Hemispheric Asymmetries in Verbal Memory

Abstract

Studies of cerebral asymmetries identify the functions of individual hemispheres to better understand how they cooperate during normal processing. Although the two cerebral hemispheres house similar anatomical structures, each is specialized for certain types of processing. Nowhere is this functional asymmetry more evident than in speech production, which, for most humans, seems to be entirely supported by the left hemisphere (LH). More general language processes also tend to be left lateralized, although the right hemisphere (RH) provides critical contributions. Although there seem to be biases in the type of information each hemisphere processes most adeptly, effects seen in stem completion, false memory, and repetition lag studies suggest that both hemispheres contribute to verbal memory, albeit differently. The data thus far suggest that the RH may tend to encode verbal stimuli more veridically, whereas the LH may tend to rapidly abstract away from the input, both at perceptual and at semantic levels of analysis. These encoding differences have consequences for what aspects of verbal stimuli can later be recovered, for the time course with which information about words will be retained, and for the types of errors that are likely to be made in memory tasks, among others. In turn, hemispheric differences in verbal memory have important implications for language processing, as comprehenders retain word and message-level information, build and link syntactic structures, map between referents in a discourse, and reanalyze words and phrases to appreciate humor and other nonliteral language.