Syntax in the brain : Linguistic versus neuroanatomical specificity

Grodzinsky examines Broca’s aphasia in terms of some specific grammatical deficits. However, his grammatical models offer no way to characterize the distinctions he observes. Rather than grammatical deficits, his patients seem to have intact grammars but defective modules of parsing and production. It is a fact about natural languages that words and phrases may be pronounced in displaced positions. In What did you buy?, what functions as the direct object of buy, but does not occur in the usual direct object position, to the right of the verb. Some generative models have used a movement operation to characterize this phenomenon. Here, Grodzinsky claims to have shown that language is not located in Broca’s area. Rather, this area is more specialized than previously thought and deals with two syntactic functions: the movement operation alluded to above insofar as it affects the understanding of language (sect. 2.1) and “the construction of higher parts of the syntactic tree in speech production” (Abstract). There are problems at two levels. First, Grodzinsky claims (sect. 2.4.1) that the key comprehension deficit of Broca’s aphasics relates to the movement of phrasal constituents, NPs and wh-phrases, but not of heads. There are difficulties in recovering the movement of phrases, but not the movement of heads: He writes that “agrammatic aphasics are capable of representing traces of [head] movement” (sect. 2.4.1). His distinction is based on a grammaticality judgment test but, because Commentary/Grodzinsky: Neurology of syntax BEHAVIORAL AND BRAIN SCIENCES (2000) 23:1 31 strategies independent of traces may be involved (for example of the type he sketches in sect. 2.6), there could be other explanations. However, his claim taken at face value raises a problem: There is no straightforward way of isolating movement of phrases from the movement of heads in the 1980s-style GovernmentBinding (GB) model he uses. Such models postulate an operation Move Alpha, by which both phrases and heads move, leave traces, and are subject to the same locality restrictions. Grodzinsky’s data do not fit neatly with his GB model, which does not cut the empirical pie in the way he needs. The problem is compounded under more recent Minimalist approaches. Not only is there no ready distinction to be found here between the movement of heads and phrases – there is no movement operation at all. Minimalist analyses dispense with a distinct level of Dstructure and therefore with D-structure-to-S-structure mappings. They also dispense with familiar top-down phrase-structure rules. Instead, phrase structure is built bottom-up through the successive merger of elements from an “array” of lexical items. For a sentence like I will visit London, visit is merged with the NP London to yield a VP; then the inflectional element will is merged with that VP to yield an IP, and so on. One type of merger involves copying an element. For the expression What did you buy?, what is copied and merged with [did you buy what], yielding [what [did you buy what]], with subsequent deletion of the lower what (we omit structural labels). This is how “movement” phenomena are handled but Minimalist approaches involve no movement as such. There is no unitary operation corresponding to GB movement. Elements are merged successively, sometimes copied and sometimes deleted; it is hard to imagine what particular function would be compromised in the people Grodzinsky describes. He notes that functions that build phrase structure are not compromised in his subjects, but in Minimalist syntax there is little beyond structure-building functions. Now to the second problem. If GB and Minimalist syntacticians do not have the means to capture naturally the descriptive generalizations that Grodzinsky reports, how should they revise their claims about grammars? They will surely want to know on what basis the descriptive generalizations are made. In his discussion of grammaticality judgments involving movement of phrasal constituents (sect. 2.4.1), he tells us that he “tested four nonfluent, agrammatic Broca’s aphasics . . . with lesions in and around Broca’s area, including white matter deep to it, ranging from the operculum, to the anterior limb of the internal capsule, to the periventricular white matter.” So, even for just these four patients, the anatomical damage covers more than Broca’s area and includes subcortical tissue. His patients show comprehension deficits relating to the movement of phrases and production deficits relating to the higher elements of tree structures. He does not argue that there are production deficits relating to movement, or comprehension deficits relating to the topmost parts of phrase structure. So movement needs to be there to account for production capabilities and the full tree needs to be available to characterize comprehension functions. If a grammar is a representation of an individual’s linguistic knowledge, which can be used for various purposes, then Grodzinsky’s results actually suggest that there is no damage to the grammar, but rather two defects in the way it is used for the purposes of parsing and production, presumably two distinct modules. Grodzinsky’s claims are based on proportions and tendencies, often just “chance” versus “above chance.” For constructions involving movement of phrasal constituents, “error rates were about 40%.” (that means 60% correct), as opposed to 10% in comparable constructions not involving that kind of movement (90% correct; sect. 2.4.1). Similarly, the data on agreement and tense errors (sect. 2.7.3) show a difference in frequency (3.9% versus 42.4%); the difference is not absolute, and if tense is available 57.6% of the time, despite the “pruning,” it is available more often than not. There is a good deal of variation being glossed over, both linguistic and anatomical, which shows that he has not yet met his goal of “a new, highly abstract and precise approach” (sect. 0). In addition, there is much normal behavior: If subjects achieve 60% correct on relevant tasks, there is no basis for saying that they lack the relevant parts of the grammar (see Crain & Thornton 1998 for an enlightening discussion of such statistics). Grodzinsky presents two important and interesting features of agrammatism, but there are other salient features that his proposals do not address. If “most human linguistic abilities, including most syntax, are not localized in the anterior language areas” (sect. 4), why do patients who have sustained lesions in these areas have problems with verb retrieval and why is their speech typically “effortful, nonfluent, and telegraphic” (sect. 2.7.1)? Broca’s aphasics generally have slow reaction times (Shapiro & Levine 1990) and it is clear from agrammatism samples in any introductory aphasia text that there is far more going on than what Grodzinsky describes. Therefore, there must be more ways to cut the empirical pie. Grodzinsky has certainly made a healthy innovation in examining aphasias in terms of grammatical deficits, integrating work on pathologies with grammatical theory. However, what the variability suggests – both within and across individuals, both anatomically and in linguistic behavior – is not a precise grammatical deficit. His grammatical models offer no obvious way to characterize his empirical distinctions. Furthermore, if individuals often behave in accordance with a normal, intact grammar, then they must have an intact grammar, but with somewhat intermittent access to it. Perhaps the modules that use the grammar (parsing and production) are defective in some fashion. In saying this, we recognize that we assume a burden of argument that goes beyond the scope of a BBS commentary. Syntax in the brain: Linguistic versus neuroanatomical specificity Angela D. Friederici and D.Yves von Cramon Department of Neuropsychology, Max Planck Institute of Cognitive Neuroscience, D-04303 Leipzig, Germany. {angelafr; cramon}@cns.mpg.de Abstract: We criticize the lack of neuroanatomical precision in the We criticize the lack of neuroanatomical precision in the Grodzinsky target article. We propose a more precise neuroanatomical characterization of syntactic processing and suggest that syntactic procedures are supported by the left frontal operculum in addition to the anterior part of the superior temporal gyrus, which appears to be associated with syntactic knowledge representation. The title of Grodzinsky’s target article, “The neurology of syntax: Language use without Broca’s area,” suggests that it provides detailed information about the functional neuroanatomy of syntactic abilities. The description he presents, however, is detailed only with respect to the psycholinguistic aspects of syntactic processing he proposes; it clearly lacks a similar precision with respect to neuroanatomy. This is rooted in the fact that Grodzinsky’s main empirical evidence for the claim that Broca’s area is the “neural home to mechanisms involved in the computation of transformational relations between moved phrasal constituents and their extraction sites” (sect. 0) stems from lesion-based studies. Nature (in almost all cases) fails to offer lesions circumscribed enough to allow a precise description of the language-brain relationship. Thus the claim Grodzinsky formulates with respect to the Broca’s area – as he acknowledges – can only hold for Broca’s area as a large area (including surrounding left anterior neural tissue). He defines this area according to Mohr (1976) to “‘encompass most of the operculum, insula, and subjacent white matter’” (sect. 0). These subregions in the left frontolateral region, however, subserve a number of different linguistic and nonlinguistic functions. The functional neuroimaging evidence Grodzinsky cites is restricted to those studies investigating syntactic aspects (Bavelier et al. 1997; Just et al. 1996; Mazoyer et al. 1993; Stromswold et al. Commentary/Grodzinsky: Neurology of syntax 32 BEHAVIORAL AND BRAIN SCIENCES (2000) 23:1