Neural correlates of syntactic transformations

Many agrammatic aphasics have a specific syntactic comprehension deficit involving processing syntactic transformations. It has been proposed that this deficit is due to a dysfunction of Broca's area, an area that is thought to be critical for comprehension of complex transformed sentences. The goal of this study was to investigate the role of Broca's area in processing canonical and non-canonical sentences in healthy subjects. The sentences were presented auditorily and were controlled for task difficulty. Subjects were asked to judge the grammaticality of the sentences while their brain activity was monitored using event-related functional magnetic resonance imaging. Processing both kinds of sentences resulted in activation of language-related brain regions. Comparison of non-canonical and canonical sentences showed greater activation in bilateral temporal regions; a greater activation of Broca's area in processing antecedent-gap relations was not found. Moreover, the posterior part of Broca's area was conjointly activated by both sentence conditions. Broca's area is thus involved in general syntactic processing as required by grammaticality judgments and does not seem to have a specific role in processing syntactic transformations.     

The processing of morphology and syntax in aphasia: A test of the fast decay and slow activation hypotheses

Abstract

Two tasks were designed to test the hypothesis that the syntactic processing deficit of non-fluent agrammatic aphasic patients may be due to either the fast decay or slow activation of syntactic information. Eight non-fluent aphasics, 11 fluent aphasics, and 15 age-matched normal control subjects participated in two auditory lexical decision tasks as well as a grammaticality judgement task. In three types of sentence structures the sentence-final word created either a grammatical sentence or a violation of a particular syntactic rule or constraint. To examine possible deficits in computational speed, the interval between the sentence frame and the sentence-final target word was set at either 100 ms (short ISI) or 1000 ms (long ISI) in the lexical decision tasks. Increased reaction time to targets in ungrammatical sentences is indicative of sensitivity to syntactic violations. With fast decay of syntactic information, sensitivity would be predicted at short but not long ISIs. With slow activation, sensitivity would be expected at long but not short ISIs. Surprisingly, results indicated that all three groups of subjects demonstrated comparable patterns of sensitivity to grammaticality as reflected in increased latencies to target words in ungrammatical contexts. The findings do not provide support for either the fast decay or the slow activation hypothesis. Possible reasons for the unexpected findings are considered.     

Syntactic processing in agrammatism: Evidence from lexical decision and grammaticality judgement tasks

Abstract

This study explored the ability of aphasic patients to process the same sentences varying in syntactic structure in an on-line task (lexical decision) and an off-line task (grammaticality judgement). Eight agrammatic and six age-matched normal subjects were tested on a lexical decision task which probed ten types of ungrammaticalty (five syntactic and five morphological). Normal subjects showed a sensitivity to ungrammaticalty as demonstrated by a significant increase in reaction time to target words in ungrammatical as compared to grammatical contexts. On a grammaticality judgement task using these same stimuli, normal subjects' performance was near ceiling level. The aphasic subjects failed to show a comparable increase in RT on the lexical decision task. In addition, while the agrammatic aphasics performed above chance, they did not perform as well as expected on the grammaticality judgement task. Results are discussed in terms of the nature of the routines involved in the processing of sentences, particularly with respect of agrammatism.     

Grammatical judgments of agrammatic aphasics

Effortful, agrammatic speech and relatively intact comprehension often appear to coexist in Broca's aphasia. The present study focusses on this discrepancy, and tests the claim that the agrammatic patient has more information about syntactic structure than is indicated in his speech. Agrammatic aphasics and non-neurological patients sorted words from a variety of sentences on the basis of how closely related they felt the words to be in each of those sentences. These word groupings served as input matrices for a hierarchical clustering analysis. The resultant subjective phrase structure trees show that while normal subjects are often constrained by surface syntactic properties, agrammatic patients operate on a hierarchical scheme that excludes anything nonessential to the intrinsic meaning of a sentence. These findings suggest that expressive agrammatism is only one aspect of an impairment involving all language modalities.     

Varieties of sentence comprehension deficits: a case study

In recent publications, Grodzinsky (1984, 1986, 1990) has offered a new theory of the disruption of sentence comprehension in so-called agrammatic aphasics. In these works Grodzinsky contends that his account, which is based in various ways on the formal apparatus of current syntactic theory (Chomsky, 1981), is an accurate and explanatory characterization of the preserved language of all those who present with both agrammatic sentence production and asyntactic sentence comprehension. We argue that this claim is not in accord with the facts. We present a detailed case study of the sentence comprehension performance of a patient who is clinically categorized as agrammatic. This patient's performance on full and truncated passives, and on subject- and object-cleft sentences fails each of Grodzinsky's predictions for these sentence types. We argue that whether there exists any patient who does exhibit the predicted performance pattern is also in serious doubt.     

Comprehension of reversible active and passive sentences in agrammatism

Agrammatism is a language disorder characterised by a morphological and/or syntactic deficit in spontaneous speech. Such deficits are usually associated with comprehension disorders - though it is said that this is not always the case - which result in a certain degree of variability in syntactic, lexical, and morpholexical performance. The purpose of this study is to reconsider the nature of comprehension disorders in agrammatism, to test whether Grodzinsky's Trace Deletion Hypothesis (TDH) can be generalised to all agrammatic patients, and to ascertain whether the pattern of impairment observed in agrammatism differs from that present in fluent aphasic patients. Eleven agrammatic patients were tested by means of a sentence comprehension task comprising simple active and passive reversible sentences. The performance of the agrammatic patients was compared to that of 16 fluent aphasic (10 Wernicke's and 6 conduction) and 10 control subjects. The deficits observed in the agrammatic subjects were compatible with the TDH, but there was also impaired processing of pronouns (elements that are also subject to movement) and a mild deficit on the processing of simple active sentences. The fluent aphasic patients showed a similar pattern of impairment. A logistic regression analysis was then applied to each single case separately, in order to study the homogeneity of the patients' performance within each aphasic subgroup. Of the 11 agrammatic patients, 3 did not show comprehension disorders, 5 had a specific deficit for passive movement, 1 a lexical deficit for pronouns only, and 1 a pattern of impairment compatible with Linebarger et al.'s trade-off theory. The last patient showed a deficit for simple active reversible sentences compatible with damage to the mapping of grammatical functions to thematic roles. Similar patterns of impairment were also found in the fluent aphasic sample. Overall, the results lead to the conclusion that the TDH cannot be generalised to all agrammatic patients, that the mechanism it invokes is not the only source responsible for agrammatic comprehension disorders and also contributes to comprehension disorders in fluent aphasic patients.     

Syntactic Processing Deficits in Aphasia

Four aphasic patients were tested in several tasks to determine their ability to use syntactic information. Two patients classified as Broca's aphasics and presenting markedly different levels of severity of aphasia were deficient in their ability to use syntactic information in sentence comprehension and construction. It is argued that the syndrome of Broca's aphasia undermines patients' ability to perform the syntactic analyses that are necessary to understand and to produce sentences in both language modalities. a third patient tested was a conduction aphasic who presented a pattern of sentence comprehension similar to the Broca patient, but produced no other evidence of syntactic impairment. The argument is advanced that the conduction patient's apparently selective impairment of syntactic .processing in comprehension is actually a reflection of a severe auditory-verbal short-term memory deficit. The fourth patient was classified as a mildly-impaired Wernicke's aphasic, who presented no evidence of a selective disturbance of syntactic processing abilities. These results are interpreted as support for the hypothesis that the syndrome of Broca's aphasia results from an impairment to the syntactic component of the language processing system.     

Neural plasticity and treatment-induced recovery of sentence processing in agrammatism

This study examined patterns of neural activation associated with treatment-induced improvement of complex sentence production (and comprehension) in six individuals with stroke-induced agrammatic aphasia, taking into account possible alterations in blood flow often associated with stroke, including delayed time-to-peak of the hemodynamic response function (HRF) and hypoperfused tissue. Aphasic participants performed an auditory verification fMRI task, processing object cleft, subject cleft, and simple active sentences, prior to and following a course of Treatment of Underlying Forms (TUF; Thompson et al., 2003), a linguistically based approach for treating aphasic sentence deficits, which targeted object relative clause constructions. The patients also were scanned in a long-trials task to examine HRFs, to account for any local deviations resulting from stroke, and perfusion images were obtained to evaluate regions of hypoperfused tissue. Region-of-interest (ROI) analyses were conducted (bilaterally), modeling participant-specific local HRFs in left hemisphere areas activated by 12 healthy age-matched volunteers performing the same task, including the middle and inferior frontal gyri, precentral gyrus, middle and superior temporal gyri, and insula, and additional regions associated with complex syntactic processing, including the posterior perisylvian and superior parietal cortices. Results showed that, despite individual variation in activation differences from pre- to post-treatment scans in the aphasic participants, main-effects analyses revealed a general shift from left superior temporal activation to more posterior temporoparietal areas, bilaterally. Time-to-peak of these responses correlated negatively with blood flow, as measured with perfusion imaging.     

Treating agrammatic aphasia within a linguistic framework: Treatment of Underlying Forms

Background : Formal linguistic properties of sentences—both lexical, i.e., argument structure, and syntactic, i.e., movement —as well as what is known about normal and disordered sentence processing and production, were considered in the development of Treatment of Underlying Forms (TUF), a linguistic approach to treatment of sentence deficits in patients with agrammatic aphasia. TUF is focused on complex, non-canonical sentence structures and operates on the premise that training underlying, abstract, properties of language will allow for effective generalisation to untrained structures that share similar linguistic properties, particularly those of lesser complexity. Aims : In this paper we summarise a series of studies focused on examining the effects of TUF. Methods & Procedures : In each study, sentences selected for treatment and for generalisation analysis were controlled for their lexical and syntactic properties, with some structures related and others unrelated along theoretical lines. We use single-subject experimental designs—i.e., multiple baseline designs across participants and behaviours—to chart improvement in comprehension and production of both trained and untrained structures. One structure was trained at a time, while untrained sentences were tested for generalisation. Participants included individuals with mild to moderately severe agrammatic, Broca's aphasia with characteristic deficits patterns. Outcomes & Results : Results of this work have shown that treatment improves the sentence types entered into treatment, that generalisation occurs to sentences which are linguistically related to those trained, and that treatment results in changes in spontaneous discourse in most patients. Further, we have found that generalisation is enhanced when the direction of treatment is from more to less complex structures, a finding that led to the Complexity Account of Treatment Efficacy (CATE, Thompson, Shapiro, Kiran, & Sobecks, 2003). Finally, results of recent work showing that treatment appears to affect processing of trained sentences in real time and that treatment gains can be mapped onto the brain using functional magnetic resonance imaging (fMRI) are discussed. Conclusions : These findings indicate that TUF is effective for treating sentence comprehension and production in patients who present with language deficit patterns like those seen in our patients. Patients receiving this treatment show strong generalisation effects to untrained language material. Given the current healthcare climate, which limits the amount of treatment that aphasic patients receive following stroke, it is important that clinicians deliver treatment that results in optimal generalisation in the least amount of time possible.     

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 & 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 & 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.     

Treating agrammatic aphasia within a linguistic framework: Treatment of Underlying Forms

BACKGROUND: Formal linguistic properties of sentences-both lexical, i.e., argument structure, and syntactic, i.e., movement-as well as what is known about normal and disordered sentence processing and production, were considered in the development of Treatment of Underlying Forms (TUF), a linguistic approach to treatment of sentence deficits in patients with agrammatic aphasia. TUF is focused on complex, non-canonical sentence structures and operates on the premise that training underlying, abstract, properties of language will allow for effective generalisation to untrained structures that share similar linguistic properties, particularly those of lesser complexity. AIMS: In this paper we summarise a series of studies focused on examining the effects of TUF. METHODS #ENTITYSTARTX00026;PROCEDURES: In each study, sentences selected for treatment and for generalisation analysis were controlled for their lexical and syntactic properties, with some structures related and others unrelated along theoretical lines. We use single-subject experimental designs-i.e., multiple baseline designs across participants and behaviours-to chart improvement in comprehension and production of both trained and untrained structures. One structure was trained at a time, while untrained sentences were tested for generalisation. Participants included individuals with mild to moderately severe agrammatic, Broca's aphasia with characteristic deficits patterns. OUTCOMES #ENTITYSTARTX00026; RESULTS: Results of this work have shown that treatment improves the sentence types entered into treatment, that generalisation occurs to sentences which are linguistically related to those trained, and that treatment results in changes in spontaneous discourse in most patients. Further, we have found that generalisation is enhanced when the direction of treatment is from more to less complex structures, a finding that led to the Complexity Account of Treatment Efficacy (CATE, Thompson, Shapiro, Kiran, & Sobecks, 2003). Finally, results of recent work showing that treatment appears to affect processing of trained sentences in real time and that treatment gains can be mapped onto the brain using functional magnetic resonance imaging (fMRI) are discussed. CONCLUSIONS: These findings indicate that TUF is effective for treating sentence comprehension and production in patients who present with language deficit patterns like those seen in our patients. Patients receiving this treatment show strong generalisation effects to untrained language material. Given the current healthcare climate, which limits the amount of treatment that aphasic patients receive following stroke, it is important that clinicians deliver treatment that results in optimal generalisation in the least amount of time possible.     

Syntactically and Semantically Based Computations: Processing of Prepositions in Agrammatism

Six Broca's and six Wernicke's aphasics were tested for their processing of prepositions in different linguistic tasks which placed increasing emphasis on the use of syntactic knowledge. Subjects performed a variety of tasks involving the production and perception of sentences containing prepositions. Agrammatics' production performance was very poor. Although their comprehension performance was superior to production when asked to complete a sentence selecting the target item out of four prepositions their comprehension performance was no longer superior to production in tasks where correct performance strongly depends upon the knowledge of sentence form. These results support the view of a general incapacity of agrammatics to use knowledge of sentence structure in production and in comprehension.     

Judgements of grammaticality in aphasia: The special case of Chinese

Theories of agrammatism have been challenged by the discovery that agrammatic patients can make above - chance judgements of grammaticality. Chinese poses an interesting test of this phenomenon, because its grammar is so austere, with few obligatory features. An on - line grammaticality judgement task was conducted with normal and aphasic speakers of Chinese, using the small set of constructions that do permit judgements of grammaticality in this language. Broca's and Wernicke's aphasics showed similar patterns, with above - chance discrimination between grammatical and ungrammatical forms, suggesting once again that Broca's aphasics are not unique in the degree of sparing or impairment that they show in receptive grammar. However, even for young normals, false - negative rates were high. We conclude that there is some sensitivity to grammatical well - formedness in Chinese aphasics, but the effect is fragile for aphasics and probabilistic for normals, reflecting the peculiar status of grammaticality in this language.     

The verb-right strategy in agrammatic aphasia

Several recent studies have used anagram tasks with agrammatic aphasics. Error patterns in these studies suggest that aphasic patients may be utilizing a more “natural”, “unmarked” SOV structure under conditions of syntactic handicap.     

Production and comprehension of unaccusatives in aphasia

Background: Recent studies have reported impairments in the production of sentences containing unaccusative verbs (e.g., The ball bounced down the street) in agrammatic patients. In these sentences, the subject is the theme of the verb, resulting in a non‐standard order of thematic roles (often called non‐canonical thematic role order).

Aims: We tested the hypothesis that aphasic patients would be affected by these features of unaccusatives in both production and comprehension, and that they would show similar deficits in sentences with unaccusative verbs and passive sentences, which also have non‐canonical thematic role order.

Methods & Procedures: Single‐word naming, sentence production, and sentence–picture matching tasks were administered to a group of 9 aphasic participants and 12 age‐ and education‐matched control participants.

Outcomes & Results: The aphasic patients performed less well than the controls, and there were effects of the presence of movement in both groups and an interaction between group and sentence type in the sentence production task.

Conclusions: These findings support the view that non‐canonical thematic role order makes action naming, sentence production, and sentence comprehension more difficult, and that aphasic patients are more affected by the demands of these tasks than controls.     

Verb and sentence production and comprehension in aphasia: Northwestern Assessment of Verbs and Sentences (NAVS)

Background: Verbs and sentences are often impaired in individuals with aphasia, and differential impairment patterns are associated with different types of aphasia. With currently available test batteries, however, it is challenging to provide a comprehensive profile of aphasic language impairments because they do not examine syntactically important properties of verbs and sentences.

Aims: This study presents data derived from the Northwestern Assessment of Verbs and Sentences (NAVS; Thompson, 2011 Thompson, C. K. 2011. Northwestern Assessment of Verbs and Sentences Evanston, IL [Google Scholar]), a new test battery designed to examine syntactic deficits in aphasia. The NAVS includes tests for verb naming and comprehension, and production of verb argument structure in simple active sentences, with each examining the effects of the number and optionality of arguments. The NAVS also tests production and comprehension of canonical and non-canonical sentences.

Methods & Procedures: A total of 59 aphasic participants (35 agrammatic and 24 anomic) were tested using a set of action pictures. Participants produced verbs or sentences for the production subtests and identified pictures corresponding to auditorily provided verbs or sentences for the comprehension subtests.

Outcomes & Results: The agrammatic group, compared to the anomic group, performed significantly more poorly on all subtests except verb comprehension, and for both groups comprehension was less impaired than production. On verb naming and argument structure production tests both groups exhibited difficulty with three-argument verbs, affected by the number and optionality of arguments. However, production of sentences using three-argument verbs was more impaired in the agrammatic, compared to the anomic, group. On sentence production and comprehension tests, the agrammatic group showed impairments in all types of non-canonical sentences, whereas the anomic group exhibited difficulty primarily with the most difficult, object relative, structures.

Conclusions: Results show that verb and sentence deficits seen in individuals with agrammatic aphasia are largely influenced by syntactic complexity; however, individuals with anomic aphasia appear to exhibit these impairments only for the most complex forms of verbs and sentences. The present data indicate that the NAVS is useful for characterising verb and sentence deficits in people with aphasia.     

The neural basis of reversible sentence comprehension: evidence from voxel-based lesion symptom mapping in aphasia

We explored the neural basis of reversible sentence comprehension in a large group of aphasic patients (n = 79). Voxel-based lesion symptom mapping revealed a significant association between damage in temporo-parietal cortex and impaired sentence comprehension. This association remained after we controlled for phonological working memory. We hypothesize that this region plays an important role in the thematic or what-where processing of sentences. In contrast, we detected weak or no association between reversible sentence comprehension and the ventrolateral pFC, which includes Broca's area, even for syntactically complex sentences. This casts doubt on theories that presuppose a critical role for this region in syntactic computations.     

Sentactics®: Computer-Automated Treatment of Underlying Forms

BACKGROUND: Treatment of Underlying Forms (TUF) is a linguistically-based treatment for improving agrammatic sentence deficits, which enjoys a substantial database attesting to its efficacy for improving both sentence comprehension and production in agrammatic aphasia. However, TUF requires considerable linguistic background to administer and administration time can exceed the number of treatment sessions allotted in toto for reimbursement by third party payors in the United States. Thus, Sentactics?, an interactive computer system that enables delivery of TUF by a virtual clinician was developed. AIMS: This study tested the effects of Sentactics? on the acquisition and generalized production and comprehension of complex sentences. Additionally, a direct comparison of the results of computer-delivered Sentactics? and clinician-delivered TUF was undertaken. METHODS #ENTITYSTARTX00026; PROCEDURES: Twelve agrammatic aphasic speakers participated in the study, with six receiving Sentactics? and six serving as experimental controls, who received no treatment. All participants were administered pre- and post-treatment sentence comprehension and production tests and other measures to evaluate the effects of Sentactics?. Performance of the Sentactics? group also was compared to eight agrammatic patients who previously received clinician-delivered TUF treatment, identical to that delivered via Sentactics?, but with a human clinician. OUTCOMES #ENTITYSTARTX00026; RESULTS: Sentactics? significantly improved all six aphasic speakers' ability to comprehend and produce both trained and untrained, linguistically related, complex sentences as compared to six agrammatic control participants who did not receive Sentactics?. In addition, comparing the results of the Sentactics? to clinician-delivered TUF revealed no significant differences between approaches with regard to acquisition or generalization patterns. CONCLUSIONS: These data provide further support for the efficacy of TUF and demonstrate the viability of computer-delivered therapies in the field of aphasia treatment.     

Neural basis of syntactic processing of simple sentences in Japanese

This study used event-related functional magnetic resonance imaging to investigate the neural basis underlying the sequential involvement of syntactic processing in the course of sentence comprehension. In experiments, a noun, case particle, and verb were presented one by one, constituting simple sentences in Japanese. Participants judged whether the sentence was syntactically correct (syntactic judgment) or whether the particle and verb had the same vowel (phonological judgment). During particle presentation, greater activation in the left inferior frontal gyrus was observed during syntactic judgment than during phonological judgment. Presentation of verbs subsequently activated the left dorsal prefrontal cortex and medial superior frontal areas in the same comparison. Our findings indicate that these regions are sequentially recruited in the syntactic processing of simple sentences in Japanese.     

The discrimination of intonational contours in Broca’s aphasia

Abstract

The observation has been made that agrammatic speakers fail in the comprehension of various sentence types, and this behaviour has been attributed to diminished syntactic capabilities, under the unverified assumption that perception of intonation is intact. Here we re-examine this assumption experimentally with a language, Catalan, which allows for intonation to be the only variable over four sentence types (declaratives, yes-no questions, topicalisations and contrastive focus constructions). We conducted a discrimination task with 10 agrammatic and 10 age- and education-matched control subjects. The subjects were asked to decide whether sentence pairs were identical or not. The overall agrammatic performance was very accurate (89.1% versus 95.6% correct of the controls). The aphasic participants performed above chance in six out of seven conditions. The results indicate that agrammatic individuals succeeded in the task and that their perception of intonation is spared. We conclude that failure in comprehension in agrammatism cannot be attributed to prosodic disruption.