A-modal versus Cross-modal: How input modality and visual experience affect categorical representation in the "visual" cortex

Abstract

It has recently been proposed that some regions of the occipital cortex, typically considered purely visual, develop a preferential tuning for specific categories independently of the sensory input and visual experience. In contrast, several studies showed that occipital responses to non-visual inputs is unique to blind individuals due to crossmodal plasticity. To further assess how the functional tuning of occipital regions is (in)dependent of visual input and experience, we characterized with fMRI brain responses to 8 categories presented acoustically in sighted and early blind individuals, and to the same stimuli presented visually in a separate sighted group. First, we observed that the posterior middle temporal gyrus (pMTG) was the most reliable region being able to decode the 8 presented categories independently of the input modality (in vision and audition in the sighted) and visual experience (in audition in the sighted and blind). Importantly, we also observed that the occipital cortex of blind individuals showed enhanced coding of acoustical stimuli. To further understand the nature of this reorganization, we used representational similarity analysis (RSA) in those regions in order to link similarities of brain activity patterns with different features similarities of the acoustical stimuli space. We found a stronger correlation between the patterns of activity in some portions of the occipital cortex with the categorical features of the stimuli (e.g. animate-inanimate), whereas we did not find any information about the physical properties (e.g. pitch) of the stimuli. Together, our results suggest that the occipital cortex shows a strong sensory tuning toward visual stimuli in the sighted and reorganizes to enhance its response toward non-visual input in case of early visual deprivation. Additional analyses on the nature of the functional reorganization show that the representation is mostly linked to "high-level" categorical tuning rather than low-level properties of the sounds (e.g. pitch).

Meeting abstract presented at VSS 2017