Hemispheric sensitivities to sentential constraint

Since Paul Broca’s discovery (1861) of an association between fluent, articulate speech and the left frontal operculum, research into the neural bases of language has uncovered a complex brain network substrate for the phonological, lexical, semantic, and syntactic functions of normal language comprehension and production (for a review, see Martin, 2003). A particularly salient feature of this brain network is its apparent strong left-laterality: Whereas damage to certain left hemisphere (LH) areas can cause profound and permanent deficits in many language functions, damage to the right hemisphere (RH) homologues of these areas generally leaves basic word and sentence processing relatively intact. This dissociation is one of the most striking and oft-cited examples of hemispheric specialization in humans. Recently, however, behavioral, neuropsychological, and imaging data have converged to suggest that the RH may play a larger and more important role in language than has been previously assumed. Data from noninvasive spatial neuroimaging techniques such as positron emission tomography and functional magnetic resonance imaging have revealed language-related activation in brain areas outside the regions classically associated with aphasia, including a number of RH areas (see, e.g., Ni et al., 2000). In fact, some imaging studies, particularly those focusing on the comprehension of complex narratives (Robertson et al., 2000; St. George, Kutas, Martinez, & Sereno, 1999) or nonliteral language (Bottini et al., 1994), have found not just bilateral activation patterns, but a predominance of RH activity. One must then ask, not why the RH is unable to process language, but what language functions the RH supports, how they differ from LH functions, and what role they play in normal language processing. Whereas patients with LH damage often show severe difficulties in the most basic aspects of language, patients with damage to the RH have also been found to show changes in their language comprehension and production. For example, language production after RH damage is marked by socially inappropriate remarks, tangential speech, circumlocutions, and digressions of topic, as well as reduced informational complexity (Joanette, Goulet, & Hannequin, 1990). Studies of language comprehension in patients with RH damage have noted difficulties extracting the main points from narratives and conversations (Gardner, Brownell, Wapner, & Michelow,