Biomedical subjects

A R Mayes

Publications and source records attributed to A R Mayes.

At least 19 recordsLinked to original sources

PubMed1996

Memory dysfunction of the frontal type in normal ageing.

In this study healthy subjects divided into five consecutive age groups (20-60 years of age) completed a series of memory tasks which had previously been shown to reveal impairments in patients with frontal lobe lesions. Significant age differences were found for free recall, retention rates for material which required effortful encoding, memory for temporal order and prospective memory. In the tests addressing these memory functions, subjects of more than 60 years of age performed more poorly than the youngest group, and they also showed evidence of false recognition (increased false alarm rates and confabulatory responses). The general pattern suggests that inefficient frontal functioning might contribute to age-related memory problems.

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PubMed1996

Stem-completion priming in Alzheimer's disease: the importance of target word articulation.

Stem-completion priming performance in patients with Alzheimer's type dementia (DAT) was explored in three experiments in which both the standard repetition priming effect and a novel indirect form of priming, cohort priming, were measured. In the first experiment, in which study stimuli were words, both priming effects were found to be markedly attenuated in the DAT group. In the second experiment, the study stimuli were specially constructed nonwords, and it was found that cohort priming was present at normal levels in the DAT group. In a third experiment we tested the specific hypothesis that the requirement to overtly articulate target stimuli during the study phase was critical for the appearance of normal cohort priming in the DAT group in Experiment 2, and also for the normal levels of repetition priming which have been reported in some published studies. Two encoding conditions were compared, one in which subjects simply had to read aloud the target words and a second in which subjects were required to make evaluative (pleasantness) ratings for each of the target words (identical to that used in Experiment 1). Stem-completion priming performance following the latter condition was significantly attenuated in the DAT group relative to a healthy control group, but following the "read aloud" encoding condition, normal levels of repetition and cohort priming were observed. It is suggested that the most fruitful approach to understanding the performance of DAT subjects on lexical repetition priming tasks will involve a detailed analysis of language functions and how they interact with other, possibly mnemonic, processes in the generation of primed responses.

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PubMed1996

Autonomic and recognition indices of memory in amnesic and healthy control subjects.

Autonomic and recognition indices were examined in six amnesic subjects of mixed aetiology and six control subjects matched with respect to age, education and intelligence. The key objectives of this study were: (a) assess amnesics level of recognition and autonomic discrimination for recently shown words compared with controls; (b) determine if amnesics' level of autonomic discrimination was preserved when compared with the control subjects, level of recognition; and (c) assess confidence in hits and false alarms. The results showed that: (1) despite showing impaired recognition, amnesics displayed significantly better autonomic discrimination; (2) the level of autonomic discrimination displayed by amnesics did not significantly differ from the control subjects' level of recognition; (3) the level of confidence expressed in false alarms and hits did not significantly differ between amnesics and controls, which is in sharp contrast to the significantly greater levels of confidence expressed by healthy subjects in hits versus false alarms. If future work shows that amnesics display preserved autonomic discrimination for novel information, then it may suggest that, at least, some amnesics can store information to an extent that is comparable to that of healthy controls.

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PubMed1996

Does context discriminate recollection from familiarity in recognition memory?

Five experiments were conducted to examine subjects' ability to make contextual judgements about recognized items for which they report recollective experience or only familiarity within the context of the experiment. In the first four experiments, subjects were able to make judgements of the spatiotemporal context of items that were accompanied by recollective experience significantly better than for items they merely found familiar. In only one of the four studies did subjects display above-chance performance on spatiotemporal judgements for merely familiar items. A fifth experiment examined the frequency with which subjects report the presence of different kinds of contextual knowledge during a standard recognition experiment. All aspects of contextual knowledge were reported with higher frequencies for recollected items than for items only found familiar, although no single contextual feature was strongly associated with recollective experience. Thus, the five studies together provide converging evidence for the validity of the "recollect-know" distinction in recognition memory and supplement studies that have already demonstrated that the two kinds of response are dissociable. The implications of these data for group comparisons of memory-impaired patients, and the role of context in recognition memory are discussed.

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PubMed1995

Memory and amnesia.

Brain damage can cause several distinct disorders of explicit memory as well as several disorders of implicit memory. Organic amnesia is the best studied explicit memory disorder. It is a syndrome that can be caused by lesions in (a) the medial temporal lobes, (b) the midline diencephalon, or (c) the basal forebrain. It remains unresolved whether one or several functional deficits underlie the syndrome, how these deficits should be characterised, and what is the exact location of the causal lesions. There is good evidence that amnesics encode information normally so their deficit(s) must be of storage or retrieval processes. If storage is disrupted, then one would expect item-specific implicit memory for certain kinds of novel information to be disrupted in amnesics. Current evidence is unable to indicate conclusively whether or not this prediction is met mainly because indirect memory test performance depends on explicit as well as implicit memory. Storage deficits should also result in accelerated forgetting in amnesic patients. Studies are described which reveal accelerated loss of free recall, but not recognition, for stories and semantically organised word lists in amnesics at delays between 15 s and 10 min. This suggests that amnesia involves a storage deficit for complex contextual associations that possibly occurs in conjunction with one or more other functional deficits.

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PubMed1995

Cognitive outcome after aneurysm rupture: relationship to aneurysm site and perioperative complications.

We evaluated cognitive outcome in a group of 37 patients who had undergone surgery for rupture and repair of a single intracranial aneurysm at least 6 months previously. We compared outcome--assessed by tests of intelligence, attention, executive functions sensitive to frontal lobe lesions, memory, neglect, and mood, as well as by a specially devised questionnaire--between a group of 20 patients who had aneurysms of the anterior communicating artery and 17 patients who had aneurysms located on other branches of the internal carotid artery. There were no differences in cognitive outcome between patients with anterior communicating artery aneurysms and those with aneurysms on other branches of the internal carotid artery. The patient group as a whole, however, showed impairment in executive functions and some aspects of memory in comparison with normative data. Overall, 65% of the patients were impaired in at least one cognitive domain, with 19% showing executive impairments alone, 14% showing memory impairments alone, and 32% showing deficits in both domains. Cognitive outcome was most strongly predicted by postoperative neurologic events, although clipping of an anterior cerebral artery was associated with a higher impairment rating on a symptom profile completed by patients' relatives, and although preoperative rebleeding of aneurysms predicted impairment of executive function.

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PubMed1994

Long lasting indirect memory performance for abstract shapes in amnesics and matched controls.

The speed with which subjects copied complex geometrical shapes was used as an indirect memory measure in a group of 12 organic amnesics of several aetiologies and their matched controls, tested at two delays. Both subject groups were found to copy previous seen shapes faster than new foil shapes, and the magnitude of the speed up effect did not differ significantly between amnesics and matched controls when tested at two delays of 10 min and 24 hr, respectively. The size of the indirect memory effect did not decline across the delay in either group. In contrast to indirect memory performance, measured by two-choice recognition of the shapes, was impaired in the amnesic group and there was some suggestion that recognition performance declined across the delay in both subject groups.

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PubMed1994

Do amnesics forget faces pathologically fast?

In 1978, Huppert and Piercy introduced a general method for comparing forgetting rates across groups differing in their baseline memory performance. The method has since become a standard for measuring rate of forgetting in amnesia. Using this method, amnesic subjects with presumed damage to midline diencephalic structures have consistently been reported to forget at a normal rate whereas patients with medial temporal lobe damage have sometimes been reported to forget pathologically fast. Conclusions about amnesic forgetting rates using Huppert and Piercy's procedure, however, are unsafe because the matching procedure results in the shortest mean item-presentation-to-test delay being longer in amnesics than control subjects. A further problem with previous work is that frequently the shortest delay at which performance is measured is 10 minutes. An alternative procedure to Huppert and Piercy's is outlined which eliminates the matching confound. An experiment was carried out using this procedure with face stimuli, and with amnesic and control performance matched immediately following study, and then tested at delays of 5, 12, and 30 minutes. Pathologically fast forgetting was observed in a group of 19 amnesics over the first 5 minutes, but between 12 and 30 minutes their controls forgot faster so that the two groups had forgotten the same amount after 30 minutes. A subgroup of nine Korsakoff patients, with probable damage to midline diencephalic structures, showed a similar abnormal forgetting pattern to the remaining 10 amnesics, some of whom had medial temporal lobe damage. A retroactive interference condition was also included for the 12 minute condition at which delay patient and control recognition was mildly and equivalently disrupted. For unknown reasons perhaps related to a storage abnormality, amnesics lose face recognition memory sooner in the first 30 minutes of forgetting than do normal people, who show accelerated forgetting later so as to match patients after 30 minutes delay.

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PubMed1994

New-association priming of word identification in normal and amnesic subjects.

Subjects took an implicit memory test in which pairs of unrelated words were flashed briefly and the ability to identify the second word of each pair was measured as a function of prior study. In young subjects, identification was better when the second word had been studied compared to when it had not been studied (word-specific priming). Identification was also better when the two words had been paired at study compared to when they had been studied separately (association-specific priming). In amnesic patients, word-specific priming was normal compared to that in age- and IQ-matched control subjects. Association-specific priming was observed, but it was below normal levels. This outcome suggests that the amnesic dysfunction can encompass priming of new verbal associations but spare priming of existing verbal information.

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PubMed1994

Dual task performance in amnesic and normal people: does resource depletion cause amnesia?

Normal peoples' memory can be seriously disrupted if their cognitive resources are depleted by means of an experimental manipulation (such as distraction at encoding or at retrieval). By analogy, it has also been suggested that amnesia might result directly from pathological loss of cognitive capacity. This hypothesis was examined in 12 mixed amnesics and 12 normal people by means of a 'dual task' study. It was argued that if amnesics have reduced cognitive resources they should be disproportionately impaired in dual task performance relative to single task performance and in comparison to controls. This result was unambiguously demonstrated using a visual (letter detection) task combined with an auditory (semantic decision) task. However, correlations with measures of frontal function and with indicants of severity of amnesia proved insignificant and so the role of resource depletion in amnesia remains, as yet, unproven.

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PubMed1994

Evidence of covert recognition in a prosopagnosic patient.

This is a case-study of a patient (ET) who suffers from prosopagnosia, in the context of impairment to cognitive functions, following traumatic brain injury. Despite severe perceptual difficulties in tests involving non-face stimuli and matching unfamiliar faces, ET showed evidence of "covert" recognition of familiar faces in a number of tasks. Although densely prosopagnosic, she performed at normal levels in word and object recognition tasks, and is unimpaired in her ability to recognise names of celebrities. She performed at the same level as controls in her ability to make a forced-choice of the correct name for a famous face, even though it evoked no feeling of familiarity for her. She performed at chance in a forced-choice face familiarity decision task, but showed evidence of covert recognition in a "true" versus "untrue" face-name learning task. ET showed overt recognition of some famous faces using a procedure based on Sergent and Poncet's (1990) semantic activation task. The pattern of impairment of ET's face processing abilities is interpreted in terms of an interactive activation model of face processing.

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PubMed1994

Two tests for assessing remote public knowledge: a tool for assessing retrograde amnesia.

Guidelines for the construction and development of tests of remote memory are provided. These guidelines follow from methodological considerations and from certain theoretical issues we believe that remote memory tests should address if they are to further our understanding of amnesia. These include: the pattern of temporal gradient; memory for different broad classes of information such as famous names and famous events; and recall and recognition of different types of detail such as contextual and non-contextual information associated with remote memory. With respect to the first of these, we argue that it is impossible to fully evaluate competing hypotheses about temporally graded retrograde amnesia unless items are selected from at least two difficulty levels, and from at least two time periods. The construction of two equivalent tests of remote memory, one for famous people, the other for famous events, is described, and the theoretical issues listed earlier were addressed using these tests in a study comparing the remote memory of 13 organic amnesics and 13 age- and IQ-matched controls. The principal findings were as follows. There was only weak evidence that amnesics' remote memory for famous people and events was temporally graded over a 20 year period, and recognition memory and memory for non-contextual detail were equally impaired. Mayes, Meudell, and Pickering's (1985) context memory deficit hypothesis was supported, however, because amnesics were more impaired in their ability to date recognised items. In addition, although there was little support for a temporally graded retrograde impairment on the recognition question, there was much clearer evidence for the temporal dating question. Also, one patient, SR, showed a selective deficit in dating recognised names and events from the 1980s. Finally, the correlations between measures of anterograde and retrograde amnesia were all non-significant. Suitable items for the construction of remote memory tests probing the four decades 1950s to 1980s are presented. A subset of these, from the 1970s and 1980s, were shown to have satisfactory psychometric qualities, and can therefore be recommended for more widespread clinical use, although more extensive normative data than that provided here will be necessary.

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PubMed1994

No selective deficit in recall in amnesia.

Are amnesic patients selectively impaired in recall relative to recognition? Experiment 1 studied a group of Korsakoff amnesics and matched the amnesic level of recognition with that of control subjects by testing control recognition of unrelated words after longer delays. It was found that under these conditions the observed levels of recall were also approximately equal. In Experiment 2, a similar result occurred when the Korsakoff amnesic level of recognition for unrelated words was matched by varying the number of presentations as well as delay before testing. In Experiment 3, a similar result occurred again with a group of amnesics of mixed aetiology and recognition levels for related words matched by varying the duration of presentation and delay before testing. In this experiment, both recognition and recall of the same items were assessed. It was found that for the amnesic group the observed level of dependency between recognition and recall was less than that for the control group. One possible interpretation of this result is that the microstructure of the recall process may be selectively disturbed in amnesia. The principal finding, however, is that in all three experiments there was no significant evidence of the existence in amnesia of a selective deficit in the overall level of recall relative to that of recognition.

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PubMed1993

Encoding ability is preserved in amnesia: evidence from a direct test of encoding.

The encoding ability of 17 amnesics of mixed aetiology and 17 matched normal controls was assessed directly using a novel procedure. On two separate occasions, subjects were shown 60 complex drawings each containing six pictures. On one occasion each drawing was shown for 6 sec, and on the other occasion it was shown for 25 sec. Immediately after presentation of each drawing subjects were asked a single unpredictable question about picture colours, location, size or semantic category. Amnesics performed normally in the 6-sec exposure condition indicating that all of the tested kinds of information were encoded at a normal rate. Performance in this condition correlated with short-term, but not long-term memory in the amnesics indicating that it depended largely on encoding and short-term memory. However, the amnesics were impaired in the 25-sec condition where performance should have depended on (long-term) memory abilities at which they were impaired. The results are inconsistent with available encoding deficit accounts of amnesia.

Adult↗

PubMed1993

Preserved pattern completion priming for novel, abstract geometric shapes in amnesics of several aetiologies.

Two experiments were conducted using a paradigm developed by Gabrieli et al., Neuropsychologia 28, 417-427, 1990, which assessed both indirect and direct memory performance in a completion task for novel abstract geometric patterns. The preferred method of scoring was the lines method, based on the number of correct and incorrect lines produced for each item. It was chosen because it is both the simplest and the most informative measure. Two methods of scoring were used in previous work, namely, the strict whole figure method and the lenient whole figure method (Gabrielli et al., 1990; Verfaelie et al., Brain Cognit. 18, 34-45, 1992). Therefore to facilitate comparisons between studies and to determine the characteristics of different scoring methods, results with all three measures were included. In Experiment 1, two different encoding strategies of naming and copying were used in order to explore the relationship between indirect and direct memory performance. Indirect memory performance in the naming condition was at baseline whereas in the copying condition it was significantly above baseline. Cued recall did not differ across encoding conditions but recognition was higher in the naming condition than the copying condition. In Experiment 2, an attempt was made to extend the findings of two studies, one with H.M. (Gabrielli et al., 1990) and one with nine Korsakoffs (Verfaelie et al., 1992), to a larger group of 14 amnesics of several aetiologies. Indirect memory performance was found to be equivalent for the amnesics and their matched controls, only when the lenient and the lines methods of scoring were used. Recognition and cued recall performance was impaired for the amnesics compared to the controls.

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PubMed1992

Priming of face matching in amnesia.

Priming was studied in a task that required a speeded response to photographs of faces. On each trial, subjects viewed two faces and decided if the same person was shown twice or if two different people were shown. Both familiar and unfamiliar (i.e., well-known and unknown) faces were used, and some face pairs were repeated with a mean delay of about 10 min. Repetition was associated with faster reaction times in young subjects (Experiment 1) as well as in amnesic patients and age-matched control subjects (Experiment 2). The patients' reaction times were slower overall, although the magnitude of the priming effect did not differ from that in the control subjects. This preservation of a normal reaction-time facilitation in subjects with impaired recognition memory for faces occurred for both familiar and unfamiliar faces, suggesting that amnesia does not necessarily interfere with the acquisition of new information as indexed by this priming effect.

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PubMed1992

Preservation of priming for interactive context in amnesics.

The performance of a group of 12 amnesics of mixed aetiology was compared with that of two groups of normal subjects on a priming task in which subjects' spontaneous definitions of homonyms were biased in accordance with the sense of interactive context words which had earlier been shown with the homonyms. The amnesics showed significant and normal levels of interactive context priming even when the amount of attention paid to the interactive context words was minimized during training. Reducing the amount of attention paid to the context words during training did, however, decrease the amount of priming, shown by both groups of subjects, to the same degree. It also decreased recognition of trained homonym-context word pairs to a similar extent in amnesics and normal people. In an additional condition of the study, it was shown that normal subjects were aware of the meaningful relationship between homonyms and context words even when the amount of attention they paid to context words was minimized during training. Priming seemed to be stochastically independent of recognition and was also unrelated to signs of frontal lobe damage, intelligence or explicit memory. All three groups of subjects showed similar and significant levels of priming regardless of whether or not only definitions that made no direct reference to the context words were scored. It was concluded that amnesics have preserved priming for interactive context words that are encoded with low levels of attention even though there is evidence that they have a disproportionate recognition deficit for this kind of information under these conditions. The theoretical implications of the results are discussed.

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PubMed1992

Amnesics have a disproportionately severe memory deficit for interactive context.

Two experiments were used to compare the recognition memory of amnesic and normal subjects for intentionally encoded words (targets) and for incidentally encoded words that were meaningfully related to the targets and presented at the same time (interactive context). In both experiments the target recognition of the two groups was matched at a high level by presenting the amnesics with much shorter lists of words to remember. Experiment 1 compared 20 amnesics and their matched controls and showed that whereas the amnesics' recognition of the target words did not benefit significantly when they were presented together with their interactive context words (relative to their recognition when the target words were presented alone), that of the controls did. Experiment 2 compared 14 amnesics and their matched controls and showed that when patients and their controls were matched on their target word recognition in isolation, then the patients still showed worse recognition for the interactive context words. These effects were not found only in Korsakoff patients, and their size did not correlate with behavioural measures of frontal-lobe damage. It is concluded that amnesics may be more impaired at recognizing incidentally encoded interactive context than they are at recognizing target material, and this deficit may be an essential feature of the syndrome.

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