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Biomedical subjects

G S Dell

Publications and source records attributed to G S Dell.

14 recordsLinked to original sources
PubMed1997

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↗
PubMed1997

Language production and serial order: a functional analysis and a model.

In speech production, previously spoken and upcoming words can impinge on the word currently being said, resulting in perseverations (e.g., "beef needle soup") and anticipations (e.g., "cuff of coffee"). These errors reveal the extent to which the language-production system is focused on the past, the present, and the future and therefore are informative about how the system deals with serial order. This article offers a functional analysis of serial order in language and develops a general formal model. The centerpiece of the model is a prediction that the fraction of serial-order errors that are anticipatory, as opposed to perseveratory, can be closely predicted by overall error rate. The lower the error rate, the more anticipatory the errors are, regardless of the factors influencing error rate. The model is successfully applied to experimental and natural error data dealing with the effects of practice, speech rate, individual differences, age, and brain damage.

Adult↗
PubMed1997

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↗
PubMed1996

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↗
PubMed1994

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↗
PubMed1994

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↗
PubMed1994

The sequential curing effect in speech production.

How are the sounds of words represented in plans for speech production? In Experiment 1, subjects produced sequences of four CVCs as many times as possible in 8s. We varied the number of repetitions of the initial consonant, vowel, final consonant, CV, rhyme, and whole CVC each sequence required, and measured subjects' speaking rate. Subjects produced more CVCs when the final consonant or whole word was repeated, but were slowed when only initial sounds or CVs were repeated. Two other experiments replicate the location-based effects and extended them to bisyllabic words. We attribute the locational effects to competition between words that are formally similar, and specifically, to competition between discrepant phonemes in the two words to occupy a particular wordframe position. The fact that only discrepant initial, but not final sounds slow production suggests that phonemes are activated sequentially, from left to right.

Humans↗
PubMed1992

Stages of lexical access in language production.

We describe two primary stages in the top-down process of lexical access in production, a stage of lemma access in which words are retrieved as syntactic-semantic entities, and a stage of phonological access in which the forms of the words are fleshed out. We suggest a reconciliation of modular and interactive accounts of these stages whereby modularity is traceable to the action of discrete linguistic rule systems, but interaction arises in the lexical network on which these rules operate. We also discuss the time-course of lexical access in multi-word utterances. We report some initial production priming explorations that support the hypothesis that lemmas are buffered in longer utterances before they are phonologically specified. Because such techniques provide a relatively direct way of assessing activation at the primary stages of lexical access they are an important new resource for the study of language production.

Female↗
PubMed1991

Mediated and convergent lexical priming in language production: a comment on Levelt et al. (1991).

Levelt et al. (1991) argued that modular semantic and phonological stage theories of lexical access in language production are to be preferred over interactive spreading-activation theories (e.g., Dell, 1986). As evidence, they show no mediated semantic-phonological priming during picture naming: Retrieval of sheep primes goat, but the activation of goat is not transmitted to its phonological relative, goal. This research reconciles this result with spreading-activation theories and shows how the absence of mediated priming coexists with the convergent priming necessary to account for mixed semantic-phonological speech errors. The analysis leads to the proposal that the language-production system may best be characterized as globally modular but locally interactive.

Attention↗
PubMed1986

A critical evaluation of the semantic-episodic distinction.

Tulving (1983, 1984) has recently claimed that a wide range of evidence supports the distinction between episodic and semantic memory systems. He has provided a list of features to describe the differences between the two systems and a set of experimental results to demonstrate the distinction. In this article, we present opposing evidence that invalidates many of the distinguishing features and contradicts interpretations of the supporting experiments. In addition, we argue that the question of whether there are two separate memory systems cannot be answered without a specific theory about the differences between the systems.

Amnesia↗
PubMed1985

The role of semantic information in episodic retrieval.

In two experiments, subjects studied lists of categorized words and then were tested for recognition of those words. Response time for a test word was speeded whenever the immediately preceding test word was from the same category. This was true even for test words (lures) from categories never studied. Thus it is argued that semantic information not present at the time of study affected retrieval. This finding is discussed with respect to the distinction between episodic and semantic memories.

Adolescent↗
PubMed1984

Some neurolinguistic implications of prearticulatory editing in production.

This paper argues that a complete model of language production must include a prearticulatory editing component. The function of this component is to monitor planned speech for deviations from the speaker's intention and repair any deviations that are found. It is claimed that adding such an editing component onto a production model fundamentally changes any account of aphasic symptoms using that model. As a case in point it is shown that E. M. Saffran's (1982, British Journal of Psychology, 73, 317-337) argument that agrammatic Broca's aphasia involves a deficit at the functional level of M. F. Garrett's (1975, in G. H. Bower (Ed.). The psychology of learning and motivation, New York: Academic Press) production model is no longer sound when prearticulatory editing processes are considered.

Aphasia↗
PubMed1984

Representation of serial order in speech: evidence from the repeated phoneme effect in speech errors.

Previous research has shown that slips of the tongue involving the exchange of phonemes (e.g., left hemisphere----left hemisphere) are often characterized by a repeated phoneme next to the exchanging ones (the vowel /epsilon/ in the above example is next to both of the exchanging sounds, /l/ and /h/). Two experiments, which elicited slips of the tongue under controlled conditions, revealed that repeated sounds in a speech plan are contributory causes of phoneme exchanges, anticipations, and perseverations. In addition, it was found that repeated sounds induce the misordering of sounds that are not adjacent to the repeated ones, as well as those that are adjacent to the repeated ones. An analysis of a collection of natural slips also supported the conclusion that repeated sounds cause nonadjacent sounds to slip. The results are seen as inconsistent with serial order theories that propose a linear structure of sounds held together by contextual influences between adjacent phonemes.

Cues↗