Visual word processing and experiential origins of functional selectivity in human extrastriate cortex

Abstract

How do category-selective regions arise in human extrastriate cortex? Visually presented words provide an ideal test of the role of experience: Although individuals have extensive experience with visual words, our species has only been reading for a few thousand years, a period not thought to be long enough for natural selection to produce a genetically specified mechanism dedicated to visual word recognition per se. Using relatively high-resolution functional magnetic resonance imaging (1.4 x 1.4 x 2-mm voxels), we identified a small region of extrastriate cortex in most participants that responds selectively to both visually presented words and consonant strings, compared with line drawings, digit strings, and Chinese characters. Critically, we show that this pattern of selectivity is dependent on experience with specific orthographies: The same region responds more strongly to Hebrew words in Hebrew readers than in nonreaders of Hebrew. These results indicate that extensive experience with a given visual category can produce strong selectivity for that category in discrete cortical regions.

Fig. 1.

Experimental design and stimuli. In blocked-design runs (A), participants saw 15-sec blocks of English words, consonant strings, Hebrew words, and line drawings interleaved with blocks of fixation only and either fixated passively (half the runs) or responded whenever there was an immediate repeat of the same stimulus. In event-related runs (B), participants saw English words, consonant strings, digit strings, Hebrew words, Chinese characters, and line drawings on interleaved trials and reported whether the stimulus was moving downward or to the right.

Fig. 2.

Regions selectively responsive to English words. Representative functional slices from 8 non-Hebrew readers showing voxels selectively responsive to English words compared with line drawings (P < 10⁻⁴). Selectively responsive voxels were predominantly found in the left (L) hemisphere close to the occipitotemporal sulcus.

Fig. 3.

Estimated hemodynamic response functions for the English words versus line drawings ROI in the event-related runs. In non-Hebrew readers (A), the response to English words was significantly greater than to all other stimuli except consonant strings. A similar pattern of response was found in the Hebrew readers (B), except that the response to Hebrew words was much greater than that seen in non-Hebrew readers.

Fig. 4.

Regions selectively responsive to English and Hebrew words in Hebrew readers. Representative functional slices from three Hebrew readers showing voxels selectively responsive to English words (Left) and Hebrew words (Right) compared with line drawings (P < 10⁻⁴). Color scale as for Fig. 2.