A left fusiform region that responds selectively to letter strings

Abstract

Can experience alone with a particular stimulus class be sufficient to produce a cortical region selectively responsive to that class of stimulus? Visual words provide an ideal test case because we have extensive experience reading yet our species has not been reading long enough for an evolutionarily-based specialization to arise. Despite reports of a region in left extrastriate cortex that responds to words or letter strings, some studies (including one of ours) have failed to show selectivity in this region for words and letters compared to other visual stimuli. Here we scanned 11 native English speaking subjects at high resolution (3T, 8 channel phased-array surface coil, voxel size = 1.4×1.4×2mm). We found a small region (average 40.5 voxels, p<0.0001) in the left fusiform gyrus of all subjects that responded more strongly to English words than to line drawings of familiar objects. This word activation was used to functionally define an ROI individually for each subject, the selectivity of which was characterized in a subsequent event-related experiment in the same scanning session. The word-selective region responded significantly more strongly to English words than to i) digit strings, ii) strings of letterlike forms, and iii) Chinese Characters and Hebrew words (which our subjects could not read). However, this same region, which appears to be in the same location as the so-called “visual word form area”, responded equally to words and to consonant strings. These data suggest that the left extrastriate cortex contains a region selectively responsive to letter strings (not words) that is not likely to reflect either phonological processing or low-level visual properties of the stimuli. These findings support the hypothesis that regions of extrastriate cortex that are selectively responsive to a particular stimulus class can arise from extensive experience alone with that stimulus class, without a specific genetic predisposition.

Footnotes

 This study is supported by NEI grant 13455 to N Kanwisher