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membrane for auditory and the skin for somatosensory) and are processed in
frequency-based codes in adjacent regions of the cerebral cortex.
In addition to cortical proximity, the somatosensory cortex projects to regions of
auditory cortex (Schroeder, et al. 2001) and neuroimaging studies have demonstrated
interactions between the somatosensory and auditory modalities in some regions of
auditory cortex (Foxe, et al. 2002). Other studies have also shown direct anatomical
connections between auditory and visual cortex at early stages of the cortical processing
hierarchy (Bizley, et al. 2007; Clavagnier, et al. 2004; Falchier, et al. 2002; Rockland and
Ojima 2003). These demonstrations of interconnectivity between the primary sensory
cortices of different Sensory modalities have led some to question whether any cortex is
truly unisensory (Ghazanfar and Schroeder 2006; Macaluso and Driver 2005; Schroeder
and Foxe 2005) and suggest that the perceptual processing of information in one
sensory modality may have systematic effects on the processing of information in a
different sensory modality.
To assess the perceptual interactions between sound and touch, we conducted
three psychophysical experiments examining the effects of a task-irrelevant auditory
stimulus on the perception of weak somatosensory events. Weak somatosensory stimuli
were used because multisensory interactions are known to be most potent for near
threshold stimuli (Stein and Meredith 1993). Experiment 1 examined whether a
simultaneously presented tone affects somatosensory perception. Experiment 2
examined whether the spatial location of the sound affects somatosensory processing in
a spatially specific manner. Experiment 3 examined whether the effects of sound on