For nearly 150 years, the language-dominant left cerebral hemisphere has dominated research and clinical concern about language disorders that accompany brain damage in adults. However, it is now well established that unilateral right hemisphere brain damage can substantially impair language and communication. The language deficits associated with right hemisphere damage, while often quite socially handicapping (Tompkins et al., 1998), are little understood. This article focuses on disorders characterized by damage restricted to the right cerebral hemisphere in adults. Such individuals may have difficulties with some basic language tasks but are not generally considered to have aphasia, because phonology, morphology, syntax, and many aspects of semantics are largely intact. About 50% of adults with right hemisphere damage have a verbal communication disorder (Joanette et al., 1990). In one study, 93% of 123 adults with right hemisphere damage in a rehabilitation center had at least one cognitive deficit with the potential to disrupt communication and social interaction (Blake et al., 2002).

Heterogeneity typifies the population of adults with right hemisphere damage: not all will have all characteristic communicative problems, and some will have no discernible problems. This heterogeneity often is unaccounted for in sample selection or data analysis, and its potential effects are compounded by the small samples in most studies of language in patients with right hemisphere damage. A related difficulty involves control group composition in research on language deficits associated with right hemisphere damage. Non-brain-damaged samples typically comprise individuals who do not have complications associated with being a patient. Individuals with left brain damage often are excluded because they cannot perform the more complex tasks that are most revealing of language functioning after right hemisphere damage, and because differences in impairment profiles make it difficult to equate groups for severity. Consequently, it is impossible to determine whether observed deficits are specific to right hemisphere damage. Another major issue is the lack of consensus on how to define or even what to call language deficits associated with right hemisphere damage (cf. Myers, 1999), either in totality or as individual components of an aggregate syndrome. Conceptual and terminological imprecision, and apparent overlap, are common in referring to targets of inquiry such as nonliteral language processing, inferencing, integration, and reasoning from a theory of mind (Blake et al., 2002). Conclusions about language deficits after right hemisphere damage also are complicated by intraindividual performance variability, whether due to factors such as differential task processing requirements (e.g., Tompkins and Lehman, 1998), or to time following onset of injury (Colsher et al., 1987). Finally, many language difficulties ostensibly related to right hemisphere damage stem from or are exacerbated by other perceptual and cognitive impairments, some of which are as yet unidentified but others of which have not been evaluated consistently. Chief among these complications are hemispatial neglect, other attentional difficulties, and impairments of working memory and related processing resources.