Feeling what you hear: Auditory signals can modulate the perception of tactile taps

Investigating multisensory integration, Shams et al (2000 Nature 408 788) recently found that the number of perceived visual flashes could be altered by a sequence of beeps presented simultaneously. Here, we tested whether auditory sequences of beeps can modulate the tactile perception of sequences of taps (2 to 4 taps per sequence). In experiment 1, the auditory and tactile sequences were presented simultaneously. The number of beeps delivered in the auditory sequence was either the same as, less than, or more than the number of tactile taps. Though task-irrelevant (subjects were instructed to focus on the tactile stimuli), the auditory stimuli significantly modulated subjects' tactile perception. Such modulation occurred only when the auditory and tactile stimuli were structurally similar. In experiment 2, we tested whether auditory - tactile interaction depends on simultaneity or whether a bias can be evoked without temporal overlap between the auditory and tactile sequences. Audition significantly modulated tactile perception when the stimuli were presented simultaneously, but this effect gradually disappeared when a temporal asynchrony was introduced between auditory and tactile stimuli. These results show that when provided with auditory and tactile signals that are likely to be generated by the same stimulus, the brain tends to automatically combine these signals