Learning to read may trigger right-left hemisphere difference for face recognition

Marlene Behrmann, Eva Dundas, David Plaut - Carnegie Mellon University


Outcome:
Whereas, in this study, adults showed the expected left and right visual field superiority for face and word discrimination, respectively, the young adolescents demonstrated only the right field superiority for words and no field superiority for faces. Although the children's overall accuracy was lower than that of the older groups, like the young adolescents, they exhibited a right visual field superiority for words but no field superiority for faces. Interestingly, the emergence of face lateralization was correlated with reading competence, measured on an independent standardized test, after regressing out age, quantitative reasoning scores and face discrimination accuracy.

Impact/benefit:
These findings suggest that the hemispheric organization of face and word recognition do not develop independently, and that word lateralization, which emerges earlier, may drive later face lateralization. These findings are consistent with a theoretical account, which argues that both word and face recognition rely on fine-grained visual representations. However, by virtue of pressure to couple visual and language areas and to keep connection length short, the left hemisphere becomes more finely tuned for word recognition and, consequently, the right hemisphere becomes more finely tuned for face recognition. These behavioral studies are being followed up at present and evoked response potentials are being collected from observers, across a wide age span, to elucidate further the neural mechanisms that underlie the emergence of hemispheric specialization over the course of development.

Future Predictions: These findings lead to many predictions, some of which are currently being examined in the Behrmann lab. One prediction is that individuals who have less strongly left-lateralized word representations should also have less strongly right-lateralized face representations. First, many left-handed individuals have a more bilateral language organization, which would be expected to lead to more bilateral orthographic word representations. Second, non-alphabetic orthographic scripts, such as Chinese, are less closely tied to phonology and hence have a more bilateral organization. As a result, we predict that both left-handed individuals and native readers of Chinese should have less strongly right-lateralized face processing (as compared to right-handed English readers).

Background/explanation:
The question addressed by the research study conducted in the lab of Dr Marlene Behrmann (member of the Perceptual Expertise Network) at Carnegie Mellon University is how the pattern of mature hemispheric specialization emerges over the course of development. We know that, in adulthood, the left hemisphere is more tuned to word recognition whereas the right hemisphere is more tuned to face recognition. The current study examines the hemispheric superiority for faces and words in children, young adolescents and adults in a discrimination task in which stimuli are presented briefly in either hemifield.
This research is conducted by Marlene Behrmann (below left) in collaboration with Eva Dundas (below middle), a graduate student in the Department of Psychology at Carnegie Mellon University, and with Dr David Plaut (below right), Professor of Psychology at Carnegie Mellon University.