Language location in the brain - ASL

American Sign Language (ASL) is a natural language started as a combination of various home pidgin languages and the French Sign Language by the American School for the Deaf. Language is dependent on cognitive structure rather than mechanical creation. This is evident when one looks at the similarities in both structure location and function between speaking and deaf individuals. Both spoken languages and sign languages are lateralized and correlated with hand dominance (90% right-handers have left-dominant language localization vs. 70% for left-handers). ASL uses a different modality for communication than spoken language; however, left hemisphere damage often causes symptoms of aphasia very similar to compatible damage in a speaking individual. In addition, the location of intonation, irony, and speech rhythm, all of which are elements of prosody, are located in similar places to speaking individuals. When ASL is spoken as a second language in an individual whose first language was spoken, the localization of ASL is similar to a second spoken language.

A researcher wanted to test whether language in right-handed deaf signers exhibited the same lateralization as right-handed English speakers. A group of deaf participants (ASL was the first language) were given a version of the Word Discrimination test assessing single word comprehension, simple sentence comprehension (single-clause), and complex sentence comprehension (multi-clause). The results (Figure 1) were sorted based on whether the lesion was on the left or right hemisphere.

Figure 1: Comparison of left hemisphere lesion (LHL) vs right hemisphere lesion (RHL) in language comprehension (p < .05).