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L K Tyler

Publications and source records attributed to L K Tyler.

At least 19 recordsLinked to original sources
PubMed1998

Sentence comprehension deficits in Alzheimer's disease: a comparison of off-line vs. on-line sentence processing.

Two studies explored whether sentence comprehension impairments in Alzheimer's disease (AD) are due to deficits in syntactic processing or memory. Study 1 used a picture-pointing sentence comprehension task to measure the final outcome of comprehension in an off-line fashion. It showed the comprehension of 30 patients with AD to be impaired, but suggested that the deficits could not be attributed solely to syntactic impairments. Study 2 investigated the effects of memory on sentence comprehension by comparing off-line (grammaticality judgment) with on-line (cross-modal naming) language processing in 11 AD and 9 control subjects. The results revealed impaired performance in the off-line task but normal performance in the on-line task using the same sentences. Performance on the off-line task correlated with independent measures of verbal working memory. These data are used to argue that sentence comprehension impairments are related to verbal working memory deficits in AD.

Aged↗
PubMed1998

Linguistic dissociations in Williams syndrome: evaluating receptive syntax in on-line and off-line tasks.

Williams syndrome (WS) is a neurodevelopmental disorder of genetic origin which results in relatively spared language in the face of serious non-verbal deficits. There is controversy, however, about how intact WS language abilities are. The discussion has focused on impairments of lexico-semantics and of morphological feature analysis, with the presumption that WS syntax is intact. We challenged this view and assessed WS receptive syntax by using two tasks testing various syntactic structures: an on-line word monitoring task and an off-line picture-pointing task. WS performance on the off-line task was generally poor. By contrast, their performance on the on-line task was far better and allowed us to ascertain precisely which aspects of WS receptive syntax are preserved and which are impaired. WS participants were sensitive to the violation of auxiliary markers and phrase structure rules but, unlike both the normal young and elderly controls, they did not show sensitivity to violations of subcategory constraints. The present study suggests that there exist dissociations within WS language which are not restricted to lexico-semantics or to morphological feature analysis, but which also invade their processing of certain syntactic structures. We conclude by arguing that WS syntax is not intact and that their language might turn out to be more like second language learning than normal acquisition.

Adolescent↗
PubMed1998

Category-specific semantic deficits: the role of familiarity and property type reexamined.

Category-specific deficits for living things have been explained variously as an artifact due to differences in the familiarity of concepts in different categories (E. Funnell & J. Sheridan, 1992) or as the result of an underlying impairment to sensory knowledge (E. K. Warrington & T. Shallice, 1984). Efforts to test these hypotheses empirically have been hindered by the shortcomings of currently available stimulus materials. A new set of stimuli are described that the authors developed to overcome the limitations of existing sets. The set consists of color photographs, matched across categories for familiarity and visual complexity. This set was used to test the semantic knowledge of a classic patient, J.B.R. (E. K. Warrington & T. Shallice, 1984). The results suggest that J.B.R.'s deficit for living things cannot be explained in terms of familiarity effects and that the most severely affected categories are those whose identification is most dependent on sensory information.

Adult↗
PubMed1997

Dissociating types of mental computation.

A fundamental issue in the study of cognition and the brain is the nature of mental computation. How far does this depend on internally represented systems of rules, expressed as strings of symbols with a syntax, as opposed to more distributed neural systems, operating subsymbolically and without syntax? The mental representation of the regular and irregular past tense of the English verb has become a crucial test case for this debate. Single-mechanism approaches argue that current multilayer connectionist networks can account for the learning and representation both of regular and of irregular forms. Dual-mechanism approaches, although accepting connectionist accounts for the irregular forms, argue that a symbolic, rule-based system is required to explain the properties of the regular past tense and, by extension, the properties of language and cognition in general. We show here that the regular and irregular past tense are supported by different neural systems, which can become dissociated by damage to the brain. This is evidence for functional and neurological distinctions in the types of mental computation that support these different aspects of linguistic and cognitive performance.

Adult↗
PubMed1997

The gradual deterioration of syntax and semantics in a patient with progressive aphasia.

FM is a progressive aphasic patient whose language comprehension we studied over a 4-year period. We developed a variety of implicit and explicit tasks to chart progressive changes in the representation of linguistic knowledge (in particular, syntax and semantics) and the automatic and controlled processes which operate on that knowledge. The representation of FM's semantic knowledge remained essentially intact over the years, but she became increasingly impaired at combining the meanings of words. She also showed progressive impairments in the processes of syntactic combination. Thus, FM's disease resulted in a progressive inability to engage in those combinatorial processes necessary for the normal comprehension of a spoken utterance. This is not a selective deficit in the traditional sense of the term, since aspects of both syntax and semantics are implicated; but it is selective in the sense that other aspects of language comprehension remain intact.

Aphasia↗
PubMed1997

Do individuals with Williams syndrome have bizarre semantics? Evidence for lexical organization using an on-line task.

Williams syndrome, a neurodevelopmental disorder, has attracted a great deal of debate concerning the purported intactness of language in the face of other serious cognitive deficits. As more in-depth studies of specific aspects of WS language have emerged, the notion of a preserved language module has been seriously challenged. Although WS vocabulary scores are often impressive, several investigators have claimed the WS semantics are aberrant. All studies hitherto have been based on off-line experiments which necessarily involve metalinguistic processes. This clearly affects the performance of individuals with cognitive deficits. We report here an on-line study probing the semantic structure of the WS lexicon, using a task-semantic priming-which minimises metalinguistic demands. We show that WS subjects display the same taxonomic/category and thematic/functional priming effects as normal controls. The results are discussed in terms of the differences between receptive and expressive language, as well as the fact that although semantic memory and the automatic access to semantic information for individual words is normal in WS, the integration of semantic information into sentence comprehension may be abnormal. The importance of online tasks to highlight such differences is stressed.

Adolescent↗
PubMed1995

Automatic access of lexical information in Broca's aphasics: against the automaticity hypothesis.

A number of recent articles have claimed that the language comprehension impairments of so-called agrammatic patients can be characterized as being due to problems with the automatic access of semantic and/or syntactic information from the lexicon. We describe three experiments, all using tasks which probe the immediate and automatic access of lexical information and compare the performance of agrammatic patients with that of an anomic and a fluent patient. We find no evidence in support of the automaticity hypothesis as an explanatory account of the language deficits of agrammatic aphasics. Further, we argue that current research does not lend itself to a single-explanation account of agrammatic comprehension problems, and that in-depth analyses of individual patients are more likely to be fruitful in terms of understanding the nature of comprehension deficits.

Aged↗
PubMed1994

The processing of simple and complex words in an agrammatic patient: evidence from priming.

We report the case of an aphasic patient. D.E., who on standard tests is classified as agrammatic. We investigate D.E.'s difficulties in comprehending derived suffixed words by using a combination of on-line tasks which probe the locus of his impairment. These tasks enable us to determine whether the representation and automatic access of derived words are impaired, or whether D.E. has problems integrating these words into the sentential context. We also compare processing of complex words with simple words. We find that the representation and access of derived words is unimpaired and conclude that D.E.'s difficulties with morphologically complex words results from his inability to integrate them into sentence contexts. In contrast, we find that the processing of simple words in isolation is impaired. We suggest that this is because the activation levels of word-competitors decay more slowly than they do for normal subjects.

Adult↗
PubMed1993

Automatic access to lexical semantics in aphasia: evidence from semantic and associative priming.

We report the auditory lexical decision performance of four patients, all of whom are clinically diagnosed as Broca's aphasics. In a task that separates associative from semantic priming, all four patients show significant priming effects and no interaction with type of relatedness. We find no evidence to support some of the current accounts of these patients' linguistic difficulties in terms of an impairment in automatic processing routines. Instead, we argue that automatic access to lexical semantics is intact.

Adult↗
PubMed1990

Processing distinctions between stems and affixes: evidence from a non-fluent aphasic patient.

In this paper, we study the ability of a non-fluent aphasic patient, BN, to comprehend morphologically complex words when they appear in utterance contexts. We first establish that he is insensitive to the contextual appropriateness of both derived and inflected words. In a further experiment we show that he has no difficulty processing the stems of complex words and conclude that his problem is with the bound morphemes themselves. We then ask whether this problem is due to his inability to access either the phonological form of a morphologically complex word or its semantic and/or syntactic content. We find that only the access of semantic and syntactic content is impaired. We conclude from these six studies that: (a) BN presents a counter-example to the claim that non-fluent patients have particular difficulty with those aspects of morphology which have a syntactic function; (b) BN processes both derived and inflected words by mapping the sensory input onto the entire full-form of a complex word, but the semantic and syntactic content of the stem alone is accessed and integrated into the context. The semantic and syntactic implications of the suffix are never evaluated. This implies separate representation of the stems and suffixes of some types of morphologically complex words.

Adult↗
PubMed1985

Real-time comprehension processes in agrammatism: a case study.

The ability of an agrammatic patient to construct structural syntactic and interpretative representations on-line was tested in two experiments. The first focused on global representations spanning an entire utterance, while the second examined lexical syntactic and semantic constraints on verb-argument relations. An off-line version of the second experiment was also carried out. There were two major findings. First, the patient could construct a semantic, but not syntactic, representation of an utterance. Second, he was much more dependent than normal upon pragmatic information. These results are discussed with respect to current claims about the nature of agrammatic comprehension deficits.

Adult↗
PubMed1983

Reply to Cowart.

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Cognition↗