Abstract
The traditionally accepted unimodal nature of primary visual cortex has been challenged by functional and anatomical evidence of early visual neurons receiving nonvisual input in cats (auditory: Morrell, 1972; Fishman and Michael, 1973), primates (auditory: Falchier et al., 2002), and blind (tactile: Sadato et al., 1996; Cohen et al., 1997; auditory: Gougoux et al., 2005) and sighted (tactile: Zangaladze et al., 1999; Merabet et al., 2004) humans. The present study measured the precision of auditory spatial coding in early visual cortex. In an fMRI experiment, subjects performed a 5AFC spatial discrimination task in which they were presented with spatially specific auditory stimuli in 5 locations across a range of 20 degrees in the frontal plane. The task was to indicate via button press the apparent location of each stimulus. We found that early visual cortex (V1/V2) as well as occipito-parietal regions (cuneus/precuneus) contained regions that discriminated between the spatial locations of the stimuli, i.e., spatially closer stimuli elicited more highly correlated activity than did more separated stimuli. Importantly, these regions often exhibited greater selectivity for the perceived, rather than physical, stimulus position, as calculated from incorrect responses. These results suggest that top-down connections to early visual areas carry spatial information from higher-order auditory cortical areas.