The cholinergic neurotransmitter system in human memory and dementia: A review

The present paper reviews three types of evidence implicating the role of acetylcholine in human memory and dementia: (1) neuropathological evidence that the cholinergic transmitter system is depleted in Alzheimer-type dementia; (2) psychopharmacological studies that have employed “cholinergic blockade” as a model of cholinergic depletion; and (3) clinical studies of cholinergic “replacement” therapy in Alzheimer-type dementia. The evidence that the cholinergic system is depleted in Alzheimer-type dementia has been complemented by the finding that cholinergic blockade in healthy subjects causes a substantial learning (or “acquisition”) deficit in episodic memory. The overall results of studies of replacement therapy have generally been disappointing, but a few have reported benefits in recall and recognition tests. The role of the cholinergic system in many aspects of memory remains to be elucidated; but it seems unlikely that cholinergic depletion accounts for all aspects of the memory disorder in Alzheimer-type dementia, and possibly the depletions of other neurotransmitters also contribute to the memory impairment.     

Does it all go together when it goes? The nineteenth Bartlett memorial lecture

As groups of people age, the differences in the cognitive abilities of the most and least able become more extreme. This increase in between-individual variance is accompanied by an increase in within-individual variance: the difference between individuals' levels of performance on their best and least well retained skills. The implications of increasing between-individual variance are discussed in terms of the range of different factors that may affect cognitive ageing. Increases in within-individual variance are discussed in terms of differences betweeen “fluid” and “crystallized” abilities. The usefulness of this distinction and its functional implications are questioned. The hypothesis that age-related declines in “fluid” abilities are best modelled in terms of declines in a single factor is evaluated. Evidence is presented of disparate rates of decline, even of “fluid” cognitive abilities, such as performance on IQ tests, ability on information-processing tasks, and efficiency on memory tasks. Data from large-scale cross-sectional studies suggests that cognitive skills do not “all go together when they go”, but that there may, rather, be characteristic patterns, or syndromes, of cognitive ageing.     

Tactile short-term memory

Subjects tried to recall the location of a tactile stimulus on the underside of the forearm after delays of 0, 3, 5, 10, 15, 30, 45 and 60 sec. When “rehearsal” was prevented by requiring subjects to count backwards during the delay, accuracy of recall decreased systematically reaching an asymptote after 45 sec. When subjects were left free to “rehearse,” this did not affect the decline in accuracy over the first 10 sec. Between 10 and 15 sec. there was a significant increase in accuracy followed by a slow decline which had not reached asymptote by 60 sec. It is suggested that tactile STM (short-term memory) depends on two processes, a fading sensory trace which is unaffected by distraction and a less labile system which does not appear to be verbal but which depends on “rehearsal.”     

Remembering, Familiarity, and Source Monitoring

Two experiments investigated recollective experience in a source monitoring task. Subjects saw an array of objects and performed, watched, or imagined actions involving pairs of objects. In a subsequent recognition test, subjects indicated whether their recognition judgements were made on the basis of conscious recollective experience (“remember” responses), or on some other basis such as familiarity (“know” responses). The proportions of correct “remember” responses for both objects and actions decreased from performed, through watched, to imagined actions, whereas the proportions of correct “know” responses were uninfluenced by the source of the memories. In addition, the relationship between recollective experience and accuracy of source judgement varied across sources. Source accuracy for performed actions was obtained only in “remember” responses, whereas source accuracy for imagined actions was obtained only in “know” responses. Source accuracy for watched actions was obtained in both “remember” and “know” responses. The findings suggest that the types of memory attributes available at retrieval determine the quality of subsequent memory experience, and it is proposed that memories with strongly self-referential attributes (arising from performed actions) powerfully cue recollective experience during retrieval.     

Short-term memory for repeated and non-repeated items

Digit sequences containing repeated items are retained differently in short-term memory from sequences containing no repeated items. The repeated items are remembered better or worse than items in the corresponding positions of “all-different” sequences depending on the number of times the item is repeated, the number of items repeated, the number of items intervening between the occurences of a repeated item, and the position of the repeated items in relation to the beginning and end of the sequence. In every type of repetition studied, except one, memory for the non-repeated items in sequences with repeated items is better than for the corresponding items of all-different sequences. This is true in some cases despite significant specific interference between the (non-repeated) items following the separated occurrences of repeated items. The negative effects in memory for repeated items and the positive effects in memory for non-repeated items are greater when the items are presented at the rate of five per sec. than at one per sec., contrary to the hypothesis that differential rehearsal is responsible for these effects. The results are interpreted as supporting an “associative,” as opposed to a “non-associative,” theory of short-term memory, as this distinction is defined in the paper.     

Some evidence for parallel comparisons in a letter recognition task

Subjects were asked to judge successively presented letter trigrams “same” or “different.” The different stimuli were divided into four groups; not confusable (NC), acoustically confusable (AC), visually confusable (VC), and both visually and acoustically confusable (VC & AC). Reaction times (RT) were lengthened only by the double confusability. It is argued that comparisons are normally made in both channels, so that confusability in a single channel has no effect since the alternative channel is unimpaired. RTs are only increased when both channels are slowed down. A further experiment confirms this interpretation. When the situation is manipulated so that only the visual channel is employed, the VC group shows the same increase as the VC & AC group.     

The effect of an irrelevant dimension on “same-different” judgements of multi-dimensional stimuli

Subjects made “same”-“different” judgements of simultaneously presented pairs of visual stimuli which could vary either in shape and colour independently, or in shape alone. In both conditions only shape was relevant to the “same”-“different” judgement. In the former condition “same” and “different” reaction times (RTs) were shorter when the states (“same” or “different”) of the relevant and the irrelevant dimension, colour, were the same. This result is interpreted as support for either a perceptual or a response interference hypothesis. The presence of an irrelevant dimension did not appear to affect differentially “same” and “different” judgements. The need for a re-evaluation of the results from other studies of multi-dimensional stimulus discrimination is discussed.     

Memory of a speaker's voice: Reaction time to same- or different-voiced letters

Subjects were presented with a sequence of two letters, each letter spoken in either a male or female voice. On each trial, the subject was required to indicate, as quickly as possible, whether the two letters had the same name. Reaction times (RTs) were faster for letters spoken in the same voice for both “same” and “different” responses, even when letters were separated by 8 s. These results are incompatible with the notion of physical and name codes in auditory memory since a “different” response should always be based on a comparison of letter names and should not be influenced by voice quality. It was also found that RTs were not influenced by the phonemic distinctive feature similarity of the letters.     

The perceptual-mnemonic/feature conjunction model of perirhinal cortex function

The perirhinal cortex was once thought to be “silent cortex”, virtually ignored by researchers interested in the neurobiology of learning and memory. Following studies of brain damage associated with cases of amnesia, perirhinal cortex is now widely regarded as part of a “medial temporal lobe (MTL) memory system”. This system is thought to be more or less functionally homogeneous, having a special role in declarative memory, and making little or no contribution to other functions such as perception. In the present article, we summarize an alternative view. First, we propose that components of the putative MTL system such as the hippocampus and perirhinal cortex have distinct and dissociable functions. Second, we provide evidence that the perirhinal cortex has a role in visual discrimination. In addition, we propose a specific role for perirhinal cortex in visual discrimination: the contribution of complex conjunctive representations to the solution of visual discrimination problems with a high degree of “feature ambiguity”. These proposals constitute a new view of perirhinal cortex function, one that does not assume strict modularity of function in the occipito-temporal visual stream, but replaces this idea with the notion of a hierarchical representational continuum.     

Acoustic similarity and interference in short-term recognition memory: Some results of a decision-theory analysis

The following three studies of single-probe recognition memory set out to show the effect on the signal-detectability measures of d' and β (Tanner and Swets, 1954) of variations in the acoustic similarity of interfering material, which may either precede or follow the item to be remembered (proactive or retroactive interference --PI or RI). The first experiment studies a situation employed by Wickelgren (1966a), who reported that acoustically similar RI substantially reduced d'. It is shown that this effect could have been due to biases in Wickelgren's original designs, and that when a bias-free design is used, the fall in d' is only of borderline significance.

To investigate this problem further, a design was evolved in which two items were presented for memorizing, which varied in acoustic similarity to each other, and (after a distracting task) a probe was presented with one of three questions: Was this the first item of the pair? Was it the second? or, Did it occur in either position? In the first case, recognition-memory with RI of varying acoustic similarity was being studied, and as in the first experiment, it was found that similarity slightly reduced d'. With the second question, PI effects were being studied, and here negligible differences were found. With the third type of question, a “location-free” test, no effects of similarity were found. The last result rules out Posner's (1967) “acid-bath” explanation of similarity effects in interference: an explanation in terms of “differentiation” (or “filtering”) was also invalidated by the results of a third experiment, in which the same effects were found even though similarity varied only between stimulus items and interference, and not between these and the probe. Wickelgren's (1966b) associative model appears to have least difficulty in accommodating these results, though even this needs certain ad hoc assumptions to be able to do so.     

Stimulus timing by people with Parkinson's disease

Previous literature suggests that Parkinson’s disease is marked by deficits in timed behaviour. However, the majority of studies of central timing mechanisms in patients with Parkinson’s disease have used timing tasks with a motor component. Since the motor abnormalities are a defining feature of the condition, the status of timing in Parkinson’s disease remains uncertain. Data are reported from patients with mild to moderate Parkinson’s disease (both on and off medication) and age- and IQ-matched controls on a range of stimulus timing tasks without counting. Tasks used were temporal generalization, bisection, threshold determination, verbal estimation, and a memory for duration task. Performance of patients was generally “normal” on all tasks, but significant differences from performance of controls were found on the memory for duration task. Among the “normal” effects noted were arithmetic mean bisection, asymmetric temporal generalization gradients, and subjective shortening on the memory for duration task. The results suggest (a) that some previous reports of timing “deficits” in Parkinson’s patients were possibly due to the use of tasks requiring a timed manual response and (b) small differences between patients and controls may be found on tasks where two stimuli are presented on each trial, whether patients are on medication or off it.     

An improved technique for monitoring fixation in tachistoscopic tasks

A monocular lens mounted behind a stimulus screen was used to monitor fixation in a tachistoscopic recognition task. This technique was found superior to the often used “sideview technique” and as accurate as the method involving identification of a fixation stimulus. It was found that the “telescope technique” is preferable in those studies where presentation of a fixation stimulus might interfere with recognition or report of the experimental stimulus.     

Assumptions underlying psychological testing

Tests purporting to reflect the learning aptitudes of school children differ much more than generally is recognized. However, error in assesing such learning aptitude inheres much more in the users of the tests than in the tests themselves. Assumptions fundamental to such assessment, or even testing, are considered. It is particularly important that the assessor, or tester, constantly be sensitive to the nature of the relationship between the psychological demands of test items or tests and the learning demands confronting the child. Even tests that generally are grossly or crudely used often can yield psychoeducationally meaninful information if their results are differentially perceived in terms of the light they throw on the psychological operations fundamental to learning, “process,” as contrasted with that thrown on the results of the functioning of such operations, “product.”     

Contextual assimilation and its effect on the division of attention between nonverbal signals

Subjects performed a recognition task in which a low or a high frequency signal was presented simultaneously with a dim or a bright intensity one. The independent variable was the degree of association between the signals on the two dimensions. Unknown to the subjects four levels were tested in separate conditions, 1.0, 0.8, 0.5 and 0.2. Increasing the positive association improved overall sensitivity as measured by d' on both dimensions, but left contingent sensitivity unchanged. Changing the association did not affect overall bias, as measured by Beta. However, holding context constant by analysis produced significant differences between individual measures of contingent bias in the direction of assimilation, for example “low” responses tended to accompany dim signals and “dim” responses. The differences were unaffected by the changes in association. The results are interpreted as favouring models of contextual assimilation which assume that biasing at some level of processing depends upon the mutually contingent interaction of discrete events rather than on memory and expectation of the relative frequency of conjoint events. Further support for this conclusion comes from previous studies which indicate that assimilation occurs with separate responses but not with unitary ones. The implications of the findings for research on the division of attention are discussed, particularly the need to control variability in measured bias to establish a true change in the allocation of attention. Two generalized models of contextual assimilation are proposed, one based on “object” and the other on “lexical” assimilation. The possible application of these models to synaesthesia is considered.     

Memory for emotionally provocative words in alexithymia: A role for stimulus relevance

Alexithymia is associated with emotion processing deficits, particularly for negative emotional information. However, also common are a high prevalence of somatic symptoms and the perception of somatic sensations as distressing. Although little research has yet been conducted on memory in alexithymia, we hypothesized a paradoxical effect of alexithymia on memory. Specifically, recall of negative emotional words was expected to be reduced in alexithymia, while memory for illness words was expected to be enhanced in alexithymia.Eighty-five high or low alexithymia participants viewed and rated arousing illness-related (“pain”), emotionally positive (“thrill”), negative (“hatred”), and neutral words (“horse”). Recall was assessed 45 min later.High alexithymia participants recalled significantly fewer negative emotion words but also more illness-related words than low alexithymia participants. The results suggest that personal relevance can shape cognitive processing of stimuli, even to enhance retention of a subclass of stimuli whose retention is generally impaired in alexithymia.     

Nonstutterers'' perceptions of stuttering and speech difficulty

Two versions of Woolf's (1967) Perception of Stuttering Inventory (PSI) were administered to nonstuttering college students in three experiments. In one (Woolf's published version) the word “stuttering” appeared and in another [a version developed by Daly, Oakes, Breen, and Mishler (1981)] “stuttering” was replaced by “speech difficulty.” Nonstutterers' scores on the PSI were found to be affected by knowledge of—or attention to—“stuttering” or “stutterers” as well as orientation toward speech or speech pathology. It was concluded that a total PSI score of 5 is presently a more defensible criterion of normality for stutterers than the more commonly used score of 10.     

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.     

Driye-leyel and flexibility in paired-associate nonsense-syllable learning

“High-anxiety” and “low-anxiety” subjects, selected for extreme scores on the Taylor Anxiety Scale, learned a list of paired-associate nonsense syllables in the belief that they were undergoing an intelligence test. Both groups were then given a second list of paired associates to learn, the stimulus-items being the same as those of the first list but the responses being changed. Before the presentation of the second list, half the subjects in each group were given anxiety-increasing instructions and the remaining half were given reassuring instructions.

The results verified two predictions made from Hull's behaviour theory, using the concept of fear or anxiety as a secondary drive:—“high anxiety” subjects took more trials to master the second learning task than “low-anxiety” subjects; and there was a significant interaction between initial anxiety-level and type of instructions, such that “high-anxiety” subjects who received drive-increasing instructions had a worse performance in the second part than all other sub-groups. There was no indication that “low-anxiety” subjects were significantly affected by the type of instructions received. The “high-anxiety” group had greater difficulty than the “low-anxiety” group in learning the first list, but the difference was non-significant.