Haptic-auditory rendering and perception of contact stiffness

This paper presents an experiment on the relative contributions of haptic and auditory information to bimodal judgments of contact stiffness using a rigid probe. Haptic feedback is rendered via a Phantom Omni device, while auditory stimuli are obtained using a physically-based audio model of impact, in which the colliding objects are described as modal resonators that interact through a non-linear impact force. The impact force can be controlled through a stiffness parameter, that influences the contact time of the impact. Previous studies have already indicated that this parameter has a major influence on the auditory perception of hardness/stiffness. In the experiment subjects had to tap on virtual surfaces, and were presented with audio-haptic feedback. In each condition the haptic stiffness had the same value while the acoustic stiffness was varied. Perceived stiffness was determined using an absolute magnitude-estimation procedure: subjects were asked to rate the surfaces on an ordered scale of verbal labels, based on their perceived stiffness. The results indicate that subjects consistently ranked the surfaces according to the auditory stimuli.