Myrna F. Schwartz

Sensitivity to grammatical structure in so-called agrammatic aphasics

Abstract Comprehension failures in agrammatic aphasics, as well as their difficulties in sentence construction, have been attributed to an underlying deficit involving the retrieval of syntactic structure. In this study we show that four agrammatic patients display a remarkable sensitivity to structural information, as indicated by their performance on a grammaticality judgment task. These results indicate significant sparing of syntactic knowledge in agrammatism, and suggest that the sentence comprehension disturbances in these patients do not reflect loss of the capacity to recover syntactic structure. In particular, accounts of the comprehension deficit in agrammatism that implicate a failure to exploit information carried by the closed class (function word) vocabulary are called seriously into question. Alternative explanations of the comprehension problem in agrammatism are explored.

The quantitative analysis of agrammatic production: procedure and data.

Despite the long-standing interest in structural aspects of aphasic production, no method has emerged for the systematic analysis of aphasic speech. This paper attempts to address that need by outlining a procedure for the quantitative assessment of narrative speech which yields measures for both morphological and structural characteristics of aphasic production. In addition to complete instructions for carrying out this analysis, data for three groups of subjects are presented: agrammatic aphasics, aphasics who are similarly nonfluent but not clinically judged as agrammatic, and normal controls. While the agrammatics were distinguishable from the nonagrammatic patients on most measures, both nonfluent groups showed comparable reductions in the structural complexity of their propositional utterances. Other findings include indications from individual patient data that aspects of grammatical morphology may dissociate in agrammatism.

Localizing interference during naming: convergent neuroimaging and neuropsychological evidence for the function of Broca's area.

To produce a word, the intended word must be selected from a competing set of other words. In other domains where competition affects the selection process, the left inferior frontal gyrus (LIFG) responds to competition among incompatible representations. The aim of this study was to test whether the LIFG is necessary for resolution of competition in word production. Using a methodological approach applying the same rigorous analytic methods to neuropsychological data as is done with neuroimaging data, we compared brain activation patterns in normal speakers (using fMRI) with the results of lesion-deficit correlations in aphasic speakers who performed the same word production task designed to elicit competition during lexical selection. The degree of activation of the LIFG in normal speakers and damage to the LIFG in aphasic speakers was associated with performance on the production task. These convergent findings provide strong support for the hypothesis that the region of cortex commonly known as Brocas area (i.e., the posterior LIFG) serves to bias competitive interactions during language production.

Anterior temporal involvement in semantic word retrieval: voxel-based lesion-symptom mapping evidence from aphasia

Analysis of error types provides useful information about the stages and processes involved in normal and aphasic word production. In picture naming, semantic errors (horse for goat) generally result from something having gone awry in lexical access such that the right concept was mapped to the wrong word. This study used the new lesion analysis technique known as voxel-based lesion-symptom mapping to investigate the locus of lesions that give rise to semantic naming errors. Semantic errors were obtained from 64 individuals with post-stroke aphasia, who also underwent high-resolution structural brain scans. Whole brain voxel-based lesion-symptom mapping was carried out to determine where lesion status predicted semantic error rate. The strongest associations were found in the left anterior to mid middle temporal gyrus. This area also showed strong and significant effects in further analyses that statistically controlled for deficits in pre-lexical, conceptualization processes that might have contributed to semantic error production. This study is the first to demonstrate a specific and necessary role for the left anterior temporal lobe in mapping concepts to words in production. We hypothesize that this role consists in the conveyance of fine-grained semantic distinctions to the lexical system. Our results line up with evidence from semantic dementia, the convergence zone framework and meta-analyses of neuroimaging studies on word production. At the same time, they cast doubt on the classical linkage of semantic error production to lesions in and around Wernickes area.

The Quantitative Description of Action Disorganisation after Brain Damage: A Case Study

Abstract This paper outlines a theoretical approach to the study of action in simple, routine activities, along with a coding system for describing and analysing performance. The approach is exemplified through a single case study involving a patient who developed a profound action disorder following rupture of a pericallosal artery aneurysm and concomitant anterior cerebral artery spasm. The Action Coding System provides a detailed, quantitative picture of this patients action disorder as it was manifested in two routine tasks and as it recovered over time. Discussion focuses on the cognitive organisation and processing of simple, everyday tasks and suggests how disruption of performance may ensue when intentional control of action is compromised.

Power in Voxel-based Lesion-Symptom Mapping

Lesion analysis in brain-injured populations complements what can be learned from functional neuroimaging. Voxel-based approaches to mapping lesion-behavior correlations in brain-injured populations are increasingly popular, and have the potential to leverage image analysis methods drawn from functional magnetic resonance imaging. However, power is a major concern for these studies, and is likely to vary regionally due to the distribution of lesion locations. Here, we outline general considerations for voxel-based methods, characterize the use of a nonparametric permutation test adapted from functional neuroimaging, and present methods for regional power analysis in lesion studies.

The dark side of incremental learning: A model of cumulative semantic interference during lexical access in speech production

Naming a picture of a dog primes the subsequent naming of a picture of a dog (repetition priming) and interferes with the subsequent naming of a picture of a cat (semantic interference). Behavioral studies suggest that these effects derive from persistent changes in the way that words are activated and selected for production, and some have claimed that the findings are only understandable by positing a competitive mechanism for lexical selection. We present a simple model of lexical retrieval in speech production that applies error-driven learning to its lexical activation network. This model naturally produces repetition priming and semantic interference effects. It predicts the major findings from several published experiments, demonstrating that these effects may arise from incremental learning. Furthermore, analysis of the model suggests that competition during lexical selection is not necessary for semantic interference if the learning process is itself competitive.

Semantic factors in verb retrieval: an effect of complexity.

Aphasic patients often have more difficulty retrieving verbs than nouns. We present data from eight aphasics demonstrating that they have a selective impairment for verb retrieval. We then explore the role of semantic complexity (i.e., the number of semantic features) in verb retrieval using a delayed repetition/story completion task. The results indicate that six of the patients are better at retrieving semantically complex verbs (e.g., run) than semantically simpler verbs (e.g., go). The results have implications for accounts of the noun/verb dissociation in aphasia, as well as for theories of verb representation.

The Role of Semantic Memory in Object Use

Does semantic knowledge of objects mediate object selection and use? We present data from two patients that speak to this question. The first, DM, is a semantic dementia patient previously reported by Breedin, Saffran, and Coslett (1994) who, despite moderate to severe loss of functional and associative object knowledge, was nevertheless able to perform almost normally on single-object use and on more complex tests of naturalistic action. The second, HB, is a dementia patient who exhibited an executive disorder but performed as well as controls on a detailed battery of semantic memory and single-object use tests. Unlike DM, he made numerous errors on the naturalistic action tests, among which were errors of object selection and usage. Taken together, these data suggestthatintactsemantic memory forobjects is neithernecessary norsufficient to ensure good object utilisation in naturalistic action. The data cannot be accommodated by accounts postulating that action with objects is performed exclusively via no...

Syntactic transparency and sentence interpretation in aphasia

Abstract A semantic anomaly judgement test was used to test the hypothesis that sentence comprehension errors by agrammatic aphasics arise as a consequence of faulty mapping from syntactic functions to thematic roles. In one condition, anomalies arose out of a thematic role reversal which was carried by the syntactic structure (e.g., # The worm swallowed the bird). Mis-mapping in these cases would have the effect of altering plausibility and hence resulting in erroneous judgments. In a second condition, mismapping was of no consequence (e.g., # The cat divorced the milk). Effects of sentence length (“Padding”) and of the transparency with which thematic roles are syntactically encoded (“Moved-arguments”) were examined across both types of anomaly. Overall, the performance pattern of agrammatics reveals considerable sensitivity to syntactic structure per se. Their difficulty seems to lie in the utilization of syntactic information for the assignment of thematic roles, particularly where the syntactic relat...