Projects

UM Computational and Cognitive Neuroscience Lab

The neural development and organization of abstract word recognition

Neuroimaging study. In a previous PET study, Petersen et al. (1990) found areas of left medial extrastriate visual cortex that were significantly more activated by passive viewing of words and pseudowords than consonant strings. This result provides evidence for the existence of visual areas that respond specifically to word-like stimuli, or so-called, visual word forms. Given the evidence for abstract word forms cited above, we wondered whether these areas were responding to the visual form of orthographically legal stimuli or to their abstract form-the specific sequence of abstract letters they contain, independent of their visual form (case, font, size, etc.)? These alternatives can be distinguished by the use of aLtErNaTiNg case stimuli, which correspond to naturally occurring abstract, but not visual, word forms (they are certainly word-like in the abstract, but they are not visually familiar and hence would not correspond to any known visual word forms).

During an fMRI session, four subjects passively viewed two sets each of concrete words, pronounceable pseudowords, consonant strings, and fixation points. In four runs stimuli were presented in aLtErNaTiNg case and in the other four runs stimuli were presented in pure case.

Left medial extrastriate visual areas were found to be significantly more activated by pure case words and pseudowords than consonant strings in all four subjects (p<0.05, corrected). These same areas were also significantly more activated by alternating case words and pseudowords than consonant strings (p<0.05, corrected). The activated areas were again on or near the left fusiform gyrus in occipitotemporal cortex (Brodmann are 37) raising the interesting possibility that it is the same area that was observed in the letter recognition study. One of the proposed experiments to be described later is designed to elucidate the relationship between these two results. Some occipital areas were significantly activated by all three stimulus types compared with fixation (p<0.05, corrected).

These results provide direct evidence for an area in extrastriate cortex that encodes abstract word forms based on orthographic regularities, rather than just the visual form of word-like stimuli.

These results were just presented at the 1996 Annual Meeting of the Society for Neuroscience (Polk, Stallcup, Aguirre, Alsop, D'Esposito, Detre, Zarahn, & Farah, 1996).

UM Computational and Cognitive Neuroscience Lab |
tpolk@umich.edu | maintained by David Krauss,
dkrauss@umich.edu | revised June 97