Abstract
The retinotopic organization of information in human visual cortex is well known. However, it has become evident that some non-visual tasks also recruit early visual cortex, especially in blind subjects (e.g. tactile: Cohen et al., 1997; auditory: Gougoux et al., 2005). We sought to determine whether such cross-modal activity can also be found for sounds presented to sighted subjects, and whether, in accordance with the spatiotopic organization of early visual cortex, it is spatially specific. In an fMRI study, we scanned subjects at 3T while presenting pink-noise moving auditory stimuli through headphones. The stimuli simulated the effect of presentation from one of eight positions in a free-field environment and were calibrated individually to subjects' ears. In other runs, we presented visual stimuli to individual quadrants of subjects' visual fields. Consistent with previous studies, no overall amplitude change in BOLD response to auditory stimuli was found in visual cortex. However, position-selective patterns of activity were found when comparing individual spatial conditions. We found that visual cortex responses to auditory and visual stimuli were more closely correlated when the stimuli occurred in the same quadrants of visual space than when they occurred in disparate quadrants. Auditory stimuli simulating presentation behind the subject did not produce spatially specific patterns of activity, demonstrating that the sensitivity of visual cortex to auditory stimuli is restricted to those that overlap the visual field.