Selective effects of auditory stimuli on tactile roughness perception.

We report two psychophysical experiments designed to investigate the effects of non touch-produced sounds on the tactile perception of roughness and length. Previous studies have demonstrated that the tactile roughness perception of object surfaces is modified by sounds elicited by rubbing the surfaces. In this study, we examined the crossmodal effects of non touch-produced sounds such as white noise (Experiment 1) and pure tones (Experiment 2). Participants touched abrasive paper, synchronizing their touch with changes in the intensity of sounds or with the onset of beeps (control condition), and judged the tactile roughness or length of the stimuli, using the magnitude estimation method. Although the white noise (complex sound) significantly decreased the slope of the roughness estimation function, it did not affect that of the length estimation function. Pure tones had no effect on roughness or length perception. The results revealed that complex sounds selectively affected tactile roughness perception, even when they were seemingly irrelevant to the exploration of the surfaces. We suggest that the processing of complex sounds may be related to the processing of tactile roughness, whereas it is independent of tactile length processing.