Jennifer Michaud

A study of syntactic processing in aphasia I: Behavioral (psycholinguistic) aspects

This paper presents the results of a study of syntactically based comprehension in aphasic patients. We studied 42 patients with aphasia secondary to left hemisphere strokes and 25 control participants. We measured off-line, end-of-sentence, performance (accuracy and reaction time) in two tasks that require comprehension--enactment and sentence-picture matching--and in grammaticality judgment, with whole sentence auditory presentation. We also used sentence-picture matching and grammaticality judgment as tasks in two self-paced listening studies with the same patients to measure on-line performance. In each task and presentation format, we presented sentences that tested the ability to assign and interpret three structural contrasts chosen to examine different basic syntactic operations: actives and passives, subject and object extracted relative clauses, and reflexive pronouns and matched sentences without these elements. We examined these behavioral data to determine patterns of impairment in individual patients and in groups of patients, using correlational analyses, factor analyses, and analyses of variance. The results showed that almost no individual patients had stable deficits referable to the ability to interpret individual syntactic structures, that a variety of structural features contributed to sentence processing complexity both on-line and off-line, that correct responses were associated with normal on-line and errors with abnormal performance, and that the major determinant of performance is a factor that affected performance on all sentence types. The results indicate that the major cause of aphasic impairments of syntactically based comprehension are intermittent reductions in the processing capacity available for syntactic, interpretive, and task-related operations.

A study of syntactic processing in aphasia II: Neurological aspects

This paper presents the results of a study of the effects of left hemisphere strokes on syntactically-based comprehension in aphasic patients. We studied 42 patients with aphasia secondary to left hemisphere strokes and 25 control subjects for the ability to assign and interpret three syntactic structures (passives, object extracted relative clauses, and reflexive pronouns) in enactment, sentence-picture matching and grammaticality judgment tasks. We measured accuracy, RT and self-paced listening times in SPM and GJ. We obtained magnetic resonance (MR) and 5-deoxyglucose positron emission tomography (FDG PET) data on 31 patients and 12 controls. The percent of selected regions of interest (ROIs) that was lesioned on MR and the mean normalized PET counts per voxel in ROIs were calculated. In regression analyses, lesion measures in both perisylvian and non-perisylvian ROIs predicted performance. Patients who performed at similar levels behaviorally had lesions of very different sizes, and patients with equivalent lesion sizes varied greatly in their level of performance. The data are consistent with a model in which the neural tissue that is responsible for the operations underlying sentence comprehension and syntactic processing is localized in different neural regions in different individuals.

Task-independent and task-specific syntactic deficits in aphasic comprehension

We present 42 case studies of aphasic syntactic comprehension performances in sentence-picture matching and object manipulation, examining the data for the existence of deficits referable to particular syntactic structures, or such structures in a single sentence form, in both tasks. No deficits affected performance on all sentence types that contained a particular structure in both tasks. Most deficits affected single sentence forms in only one task, and no isolated deficits occurred. The implications of the pattern of performance for the nature of aphasic deficits are discussed.

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.

Dissociations and associations of performance in syntactic comprehension in aphasia and their implications for the nature of aphasic deficits.

Sixty-one pwa were tested on syntactic comprehension in three tasks: sentence-picture matching, sentence-picture matching with auditory moving window presentation, and object manipulation. There were significant correlations of performances on sentences across tasks. First factors on which all sentence types loaded in unrotated factor analyses accounted for most of the variance in each task. Dissociations in performance between sentence types that differed minimally in their syntactic structures were not consistent across tasks. These results replicate previous results with smaller samples and provide important validation of basic aspects of aphasic performance in this area of language processing. They point to the role of a reduction in processing resources and of the interaction of task demands and parsing and interpretive abilities in the genesis of patient performance.

Short-term memory, working memory, and syntactic comprehension in aphasia.

Sixty-one people with aphasia were tested on 10 tests of short-term memory (STM) and for the ability to use syntactic structure to determine the meanings of 11 types of sentences in three tasks—object manipulation, picture matching, and picture matching with self-paced listening. Multilevel models showed relationships between measures of the ability to retain and manipulate item and order information in STM and accuracy and reaction time (RT), and a greater relationship between these STM measures and accuracy and RT for several more complex sentence types in individual tasks. There were no effects of measures of STM that reflect the use of phonological codes or rehearsal on comprehension. There was only one effect of STM measures on self-paced listening times. There were double dissociations between performance on STM and individual comprehension tasks, indicating that normal STM is not necessary to perform normally on these tasks. The results are most easily related to the view that STM plays a facilitatory role in supporting the use of the products of the comprehension process to accomplish operations related to tasks.

Rasch models of aphasic performance on syntactic comprehension tests.

Responses of 42 people with aphasia to 11 sentence types in enactment and sentence–picture matching tasks were characterized using Rasch models that varied in the inclusion of the factors of task, sentence type, and patient group. The best fitting models required the factors of task and patient group but not sentence type. The results provide evidence that aphasic syntactic comprehension is best accounted for by models that include different estimates of patient ability in different tasks and different difficulty of all sentences in different groups of patients, but that do not include different estimates of patient ability for different types of sentences.

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.

Working memory and the revision of syntactic and discourse ambiguities.

Two hundred participants, 50 in each of 4 age ranges (19-29 years, 30-49 years, 50-69 years, 70-90 years) were tested for short-term working memory, speed of processing, and online processing of 3 types of sentences in which an initially assigned syntactic structure and/or semantic interpretation had to be revised. Self-paced reading times were longer for the segments that signaled the need for revision; there also were interactions of age and sentence type and speed of processing and sentence type, but not of working memory and sentence type on reading times for these segments. The results provide evidence that working memory does not support the processes that revise the structure and interpretation of sentences and discourse.