Reception of language in broca's aphasia

Lesion-symptom Mapping of Acceptability Judgments in Chronic Poststroke Aphasia Reveals the Neurobiological Underpinnings of Receptive Syntax

Disagreements persist regarding the neural basis of syntactic processing, which has been linked both to inferior frontal and posterior temporal regions of the brain. One focal point of the debate concerns the role of inferior frontal areas in receptive syntactic ability, which is mostly assessed using sentence comprehension involving complex syntactic structures, a task that is potentially confounded with working memory. Syntactic acceptability judgments may provide a better measure of receptive syntax by reducing the need to use high working memory load and complex sentences and by enabling assessment of various types of syntactic violations. We therefore tested the perception of grammatical violations by people with poststroke aphasia (n = 25), along with matched controls (n = 16), using English sentences involving errors in word order, agreement, or subcategorization. Lesion data were also collected. Control participants performed near ceiling in accuracy with higher discriminability of agreement and subcategorization violations than word order; aphasia participants were less able to discriminate violations, but, on average, paralleled control participants discriminability of types of violations. Lesion-symptom mapping showed a correlation between discriminability and posterior temporal regions, but not inferior frontal regions. We argue that these results diverge from models holding that frontal areas are amodal core regions in syntactic structure building and favor models that posit a core hierarchical system in posterior temporal regions.

Agrammatic output in non-fluent, including Broca's, aphasia as a rational behavior

Background

Speech of individuals with non-fluent, including Broca's, aphasia is often characterized as "agrammatic" because their output mostly consists of nouns and, to a lesser extent, verbs and lacks function words, like articles and prepositions, and correct morphological endings. Among the earliest accounts of agrammatic output in the early 1900s was the "economy of effort" idea whereby agrammatic output is construed as a way of coping with increases in the cost of language production. This idea resurfaced in the 1980s, but in general, the field of language research has largely focused on accounts of agrammatism that postulated core deficits in syntactic knowledge.

Aims

We here revisit the economy of effort hypothesis in light of increasing emphasis in cognitive science on rational and efficient behavior.

Main contribution

The critical idea is as follows: there is a cost per unit of linguistic output, and this cost is greater for patients with non-fluent aphasia. For a rational agent, this increase leads to shorter messages. Critically, the informative parts of the message should be preserved and the redundant ones (like the function words and inflectional markers) should be omitted. Although economy of effort is unlikely to provide a unifying account of agrammatic output in all patients-the relevant population is too heterogeneous and the empirical landscape too complex for any single-factor explanation-we argue that the idea of agrammatic output as a rational behavior was dismissed prematurely and appears to provide a plausible explanation for a large subset of the reported cases of expressive aphasia.

Conclusions

The rational account of expressive agrammatism should be evaluated more carefully and systematically. On the basic research side, pursuing this hypothesis may reveal how the human mind and brain optimize communicative efficiency in the presence of production difficulties. And on the applied side, this construal of expressive agrammatism emphasizes the strengths of some patients to flexibly adapt utterances in order to communicate in spite of grammatical difficulties; and focusing on these strengths may be more effective than trying to "fix" their grammar.

Clinical Outcomes Following Language-Specific Attention Treatment Versus Direct Attention Training for Aphasia: A Comparative Effectiveness Study

Purpose This study was conducted to examine the comparative effectiveness of 2 different approaches, 1 domain-specific and the other domain-general, to language and attention rehabilitation in participants with stroke-induced aphasia. The domain-specific treatment consisted of language-specific attention treatment (L-SAT), and the domain-general treatment consisted of direct attention training (DAT) using the computerized exercises included in Attention Process Training-3 (Sohlberg & Mateer, 2010). Method Four individuals with mild-moderate aphasia participated in this study. A randomized controlled cross-over single-subject design was used to assess the effectiveness of the 2 treatments administered in this study. Treatment outcomes were evaluated in terms of participants' task performance for each program, standardized language and attention measures, tests of functional abilities, and patient-reported outcomes. Results Visual comparisons demonstrated linear improvements following L-SAT and variable patterns following DAT. Omnibus effect sizes were statistically significant for 9 of the 13 L-SAT tasks. The weighted standardized effect sizes for posttreatment changes following L-SAT ranged from small to large, with the exception of 1 task. The average group gain following DAT was 5%. The Western Aphasia Battery-Revised Aphasia Quotients (Kertesz, 2007) demonstrated reliable improvements for 3 of the 4 participants following L-SAT, whereas only 1 of the participants improved reliably following DAT. The margins of improvements in functional language were substantially larger following L-SAT than DAT. Performance on the Test of Everyday Attention improved significantly for 2 participants following L-SAT and for 1 participant following DAT on selected Test of Everyday Attention (Robertson, Ward, Ridgeway, & Nimmo-Smith, 1994) subtests. Patient-reported outcomes for communication and attention following treatment favored L-SAT compared to DAT. Conclusions The results support the view that attention is allocated in ways that are particular to specific tasks rather than as a general resource that is allocated equivalently to all processing tasks. Domain-specific treatment for language deficits due to attentional impairment appears to be a suitable, if not preferable, approach for aphasia rehabilitation. Supplemental Material https://doi.org/10.23641/asha.8986427.

Evaluating Treatment and Generalization Patterns of Two Theoretically Motivated Sentence Comprehension Therapies

Purpose

The current study examined treatment outcomes and generalization patterns following 2 sentence comprehension therapies: object manipulation (OM) and sentence-to-picture matching (SPM). Findings were interpreted within the framework of specific deficit and resource reduction accounts, which were extended in order to examine the nature of generalization following treatment of sentence comprehension deficits in aphasia.

Method

Forty-eight individuals with aphasia were enrolled in 1 of 8 potential treatment assignments that varied by task (OM, SPM), complexity of trained sentences (complex, simple), and syntactic movement (noun phrase, wh-movement). Comprehension of trained and untrained sentences was probed before and after treatment using stimuli that differed from the treatment stimuli.

Results

Linear mixed-model analyses demonstrated that, although both OM and SPM treatments were effective, OM resulted in greater improvement than SPM. Analyses of covariance revealed main effects of complexity in generalization; generalization from complex to simple linguistically related sentences was observed both across task and across movement.

Conclusions

Results are consistent with the complexity account of treatment efficacy, as generalization effects were consistently observed from complex to simpler structures. Furthermore, results provide support for resource reduction accounts that suggest that generalization can extend across linguistic boundaries, such as across movement type.

Deficit-lesion correlations in syntactic comprehension in aphasia

The effects of lesions on syntactic comprehension were studied in thirty-one people with aphasia (PWA). Participants were tested for the ability to parse and interpret four types of syntactic structures and elements - passives, object extracted relative clauses, reflexives and pronouns - in three tasks - object manipulation, sentence picture matching with full sentence presentation and sentence picture matching with self-paced listening presentation. Accuracy, end-of-sentence RT and self-paced listening times for each word were measured. MR scans were obtained and analyzed for total lesion volume and for lesion size in 48 cortical areas. Lesion size in several areas of the left hemisphere was related to accuracy in particular sentence types in particular tasks and to self-paced listening times for critical words in particular sentence types. The results support a model of brain organization that includes areas that are specialized for the combination of particular syntactic and interpretive operations and the use of the meanings produced by those operations to accomplish task-related operations.

Mechanisms underlying syntactic comprehension deficits in vascular aphasia: new evidence from self-paced listening

Sixty-one people with aphasia (pwa) and 41 matched controls were tested for the ability to understand sentences that required the ability to process particular syntactic elements and assign particular syntactic structures. Participants paced themselves word-by-word through 20 examples of 11 spoken sentence types and indicated which of two pictures corresponded to the meaning of each sentence. Sentences were developed in pairs such that comprehension of the experimental version of a pair required an aspect of syntactic processing not required in the corresponding baseline sentence. The need for the syntactic operations required only in the experimental version was triggered at a "critical word" in the experimental sentence. Listening times for critical words in experimental sentences were compared to those for corresponding words in the corresponding baseline sentences. The results were consistent with several models of syntactic comprehension deficits in pwa: resource reduction, slowed lexical and/or syntactic processing, abnormal susceptibility to interference from thematic roles generated non-syntactically. They suggest that a previously unidentified disturbance limiting the duration of parsing and interpretation may lead to these deficits, and that this mechanism may lead to structure-specific deficits in pwa. The results thus point to more than one mechanism underlying syntactic comprehension disorders both across and within pwa.

Testing the limits of language production in long-term survivors of major stroke: A psycholinguistic and anatomic study

BACKGROUND: There is still a dearth of information about grammatical aspects of language production in aphasia. AIMS: Making novel use of methods of elicited production aimed at testing the limits of competence, we studied three cases of chronic aphasia, stemming from major stroke. We asked: (1) Whether the elicited production method reveals sparing of language abilities not readily evidenced in spontaneous utterances or on conventional aphasia tests. (2) Which language production abilities survive damage to both Broca's region and Wernicke's region? MATERIALS & PROCEDURES: Targeted words, morphological and syntactic structures were elicited by sentence completion with supporting linguistic and visual context. Targets were never modelled during the procedure. For verbs, visual and auditory contexts emphasise completed actions, targeting past tense forms. Lesion description was based on structural MRI scans. OUTCOMES & RESULTS: The three participants showed partially spared ability to produce nouns, adjectives, and verb stems in context. The elicitation method proved more productive in some cases than picture prompts or sentence prompts. Past tense inflections were usually omitted. Hence stems and inflections were dissociable. Two participants showed partial success with the passive, and no participant produced a full relative clause, including the relative pronoun, but two produced reduced forms of subject relatives. Partial sparing of production capability in these cases points to the likely importance of portions of the left hemisphere remote from Broca and Wernicke regions. CONCLUSIONS: This application of elicited production methodology demonstrates possibilities of lexical, morphological, and syntactic production not evident in spontaneous utterances or by conventional aphasia tests. Some lexical and grammatical capabilities survived massive damage to both anterior and posterior portions of the left hemisphere.

Syntax and conversation in aphasia. A strategic restrictive use of Spanish and Catalan connector QUE by aphasic speakers

Oral conversational data are deemed to be a relevant empirical source when it comes to formulating and supporting hypotheses about cognitive processes involved in aphasic linguistic production. With this assumption in mind, free conversational uses of the Spanish and Catalan connector QUE by fluent and non-fluent aphasic speakers are examined by contrasting them with normal speakers' (i.e. conversational partners') productions. Strictly ungrammatical uses in aphasic speakers are practically non-existent in free conversation. Nevertheless, this data permits one to characterize the aphasic production of the morpheme QUE as restrictive--to different degrees--with respect to normal production. Moreover, this restriction, selectively affecting the types of syntactic environments examined, can be considered strategic in nature: it is guided by some kind of knowledge about the administration of remnant linguistic resources.

Asyntactic thematic role assignment by Mandarin aphasics: a test of the Trace-Deletion Hypothesis and the Double Dependency Hypothesis

This study examines the comprehension patterns of various sentence types by Mandarin-speaking aphasic patients and evaluates the validity of the predictions from the Trace-Deletion Hypothesis (TDH) and the Double Dependency Hypothesis (DDH). Like English, the canonical word order in Mandarin is SVO, but the two languages differ in that the head noun precedes the relative clause in English, but it follows the relative clause in Chinese. According to the Default Principle as stated in the TDH, the word order discrepancy will make subject relative clauses more difficult to comprehend for Mandarin agrammatics than object relative clauses, but the DDH predicts that agrammatic patients from the two languages have the same pattern of selective deficits. The results of this study support the prediction of the TDH.

Processing of disyllabic compound words in Chinese aphasia: evidence for the processing limitations account

The current study addresses the debate between so-called 'structural' and 'processing limitation' accounts of aphasia, i.e., whether language impairments reflect the 'loss' of linguistic knowledge or its representations, or instead reflect a limitation in processing resources. Confrontation-naming task and category-judgment tasks were used to examine and compare the performance of non-fluent and fluent aphasics on different compound types of nouns and verbs. We demonstrate that aphasic patients' performance is modulated by the canonicity of the particular compound type, a result that holds true even for the category in which patients show a 'selective category deficit.' These findings weigh against the 'loss' of linguistic representations as the underlying cause of noun-verb deficits, instead supporting a 'processing limitations' approach.

Language processing: functional organization and neuroanatomical basis

Earlier formulations of the relation of language and the brain provided oversimplified accounts of the nature of language disorders, classifying patients into syndromes characterized by the disruption of sensory or motor word representations or by the disruption of syntax or semantics. More recent neuropsychological findings, drawn mainly from case studies, provide evidence regarding the various levels of representations and processes involved in single-word and sentence processing. Lesion data and neuroimaging findings are converging to some extent in providing localization of these components of language processing, particularly at the single-word level. Much work remains to be done in developing precise theoretical accounts of sentence processing that can accommodate the observed patterns of breakdown. Such theoretical developments may provide a means of accommodating the seemingly contradictory findings regarding the neural organization of sentence processing.

The resolution and recovery of filler-gap dependencies in aphasia: evidence from on-line anomaly detection

This study examines the on-line processing of sentences with movement using an auditory anomaly detection task (after Borland, Tanenhaus, Garnsey, & Carlson, 1995). Eight agrammatic aphasic participants (four of whom had undergone treatment focused on comprehension and production of filler-gap sentences) and 24 young normal participants listened to sentences and pressed a button when the sentences "stopped making sense." Critical sentences contained an anomaly in object relative clauses or conjoined clauses. Results showed that both young normals and aphasic participants were able to reject anomalous sentences of both types. In addition, both groups showed evidence of filler-gap resolution on-line. Importantly, however, there was evidence of a treatment effect for the aphasic patients: those who received treatment showed better performance than those who had not. Treated patients were more successful than the untreated patients in detecting the anomaly in filler-gap conditions, rejecting the anomalous filler-gap sentences reliably more often than the non-anomalous ones, like the young normals. This effect was not noted for untreated participants, i.e., there was no statistical difference between their rejection of anomalous and non-anomalous filler gap sentences. Further, the reaction time data showed that the treated aphasic patients' rejections came before sentence's end (within 2000 ms), while the majority of responses made by untreated patients did not. These results indicate that individuals with agrammatic aphasia appear to retain some gap-filling capacity and that treatment can improve their ability to make use of this capacity.

On the nature and evolution of the neural bases of human language

The traditional theory equating the brain bases of language with Broca's and Wernicke's neocortical areas is wrong. Neural circuits linking activity in anatomically segregated populations of neurons in subcortical structures and the neocortex throughout the human brain regulate complex behaviors such as walking, talking, and comprehending the meaning of sentences. When we hear or read a word, neural structures involved in the perception or real-world associations of the word are activated as well as posterior cortical regions adjacent to Wernicke's area. Many areas of the neocortex and subcortical structures support the cortical-striatal-cortical circuits that confer complex syntactic ability, speech production, and a large vocabulary. However, many of these structures also form part of the neural circuits regulating other aspects of behavior. For example, the basal ganglia, which regulate motor control, are also crucial elements in the circuits that confer human linguistic ability and abstract reasoning. The cerebellum, traditionally associated with motor control, is active in motor learning. The basal ganglia are also key elements in reward-based learning. Data from studies of Broca's aphasia, Parkinson's disease, hypoxia, focal brain damage, and a genetically transmitted brain anomaly (the putative "language gene," family KE), and from comparative studies of the brains and behavior of other species, demonstrate that the basal ganglia sequence the discrete elements that constitute a complete motor act, syntactic process, or thought process. Imaging studies of intact human subjects and electrophysiologic and tracer studies of the brains and behavior of other species confirm these findings. As Dobzansky put it, "Nothing in biology makes sense except in the light of evolution" (cited in Mayr, 1982). That applies with as much force to the human brain and the neural bases of language as it does to the human foot or jaw. The converse follows: the mark of evolution on the brains of human beings and other species provides insight into the evolution of the brain bases of human language. The neural substrate that regulated motor control in the common ancestor of apes and humans most likely was modified to enhance cognitive and linguistic ability. Speech communication played a central role in this process. However, the process that ultimately resulted in the human brain may have started when our earliest hominid ancestors began to walk.

On-line syntactic processing in aphasia: studies with auditory moving window presentation

Twenty-eight aphasic patients with left hemisphere strokes and matched control subjects were tested on an auditory moving windows task in which successive phrases of a sentence were presented in response to subjects' self-paced button presses and subjects made timed judgments regarding the plausibility of each sentence. Pairs of sentences were presented that differed in syntactic complexity. Patients made more errors and/or took longer in making the plausibility judgments than controls, and were more affected than controls by the syntactic complexity of a sentence in these judgments. Normal subjects showed effects of syntactic structure in self-paced listening. On-line syntactic effects differed in patients as a function of their comprehension level. High-performing patients showed the same effects as normal control subjects; low performing patients did not show the same effects of syntactic structure. On-line syntactic effects also differed in patients as a function of their clinical diagnosis. Broca's aphasic patients' on-line performances suggested that they were not processing complex syntactic structures on-line, while fluent aphasics' performances suggested that their comprehension impairment occurred after on-line processing was accomplished. The results indicate that many aphasic patients retain their ability to process syntactic structure on-line, and that different groups of patients with syntactic comprehension disorders show different patterns of on-line syntactic processing.

Language deficits, localization, and grammar: evidence for a distributive model of language breakdown in aphasic patients and neurologically intact individuals

Selective deficits in aphasic patients' grammatical production and comprehension are often cited as evidence that syntactic processing is modular and localizable in discrete areas of the brain (e.g., Y. Grodzinsky, 2000). The authors review a large body of experimental evidence suggesting that morpho-syntactic deficits can be observed in a number of aphasic and neurologically intact populations. They present new data showing that receptive agrammatism is found not only over a range of aphasic groups, but is also observed in neurologically intact individuals processing under stressful conditions. The authors suggest that these data are most compatible with a domain-general account of language, one that emphasizes the interaction of linguistic distributions with the properties of an associative processor working under normal or suboptimal conditions.

Psycholinguistics: a cross-language perspective

Cross-linguistic studies are essential to the identification of universal processes in language development, language use, and language breakdown. Comparative studies in all three areas are reviewed, demonstrating powerful differences across languages in the order in which specific structures are acquired by children, the sparing and impairment of those structures in aphasic patients, and the structures that normal adults rely upon most heavily in real-time word and sentence processing. It is proposed that these differences reflect a cost-benefit trade-off among universal mechanisms for learning and processing (perception, attention, motor planning, memory) that are critical for language, but are not unique to language.

Grammatical encoding in aphasia: evidence from a "processing prosthesis"

Agrammatic aphasia is characterized by severely reduced grammatical structure in spoken and written language, often accompanied by apparent insensitivity to grammatical structure in comprehension. Does agrammatism represent loss of linguistic competence or rather performance factors such as memory or resource limitations? A considerable body of evidence supports the latter hypothesis in the domain of comprehension. Here we present the first strong evidence for the performance hypothesis in the domain of production: an augmentative communication system that markedly increases the grammatical structure of agrammatic speech while providing no linguistic information, functioning merely to reduce on-line processing demands.

Sentence processing deficits in two Cantonese aphasic patients

This paper reports the performances of two Cantonese aphasics on tasks examining their sentence processing deficits. The data on sentence comprehension show that thematically noncanonical sentences, full passives, and subject-gap sentences present greater difficulty to these patients than canonical sentences, truncated passives, and object-gap sentences, respectively. These patterns are consistent with previous observations on Chinese aphasics and are expected given the structural differences between Chinese and English. In a Cantonese grammaticality judgment test, a set of structures are identified that can elicit clear judgments from normal subjects and aphasics, contrary to the claim that grammaticality judgments in Chinese are probabilistic and fragile. Most interestingly, the patients' overall performance patterns reveal a double dissociation between sentence comprehension and judgment of sentence well-formedness, suggesting that the two tasks are supported by independent processing mechanisms.

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.

Structural prominence and agrammatic theta-role assignment: a reconsideration of linear strategies

In this paper we examine the tendency for agrammatic aphasics to make thematic reversal errors in comprehension, e.g., a tendency for English-speaking agrammatics to assign a preposed object the subject role. Although this tendency has been argued to follow from either a linear (Grodzinsky, 1995) or a directionality (Hagiwara & Caplan, 1990) strategy, we show that such proposals can, at best, function as language-particular strategies. We examine data from English, Japanese, German and Dutch, and propose a Structural Prominence Hypothesis which captures the following cross-linguistic generalization: thematic reversal errors result from a tendency to assign thematic roles based on the relative structural prominence of the candidate NPs.

Semantic influences on thematic role assignment: evidence from normals and aphasics

We report two studies that examine the role of semantic influences in the assignment of thematic roles. Semantic factors were manipulated by contrasting sentences in which one noun argument was a plausible filler of only one thematic role (e.g., the painting in The artist disliked the painting) with sentences in which both noun arguments were plausible fillers of both thematic roles (e.g., The robin ate the insect). Subjects were required to make plausibility judgments to sentences presented auditorily. Experiment 1 examined RTs of normal subjects on the plausibility judgment task. In Experiment 2, the same sentences were presented to aphasic patients identified as "asyntactic" comprehenders. In Experiment 1, RTs were speeded by semantic constraints on thematic assignment, particularly when the role-constrained NP occurred early in the sentence (as in The painting was disliked by the artist). The aphasic performance patterns in Experiment 2 paralleled those of normal subjects, but in greatly exaggerated fashion. The patients exhibited high error rates on sentences where semantic constraints conflicted with the syntactically based assignments, even on sentences with canonical (S-V-O) word order (e.g., #The deer shot the hunter).

Patterns of sentence comprehension in aphasia: a consideration of three hypotheses

Three hypotheses concerning the functional source of aphasic patients' difficulty comprehending semantically reversible sentences were tested using declarative sentences in active and passive voice and sentences with center-embedded relative clauses. Each of the three hypotheses is predicated on relative patterns of impairment and sparing of patient performance on these (and other) sentence types, yet the three hypotheses make somewhat different predictions about performance patterns across these types. Results from 5 Broca's aphasic patients were not consistent with the predictions of the linguistically motivated Trace Deletion Hypothesis or of a hypothesis based on an impairment involving grammatical morphemes. The hypothesis that aphasic comprehension impairments reflect a general limitation of working memory capacity was given partial support by the ordinal pattern of difficulty for a mixed group of 10 patients, but failed to account for patterns obtained from individual patients. Results are interpreted as having relevance for methodological as well as theoretical aspects of research on aphasic sentence comprehension.

Aphasic sentence comprehension as a resource deficit: a computational approach

This article describes a new computational model of aphasic sentence comprehension. The model is based on the premise that all aphasics, however different, share a common deficit which determines a considerable amount of the individual variation observed in their sentence comprehension performance. This common deficit is construed as a pathological reduction in the activation resources of a working memory system that subserves sentence comprehension (Miyake, Carpenter, & Just, 1994). To test the theoretical feasibility of the resource reduction hypothesis, a new computer model of aphasic sentence comprehension was developed and tested. We describe the model as well as some initial simulation results, indicating that the model can account for some of the sentence complexity and severity effects that have been reported in the aphasia literature.

Dual processing of open- and closed-class words

A series of articles in the past two decades has suggested differential processing of open- and closed-class lexical items by normal adults. Difficulties in replicating a crucial study (Bradley, 1978), however, have weakened the dual route hypothesis. We matched 16 French open-class items to 16 closed-class items for phonological structure, world length, and relative word frequency. Three agrammatic aphasics revealed strikingly more phonological errors on closed-class than open-class items. Dysfluencies were greater on closed-class items and contributed to greater overall reading time for the closed-class words, consistent with a two-route model for the production of closed- and open-class lexical items in Broca's aphasics and, thus, normals.

Comprehension of reversible sentences in "agrammatism": a meta-analysis

The functional source(s) of agrammatic aphasic patients' difficulty comprehending semantically reversible active and passive sentences was investigated in a meta-analysis of published sentence/picture matching data from patients with agrammatic production. The analysis revealed approximately equal distributions of three distinct patterns of performance on active and passive voice sentences relative to what would be expected by chance: both structures comprehended better than chance; both structures comprehended no better than chance; active voice sentences comprehended better than chance, while passive voice sentences were comprehended at levels no better than (or worse than) chance. These results are in conflict with explanations of aphasic sentence comprehension failure in which a single pattern of relative performance on active and passive voice structures is asserted to be characteristic of the comprehension of all agrammatic speakers. They also highlight the difficulty of identifying any single causal factor to account for sentence comprehension failure in patients with "agrammatic" sentence production. Results are interpreted with regard to the role of data from aphasic patients in the testing of hypotheses about the organization of normal language processes.

Processing relative clauses varying on syntactic and semantic dimensions: an analysis with event-related potentials

Event-related potentials were used to study how parsing of German relative clauses is influenced by semantic information. Subjects read well-formed sentences containing either a subject or an object relative clause and answered questions concerning the thematic roles expressed in those sentences. Half of the sentences contained past participles that on grounds of semantic plausibility biased either a subject or an object relative reading; the other half contained past participles that provided no semantic information favoring either reading. The past participle elicited an N400 component, larger in amplitude for neutral than for semantically biased verbs, but this occurred only in the case of subject relative clauses. More specific effects were obtained only for a subgroup of subjects, when these were grouped into fast and slow comprehenders on the basis of their question-answering reaction times. Fast comprehenders showed larger N400 amplitudes for neutral than for semantically biased past participles in general and larger N400s for the latter when there was a bias for an object relative reading as opposed to a subject relative reading. Syntactic ambiguity resolution, indicated by an auxiliary in sentence final position, was associated in this subgroup with a positive component (P345), larger in amplitude for auxiliaries indicating an object relative reading than for those indicating a subject relative reading. The latter component was independent of semantically biasing information given by a preceding past participle. Implications of these findings for models of language comprehension are considered.

Comprehension of nonlexical categories in agrammatism

The focus of the paper is a proposal advanced by Grodzinsky (1984, 1986, 1990) concerning a possible syntactic deficit in agrammatism with respect to nonlexical categories. Eight native speakers of Serbo-Croatian, who presented a clinical picture of Broca's aphasia with agrammatism, were tested. Subjects' sensitivity to traces and their knowledge of the inflectional and determiner system was investigated using a grammaticality judgment paradigm. The processing load was further minimized by use of short sentences that unequivocally exemplified different syntactic violations. These steps led to significant improvement in the performance of agrammatic aphasics, a result that is incompatible with the claim that the content of nonlexical elements is lost in agrammatism.

Disorders of lexical selection

Errors in lexical processing are commonplace in language pathologies resulting from brain injury or disease. This discussion considers some of the major recent developments in the interpretation of such errors. The focus is on behavioral systems, rather than neuroanatomical or neurophysiological issues. The objective is to comment on some plausible mutual implications of generally attested pathologies and normal models of lexical retrieval for production, particularly with respect to the roles of semantic and syntactic categories.