© 2001 Elsevier Science B.V. All rights reserved 31 Handbook of Neuropsychology, 2nd Edition, Vol. 3 R.S. Berndt (Ed) CHAPTER 3 The signs of aphasia Gregory Hickok a and Ursula Bellugi b a Department of Cognitive Sciences, University of California, Irvine, CA 92697, USA Laboratoryfor Cognitive Neuroscience, The Salk Institutefor Biological Studies, 10010 N. Torrey Pines Rd., La Jolla, CA 92037, USA Introduction to language in another modality to suggest that there are both intrinsic and extrinsic influences driving neocortical organization (Nothias, Theoretical issues Fishell and Ruiz i Altaba, 1998). If this view is correct, a major task in developmental neuroscience Much debate in 19th century neurology centered will be to map out the contributions of intrinsic and around the question of whether there is functional extrinsic factors, and their interaction. specialization within the neocortex. Today, this is no In this chapter, we will present data which bear on longer a contentious issue: functional specialization these general issues from the perspective of the orga- in the adult neocortex is well established. Nonethe- nization of a higher-order cortical system: language. less, a form of this old debate rages on in research on In particular, we will address the question neocortical development. At issue is whether neocor- of the extent to which the functional neuroanatomy tical regionalization arises from properties intrinsic to of language is dependent on the sensory and motor the neocortex itself (Rakic, 1988), or whether it devel- modalities through which it is perceived and pro- ops in response to extrinsic factors, such as pat-terns duced. There are many reasons to think that the neu- of thalamocortical input (O’Leary, 1989). Over ral organization of language should be profoundly the last decade, evidence has accumulated on both influenced by extrinsic factors in development, such sides of the fence. Many studies, for example, have as sensory and motor experience. The temporal pro- demonstrated a fair degree of neocortical reorgani- cessing demands imposed by the auditory system have zation in response to a variety of sensory-input ma- been argued to favor left hemisphere systems which nipulations (Katz and Shatz, 1996; Pons, Garraghty, could, in turn, determine aspects of the lateralization Ommaya et al., 1991; Sadato, Pascual-Leone, Graf- pattern of auditory-mediated language (Tallal, Miller man et al., 1996; Schlaggar and OLeary, 1991; Sur, and Fitch, 1993). Superior temporal lobe regions Garraghty and Roe, 1988), suggesting that extrinsic thought to be important for language comprehension factors exert an influence on neocortical organiza- are situated in and around auditory cortices - a natu- tion. Other studies, however, have shown that some ral location given auditory sensory input of language. regional specific features of neocortex (e.g. gene Likewise, Broca’s area, which is thought to play a expression) emerge independent of extra-neocortical role in speech production, is situated just anterior to influence (Afimatsu, Miyamoto, Nihonmatsu et al., motor cortex controlling the speech articulators. Thus, 1992; Miyashita-Lin, Hevner, Wassarman et al., 1999). it would not be unreasonable to hypothesize that the Taken together, this collection of work seems neural organization of language - including its lat- eralization and within-hemisphere organization - is determined, in large part, by the particular demands *Corresponding author. Tel.: + 1 (858) 453-4100, ext. 1222. imposed by the sensory and motor interface systems. 32 By studying the functional neuroanatomy of signed ical level, ASL, for example, has developed grammat- language, we can test this hypothesis in a straightfor- ical markers that serve as inflectional and derivational ward manner. It has been shown that signed languages morphemes; these are regular changes in form across share a good deal of the formal linguistic structure classes of lexical items associated with systematic found in spoken languages, but differ radically in the changes in meaning (Klima and Bellugi, 1979). At the sensory and motor systems through which language is syntactic level, ASL specifies relations among signs transmitted (Klima and Bellugi, 1979; Lillo- Martin, using a variety of mechanisms including sign order, 1991; Perlmutter, 1992). In essence, signed language the manipulation of sign forms (usually verbs) in offers a kind of natural experimental manipulation: space, where different spatial relations between signs central linguistic structure and function are held con- have systematic differences in meaning, and a spe- stant, while peripheral sensory and motor experience cific set of grammaticized facial expressions that are is varied. Thus, a comparison of the neural organiza- used to mark questions, topicalized sentences, and tion of signed versus spoken language will provide conditionals (Liddell, 1980; Lillo-Martin, 1991). Fig. clues concerning the factors which drive the develop- I shows aspects of the spatial organization of ASL at ment of the functional neuroanatomy of language. (A) the lexical level, (B) the morphological level, and (C) the level of spatially organized syntax. The structure of sign language In summary, ASL has developed as a fully auton- omous language with grammatical structuring at the Like spoken languages, signed languages of the deaf same levels as spoken language and with similar kinds are formal, highly structured linguistic systems, passed of organizational principles. Yet the surface form that down from one generation to the next, with a typical this grammatical structuring assumes in a visual-spa- developmental course, including a critical period tial language is deeply rooted in the modality in which for acquisition (Newport and Meier, 1985; Newport, the language developed in that there is a strong ten- 1991). Signed languages have emerged independently dency to encode grammatical relations spatially rather of the language used among hearing individuals in the than temporally. The implication of this situation for surrounding community: American Sign Language research on the neurobiology of language is that we (ASL) and British Sign Language, for example, are have the opportunity to study a linguistic system that mutually incomprehensible, despite the fact that Eng- is essentially identical to that of spoken language lish is the dominant spoken language in both sur- in terms of its underlying linguistic (i.e. representa- rounding communities. tional) structure, but that is implemented in a radically Signed and spoken languages, however, share different perceptual signal. the underlying structural complexities of human lan- guage. That is, all natural human languages have lin- Brain organization for language and spatial cogni- guistic structure at phonological, morphological, and tion in deaf signers syntactic levels, and signed languages are no excep- tion. At the phonological level, research has shown Hemispheric asymmetries.for aspects of sign lan- that like the words of spoken languages, signs are guage fractionated into sublexical elements, including vari- ous recurring handshapes, articulation locations, and Left hemisphere damage in hearing/speaking individ- limb/hand movements, among other features (Corina uals is associated with deficits at sublexical (‘phonetic/ and Sandler, 1993; Perlmutter, 1992). Furthermore, phonemic’), lexical, and sentence levels, both in pro- comparison of two different signed languages (ASL duction and in comprehension (Damasio, 1992; Good- and Chinese Sign Language) reveals that there are glass, 1993). Supra- sentential (e.g. discourse) deficits, even fine-level systematic phonetic differences lead- on the other hand, have been associated with right- ing to an ‘accent’ when native users of one sign hemisphere damage (Brownell, Potter, Bihrle et al., language learn another (Klima and Bellugi, 1979; 1986). A similar pattern of hemispheric asymmetries Poizner, Klima and Bellugi, 1987). At the morpholog- has been observed in the deaf signing population. 33 A B C Fig. 1. Spatialized linguistic contrasts in ASL structure. (A) Spatial contrasts at the lexical level. The signs for SUMMER, UGLY arul DRY, are distinguished only by the place of articulation on the face. (B) Spatial contrasts at the morphological level. Various modula- tions on the movement of the sign GIVE, for example, can modify the meaning of the verb as indicated. The modulations can be nested to yield complex morphological forms. (C) Spatialized organization underlying the syntax of ASL. Signs can be indexed to specific locations in signing space, and the direction of movement of the verb between spatial endpoints indicate grammatical relations, such as subject and object. 34 the BDAE ratings of signing characteristics, as well Sublexical-, lexical-, and sentence-level processes as a count of the number of paraphasic errors per A variety of sublexical-, lexical-, and sentence-level minute of signing. Comprehension measures included deficits (i.e. typical aphasic symptomology) have been a set of one-, two-, and three-step commands (BDAE found in individual left-hemisphere-damaged (LHD) ‘Commands’ subtest) and an ASL-adapted version of deaf signers (Bellugi, Poizner and Klima, 1989; the Token Test (DeRenzi and Vignolo, 1962). Naming Corina, 1998; Hickok, Bellugi and Klima,1998a; assessment included two BDAE subtests: Visual Con- Hickok, Klima and Bellugi, 1996a; Hickok,Klima, frontation Naming (naming in response to pictures) Kritchevsky