Impact of Deafness on the Development of Face Processing

(Perceptual Development Lab)

The face carries a great deal of information – identity, emotion, social cues – and humans are incredibly adept at extracting this information within as little as one second of seeing a face.  For deaf individuals, the face carries even more information in part because of its central role in American Sign Language (ASL).  In ASL, information about both linguistic meaning and linguistic structure or grammar is carried on the face and this information is important for correct interpretation of the word or phrase being signed.  I hypothesized that the neural systems involved in face processing may be re-organized in the deaf because of the use of a visuospatial language and because information in the face may become more important in the absence of other auditory information in perceiving identity, emotion, and social cues; this may enhance the functioning of brain regions known to be activated by faces and it may recruit additional brain regions for basic face processing.  In an fMRI study, I compared activation in hearing and congenitally deaf adults evoked by photographs faces of unknown people to activation evoked by scrambled photographs.  As shown in the figure below, within-group analyses showed that deaf and hearing participants displayed activation in the classic fusiform region and the lingual gyrus, but that deaf participants activated

additional brain regions, including cortex along the upper lip of the lateral fissure.  These preliminary data suggest that the neural substrate for face processing, a ventral stream function often held as an example of a brain module, may be modified by auditory deprivation and/or the use of a visuospatial language.  It also demonstrates that although the ventral stream functions of form and color processing appear thus far to be unaffected by deafness, face processing is. 

Future studies along this line will be conducted with deaf and hearing children and adults.  We are interested in further characterizing the nature of the effects of deafness on basic face processing by using behavioral, electrophysiological (EEG) and fMRI measures.   We will explore factors related to auditory deprivation and to the use of American Sign Language.  We are also interested in exploring how the perception of facial expressions is affected by deafness across the lifespan.  We will study the perception of facial expressions related to basic emotions and expressions related to linguistic factors in American Sign Language.

Mitchell, T., Tomann, A., Bavelier, D., Murray, S., Corina, D., Hutton, C., Liu, G. and Neville, H.  (November, 1998).  Cortical Re-organization for Visual Functions in Congenitally Deaf Subjects:  Part II. Object and Face Processing.  Society for Neuroscience.