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

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.

Rational Adaptation in Using Conceptual Versus Lexical Information in Adults With Aphasia

The information theoretic principle of rational adaptation predicts that individuals with aphasia adapt to their language impairments by relying more heavily on comparatively unimpaired non-linguistic knowledge to communicate. This prediction was examined by assessing the extent to which adults with chronic aphasia due to left-hemisphere stroke rely more on conceptual rather than lexical information during verb retrieval, as compared to age-matched neurotypical controls. A primed verb naming task examined the degree of facilitation each participant group received from either conceptual event-related or lexical collocate cues, compared to unrelated baseline cues. The results provide evidence that adults with aphasia received amplified facilitation from conceptual cues compared to controls, whereas healthy controls received greater facilitation from lexical cues. This indicates that adaptation to alternative and relatively unimpaired information may facilitate successful word retrieval in aphasia. Implications for models of rational adaptation and clinical neurorehabilitation are discussed.

Syntactic Complexity as a Linguistic Marker to Differentiate Mild Cognitive Impairment From Normal Aging

Purpose In this study, we sought to identify critical linguistic markers that can differentiate sentence processing of individuals with mild cognitive impairment (MCI) from the sentence processing of normal-aging populations by manipulating sentences' linguistic complexity. We investigated whether passive sentences, as linguistically complex structures, can serve as linguistic markers that can contribute to diagnoses that distinguish MCI from normal aging. Method In total, 52 participants, including 26 adults with amnestic MCI and 26 cognitively unimpaired adults, participated in the study. All participants were native speakers of Korean. We administered the two subsets of active and passive conditions using a sentence-picture paradigm with semantically reversible sentences to both groups. Results A mixed-effects model using PROC NLMIXED demonstrated that the MCI group exhibited differentially greater difficulty in processing passive than active sentences compared to the normal-aging group. A logistic regression fitted with the PROC LOGISTIC model identified the sum of the passive sentences, with age and education effects as the best models to distinguish individuals with MCI from the normal-aging group. Conclusion Sentence comprehension deficits emerged in the MCI stage when the syntactic complexity was increased. Furthermore, a passive structure was the best predictor for efficiently distinguishing the MCI group from the normal-aging group. These results are clinically and theoretically important, given that linguistic complexity can serve as a critical behavioral marker in the detection of early symptoms associated with linguistic-cognitive decline.

The Neurobiology of Agrammatic Sentence Comprehension: A Lesion Study

Broca's area has long been implicated in sentence comprehension. Damage to this region is thought to be the central source of "agrammatic comprehension" in which performance is substantially worse (and near chance) on sentences with noncanonical word orders compared with canonical word order sentences (in English). This claim is supported by functional neuroimaging studies demonstrating greater activation in Broca's area for noncanonical versus canonical sentences. However, functional neuroimaging studies also have frequently implicated the anterior temporal lobe (ATL) in sentence processing more broadly, and recent lesion-symptom mapping studies have implicated the ATL and mid temporal regions in agrammatic comprehension. This study investigates these seemingly conflicting findings in 66 left-hemisphere patients with chronic focal cerebral damage. Patients completed two sentence comprehension measures, sentence-picture matching and plausibility judgments. Patients with damage including Broca's area (but excluding the temporal lobe; n = 11) on average did not exhibit the expected agrammatic comprehension pattern-for example, their performance was >80% on noncanonical sentences in the sentence-picture matching task. Patients with ATL damage ( n = 18) also did not exhibit an agrammatic comprehension pattern. Across our entire patient sample, the lesions of patients with agrammatic comprehension patterns in either task had maximal overlap in posterior superior temporal and inferior parietal regions. Using voxel-based lesion-symptom mapping, we find that lower performances on canonical and noncanonical sentences in each task are both associated with damage to a large left superior temporal-inferior parietal network including portions of the ATL, but not Broca's area. Notably, however, response bias in plausibility judgments was significantly associated with damage to inferior frontal cortex, including gray and white matter in Broca's area, suggesting that the contribution of Broca's area to sentence comprehension may be related to task-related cognitive demands.

A rational inference approach to group and individual-level sentence comprehension performance in aphasia

The rational inference, or noisy channel, account of language comprehension predicts that comprehenders are sensitive to the probabilities of different interpretations for a given sentence and adapt as these probabilities change (Gibson, Bergen & Piantadosi, 2013). This account provides an important new perspective on aphasic sentence comprehension: aphasia may increase the likelihood of sentence distortion, leading people with aphasia (PWA) to rely more on the prior probability of an interpretation and less on the form or structure of the sentence (Gibson, Sandberg, Fedorenko, Bergen & Kiran, 2015). We report the results of a sentence-picture matching experiment that tested the predictions of the rational inference account and other current models of aphasic sentence comprehension across a variety of sentence structures. Consistent with the rational inference account, PWA showed similar sensitivity to the probability of particular kinds of form distortions as age-matched controls, yet overall their interpretations relied more on prior probability and less on sentence form. As predicted by rational inference, but not by other models of sentence comprehension in aphasia, PWA's interpretations were more faithful to the form for active and passive sentences than for direct object and prepositional object sentences. However contra rational inference, there was no evidence that individual PWA's severity of syntactic or semantic impairment predicted their sensitivity to form versus the prior probability of a sentence, as cued by semantics. These findings confirm and extend previous findings that suggest the rational inference account holds promise for explaining aphasic and neurotypical comprehension, but they also raise new challenges for the account.

Adaptive significance of right hemisphere activation in aphasic language comprehension

Aphasic patients often exhibit increased right hemisphere activity during language tasks. This may represent takeover of function by regions homologous to the left-hemisphere language networks, maladaptive interference, or adaptation of alternate compensatory strategies. To distinguish between these accounts, we tested language comprehension in 25 aphasic patients using an online sentence-picture matching paradigm while measuring brain activation with MEG. Linguistic conditions included semantically irreversible ("The boy is eating the apple") and reversible ("The boy is pushing the girl") sentences at three levels of syntactic complexity. As expected, patients performed well above chance on irreversible sentences, and at chance on reversible sentences of high complexity. Comprehension of reversible non-complex sentences ranged from nearly perfect to chance, and was highly correlated with offline measures of language comprehension. Lesion analysis revealed that comprehension deficits for reversible sentences were predicted by damage to the left temporal lobe. Although aphasic patients activated homologous areas in the right temporal lobe, such activation was not correlated with comprehension performance. Rather, patients with better comprehension exhibited increased activity in dorsal fronto-parietal regions. Correlations between performance and dorsal network activity occurred bilaterally during perception of sentences, and in the right hemisphere during a post-sentence memory delay. These results suggest that effortful reprocessing of perceived sentences in short-term memory can support improved comprehension in aphasia, and that strategic recruitment of alternative networks, rather than homologous takeover, may account for some findings of right hemisphere language activation in aphasia.

Verb Transitivity Bias Affects On-line Sentence Reading in People with Aphasia

BACKGROUND

Studies of sentence comprehension in non-disordered populations have convincingly demonstrated that probabilistic cues influence on-line syntactic processing. One well-studied cue is verb argument structure bias, which refers to the probability that a verb will occur in a particular syntactic frame. According to the Lexical Bias Hypothesis, people with aphasia have difficulty understanding sentences in which the verb's argument structure bias conflicts with the sentence structure (e.g., a transitively biased verb in an intransitive sentence). This hypothesis may provide an account of why people with aphasia have difficulty understanding both simple and complex sentences.

AIMS

The purpose of this study was to test the Lexical Bias Hypothesis using an on-line measure of written sentence comprehension, self-paced reading.

METHODS PROCEDURES

The participants were ten people with aphasia and ten non-brain-damaged controls. The stimuli were syntactically simple transitive and intransitive sentences that contained transitively- or intransitively-biased verbs. For example, the transitively-biased verb "called" appeared in sentences such as "The agent called (the writer) from overseas to make an offer." The intransitively-biased verb "danced" appeared in sentences such as "The couple danced (the tango) every Friday night last summer."

OUTCOMES RESULTS

Both groups' reading times for critical segments were longer when the verb's transitivity bias did not match the sentence structure, particularly in intransitive sentences.

CONCLUSIONS

The results were generally consistent with the Lexical Bias Hypothesis, and demonstrated that lexical biases affect on-line processing of syntactically simple sentences in people with aphasia and controls.

Lexical and prosodic effects on syntactic ambiguity resolution in aphasia

The purpose of this study was to determine whether and when individuals with aphasia and healthy controls use lexical and prosodic information during on-line sentence comprehension. Individuals with aphasia and controls (n = 12 per group) participated in a self-paced listening experiment. The stimuli were early closure sentences, such as "While the parents watched(,) the child sang a song." Both lexical and prosodic cues were manipulated. The cues were biased toward the subject- or object- of the ambiguous noun phrase (the child). Thus, there were two congruous conditions (in which both lexical cues and prosodic cues were consistent) and two incongruous conditions (in which lexical and prosodic cues conflicted). The results showed that the people with aphasia had longer listening times for the ambiguous noun phrase (the child) when the cues were conflicting, rather than consistent. The controls showed effects earlier in the sentence, at the subordinate verb (watched or danced). Both groups showed evidence of reanalysis at the main verb (sang). These effects demonstrate that the aphasic group was sensitive to the lexical and prosodic cues, but used them on a delayed time course relative to the control group.

Language disorders and brain lesion topography in aphasics after stroke

Aphasia is a language disorder associated with focal brain lesions. Although the topographic definition of the language area has been widely accepted, there is not necessarily any direct correlation between the lesion site and the manifested symptoms.

OBJECTIVE

To analyze aspects of language in aphasics in relation to lesion topography.

METHODS

A prospective, descriptive study of qualitative nature was conducted on 31 individuals, aged older than 15 years, with at least three years of schooling, and a confirmed diagnosis of stroke. Language assessment was carried out using the Montreal Toulouse battery (alpha version), Boston naming test, and FAS test. Language test results were compared against lesion topography findings from magnetic resonance imaging.

RESULTS

Heterogeneous results were found when comparing topography with aphasia, non-aphasia, and performance on language scales.

CONCLUSION

No direct relationship was evident between lesion topography, aphasia, and language test performance.

Aphasia and herpes virus encephalitis: a case study

CONTEXT

Meningoencephalitis early in life, of any etiology, is a risk factor for development of subsequent sequelae, which may be of physical, psychiatric, behavioral or cognitive origin. Anomia is a language abnormality frequently found in such cases, and other language deficits are rarely described. The aim of this study was to describe the cognitive and linguistic manifestations following a case of herpetic meningoencephalitis in a 13-year-old patient with eight years of schooling.

CASE REPORT

The patient underwent a speech-language audiology assessment nine months after the neurological diagnosis. The battery of tests included the Montreal-Toulouse Language Assessment test protocol (MT Beta-86, modified), the description from the Cookie Theft task of the Boston Diagnostic Aphasia Examination (BDAE), an informal assessment of the patient's logical and mathematical reasoning, and the neuropsychological subtests from the WAIS-III scale, which assess working memory. The patient presented mixed aphasia, impairment of short-term memory and working memory, and dyscalculia. This case also presented severe cognitive and linguistic deficits. Prompt diagnosis is crucial, in order to enable timely treatment and rehabilitation of this neurological infection and minimize the cognitive deficits caused by the disease.

Language disorders in children with central nervous system injury

Children with injury to the central nervous system (CNS) exhibit a variety of language disorders that have been described by members of different disciplines, in different journals, using different descriptors and taxonomies. This paper is an overview of language deficits in children with CNS injury, whether congenital or acquired after a period of normal development. It first reviews the principal CNS conditions associated with language disorders in childhood. It then describes a functional taxonomy of language, with examples of the phenomenology and neurobiology of clinical deficits in children with CNS insults. Finally, it attempts to situate language in the broader realm of cognition and in current theoretical accounts of embodied cognition.

Binding in agrammatic aphasia: Processing to comprehension

BACKGROUND: Theories of comprehension deficits in Broca's aphasia have largely been based on the pattern of deficit found with movement constructions. However, some studies have found comprehension deficits with binding constructions, which do not involve movement. AIMS: This study investigates online processing and offline comprehension of binding constructions, such as reflexive (e.g., himself) and pronoun (e.g., him) constructions in unimpaired and aphasic individuals in an attempt to evaluate theories of agrammatic comprehension. METHODS #ENTITYSTARTX00026; PROCEDURES: Participants were eight individuals with agrammatic Broca's aphasia and eight age-matched unimpaired individuals. We used eyetracking to examine online processing of binding constructions while participants listened to stories. Offline comprehension was also tested. OUTCOMES #ENTITYSTARTX00026; RESULTS: The eye movement data showed that individuals with Broca's aphasia were able to automatically process the correct antecedent of reflexives and pronouns. In addition, their syntactic processing of binding was not delayed compared to normal controls. Nevertheless, offline comprehension of both pronouns and reflexives was significantly impaired compared to the control participants. This comprehension failure was reflected in the aphasic participants' eye movements at sentence end, where fixations to the competitor increased. CONCLUSIONS: These data suggest that comprehension difficulties with binding constructions seen in agrammatic aphasic patients are not due to a deficit in automatic syntactic processing or delayed processing. Rather, they point to a possible deficit in lexical integration.

Pronominal resolution and gap filling in agrammatic aphasia: evidence from eye movements

This paper reports the results of three studies examining comprehension and real-time processing of pronominal (Experiment 1) and Wh-movement (Experiments 2 and 3) structures in agrammatic and unimpaired speakers using eyetracking. We asked the following questions: (a) Is off-line comprehension of these constructions impaired in agrammatic listeners?, (b) Do agrammatic, like unimpaired, listeners show eye movement patterns indicative of automatic pronominal reference resolution and/or gap-filling?, and (c) Do eyetracking patterns differ when sentences are correctly versus incorrectly interpreted, or do automatic processes prevail in spite of comprehension failure? Results showed that off-line comprehension of both pronoun and Wh-movement structures was impaired in our agrammatic cohort. However, the aphasic participants showed visual evidence of real-time reference resolution as they processed binding structures, including both pronouns and reflexives, as did our unimpaired control participants. Similarly, both the patients and the control participants showed patterns consistent with successful gap filling during processing of Wh-movement structures. For neither pronominal nor movement structures did we find evidence of delayed processing. Notably, these patterns were found for the aphasic participants even when they incorrectly interpreted target sentences, with the exception of object relative constructions. For incorrectly interpreted sentences, we found end of sentence lexical competition effects. These findings indicate that aberrant lexical integration, rather than representational deficits or generally slowed processing, may underlie agrammatic aphasic listener's comprehension failure.

Influence of brain lesion and educational background on language tests in aphasic subjects

In language assessment, several socio-demographic variables must be taken into account.

The Functional Neuroanatomy of Thematic Role and Locative Relational Knowledge

Lexical-semantic investigations in cognitive neuroscience have focused on conceptual knowledge of concrete objects. By contrast, relational concepts have been largely ignored. We examined thematic role and locative knowledge in 14 left-hemisphere-damage patients. Relational concepts shift cognitive focus away from the object to the relationship between objects, calling into question the relevance of traditional sensory-functional accounts of semantics. If extraction of a relational structure is the critical cognitive process common to both thematic and locative knowledge, then damage to neural structures involved in such an extraction would impair both kinds of knowledge. If the nature of the relationship itself is critical, then functional neuroanatomical dissociations should occur. Using a new lesion analysis method, we found that damage to the lateral temporal cortex produced deficits in thematic role knowledge and damage to inferior fronto-parietal regions produced deficits in locative knowledge. In addition, we found that conceptual knowledge of thematic roles dissociates from its mapping onto language. These relational knowledge deficits were not accounted for by deficits in processing nouns or verbs or by a general deficit in making inferences. Our results are consistent with the hypothesis that manners of visual motion serve as a point of entry for thematic role knowledge and networks dedicated to eye gaze, whereas reaching and grasping serve as a point of entry for locative knowledge. Intermediary convergence zones that are topographically guided by these sensory-motor points of entry play a critical role in the semantics of relational concepts.

Thematic role assignment in patients with Broca's aphasia: Sentence–picture matching electrified

An event-related brain potential experiment was carried out to investigate on-line thematic role assignment during sentence-picture matching in patients with Broca's aphasia. Subjects were presented with a picture that was followed by an auditory sentence. The sentence either matched the picture or mismatched the visual information depicted. Sentences differed in complexity, and ranged from simple active semantically irreversible sentences to passive semantically reversible sentences. ERPs were recorded while subjects were engaged in sentence-picture matching. In addition, reaction time and accuracy were measured. Three groups of subjects were tested: Broca patients (N=10), non-aphasic patients with a right hemisphere (RH) lesion (N=8), and healthy aged-matched controls (N=15). The results of this study showed that, in neurologically unimpaired individuals, thematic role assignment in the context of visual information was an immediate process. This in contrast to patients with Broca's aphasia who demonstrated no signs of on-line sensitivity to the picture-sentence mismatches. The syntactic contribution to the thematic role assignment process seemed to be diminished given the reduction and even absence of P600 effects. Nevertheless, Broca patients showed some off-line behavioral sensitivity to the sentence-picture mismatches. The long response latencies of Broca's aphasics make it likely that off-line response strategies were used.

Processing homonymy and polysemy: effects of sentential context and time-course following unilateral brain damage

The present study investigated the abilities of left-hemisphere-damaged (LHD) non-fluent aphasic, right-hemisphere-damaged (RHD), and normal control individuals to access, in sentential biasing contexts, the multiple meanings of three types of ambiguous words, namely homonyms (e.g., "punch"), metonymies (e.g., "rabbit"), and metaphors (e.g., "star"). Furthermore, the predictions of the "suppression deficit" and "coarse semantic coding" hypotheses, which have been proposed to account for RH language function/dysfunction, were tested. Using an auditory semantic priming paradigm, ambiguous words were incorporated in dominant- or subordinate-biasing sentence-primes followed after a short (100 ms) or long (1,000 ms) interstimulus interval (ISI) by dominant-meaning-related, subordinate-meaning-related or unrelated target words. For all three types of ambiguous words, both the effects of context and ISI were obvious in the performance of normal control subjects, who showed multiple meaning activation at the short ISI, but eventually, at the long ISI, contextually appropriate meaning selection. Largely similar performance was exhibited by the LHD non-fluent aphasic patients as well. In contrast, RHD patients showed limited effects of context, and no effects of the time-course of processing. In addition, although homonymous and metonymous words showed similar patterns of activation (i.e., both meanings were activated at both ISIs), RHD patients had difficulties activating the subordinate meanings of metaphors, suggesting a selective problem with figurative meanings. Although the present findings do not provide strong support for either the "coarse semantic coding" or the "suppression deficit" hypotheses, they are viewed as being more consistent with the latter, according to which RH damage leads to deficits suppressing alternative meanings of ambiguous words that become incompatible with the context.

Alterações de linguagem nas fases iniciais da doença de Alzheimer

A doença de Alzheimer (DA) está associada a alterações cognitivas, de linguagem e de comportamento que se agravam durante seu curso. O objetivo deste estudo foi verificar a presença de alterações de linguagem, em pacientes com DA em fase inicial. Foram avaliados 12 pacientes com diagnóstico de provável (DA). Todos tinham pontuação no Mini Exame do Estado Mental acima de 23 pontos. Os pacientes foram submetidos à aplicação do Teste de Boston e os resultados comparados aos da população normal. Todos os pacientes apresentaram alterações de linguagem. Foram encontradas diferenças estatisticamente significantes nas tarefas de Compreensão auditiva e na tarefa de denominação. Nas demais tarefas de expressão e compreensão oral, bem como nas de leitura e escrita, os pacientes tiveram desempenho similar aos normais. Embora com um grupo pequeno,esta investigação identificou alterações bem definidas de linguagem em uma fase bastante inicial da DA.

The effects of motor neurone disease on language: further evidence

It might sound surprising that Motor Neurone Disease (MND), regarded still by many as the very example of a neurodegenerative disease affecting selectively the motor system and sparing the sensory functions as well as cognition, can have a significant influence on language. In this article we hope to demonstrate that language dysfunction is not only a pronounced and well documented symptom in some MND patients but also that the study of language in MND can address interesting theoretical questions about the representation of language and conceptual knowledge in the brain. After a brief introduction delineating clinical and pathological features of the disease we discuss the evidence available in the literature for language dysfunction in MND. We then present linguistic data from our own study of seven patients with MND/dementia/aphasia syndrome focusing on the dissociation between noun and verb processing. To illustrate the clinical, neuropsychological and linguistic aspects of MND we describe in more detail the patient E.N., a pathologically confirmed case of MND/dementia. Finally, we attempt to characterise the nature of the linguistic impairment in MND in the light of current debates about the mechanisms underlying noun/verb dissociation.

Remediation of asyntactic sentence comprehension using a multimedia microworld

We report the evaluation of a new automated protocol for the treatment of asyntactic comprehension. This is a follow-up study to the "Microworld for Aphasia" work of Crerer, Ellis, and Dean (1996). An efficacy study involving three patients is reported. All three patients achieved statistically significant improvements in written sentence comprehension as a result of eight hours of treatment focusing on active, passive, and object cleft sentence structures. Treatment effects generalized both to untreated Microworld sentences and to the more naturalistic sentences of the Philadelphia Comprehension Battery (Saffran, Schwartz, Linebarger, Martin, & Bochetto, 1988), with some further evidence of generalization to spoken sentence comprehension. Treatment effects were obtained with minimal input from a clinician.

How the brain encodes the order of letters in a printed word: the SERIOL model and selective literature review

This paper describes a novel theoretical framework of how the position of a letter within a string is encoded, the SERIOL model (sequential encoding regulated by inputs to oscillations within letter units). Letter order is represented by a temporal activation pattern across letter units, as is consistent with current theories of information coding based on the precise timing of neural spikes. The framework specifies how this pattern is invoked via an activation gradient that interacts with subthreshold oscillations and how it is decoded via contextual units that activate word units. Using mathematical modeling, this theoretical framework is shown to account for the experimental data from a wide variety of string-processing studies, including hemispheric asymmetries, the optimal viewing position, and positional priming effects.

Agrammatic Broca's aphasia is not associated with a single pattern of comprehension performance

One influential hypothesis posits that the brain regions implicated in Broca's aphasia are responsible for specific syntactic operations that are necessary for the comprehension and production of sentences (Grodzinsky, 1986, 1990, in press). The empirical basis of this hypothesis is the claim that Broca's aphasics have no difficulty understanding sentences in the active voice (and other "canonical" sentence types, such as subject relatives and clefts with negative predicates), but perform at chance level with passive voice constructions (and other "noncanonical" sentences such as object-gap relatives and object clefts). In the face of well-established results indicating that Broca's aphasics can exhibit several different performance patterns on these sentence types, Grodzinsky, Piñango, Zurif, and Drai (1999) argued that these conflicting results do not challenge the theory when the data are analyzed appropriately. They carried out a creative statistical analysis of the comprehension performance of published cases of Broca's aphasia and concluded that all of these cases are in agreement with the predicted pattern: chance on passives and 100% correct on actives. Here we show that the statistical reasoning adopted by Grodzinsky et al. (1999) is flawed. We also show that the comprehension performance of a substantial number of the Broca's aphasics in their own sample does not conform to the pattern required. Rather, contrary to these authors' claim, Broca's aphasia is not associated with a consistent pattern of sentence comprehension performance, but allows for a number of distinct patterns in different patients.

Verb retrieval in brain-damaged subjects: 1. Analysis of stimulus, lexical, and conceptual factors

Verb retrieval for action naming was assessed in 53 brain-damaged subjects by administering a standardized test with 100 items. The goal of the study was to gain further insight into the nature of verb processing impairments by investigating the influence of several kinds of stimulus, lexical, and conceptual factors on the subjects' performance at the level of group tendencies and also at the level of individual differences. (1) Stimulus factors: visual complexity, familiarity, image agreement, and one vs. two pictures (which corresponds to ongoing vs. completed actions); (2) lexical factors: name agreement, verb frequency, and whether the root of the target verb has a homophonous noun; (3) conceptual factors: whether the action is done with the hand or the body, whether the action involves one or two core participants, whether the undergoer of the action has a change of internal state, whether the undergoer has a change of spatial location, and whether the actor makes use of an instrument in carrying out the action. The subjects were divided into an impaired group (n = 19) and an unimpaired group (n = 34) on the basis of their overall performance on the test. For both groups of subjects, verb retrieval was significantly affected by the following factors: familiarity, image agreement, name agreement, homophonous noun, and undergoer change of location. These results indicate that, at the level of group analysis, some factors have a stronger influence on verb retrieval for action naming than others. Moreover, the finding that the two groups exhibited the same general pattern of factor sensitivity suggests that although the processing efficiency of the mechanisms that subserve verb retrieval is degraded in the impaired group, the basic functional properties of these mechanisms may not be qualitatively very different from those of the unimpaired group. Further analyses were conducted at the level of individual subjects and revealed a considerable amount of variation with regard to factor sensitivity. Many patterns of associations and dissociations of factors were found across the subjects, which suggests that the task of retrieving verbs for naming actions is quite complex and that different subjects can be influenced by different properties of both the stimuli and the target verbs.

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.

Impaired comprehension of raising-to-subject constructions in Parkinson's disease

This paper describes an experiment which shows that roughly half of nondemented patients with Parkinson's disease (PD) have impaired comprehension of subject-to-subject and object-to-subject raising constructions (e.g., Susan seems to Bill to be tall and Susan is hard for Bill to catch), but have normal comprehension of the counterpart constructions (e.g., It seems to Bill that Susan is tall and It's hard for Bill to catch Susan). Several possible explanations for this pattern of performance are considered, including a parsing disorder, a syntactic-semantic linking disorder, a reduction of working memory capacity, slowed speed of syntactic processing, and difficulty with the experimental task. Although some of these explanations are arguably more plausible than others, the exact nature of the comprehension impairment remains unclear.