of spheres and determine whether a hard target was present among soft spheres or vice versa (Figure 1). When the difference in compliance between target and distractors was small, reaction times increased with the number of items and participants used a serial strategy. With a large difference in compliance, the reaction times did not depend on the number of items and a parallel strategy was used. This was found for both hard and soft spheres. In Experiment 2, participants had to press their hand on a display filled with hard and soft spheres (Figure 2). In the search for a soft target, the slopes of reaction times against the number of items were high, but the locations of target and distractors had a large influence on the search difficulty. With a hard target, the reaction time was independent of the number of items. Overall, these results show that both hardness and softness are salient features. Acknowledgements This work was supported by the European Commission with the Collaborative Project no. 248587, “THE Hand Embodied”.