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T Shallice

Publications and source records attributed to T Shallice.

At least 55 records · Page 3Linked to original sources
PubMed1995

Brain systems for encoding and retrieval of auditory-verbal memory. An in vivo study in humans.

Long-term auditory-verbal memory comprises, at a neuropsychological level, a number of distinct cognitive processes. In the present study we determined the brain systems engaged during encoding (experiment 1) and retrieval (experiment 2) of episodic auditory-verbal material. In the separate experiments, PET measurements of regional cerebral blood flow (rCBF), an index of neural activity, were performed in normal volunteers during either the encoding or the retrieval of paired word associates. In experiment 1, a dual task interference paradigm was used to isolate areas involved in episodic encoding from those which would be concurrently activated by other cognitive processes associated with the presentation of paired associates, notably priming. In experiment 2, we used the cued retrieval of paired associates from episodic or from semantic memory in order to isolate the neural correlates of episodic memories. Encoding of episodic memory was associated with activation of the left prefrontal cortex and the retrosplenial area of the cingulate cortex, while retrieval from episodic memory was associated with activation of the precuneus bilaterally and of the right prefrontal cortex. These results are compatible with the patterns of activation reported in a previous PET memory experiment in which encoding and retrieval were studied concurrently. They also indicate that separate brain systems are engaged during the encoding and retrieval phases of episodic auditory-verbal memory. Retrieval from episodic memory engages a different, but overlapping, system to that engaged by retrieval from semantic memory, a finding that lends functional anatomical support to this neuropsychological distinction.

Adult↗
PubMed1994

Brain regions associated with acquisition and retrieval of verbal episodic memory.

It is widely held that conscious recall of past experiences involves a specific system--episodic memory. Patients with amnesia have gross impairments of episodic memory while other kinds of memory remain intact, suggesting that a separable brain system underlies episodic memory. We have used positron emission tomography (PET) to identify components of this system in normal volunteers. A dual-task interference paradigm was used to isolate brain areas associated with acquisition, and a cueing paradigm to isolate the areas concerned with retrieval from verbal episodic memory. Acquisition was associated with activity in the left prefrontal cortex and the retrosplenial area, whereas retrieval was associated with activity in right prefrontal cortex and the precuneus. Our results provide clear evidence that episodic memory involves a network of specific prefrontal and posterior structures which can be fractionated into different component processes.

Brain↗
PubMed1993

Selective impairment of retrieving people's names: a category specific disorder?

A patient with an extremely long-standing low grade glioma affecting the left temporal lobe is described. The patient was almost entirely unable to retrieve the names of current personalities, although in other respects identification was unimpaired and nominal functions were only mildly inefficient. In particular geographical features and historical figures were generally appropriately named. The problem was equally severe whether naming was to confrontation, from description or by generation. A similarly severe impairment was also found for the retrieval of new words that had come into the language in the last twenty years (eg. aids). The impairment of retrieving people's names was interpreted in terms of a long-standing inability to form new associations between meaning and phonological word-forms.

Amnesia↗
PubMed1991

Can the neuropsychological case-study approach be applied to schizophrenia?

Neuropsychological studies of schizophrenia typically apply a small number of tests to a large group of patients. This approach has at least two drawbacks. First, the heterogeneity of the condition will lead to group means which may not reflect the behaviour of any individual. Secondly, it is difficult to infer the nature of the underlying cognitive impairments from a small number of tests, since good performance on a particular test depends on many different cognitive processes. In these circumstances it is more appropriate to apply the methods of cognitive neuropsychology where a large number of tests are used on a single case. This approach has proved fruitful in the study of neurological patients. We have intensively studied 5 chronic schizophrenic patients. These patients varied greatly in terms of overall ability. However, all patients, whatever their overall ability, performed badly on tests sensitive to frontal lobe lesions. This result suggests impairment of the supervisory attentional system in these patients. In addition, one patient suffered from a visual agnosia.

Adult↗
PubMed1991

Lesioning an attractor network: investigations of acquired dyslexia.

A recurrent connectionist network was trained to output semantic feature vectors when presented with letter strings. When damaged, the network exhibited characteristics that resembled several of the phenomena found in deep dyslexia and semantic-access dyslexia. Damaged networks sometimes settled to the semantic vectors for semantically similar but visually dissimilar words. With severe damage, a forced-choice decision between categories was possible even when the choice of the particular semantic vector within the category was not possible. The damaged networks typically exhibited many mixed visual and semantic errors in which the output corresponded to a word that was both visually and semantically similar. Surprisingly, damage near the output sometimes caused pure visual errors. Indeed, the characteristic error pattern of deep dyslexia occurred with damage to virtually any part of the network.

Brain↗
PubMed1991

Deficits in strategy application following frontal lobe damage in man.

A quantitative investigation of the ability to carry out a variety of cognitive tasks was performed in 3 patients who had sustained traumatic injuries which involved prefrontal structures. All 3 had severe difficulties in 2 tests which required them to carry out a number of fairly simple but open-ended tasks over a 15-30 min period. They typically spent too long on individual tasks. All patients scored well on tests of perception, language and intelligence and 2 performed well on a variety of other tests of frontal lobe function. Explanations for their difficulty on the multiple subgoal tasks in terms of memory or motivational problems could be excluded. It is argued that the problem arose from an inability to reactivate after a delay previously-generated intentions when they are not directly signalled by the stimulus situation.

Accidents, Traffic↗
PubMed1990

Preserved recall versus impaired recognition. A case study.

A very pure and most unusual case of memory impairment is reported in a patient operated on for an aneurysm of the anterior communicating artery. Neuropsychological investigation performed about 8 yrs after the operation revealed a dissociation between very poor performance on recognition tests (on which the patient's performance was as poor as that in classical amnesic patients) and normal performance (estimated by the number of correct responses) in recall. This pattern has not previously been reported and is the reverse of that observed both in normal subjects and in amnesic patients. In addition, the patient was able to achieve a number of difficult learning tasks, at times normally; the relearning of one of these tasks after a delay of 1 h was perfectly normal. The recognition failure is interpreted in terms of the suggestion that memory performance results from an interaction between knowledge and subjective experience of remembering.

Brain↗
PubMed1989

The origins of utilization behaviour.

Utilization behaviour has previously been described clinically by Lhermitte (1983). An experimental investigation is reported of utilization behaviour in a patient with a localized inferior medial bifrontal lesion. The patient picked up and used irrelevant objects not only when place directly in front of him--the procedure developed by Lhermitte--but also when he had been instructed to carry out other tasks and his attention had not been directed to the objects. The behaviour occurred most frequently in the brief intervals between tasks, and more often when auditory-verbal rather than visuomotor tasks were being performed. The results are interpreted within an information-processing model of frontal lobe function. A differentiation is made between two forms of utilization behaviour--an 'incidental' form, as exhibited by the patient, and an 'induced' form where it occurs only when Lhermitte's procedure is adopted.

Behavior↗
PubMed1987

Frontal lesions and sustained attention.

Neurological patients were presented with a succession of 2-11 stimuli which they were required to count, reporting the number in the series when it finished. The stimuli were binaural clicks, or pulses on the right or on the left index finger. Regardless of stimulus modality or lateralization, patients with lesions involving the right frontal lobe were impaired when the presentation rate was 1/sec. There was no corresponding impairment when the presentation rate was increased to 7/sec. It is argued that at slow rates when the task was monotonous patients with right-frontal lesions were less able than others to sustain attention voluntarily.

Adult↗
PubMed1984

Category specific semantic impairments.

We report a quantitative investigation of the visual identification and auditory comprehension deficits of 4 patients who had made a partial recovery from herpes simplex encephalitis. Clinical observations had suggested the selective impairment and selective preservation of certain categories of visual stimuli. In all 4 patients a significant discrepancy between their ability to identify inanimate objects and inability to identify living things and foods was demonstrated. In 2 patients it was possible to compare visual and verbal modalities and the same pattern of dissociation was observed in both. For 1 patient, comprehension of abstract words was significantly superior to comprehension of concrete words. Consistency of responses was recorded within a modality in contrast to a much lesser degree of consistency between modalities. We interpret our findings in terms of category specificity in the organization of meaning systems that are also modality specific semantic systems.

Adult↗
PubMed1982

Specific impairments of planning.

An information-processing model is outlined that predicts that performance on non-routine tasks can be impaired independently of performance on routine tasks. The model is related to views on frontal lobe functions, particularly those of Luria. Two methods of obtaining more rigorous tests of the model are discussed. One makes use of ideas from artificial intelligence to derive a task heavily loaded on planning abilities. A group of patients with left anterior lesions has a specific deficit on the task. Subsidiary investigations support the inference that this is a planning impairment.

Attention↗
PubMed1981

Phonological agraphia and the lexical route in writing.

A new agraphia syndrome is described in which the patient can write certain classes of words virtually perfectly but is very poor at writing non-words. It is shown that this difficulty cannot be explained by perceptual or memory problems. A number of aspects of the syndrome are shown to correspond to those of phonological alexia within the acquired dyslexias. It thus appears that agraphia syndromes can be analysed by methods analogous to those recently developed for the study of the acquired dyslexias.

Agraphia↗
PubMed1980

Word-form dyslexia.

In this study we have reported our investigation of two patients with an acquired dyslexia characterized by letter-by-letter reading, whole word reading being apparently impossible. It has been shown that this phenomenon of letter-by-letter reading cannot be accounted for by visual or perceptual factors nor by impairment of visual span of apprehension. The exceptionally slow speed of reading was documented and a clear relationship between word length and reading speed established. Performance on tasks considered to maximize whole word reading which at the same time prevent the possibility of letter-by-letter reading, namely, reading script and reading with tachistoscopic presentation, was impaired. The satisfactory performance of these two patients on tasks of picture interpretation suggests that the two components of the syndrome simultanagnosia, letter-by-letter reading and piecemeal perception of complex scenes, are dissociable. Three alternative explanations of letter-by-letter reading are considered and we conclude that in this type of acquired dyslexia there is damage to the system through which a visual word-form is attained.

Adult↗