Perception of material from contact sounds

Contact sounds can provide important perceptual cues in virtual environment s. We investigated the relation between material perception and variables t hat govern the synthesis of contact sounds. A shape-invariant, auditory-dec ay parameter was a powerful determinant of the perceived material of an obj ect. Subjects judged the similarity of synthesized sounds with respect to m aterial (Experiment 1 and 2) or length (Experiment 3). The sounds correspon ded to modal frequencies of clamped bars struck at an intermediate point, a nd they varied in fundamental frequency and frequency-dependent rate of dec ay. The latter parameter has been proposed as reflecting a shape-invariant material property: damping. Differences between sounds in both decay and fr equency affected similarity judgments (magnitude of similarity and judgment duration), with decay playing a substantially larger role. Experiment 2, w hich varied the initial sound amplitude, showed that decay rate-rather than total energy or sound duration-was the critical factor in determining simi larity. Experiment 3 demonstrated that similarity judgments in the first tw o studies were specific to instructions to judge material. Experiment 4, in which subjects assigned the sounds to one of four material categories, sho wed an influence of frequency and decay, but confirmed the greater importan ce of decay. Decay parameters associated with each category were estimated and found to correlate with physical measures of damping. The results suppo rt the use of a simplified model of material in virtual auditory environmen ts.