Brain and Language: Minireview a Perspective from Sign Language

Psychology Department representations found in spoken language, includingUniversity of Oregon phonology, morphology, syntax, semantics, and prag-Eugene, Oregon 97403 matics (Lillo-Martin, 1991; Corina and Sandler, 1993).Thus, similar linguistic structures are found in spokenand signed languages. A number of authors have pro-One of the most enduring and significant findings from posed that the left hemisphere recruitmentfor languageneuropsychology is the left hemisphere dominance for results from aspecialization oftheseareas forthe analy-language processing. Studies both past and present sis of linguistic structures. By this view, the structuralconverge to establish a widespread language network similarity between signed and spoken languages pre-in the left peri-sylvian cortex which encompasses at dicts that left hemisphere language areas should alsoleast four main regions: Broca’s area, within the inferior be recruited during ASL processing.prefrontal cortex; Wernicke’s area, within the posterior On the surface, however, ASL differs markedly fromtwo-thirds of the superior temporal lobe; the anterior spoken languages. For example, in ASL, phonologicalportion of the superior temporal lobe; and the middle distinctions are created by the positions and shape ofprefrontal cortex (Neville and Bavelier, 1998). While the the hands relative to the body rather than by acousticlanguage processing abilities of the left hemisphere are features such as nasality and voicing found in spokenuncontroversial, little is known about the determinants languages. The fact that signed and spoken languagesof this left hemisphere specialization for language. Are rely on different input and output modalities carries im-these areas geneticallydetermined to processlinguistic portant consequences for theories on the origin of theinformation? To what extent is this organization influ- left hemisphere dominance for language. It is often ar-enced by the language experience of each individual? gued that the left hemisphere specialization for lan-guage originates from a left hemisphere advantage toWhat role doesthe acoustic structure of languagesplayexecute fine temporal discrimination, such as the fastin this pattern of organization?acoustic processingrequired during speech perceptionTodate,mostofourunderstandingoftheneuralbases(Tallal et al., 1993). By this view, the standard left hemi-of language is derived from the studies of spoken lan-sphere language areas may not be recruited during theguages. Unfortunately, this spoken language bias limitsprocessing of visuo-spatial languages such as ASL.our ability to infer the determinants of left hemisphere Signed and spoken languages also differ by the wayspecialization for human language. For example, weare they convey linguistic information. While most aspectsunable to assess whether left hemisphere dominance of spoken languages rely on fast acoustic transitionsarises from the analysis of the sequential/hierarchical (e.g., consonant contrast) and temporalorderingof con-structures that are the building blocks of natural lan- stituents (e.g., suffixation, prefixation, word order, etc.),guages or rather is attributable to processing of the sign languages make significant use of visuo-spatialacoustic signal of spoken language. devices. For example, the use of signing space as aAmerican Sign Language (ASL), which makes use of staging ground for the depiction of grammatical rela-spatial location and motion of the hands in encoding tions is a prominent feature of ASL syntax. As shown inlinguistic information, enables us to investigate this is- Figure 1, in ASL,nominals introducedinto the discoursesue. The comparison of the neural representations of are assigned arbitrary reference points in a horizontalspoken and signed languages permits the separationof plane of signing space. Signs with pronominal functionthose brain structures that are common to all natural are directedtoward thesepoints, and verb signs obliga-human languages from those that are determined by torilymovebetweensuchpointsinspecifyinggrammati-the modality in which a language develops, providing cal relations (subject of, object of). Thus, grammaticalnew insight into the specificity of left hemisphere spe- functions served in many spoken languages by casecialization for language. marking or by linear ordering of words are fulfilled inIn this paper, we will first review some properties of ASL by spatial mechanisms; this is often referred to asASL and then discuss the contribution of the left hemi- “spatialized syntax” (Lillo-Martin, 1991; Poizner et al.,sphere and that of the right hemisphere to ASL pro- 1987; but see Liddell, 1998, for an alternative view).cessing. Another example of ASL processing that makes specialuse of visuo-spatial information is the classifier system.