Sound enhances touch perception.

Certain sounds, such as fingernails screeching down a chalkboard, have a strong association with somatosensory percepts. In order to assess the influences of audition on somatosensory perception, three experiments measured how task-irrelevant auditory stimuli alter detection rates for near-threshold somatosensory stimuli. In Experiment 1, we showed that a simultaneous auditory stimulus increases sensitivity, but not response biases, to the detection of an electrical cutaneous stimulus delivered to the hand. Experiment 2 demonstrated that this enhancement of somatosensory perception is spatially specific--only monaural sounds on the same side increased detection. Experiment 3 revealed that the effects of audition on touch are also frequency dependent--only sounds with the same frequency as the vibrotactile frequency enhanced tactile detection. These results indicate that auditory information influences touch perception in highly systematic ways and suggest that similar coding mechanisms may underlie the processing of information from these different sensory modalities.

Touch, sound and vision in human superior temporal sulcus.

Human superior temporal sulcus (STS) is thought to be a key brain area for multisensory integration. Many neuroimaging studies have reported integration of auditory and visual information in STS but less is known about the role of STS in integrating other sensory modalities. In macaque STS, the superior temporal polysensory area (STP) responds to somatosensory, auditory and visual stimulation. To determine if human STS contains a similar area, we measured brain responses to somatosensory, auditory and visual stimuli using blood-oxygen level dependent functional magnetic resonance imaging (BOLD fMRI). An area in human posterior STS, STSms (multisensory), responded to stimulation in all three modalities. STSms responded during both active and passive presentation of unisensory somatosensory stimuli and showed larger responses for more intense vs. less intense tactile stimuli, hand vs. foot, and contralateral vs. ipsilateral tactile stimulation. STSms showed responses of similar magnitude for unisensory tactile and auditory stimulation, with an enhanced response to simultaneous auditory-tactile stimulation. We conclude that STSms is important for integrating information from the somatosensory as well as the auditory and visual modalities, and could be the human homolog of macaque STP.

Human MST but not MT responds to tactile stimulation.

Previous reports of tactile responses in human visual area MT/V5 have used complex stimuli, such as a brush stroking the arm. These complex moving stimuli are likely to induce imagery of visual motion, which is known to be a powerful activator of MT. The area described as "MT" in previous reports consists of at least two distinct cortical areas, MT and MST. Using functional magnetic resonance imaging, we separately localized human MT and MST and measured their response to vibrotactile stimuli unlikely to induce imagery of visual motion. Strong vibrotactile responses were observed in MST but not in MT. Vibrotactile responses in MST were approximately one-half as large as the response to visual motion and were distinct from those in another visual area previously reported to respond to tactile stimulation, the lateral occipital complex. To examine somatotopic organization, we separately stimulated the left and right hand and foot. No spatial segregation between hand and foot responses was observed in MST. The average response profile of MST was similar to that of somatosensory cortex, with a strong preference for the contralateral hand. These results offer evidence for the existence of somatosensory responses in MST, but not MT, independent of imagery of visual motion.