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Conference Paper

Friction and curature judgement


Christou,  CG
Department Human Perception, Cognition and Action, Max Planck Institute for Biological Cybernetics, Max Planck Society;

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Christou, C. (2001). Friction and curature judgement. In EuroHaptics 2001 (pp. 36-40). Birmingham, UK: University of Birmingham.

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Local shape is an important attribute that can be sensed by exploratory movements of the finger. Normally this involves a blend of tactile and proprioceptive cues. A curved surface will deform the pad of a single finger and so tactile cues can indicate whether a surface is convex or concave or whether it slopes one way or another. When more subtle discriminations must be made between different degrees of curvature, scanning motions are made in which the finger sweeps along the surface. In this case the cue to curvature is the change in position of the finger tip over time and here proprioceptive input is important. We have been examining how curvature judgements are affected by the force reflected back from the curved surface during scanning. Normally when you run your finger over a surface, you experience resistance to motion due to friction. This resistance creates a force vector which varies in direction with friction. But the vector also varies in direction with the curvature of the surface traversed by the finger. We used a two-alternative forced-choice (2AFC) task in an adaptive staircase in which subjects made comparisons between various test curvatures and a reference curvature in order to find the point of subject equality (PSE) between the two. Differences in friction between reference and test stimuli were found to alter the PSE in a consistent manner. In particular, we found that the reference curvature was only closely matched when no frictional disparity existed between reference and test surface. Reference surfaces that exerted high frictional forces produced smaller curvatures as PSEs while surfaces with low friction produced high curvature matches. These results suggest that forces experienced in palpating a surface may be utilised in the comparison of curvature.