Sign Language in the Brain

Hickok, G., Bellugi, U. & Klima, E.S. (June 2001). Sign Language in the Brain. Scientific American.

Because sign language relies heavily upon visual-spatial contrast, one might expect sign language to be supported by systems in the right hemisphere rather than the traditional left hemisphere language systems. However, this does not appear to be the case. A deaf signer with damage to Wernicke's area is likely to have comprehension difficulties and one with damage to Broca's area may have difficulty producing signs, just like normal speakers. And signers with right hemisphere damage continued to be fluent and accurate in their production of signs, used normal grammar, and comprehended signs with ease. One exception of the left hemisphere's monopoly on language production is creation of a coherent discourse, where right hemisphere damage may lead to rambling as it tends to be involved in more global-level processes. Generally speaking, sign language abilities of lifelong signers appear to be independent of their nonlinguistic spatial skills. Thus, it is likely that signers maintain unique early stages of processing compared to regular speakers, but thereafter neural organization is quite similar, being translated into a format optimized for linguistic processing and being routed to central linguistic systems.

Language Interpretation and the Immediacy Assumption

Hagoort, P. & von Berkum, J. (April 3, 2007). Beyond the sentence given. Philosophical Transactions of the Royal Society, 362, 801-811.

The view that language interpretation takes place in a two-step process has predominated, with the meaning of the sentence being computed first and the sentence meaning then being integrated with other sources of information (e.g. context, world knowledge). However, event-related brain potentials (ERPs) appear to be inconsistent with this model, finding strong empirical evidence that linguistic and extra-linguistic information are integrated in the same time-frame during sentence interpretation. Similar latencies and amplitudes of the N400 effect witnessed for all types of semantic mismatches support the immediacy assumption, that disparate information is brought to bear on language interpretation as soon as it becomes available. Neuroimaging studies suggest that the left inferior frontal cortex, including Broca's area, is an important node in the semantic unification network, and that this area is not language specific but acts as a single integration space.