Peter R. Meudell

Location of lesions in Korsakoff's syndrome: neuropsychological and neuropathological data on two patients.

Psychometric and neuropathological findings on two Korsakoff amnesics are described. Both patients showed anterograde and retrograde amnesia, poor performance on the Peterson short-term memory task, on the Wisconsin card sort test and on certain visuo-spatial tasks. Patient J.W. performed consistently worse on tests of anterograde, but not retrograde amnesia, whereas patient B.C. showed more perseverative difficulties and, unlike J.W., his measured intelligence seemed to have declined from its premorbid level. Both patients showed marked neuronal loss from the medial mammillary bodies and a narrow band of gliosis in the medial thalamus, adjacent to the wall of the third ventricle, a region known as the paratenial nucleus. Only B.C. showed visible signs of cortical atrophy. Morphometric measures did, however, reveal reduced nucleolar volumes in layers III and V of the frontal cortex, with B.C. also showing more marked neuronal loss from these layers. B.C. also showed neuronal loss from the CA1 region of the hippocampus and reduced nucleolar volumes in the septum. Significantly, both patients had normal neuronal numbers and nucleolar volumes in the nucleus basalis of Meynert. J.W. only showed greater dysfunction than B.C. in one region: the locus caeruleus. This finding was related to his more severe amnesia.

Is Organic Amnesia Caused by a Selective Deficit in Remembering Contextual Information

An influential view of amnesia is that the recognition and recall failure is a consequence of a selective loss of memory for contextual, rather than target, information. The various forms of this viewpoint are outlined and one is considered in more detail. This hypothesis claims that amnesics suffer from a selective inability to remember background context i.e. spatiotemporal or extrinsic context. The evidence cited in support of this hypothesis is then critically reviewed and assessed in relation to two methodological problems. The first problem shows that when weak amnesic memory is compared with good normal memory qualitative differences in contextual memory may arise artefactually. The second problem is that contextual memory deficits, found in amnesics, may be incidental consequences of frontal cortex damage rather than essential to the core memory deficit. In the light of these problems it is concluded that currently there is no convincing support for the contextual memory deficit hypothesis of amnesia. Finally, guidelines are laid down which should enable the hypothesis to be more appropriately assessed, and an alternative kind of hypothesis is briefly outlined.

Mutual inhibition in collaborative recall: evidence for a retrieval-based account.

In Experiment 1 participants gave 3 successive free recalls of items learned either individually or in pairwise collaboration. The first and third recalls were performed individually, the second alone or in collaboration. Collaborative recall led to an inhibitory effect after individual learning but not after collaborative learning, in which partners had similar retrieval strategies. Consistent with a retrieval locus for collaborative inhibition, non-recalled items reappeared in subsequent individual recall. Experiment 2 showed that collaborative inhibition was eliminated when a separate retrieval cue was given for each item. Experiments 2 and 3 also showed that when participants learned items in the same order, their retrieval strategies were more similar and they showed less collaborative inhibition. It is concluded that mutual interference in collaborative recall is due to the mutual disruption of individual retrieval strategies.

Collaboration in Recall: Do Pairs of People Cross-cue Each Other to Produce New Memories?

When people collaborate over their recall of a shared experience, it might be expected that they could “cross-cue” each other so as to produce new memories not available to either member of the pair on their own. In a previous series of experiments (Meudell et al., 1992), we found that pairs of people always recalled more than one person, but we failed to show that social interaction facilitated performance so as to produce such “emergent” new memories. However, a phenomenon akin to cross-cuing was employed by Tulving and Pearlstone (1966) in their classic study of the availability and accessibility of memories; accordingly, in this study, we repeated Tulving and Pearlstones work directly in a social context. So as to assess whether new memories emerged in collaborating pairs, a sequential design was employed. People learned categorized lists of words, and then all the subjects recalled the items strictly on their own. Subjects then recalled again in pairs (collaboratively) or once more on their own. The results showed that even when the opportunity for cross-cuing was directly manipulated through the provision of categorized lists, no additional new memories emerged in the collaborating groups. Possible mechanisms for the results are considered.

Regency and Frequency Judgements in Alcoholic Amnesics and Normal People with Poor Memory

Alcoholic amnesics have been reported to confuse when an event occurred with how frequently it occurred and conversely, how frequently something took place with when it happened. This lack of independence of recency and frequency judgements, shown by these amnesics (but not shown by normal people) has been interpreted as reflecting a selective amnesic failure in memory for contextual information; this failure, in turn, leading to poor recall and recognition memory. The effect is replicated on another group of Korsakoff patients and, by manipulations of retention intervals and of learning opportunity, it is also shown that normal people with memory that is as poor overall as that of amnesics still have specific contextual memory with which to make temporal judgements independently of frequency of presentation and (somewhat less obviously) frequency judgements independently of recency of presentation. The qualitative differences between amnesic and normal people cannot therefore be an artefact of testing generally poor memory in amnesics. While it is possible that the unavailability or inaccessibility of contextual information may cause amnesia, an alternative hypothesis, that poor contextual knowledge is an incidental feature in alcoholic amnesia (related to frontal lobe dysfunction), is also considered.

Long term memory for famous voices in amnesic and normal subjects

Abstract Patients with alcoholic amnesia and control subjects were played voices of famous people recorded in the last 50 yr and were required to identify them. The results for the amnesic group showed a retrograde amnesia for voices extending over several decades and relative preservation of memories for the more remote past; the absence of differential improvement in recall following cueing in the amnesic group suggested that the retrograde amnesia could not be explained solely in terms of a specific retrieval deficit. The ability to assign identified voices to their correct recorded decade was also tested and the amnesics were found to perform significantly worse on this task than controls.

The role of rehearsal in the short-term memory performance of patients with Korsakoff's and Huntington's disease

Abstract Alcoholic Korsakoff patients, patients with Huntingtons disease and a notmal control group were given a Peterson short-term memory task. All three groups were required to recall three word trigrams after a 0 sec retention interval, a 20 sec retention interval filled with counting backwards in ones or twos and a 20 sec unfilled retention interval with no distractor task. It was found that all groups were able to rehearse information over the unfilled retention interval but all groups showed a drop in recall performance with a distraction task, counting in twos causing more forgetting than counting in ones and both patient groups were inferior to the control group. Analysis of the error data showed that while Korsakoffs made more prior item intrusion errors than omissions, the converse was the case for the Huntington group. It is argued the results indicate a storage deficit and/or encoding deficit for the Huntington patients.

Short report: is spatial information encoded automatically in memory?

A dual-task paradigm was used to test Hasher and Zacks’ (1979) hypothesis that spatial memory is automatic. Subjects saw two sets of 16 words each, the words being presented singly in random corners of a monitor screen. They were asked to remember the words and the corner in which each word was shown. In addition, subjects were given a concurrent task to perform. This task was either “easy” (counting aloud by ones) or “difficult” (counting aloud by sevens). Attention was focused either on the memory task or on the counting task. Word recognition was better when subjects carried out the easier competing counting task and when subjects concentrated mainly upon remembering the words and their positions. Contingent spatial memory was unaffected by either manipulation, supporting the hypothesis that spatial memory is automatic.

Amnesia can facilitate memory performance evidence from a patient with dissociated retrograde amnesia

A case is reported of a patient who experienced numerous episodes of transient global amnesia (TGA) during which anterograde amnesia was less prominent than usual, and who developed a permanent selective retrograde amnesia. On formal testing, he performed well on traditional verbal memory tests, but showed marked retrograde amnesia for verbal material, including items on a famous voices recognition test. He was administered a paired-associate learning test where the names of famous personalities for which he was amnesic were associated with incongruous activities (e.g. John Newcombe-singing). Our patient performed better on this task than a group of five matched control subjects. Our observations indicate that in the organization of human memory retrograde amnesia may be fractionated from anterograde amnesia and that in certain situations specific types of amnesia can produce a facilitation effect compared to the performance of control subjects.

Do amnesics adopt inefficient encoding strategies with faces and random shapes

Abstract These experiments compared recognition memory for pictures of faces and random shapes in a group of alcoholic amnesics and matched control subjects. Material was presented either with unguided learning instructions, or with “high”-and “low”-level orienting tasks. Recognition level was equated across groups by varying the retention interval. Measures of orienting task performance were taken and confidence with face recognition was recorded in Experiment 2. Amnesics performed all tasks similarly to controls and their recognition levels were also similarly affected. They also displayed normal confidence judgments. Results are discussed in terms of the encoding deficit and familiarity loss hypotheses.