Using behavioral and electrophysiological measures, in adults, Eva Dundas, David Plaut, and Marlene Behrmann observed the standard finding of greater accuracy and a larger N170 ERP component in the left over right hemisphere for words, and conversely, greater accuracy and a larger N170 in the right over the left hemisphere for faces. We also found that, although children aged 7-11 years revealed the adult hemispheric pattern for words, they showed neither a behavioral nor a neural hemispheric superiority for faces. Of particular interest, the magnitude of their N170 for faces in the right hemisphere was related to that of the N170 for words in their left hemisphere. Additionally, the mean gamma-band power in the N170 time range for faces in their RH was correlated with that for words in their LH. This result is really surprising, as one might have predicted that the mature brain organization would be evident earlier with faces (with which even young kids have a lot of experience) than with words. Our findings show the opposite, and the explanation is that it is only once children begin to read that the pressure for more organized brain function (for complex visual stimuli such as words and faces) begins. The acquisition of word recognition serves as the trigger for the brain to begin a reorganization that brings it to its adult-like profile.
These findings suggest that the hemispheric organization of face and word recognition do not develop independently, and that word lateralization may precede and drive later face lateralization. A theoretical account for the findings, in which competition for visual representations unfolds over the course of development, is discussed. A paper describing these results is under review for publication.
This past year, the major project concerned the emergence, over developmental time, of the apparently specialized and independent neural systems for the visual processing of words and faces. Extensive evidence has demonstrated greater selectivity for written words in the left over right hemisphere, and, conversely, greater selectivity for faces in the right over left hemisphere. This research examines the emergence of these complementary neural profiles, as well as a possible relationship between them.
Dundas, E, M., Plaut, D. C. and Behrmann, M. (in press). An ERP investigation of the co-development of hemispheric lateralization of face and word recognition. Neuropsychologia.