Semantic operations in aphasic comprehension: implications for the cortical organization of language.

We provide data on the neurological basis of two semantic operations at the sentence level: aspectual coercion and complement coercion. These operations are characterized by being purely semantic in nature; that is, they lack morphosyntactic reflections. Yet, the operations are mandatory (i.e., they are indispensable for the semantic well formedness of a sentence). Results indicate that, whereas Broca's patients have little or no trouble understanding sentences requiring these operations (performance was above chance for all conditions), Wernicke's patients performed at normal-like levels only for sentences that did not require these operations. These findings suggest that sentence-level semantic operations rely very specifically on the integrity of the cortical area associated with Wernicke's aphasia, but not on the region corresponding to Broca's aphasia. In the context of other findings from lesion and imaging studies, this evidence allows a view of the cortical distribution of language capacity that is drawn along a linguistic line, one which distinguishes syntactic from semantic operations.

The existence of comprehension patterns in Broca's aphasia.

Berndt and Caramazza (1999) claim that Grodzinsky, Piñango, Zurif, and Drai (1999) were able to show a canonical-noncanonical difference (e.g., actives vs. passives) in the comprehension of Broca's aphasic patients only because of a patient selection bias. We show that the canonical-noncanonical comprehension pattern exists apart from any such bias, and that this pattern bears importantly on our understanding of the neuroanatomical organization of comprehension capacity at the sentence level.

Real-time processing implications of enriched composition at the syntax-semantics interface.

This study reports results on the real-time consequences of aspectual coercion. We define aspectual coercion as a combinatorial semantic operation requiring computation over and above that provided by combining lexical items through expected syntactic processes. An experiment is described assessing whether or not parsing of a string requiring coercion--in addition to syntactic composition--is more computationally costly than parsing a syntactically transparent counterpart, a string that provides for an interpretable representation via syntactic composition alone. The prediction of a higher computational cost for this process is borne out by the results.

The critical role of group studies in neuropsychology: comprehension regularities in Broca's aphasia.

We reexamine the empirical record of the comprehension abilities of Broca's aphasic patients. We establish clear, commonly accepted, selection criteria and obtain a pool of results. We then subject these results to a detailed statistical analysis and show that these patients comprehend certain canonical sentences (actives, subject relatives, and clefts with agentive predicates) at above-chance levels, whereas comprehension of sentences that contain deviations from canonicity (passives, object-gap relatives, and clefts) is distinct and is at chance. That the latter is the case, and patients indeed guess at such structures, we show by comparing the distribution of individual results in passive comprehension to that of a model for such guessing-an analogous series of tosses of an unbiased coin. The two distributions are virtually identical. We conclude that the group's performance is stable, and well-delineated, despite intersubject variation whose source is now identified. This means that certain comprehension tests may not always be used for the diagnosis of individual patients, but they do characterize the group. It also means that group studies are not just a valid option in neuropsychology; they are a must, since demonstrations like ours indiciate very clearly that single-case studies may be misleading. As we show, the findings from any one patient, without the context of a group, may give a distorted picture of the pathological reality. Our conclusions thus promote studies of groups of brain-damaged patients as a central tool for the investigation of brain/behavior relations.

The neurological organization of some aspects of sentence comprehension.

I briefly review 25 years of aphasia research directed to uncovering the neurological organization of sentence comprehension capacity. I provide a description of aphasic comprehension disorders offered along syntactic lines, and I connect the syntactic limitation (revealed in this description) to the disruption of cortically localizable processing resources.

Gap-filling and end-of-sentence effects in real-time language processing: implications for modeling sentence comprehension in aphasia.

We present an on-line study showing different sources of lexical activation during sentence comprehension, distinguishing in this respect between reflexive syntactic and less temporarily constrained nonsyntactic sources. Specifically, we show that both the syntactic process of gap filling and a nonsyntactic end-of-sentence effect can be measurable in real time and can be temporally separated. The distinction between activation sources provides a new perspective on real-time sentence comprehension in aphasia and accounts for the disparate results reported in the literature.

Speed of lexical activation in nonfluent Broca's aphasia and fluent Wernicke's aphasia.

Rapid, automatic access to lexical/semantic knowledge is critical in supporting the tight temporal constraints of on-line sentence comprehension. Based on findings of "abnormal" lexical priming in nonfluent aphasics, the question of disrupted automatic lexical activation has been the focus of many recent efforts to understand their impaired sentence comprehension capabilities. The picture that emerges from this literature is, however, unclear. Nonfluent Broca's aphasic patients show inconsistent, not absent, lexical priming, and there is little consensus about the conditions under which they do and do not prime. The most parsimonious explanation for the variable findings from priming studies to date is that the primary disturbance in Broca's lexical activation has something to do with speed of activation. Broca's aphasic patients prime when sufficient time is allowed for activation to spread among associates. To examine this "slowed activation" hypothesis, the time course of lexical activation was examined using a list priming paradigm. Temporal delays between successive words ranged from 300 to 2100 msec. One nonfluent Broca's aphasic patient and one fluent Wernicke's patient were tested. Both patients displayed abnormal priming patterns, though of different sorts. In contrast to elderly subjects, who prime at relatively short interstimulus intervals (ISIs) beginning at 500 msec, the Broca's aphasic subject showed reliable automatic priming but only at a long ISI of 1500 msec. That is, this subject retained the ability to access lexical information automatically if allowed sufficient time to do so, a finding that may help explain disrupted comprehension of normally rapid conversational speech. The Wernicke's aphasic subject, in contrast, showed normally rapid initial activation but continued to show priming over an abnormally long range of delays, from 300 msec through 1100 msec. This protracted priming suggests failure to dampen activation and might explain the semantic confusion exhibited by fluent Wernicke's patients.

Grammatical theory and the study of sentence comprehension in aphasia: comments on Druks and Marshall (1995).

Druks and Marshall (1995) argue that aphasic comprehension problems are accountable as the consequence of a disrupted Case assignment module. But the analysis they present does not support their argument and it provides a distorted view of grammatically based analyses of brain-language relations.

Neurological distribution of processing resources underlying language comprehension.

Using a cross-modal lexical priming technique we provide an on-line examination of the ability of aphasic patients to construct syntactically licensed dependencies in real time. We show a distinct difference between Wernicke's and Broca's aphasic patients with respect to this form of syntactic processing: the Wernicke's patients link the elements of dependency relations in the same manner as do neurologically intact individuals; the Broca's patients show no evidence of such linkage. These findings indicate that the cerebral tissue implicated in Wernicke's aphasia is not crucial for recovering syntactically licensed structural dependencies, while that implicated in Broca's aphasia is. Moreover, additional considerations suggest that the latter region is not the locus of syntactic representations per se, but rather provides the resources that sustain the normal operating characteristics of the lexical processing system-characteristics that are, in turn, necessary for building syntactic representations in real time.

Syntactic processing in aphasia.

In this report we comment upon subject selection and methodology, and we describe some recent studies of syntactic processing in aphasia. Our data show that, like neurologically intact subjects, Wernicke's patients reactivate moved constituents (instantiate coreference) at the site of their extraction (even for sentences that they do not understand). Broca's patients, by constrast, are shown not to create such syntactically governed links (even for sentences that they do understand). These data isolate the processing bottleneck in Broca's aphasia and more generally suggest that syntactic comprehension limitations can be traced to changes in cortically localizable resources that sustain lexical processing.

The allocation of memory resources during sentence comprehension: evidence from the elderly.

Two experiments were carried out to examine the ability of elderly subjects to establish syntactically governed dependency relations during the course of sentence comprehension. The findings reveal the manner in which memory constraints operate during syntactic processing.

Functional localization in the brain with respect to syntactic processing.

This report describes some recent examinations of the ability of aphasic patients to construct syntactically governed dependency relations in real time. The data show that Wernicke's patients can link the elements of dependency relations in the same way as neurologically intact subjects, even for sentences that they do not understand. Broca's patients, by contrast, are shown to be unable to create such links, even for sentences that they do understand. These data underline the isolability of this stage of syntactic analysis and they suggest that comprehension limitations statable in syntactic terms can be traced to changes in cortically localizable processing resources.

Structural description of agrammatic comprehension.

The trace-deletion hypothesis (Grodzinsky, 1990) holds that the comprehension deficit apparent in most agrammatic aphasics results from the absence of traces at the level of S-structure. This paper reports a test of this hypothesis in a case study of an agrammatic aphasic. Two experiments--one using a sentence-picture matching task, one using the truth-value judgment task-examined the comprehension of the matrix clause in center-embedded relatives such as, The tiger that chased the lion is big. These structures provide a crucial test of the trace-deletion hypothesis because comprehension of the matrix clause (i.e., knowing that the tiger is big and not the lion) is predicted to be unimpaired. Contrary to this prediction, however, the results of the present work show that comprehension of the matrix clause in such sentences is significantly impaired. We argue that a revised version of the trace-deletion hypothesis proposed by Hickok (1992a,b) can explain the present data and other previously unaccountable findings.

An on-line analysis of syntactic processing in Broca's and Wernicke's aphasia.

This paper is about syntactic processing in aphasia. Specifically, we present data concerning the ability of Broca's and Wernicke's aphasic patients to link moved constituents and empty elements in real time. We show that Wernicke's aphasic patients carry out this syntactic analysis in a normal fashion, but that Broca's aphasic patients do not. We discuss these data in the context of some current grammar-based theories of comprehension limitations in aphasia and in terms of the different functional commitments of the brain regions implicated in Broca's and Wernicke's aphasia, respectively.

Slowed lexical access in nonfluent aphasia: a case study.

A list priming paradigm (LPP) was used to examine the hypothesis that nonfluent aphasics are literally slowed down in automatic access to lexical information. In this paradigm, words are presented visually, and the subject's task is to make a lexical decision on each word as quickly as possible after its presentation. As soon as a lexical decision is made on one word, that word is removed and, after a predetermined interword interval, the next word is presented. In this way, a continuous "list" effect is obtained. Prior studies with both college-age and elderly subjects using the LPP have shown that, independently of age, on the LPP, priming obtains at interword delays of 500 to 800 msec, but not at either shorter or longer interword delays. In the study reported here, the LPP was used to examine delays at which priming obtained for LD, a nonfluent aphasic with a lesion primarily in the left frontal region. Examining interword delays ranging from 500 to 1800 msec, the subject showed priming only at a delay of 1500 msec, a considerably longer delay than that at which neurologically intact subjects have shown priming. Based on these results, it is argued that while automatic access is retained, that access is much slower in a nonfluent aphasic than in neurologically intact elderly subjects. These results are discussed in terms of how slowed lexical access might impact on discourse comprehension.

Processing complexity and sentence memory: evidence from amnesia.

This study examines sentence memory as a function of linguistic processing complexity in amnesic patients. Sentence length as well as lexical and syntactic complexity were manipulated in two sentence repetition experiments. It was found that the amnesic patients performed considerably worse than the control subjects and that performance decreased: (1) when sentence length was increased by the addition of adjuncts compared to arguments of the verb; (2) when the verb selected more thematic frames; and (3) when sentences involved "empty" argument positions that must be linked to antecedents, particularly across clausal boundaries. These data showed how linguistic complexity affects sentence memory and implied that the amnesic deficit did not involve a generalized difficulty for materials of similar length, rather, the deficit was specific to certain representational types and processing routines.

An evaluation of assumptions underlying the single-patient-only position in neuropsychological research: a reply.

This note challenges the position adopted by A. Caramazza and W. Badecker (1989, Brain and Cognition 10, 256-295) that, since the a priori classification of patients can only be theoretically arbitrary, the basic unit of analysis in cognitive neuropsychology must be the individual patient. We argue that even if there is no prior theory to justify patient classification, this does not preclude group studies; syndromes are what the world gives us--they constrain theory, permitting groups to be formed for research purposes. We also reexamine a particular example of group-based research that was extensively criticized by Caramazza and Badecker. We confront each of their criticisms, and, again, demonstrate the validity of group-based research.