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Shipra Kanjlia, Connor Lane, Lisa Feigenson, Marina Bedny; Visual cortex of congenitally blind individuals responds to symbolic number. Journal of Vision 2015;15(12):194. doi: 10.1167/15.12.194.
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© 2017 Association for Research in Vision and Ophthalmology.
Numerical processing is considered to be a highly visual capacity. Like other early visual features, numerosity is susceptible to visual adaptation. Numerosity-selective neurons naturally emerge in the dorsal visual stream of monkeys. Math abilities are predicted by both visual numerical estimation abilities and visuospatial abilities. Math calculation also activates the intraparietal sulcus (IPS), which responds to visual numerosity. Do numerical processing abilities depend on visual experience? We asked whether the cortical circuits involved in numerical processing develop normally in individuals who are blind from birth. While undergoing fMRI, 17 blind and 19 sighted participants heard pairs of equations (e.g. X-2=5, X-4=3) and judged whether the value of “X” was the same. Equations were either simple (single-digit, e.g. X-2=7) or complex (double-digit, e.g. X-12=17). In a control task, participants judged whether pairs of sentences had the same meaning. In a second experiment, participants heard syntactically simple and complex sentences and answered yes/no questions about them. Just as in sighted individuals, the IPS in blind individuals responds more to math than sentences and is sensitive to math complexity. In blind individuals the typical IPS activity extended posteriorly into “visual” occipital cortex. We found responses to auditory number symbols in the anatomical territory of dorsal V1 to V3. The response profile of this “visual” number area was similar to the IPS: 1) it responded more to math than sentences 2) was sensitive to math difficulty and 3) was not sensitive to syntactic complexity. We find that blind individuals develop typical IPS responses to number. This suggests that numerical representations in the IPS are not tied to visual processing abilities. Blind but not sighted individuals also activate “visual” cortical areas during numerical tasks. Together with prior data from our lab, these results suggest that higher cognitive functions expand into deafferented visual cortex of humans.
Meeting abstract presented at VSS 2015
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