Cerebral Cortex Advance Access originally published online on September 6, 2006
Cerebral Cortex 2007 17(7):1604-1611; doi:10.1093/cercor/bhl071
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Differential Sensitivity to Words and Shapes in Ventral Occipito-Temporal Cortex
1 Stanford Institute for Reading and Learning, 2 Psychology Department, Stanford University, Stanford, CA 94305, USA
Address correspondence to Michal Ben-Shachar, Jordan Hall, Building 420, Stanford University, Stanford, CA 94305, USA. Email: michal{at}white.stanford.edu.
Efficient extraction of shape information is essential for proficient reading but the role of cortical mechanisms of shape analysis in word reading is not well understood. We studied cortical responses to written words while parametrically varying the amount of visual noise applied to the word stimuli. In only a few regions along the ventral surface, cortical responses increased with word visibility. We found consistently increasing responses in bilateral posterior occipito-temporal sulcus (pOTS), at an anatomical location that closely matches the "visual word form area". In other cortical regions, such as V1, responses remained constant regardless of the noise level. We performed 3 additional tests to assess the functional specialization of pOTS responses for written word processing. We asked whether pOTS responses are 1) left lateralized, 2) more sensitive to words than to line drawings or false fonts, and 3) invariant for visual hemifield of words but not other stimuli. We found that left and right pOTS response functions both had highest sensitivity for words, intermediate for line drawings, and lowest for false fonts. Visual hemifield invariance was similar for words and line drawings. These results suggest that left and right pOTS are both involved in shape processing, with enhanced efficiency for processing visual word forms.
Key Words: false fonts line drawings parametric fMRI phase scrambling word reading
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