Emmorey, K. (1997). The neural substrate for spatial cognition and language: Insights from sign language. Paper presented at the Cognitive Science Society Meeting, Stanford.
Collaborators: Ursula Bellugi, Antonio Damasio, Hanna Damasio, Paul German, Ed Klima, Dan Tranel
To describe what they see, English speakers map a visually observed spatial relation to a spoken word such as in or under. In contrast, users of American Sign Language (ASL) map this relation to the spatial relation expressed by the hands positioned in a classifier construction (a locative predicate in which each handshape represents an object of a specific type). The position of the hands in space is isomorphically mapped to the visually perceived spatial relation. Given this overlap between the visual spatial representation and the linguistic representation, we hypothesized that the production of classifier constructions may engage some of the spatial cognitive processes within the right hemisphere. Evidence from a right hemisphere damaged (RHD) signer and two left hemisphere damaged (LHD) signers supports this hypothesis. Subjects were given a Classifier Comprehension Task which required them to understand the spatial mapping between the position of the hands in signing space and the position of objects within a picture (minimal understanding of the classifier handshape was required). Subjects were also given a Preposition Comprehension Task which required subjects to match an ASL preposition (e.g., ON, IN) to a picture. ASL prepositions are less frequently used for spatial description, and the mapping between the position of the hands and the position of objects in space is much less isomorphic. Both LHD signers had clear sign language aphasia, and they exhibited poor performance on the Preposition Task. In contrast, the LHD signers were unimpaired on the Classifier Task. The RHD signer did not exhibit aphasia for ASL, and he performed well on the Preposition Task. However, he exhibited impaired performance on the Classifier Task. Thus, although the RHD signer could understand the spatial relation encoded by ASL prepositions, he was not able to perform the spatial mapping function between the position of the hands in signing space to the position of objects in space that was required by the Classifier Task. There is also some evidence that he cannot perform such a mapping function for non-linguistic stimuli. Finally, we are finding that, like deaf ASL signers, hearing English speakers with left hemisphere damage are impaired on the English Preposition Task, but RHD English speakers are not. We hypothesize that the increased involvement of the right hemisphere when understanding spatial information within ASL classifier constructions compared to English or ASL prepositions arises from the spatialized nature of these constructions, i.e., the fact that signing space itself is used to directly represent spatial relations.