The organization of semantic memory: in support of a distributed model.
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Aphasia↗
Biomedical subjects
E M Saffran
Publications and source records attributed to E M Saffran.
Quantitative analysis of aphasic sentence production: further development and new data.
The narrative production of patients with Broca's aphasia and age-and education-matched control subjects was analyzed using the Quantitative Production Analysis (Saffran et al., 1989), a procedure designed to provide measures of morphological and structural characteristics of aphasic production. In addition to providing data for a larger number of subjects than in the original study, we provide data on interrater and test-retest reliability. The data were also submitted to factor and cluster analyses. Two factors characterized the data and the cluster analysis yielded four sets of patients who performed differently on these factors. In particular, there is evidence that agrammatic patients can differ in their production of free and bound grammatical morphemes, substantiating earlier claims in the literature.
Adult↗
The role of computational models in neuropsychological investigations of language: reply to Ruml and Caramazza (2000).
W. Ruml and A. Caramazza's (2000) analysis of the model of normal and aphasic lexical access proposed by G. S. Dell, M. F. Schwartz, N. Martin, E. M. Saffran, and D. A. Gagnon (1997) is completely at odds with current practice concerning the use of models in psychology. An evaluation of Dell et al.'s original claims using Ruml and Caramazza's model parameters sustains these claims in all respects.
Aphasia↗
Aphasia and the relationship of language and brain.
This article provides a brief history of the study of aphasia, along with current data on aphasic syndromes and their localization in the brain as well as information on testing procedures. A brief examination of language from a functional perspective is also provided, as it is difficult to understand the breakdown patterns without an appreciation for the complexities of language processing per se.
Aphasia↗
Sentence processing in the face of semantic loss: a case study.
The modularity of the sentence processor, or lack thereof, remains a much-debated issue in psycholinguistics. The authors present evidence from a semantically impaired patient (DM) that bears on this issue. As demonstrated elsewhere (S. D. Breedin, E. M. Saffran, & H. B. Coslett, 1994), DM suffered a significant loss of semantic knowledge. Here, the authors show that this impairment did not compromise DM's ability to process syntactic information. DM performed well on grammaticality judgment tasks and on sentence comprehension tasks that required the use of syntactic information for the assignment of thematic roles. The resistance of syntactic operations to semantic loss would seem to pose a challenge for models in which "the syntactic and conceptual aspects of processing are ... inextricably intertwined" (J. L. McClelland, M. St. John, & R. Taraban, 1989, p. 329).
Atrophy↗
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.
Aphasia↗
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).
Aged↗
The origins of formal paraphasias in aphasics' picture naming.
Accounts of spoken word production differ on whether aphasics' formal paraphasias derive solely from segmental distortion or whether some derive instead from whole word substitution. Form-related paraphasias produced by nine aphasics during picture naming were examined for evidence of lexical effects (word, frequency, and grammatical class biases) and for the manner in which target phonemes and word shape were preserved. Preservation patterns were consistent with previous descriptions of aphasic and nonaphasic form-related speech errors. Evidence for word and frequency biases was found, as well as a grammatical class bias sensitive to the degree of target-response segmental overlap. In conjunction, the results indicate that formal paraphasias arise, at least in part, via word substitution. The findings are supportive of interactive models with phonological-to-lemma feedback and/or modular models with a grammatically organized lexeme level.
Adult↗
Lexical access in aphasic and nonaphasic speakers.
An interactive 2-step theory of lexical retrieval was applied to the picture-naming error patterns of aphasic and nonaphasic speakers. The theory uses spreading activation in a lexical network to accomplish the mapping between the conceptual representation of an object and the phonological form of the word naming the object. A model developed from the theory was parameterized to fit normal error patterns. It was then "lesioned" by globally altering its connection weight, decay rates, or both to provide fits to the error patterns of 21 fluent aphasic patients. These fits were then used to derive predictions about the influence of syntactic categories on patient errors, the effect of phonology on semantic errors, error patterns after recovery, and patient performance on a single-word repetition task. The predictions were confirmed. It is argued that simple quantitative alterations to a normal processing model can explain much of the variety among patient patterns in naming.
Adult↗
Recovery in deep dysphasia: evidence for a relation between auditory - verbal STM capacity and lexical errors in repetition.
This study investigates the changes in auditory-verbal short-term memory (AVSTM) and error patterns in repetition observed in a Wernicke's aphasic, NC, over a period of about 2 years following the onset of a left middle cerebral artery aneurysm. When first tested, NC demonstrated deep dysphasia, a disorder characterized by the production of semantic errors in repetition and a severe disability in repeating nonwords. At this stage, his AVSTM span, assessed in a pointing task, was less than one item. As NC recovered somewhat, his performance on AVSTM tasks improved (span increased to two items), and his pattern of error in word repetition changed (fewer semantic errors, more formal paraphasias and neologisms). Other features of his span performance after some recovery resembled patterns associated with STM-based repetition impairments (reduced recency effects and reduced word length effects). In a series of computer simulation and empirical studies, we show that NC's repetition performance can be accounted for by varying two parameters of an interactive activation model of repetition adapted from Dell and O'Seaghdha's (1991) model of production: decay rate and temporal interval. These results provide support for the view that AVSTM performance depends on storage capacities intrinsic to the language processing system. Such a model allows deep dysphasia and STM-based repetition disorders to be seen as quantitative variants of the same underlying disturbance.
Adult↗
Impairment of sentence comprehension.
We examine two different forms of comprehension impairment, 'semantic dementia' and 'asyntactic comprehension', focusing on the assignment of thematic roles; the determination of who did it to whom. We show, first, that the loss of word meaning does not impede thematic assignment in semantic dementia, demonstrating that syntactic information, along with some knowledge of the verb, is sufficient for the assignment of thematic roles. Studies of normal subjects indicate, however, that this process is normally subject to semantic influences; asked to judge the plausibility of sentences, subjects respond faster when thematic assignment is semantically constrained. The sentence plausibility judgments of 'asyntactic' comprehenders (aphasics with diminished syntactic control over thematic assignment) show increased effects of these semantic constraints. We discuss these results in relation to current issues in sentence processing.
Aphasia↗
Disordered speech production in aphasic and normal speakers.
Two empirical studies are presented which seek to extend the parallels between disordered speech production in aphasia and in normals. Study 1 compares the rate and distribution of some theoretically interesting error types in a jargon aphasic and a normal error corpus. Study 2 is an investigation of how the error pattern of normal speakers evolves as utterances become more practiced. On the basis of these studies, we offer a hypothesis about the nature of the variation between more and less disordered systems. Our claim, which is developed in the context of spreading activation models of production, is that such variation is tied to the ability of the system to deliver activation to intended units, relative to that of unintended units, within the time required by the task at hand.
Aphasia↗
Origins of paraphasias in deep dysphasia: testing the consequences of a decay impairment to an interactive spreading activation model of lexical retrieval.
This study investigates an account of atypical error patterns within the framework of an interactive spreading activation model. Martin and Saffran (1992) described a patient, NC, whose error pattern was unusual for the occurrence of higher rates of form-related than meaning-related word substitutions in naming and the production of semantic errors in repetition. They proposed that NC's error pattern could be accounted for by a pathologically rapid decay of primed nodes in the semantic-lexical-phonological network that shifts the probabilities of error outcome in lexical retrieval. In the present study, Martin and Saffran's account was tested and supported in a series of simulations that reproduce essential features of NC's lexical error pattern in naming and repetition. Also described here are the results of a longitudinal study of NC's naming and repetition, which revealed a shift in relative lexical error rates toward a qualitatively normal pattern. This change in error pattern was simulated by assuming that recovery reflects resolution of the rapid decay rate toward normal levels. The patient data and computational studies are discussed in terms of their significance for the understanding of aphasic impairments and their implications for models of lexical retrieval.
Acute Disease↗
Reading in pure alexia. The effect of strategy.
A number of investigators have demonstrated that patients with pure alexia comprehend briefly presented words which they are unable to explicitly identify. We suggested previously that these patients may read by means of two distinct procedures: a laborious letter-by-letter method and a 'whole-word' procedure which, at least initially, does not support explicit word identification. We report a test of this proposal in a patient with pure alexia. We reasoned that if the patient had access to two distinct and incompatible procedures, he might be induced to switch from one to the other by changing task demands. We found that when instructed to name words, the patient employed a letter-by-letter strategy; in contrast, when instructed to make lexical decision or semantic judgements about rapidly presented words, he appeared to use a 'whole-word' strategy. These data support the hypothesis that two distinct procedures are available to this patient. We argue, further, that is necessary to suppress use of the letter-by-letter strategy to demonstrate whole word reading capability in pure alexics, and that failure to do so may account for negative findings in other cases reported in the literature.
Cerebral Infarction↗
Optic aphasia and the right hemisphere: a replication and extension.
Optic aphasia is a rare, visual modality-specific naming disorder. We describe a patient who developed this disorder subsequent to a left occipital lobe infarction. Like another case that we described previously, this patient performed normally on a variety of tasks assessing the recognition of objects he could not name. Additionally, although he never read aloud a single word, his performance on lexical decision and word comprehension tasks was far better than chance. We suggest that his performance was mediated by a right hemisphere semantic system.
Aged↗
A computational account of deep dysphasia: evidence from a single case study.
We present a case study of a patient, NC, who demonstrates the defining characteristics of deep dysphasia including semantic errors in repetition and an inability to repeat nonwords. In addition, NC's single word repetition and lexical decision performances are influenced by the imageability of the word input. NC also demonstrates a severely restricted phonological short-term memory (one digit, one word). Although his phonological discrimination is good in a minimal pairs judgment task, it becomes impaired when a delay is imposed or rehearsal is prevented between presentation of each member of a pair. NC's output is fluent but contains many formal paraphasias and neologisms. NC's total language profile is evaluated within the framework of Dell's (1986) interactive spreading activation model of language production. Adapting this output model to input processes, we account for all of NC's deep dysphasic symptoms as well as his pattern of production in a way that is more parsimonious than other attempts to model this disorder. In particular, we suggest that the semantic and formal paraphasias in naming and repetition result from a pathological increase in the rate of decay of primed nodes in the semantic-lexical-phonological network. This rapid decay increases the probability that phonologically and/or semantically related lexical nodes primed by top-down and bottom-up feedback during the operation of lexical activation and retrieval will be activated and selected instead of the lexical target. The advantages of using this model to account for aphasic symptoms and the implications for other lexical theories are discussed.
Adult↗
Repetition and verbal STM in transcortical sensory aphasia: a case study.
The repetition performance of a patient (S.T.) with transcortical sensory aphasia is examined in four experiments with particular emphasis on the STM capacities underlying her performance. S.T.'s repetition of word strings exceeding her span (two words) is characterized by good recall of the final items and a strong tendency to lose the initial items in the input string. This pattern contrasts with the serial position effects observed in a phonologically based STM impairment, and it is suggested that a lexical-semantic impairment, also evident in S.T.'s naming and lexical comprehension, contributes to her inability to retain the primacy portions of the input string. Lexical effects obtained in her reproduction of words and nonwords, as well as word strings (Experiments 1 and 2), indicate that under conditions of impaired semantics S.T. is relying on lexical phonological information to repeat. Priming by repeated exposure (Experiment 3) failed to improve her repetition performance, indicating that access to lexical information is brief and dependent on recent phonological input. In Experiment 4, the role of syntactic structure in S.T.'s sentence repetition was examined, and it was shown that syntactic structure affects the recall of order information, but not the number of items recalled. The repetition and verbal STM abilities of this patient, in light of her total language profile, are then evaluated in the context of a language-based view of verbal STM.
Aged↗
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.
Adult↗