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Michele Fornaciai, Joonkoo Park; Dynamics of numerosity representation in early visual cortex.. Journal of Vision 2018;18(10):87. doi: https://doi.org/10.1167/18.10.87.
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© ARVO (1962-2015); The Authors (2016-present)
While the representation of numerical magnitude is thought to reside in the parietal cortex, recent studies have started to reveal the role of early visual cortex in numerical magnitude processing. Here, we provide novel evidence for the critical involvement of early visual regions in numerosity perception. By using the connectedness illusion, whereby arrays with pairwise connected dots are perceived to be less numerous compared to arrays containing isolated dots, we dissociated veridical (i.e. the actual number of dots) and perceived (i.e. numerosity reduced by connectedness) numerosity. Exploiting this illusion, we trace the temporal (using EEG) and anatomical (using fMRI) evolution of numerosity representation from veridical to perceived representations in the cortical visual pathways. The results show that while visual area V2 mainly respond to the veridical numerical magnitude of the stimuli, activity in area V3 reflects both veridical and perceived numerosity, at different latencies. Namely, V3 encodes veridical numerosity earlier in the processing stream (100ms), while it encodes perceived numerosity at a later time point (150ms). These findings highlight the neural dynamics in early visual areas underpinning numerosity perception and indicate that area V3 represents a crucial node mediating the transformation of sensory information into subjective experience.
Meeting abstract presented at VSS 2018
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