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Santani Teng, Radoslaw Cichy, Dimitrios Pantazis, Aude Oliva; Spatiotemporal dynamics of braille letter perception in blind readers. Journal of Vision 2017;17(10):358. doi: https://doi.org/10.1167/17.10.358.
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© ARVO (1962-2015); The Authors (2016-present)
Traditionally "visual" cortical regions in blind persons are known to activate in response to a wide range of nonvisual tasks, suggesting a functional reorganization in response to blindness. However, the functional correlates of specific regional activations and, more generally, the principles governing the reorganization of cortical processing remain unclear. This is in part because the underlying dynamics of crossmodal plasticity are not well understood. Previously, we measured brain responses to Braille letter stimuli using MEG alone, finding that sensory representations are widely variable and idiosyncratic across subjects. Thus, to elucidate the braille processing stream in blind individuals with high spatial resolution, here we additionally measure fMRI responses in repeated sessions for individual subjects. Early-blind, braille-proficient participants were presented with single-letter stimuli to the left index finger in random order, responding to occasional deviants. Univariate contrasts yielded reliable BOLD activation in right somatosensory and bilateral occipital and parietal cortices. Further, we use MVPA to generate similarity matrices between letter identities from MEG and fMRI data. We then relate these results with representational similarity analysis, leveraging the spatial resolution of fMRI and the temporal resolution of MEG in a spatiotemporal fusion analysis: Significant correlations between MEG and fMRI representations index the propagation of braille information between its arrival in somatosensory cortex and its subsequent evolution along the processing stream. We interpret results in the context of competing proposals of processing hierarchies, e.g. whether a visually deprived cortex reverses the typical visual hierarchy or largely co-opts it using tactile input.
Meeting abstract presented at VSS 2017
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