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Abstract

Compliance of deformable materials is perceived through signals about resistive force and displacement. During visual-haptic interactions, visual and proprioceptive signals about material displacement are combined over time with the force signal. Here we asked whether multisensory compliance perception is affected by the timing of signals by introducing an asynchrony between the participant's movement (sensed proprioceptively) and force information or visual information. Visual-proprioceptive asynchronies are obtained by making participants see a delayed video of their haptic interaction with an object rather than the real interaction. Force-proprioceptive asynchronies are instead obtained by making participants compress a virtual object with their hand and sense the resistive force generated by a force feedback device.

Results indicate that force-proprioceptive asynchronies can significantly alter the perception of object stiffness. Moreover, we find that perceived compliance changes also as a function of the delay of visual information. These effects of asynchrony on perceived compliance would not be present if all force-displacement information would be utilized equally over time, as both delays generate a bias in compliance which is opposite in the compression and release phases of the interaction. To explain these findings we hypothesized instead that information during object compression is weighted more than information obtained during object release and that visual and proprioceptive information about the hand position are used for compliance perception depending on the relative reliability of the estimate obtained. We confirm these hypotheses by showing that sensitivity to compliance is much higher during object compression and that degradation of visual and proprioceptive information can modify the weights assigned to the two sources. Moreover, by analyzing participants' movements and feedback forces we show that the two hypothesized factors (compression-release and visual-proprioceptive reliability) can account for the change in perceived compliance due to force-proprioceptive and force-displacement asynchronies.