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Word-response functions in occipitotemporal sulcus are modulated by age and reading skills in 7- to 12-year-old children

M Ben-Shachar, RF Dougherty, GK Deutsch, P Potanina and BA Wandell
Stanford Institute for Reading and Learning

INTRO We have previously demonstrated that the amplitude of BOLD responses in left and right occipito-temporal sulcus (OTS) covaries with word visibility in adults. Here we examine the development of this visual sensitivity to words in children.
METHODS Fifty children ages 7-12y participated in four testing sessions, including behavioral assessment, anatomical, DTI and functional MRI sessions. In fMRI scans we presented visual words masked by phase-scrambled noise, while children were engaged in a fixation task (implicit reading). Noise level was manipulated parametrically.
Measurements covered ventral occipito-temporal cortex (GE Signa 3T, spiral acquisition, 26 oblique slices, 3x3x3 mm voxels). ROIs in OTS and early visual cortex were defined functionally in individual brains by contrasting the word conditions against fixation and anatomically using sulcal landmarks. Within ROIs, BOLD signal changes were plotted as a function of noise level, resulting in a 'word-visibility response function'.
RESULTS Word-visibility response functions were present in bilateral OTS in children as young as 7y. Such sensitivity to word-visibility was not evident in early visual cortex (V1/2/3 foveal confluence). BOLD signals in OTS were higher for the most visible words, and decreased with noise. The steepness of the OTS response function depended on age and reading skills. Older children (age>10y) showed a steeper response function. Also, better readers (word ID standard score >100) showed higher BOLD signal for low-visibility words.
CONCLUSIONS BOLD responses in left and right OTS are related to word-visibility in children. The quantitative form of this relationship changes between the ages of 7-12. Preliminary results from adult studies we have preformed suggest that the OTS response functions are not specific to word stimuli, but generalize to line drawings of common objects. One interpretation is that visual word recognition takes advantage of an existing OTS system that analyzes contours.
Support Contributed By: NIH grant NEI RO1 EY15000

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