Adi Cohen

Perception of compliant objects demands integration of haptic and visual position information with force information (Freyberger et al., 2007). Past research has mainly concentrated on the psychophysical properties of compliance, yet ways of improving such capabilities were thus far not examined. The present research examines human ability to detect differences in stiffness (the reciprocal of compliance) based either on haptic feedback only or with matched and non-matched visual cues. The aim of the current study is to evaluate human ability to detect differences in stiffness using a 2AFC task and specifically, to explore the effects of practice and multimodal information on stiffness sensitivity. The findings suggest a complex manifestation of multimodal experience during stiffness perception. A window of differences between uni-modal and multi-modal performance appears to exist within the supra-threshold range of stiffness values, 20-30% from a standard comparison value. At this range, multimodal cues may significantly affect the discrimination ability, either positively or negatively, depending on the congruency between the modalities and the order of experience with uni-modal and multimodal conditions. The findings from the present study are important for the development of optimized training protocols aiming to facilitate haptic perception and acquisition of haptic skills in virtual environments.