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enhancement for auditory-tactile multisensory stimulation compared to the maximum
unisensory response in the present study was 23%, similar to the 17% enhancement for
auditory-visual multisensory stimuli in STSms observed in a previous study (Beauchamp,
et al. 2∞4b). These results add to a body of evidence showing multisensory interactions
between touch and sound in auditory cortex, sometimes extending into the STS (Foxe,
et al. 2002; Kayser, et al. 2005; Murray, et al. 2005; Schroeder, et al. 2001).
In the present study, "super-additive" multisensory responses were not
observed. That is, the response to auditory-tactile stimuli was greater than the
response to auditory or tactile stimuli in isolation, but was not greater than the summed
response to auditory and tactile unisensory stimuli (Stein and Meredith 1993). Previous
fMRI studies Ofauditory-Visual integration in STS (Beauchamp, et al. 2004a;
Beauchamp, et al. 2004b; Hein, et al. 2007; van Atteveldt, et al. 2004; van Atteveldt, et
al. 2007) and auditory-tactile integration in auditory cortex (Kayser, et al. 2∞5) have
also not observed super-additive changes in the BOLD signal, perhaps because only a
few single neurons show superadditivity (Laurienti, et al. 2005; Perrault, et al. 2005).
Supporting this idea, in single-unit recording studies, only a small fraction of STP
neurons respond to both auditory and tactile stimulation (Bruce, et al. 1981; Hikosaka,
et al. 1988); the same is true in multisensory regions of cat cortex (Clemo, et al. 2007).
Conversely, many single neurons may show no response to a sensory stimulus in
isolation, but the same stimulus may modulate responses when presented with other
sensory modalities (Allman and Meredith 2007). In macaque auditory cortex, auditory-
tactile integration increases as the auditory stimulus decreases in intensity (Lakatos, et