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Abstract

Previous research indicated that sound can bias visual [1-4] as well as tactile perception [5,6]. The present experiment tested whether auditory stimuli can alter the tactile perception of sequences of taps (2 to 4 taps per sequence) delivered on the index ngertip. The taps were delivered using a PHANToM force feedback device. The subjects did not have any visual or auditory feedback about the tactile stimulation and their task was to report after each sequence how many taps they felt. In the rst experiment, for some trials, auditory sequences of beeps were presented concomitantly with the tactile sequences (through earphones). The number of beeps diffused in the auditory sequence could be the same as, less, or more than the number of taps of the simultaneously presented tactile sequence. Though irrelevant (subjects were instructed to focus on the tactile stimuli), the auditory stimuli systematically biased subjects' tactile perception, i.e. subjects' responses depended signicantly on the number of diffused beeps. The results also suggested that for such an auditory-tactile interaction to occur, a certain amount of “structural” congruency between the simultaneously presented stimuli is required. Indeed, the diffusion of an auditory stimulus obviously incongruent with the tactile sequence failed to evoke any bias of tactile perception. In the second experiment, we tested whether the auditory-tactile interaction also requires temporal congruency or whether a bias can be evoked without temporal overlapping between the auditory and tactile presented sequences. The tactile and auditory stimuli were the same as in the rst experiment (the structurally incongruent auditory stimulus was not used here) but the auditory sequences were presented either simultaneously with, before the beginning, or after the end of the tactile sequences. Audition strongly biased tactile perception when the stimuli were temporally concomitant (reproduction of the results obtained in the rst experiment). With a temporally asynchronous audio-tactile stimulus the interaction gradually disappeared. We conclude that auditory and tactile sensory signals are integrated when they both provide redundant information in good temporal coherence.