The Deaf, Sign Langague, and Spatial Cognition; by Jennifer Milner, March 22, 2002

Sign in the Brain

In most adults, analytical tasks like understanding spoken language occur in the left hemisphere of the brain while the right hemisphere is where processing of non-language perception takes place. For these reasons, it was once uncertain where sign language processing would occur. While sign language has a lexical and grammatical structure like spoken language, it relies on visual and spatial processing to be understood (Sacks, 1990).

Studies of native deaf signers who have suffered an injury to one hemisphere or the other of their brain have shown that sign language is understood primarily in the left temporal lobe despite its spatial organization. Research by Helen Neville and Ursula Bellugi found that deaf signers with damage to their right hemisphere distort the spatial layout of sign language while those with damage to their left hemisphere often suffer a complete breakdown in the use of sign. In addition to confirming that sign functions as a language in the brain, this also indicates that the brain has the potential to represent a completely different kind of space than the usual topographical space (Neville and Bellugi, 1978).

Further study by Neville has made use of functional magnetic resonance imaging (fMRI) to compare language processing between the hearing and the deaf. Both hearing and deaf subjects use classical anterior and posterior language areas within the left hemisphere when recognizing their native language, English or American Sign Language respectively. However, activity is also observed in right hemisphere prefrontal regions and posterior and anterior parts of the superior temporal sulcus when native signers, both deaf and hearing, recognize and process sentences in sign. These findings imply that the specific nature and structure of ASL results in employing the right hemisphere in processing language. This "[activity] within the right hemisphere may be specifically linked to the linguistic use of space" (Corina, 2002).

These studies indicate that the inferior frontal and posterior temporal parietal regions of the left hemisphere are ideally suited to the processing of natural languague whether that language is oral or visuo-spatial. However, it is also apparent that activity is occurring in the brain of native deaf users of sign, and also in native hearing signers, that is not happening in the hearing brain of non-signers. This leads to differences in abilities between signers and non-signers, specifically differences in spatial cognition.

Next Section: Differences in Spatial Cognition