Heavy schistosomiasis associated with poor short-term memory and slower reaction times in Tanzanian schoolchildren.

Cross-sectional studies of the relationship between helminth infection and cognitive function can be informative in ways that treatment studies cannot. However, interpretation of results of many previous studies has been complicated by the failure to control for many potentially confounding variables. We gave Tanzanian schoolchildren aged 9-14 a battery of 11 cognitive and three educational tests and assessed their level of helminth infection. We also took measurements of an extensive range of potentially confounding or mediating factors such as socioeconomic and educational factors, anthropometric and other biomedical measures. A total of 272 children were moderately or heavily infected with Schistosoma haematobium, hookworm or both helminth species and 117 were uninfected with either species. Multiple regression analyses, controlling for all confounding and mediating variables, revealed that children with a heavy S. haematobium infection had significantly lower scores than uninfected children on two tests of verbal short-term memory and two reaction time tasks. In one of these tests the effect was greatest for children with poor nutritional status. There was no association between infection and educational achievement, nor between moderate infection with either species of helminth and performance on the cognitive tests. We conclude that children with heavy worm burdens and poor nutritional status are most likely to suffer cognitive impairment, and the domains of verbal short-term memory and speed of information processing are those most likely to be affected.

Short-term memory in Down syndrome: applying the working memory model.

This paper is divided into three sections. The first reviews the evidence for a verbal short-term memory deficit in Down syndrome. Existing research suggests that short-term memory for verbal information tends to be impaired in Down syndrome, in contrast to short-term memory for visual and spatial material. In addition, problems of hearing or speech do not appear to be a major cause of difficulties on tests of verbal short-term memory. This suggests that Down syndrome is associated with a specific memory problem, which we link to a potential deficit in the functioning of the 'phonological loop' of Baddeley's (1986) model of working memory. The second section considers the implications of a phonological loop problem. Because a reasonable amount is known about the normal functioning of the phonological loop, and of its role in language acquisition in typical development, we can make firm predictions as to the likely nature of the short-term memory problem in Down syndrome, and its consequences for language learning. However, we note that the existing evidence from studies with individuals with Down syndrome does not fit well with these predictions. This leads to the third section of the paper, in which we consider key questions to be addressed in future research. We suggest that there are two questions to be answered, which follow directly from the contradictory results outlined in the previous section. These are 'What is the precise nature of the verbal short-term memory deficit in Down syndrome', and 'What are the consequences of this deficit for learning'. We discuss ways in which these questions might be addressed in future work.

A longitudinal assessment of diverging verbal and non-verbal abilities in the Williams syndrome phenotype.

Jarrold et al. (1998) presented evidence to suggest that verbal and non-verbal abilities develop at different rates in individuals with the Williams syndrome phenotype. However, this evidence was derived from cross-sectional rather than longitudinal data. The current report presents data from a series of follow up assessments which examine the development of vocabulary and pattern construction abilities in 15 of the original sample of 16 individuals, over a 40 month period. The results confirm the original predictions, as mental age equivalent scores for vocabulary increase more rapidly than scores for the pattern construction test; a finding, which appears unlikely to be due to practice effects.

Attentional control in Alzheimer's disease.

Attentional control of executive function declines during the early stages of Alzheimer's disease. Controversy exists as to whether this decline results from a single global deficit or whether attentional control can be fractionated, with some aspects being more vulnerable than others. We investigated three proposed domains of attention, namely (i) focal attention, based on simple and choice reaction times; (ii) the capacity to resist distraction in a visual search task; and (iii) the capacity to divide attention between two simultaneous tasks. For each domain, two levels of difficulty were used to study Alzheimer's disease patients, who were compared with elderly and young control subjects. The unitary attentional hypothesis predicted that the impacts of level of difficulty, age and disease would be qualitatively similar across the three attentional domains. In fact we observed different patterns for each domain. We obtained no differential impairment for patients in the focal attentional task, whereas patients were somewhat more susceptible than control subjects to the similarity of the distractor items in visual search. Finally, we observed marked impairment in the capacity of Alzheimer's disease patients to combine performance on two simultaneous tasks, in contrast to preserved dual-task performance in the normal elderly group. These results suggest a need to fractionate executive processes, and reinforce earlier evidence for a specific dual-task processing deficit in Alzheimer's disease.

Is working memory still working?

The current state of A. D. Baddeley and G. J. Hitch's (1974) multicomponent working memory model is reviewed. The phonological and visuospatial subsystems have been extensively investigated, leading both to challenges over interpretation of individual phenomena and to more detailed attempts to model the processes underlying the subsystems. Analysis of the controlling central executive has proved more challenging, leading to a proposed clarification in which the executive is assumed to be a limited capacity attentional system, aided by a newly postulated fourth system, the episodic buffer. Current interest focuses most strongly on the link between working memory and long-term memory and on the processes allowing the integration of information from the component subsystems. The model has proved valuable in accounting for data from a wide range of participant groups under a rich array of task conditions. Working memory does still appear to be working.

The phonological loop and the irrelevant speech effect: some comments on Neath (2000).

Neath (2000) presents a useful overview of the evidence to be explained by any model of the effects of irrelevant speech on immediate serial memory and proposes a model accompanied by computational simulation. While his review is in general accurate, it is limited in its explanation of the crucial characteristics of the disrupting sounds. It also neglects strategic issues, particularly the tendency for subjects to switch strategy as list length increases. As a result, his model fails to account for the absence of an interaction between irrelevant speech and acoustic similarity for lists of span length. Points of issue between Neath's feature hypothesis and the phonological loop interpretation are outlined, and the contribution of his computational simulation is discussed.

Development of working memory: should the Pascual-Leone and the Baddeley and Hitch models be merged?

The data presented by Kemps, De Rammelaere, and Desmet (2000, this issue) appear to have some aspects that fit most readily into our own model (Baddeley & Hitch, 1974), while others appear to support that of Pascual-Leone (1970). We accept that our initial model said little about development and was better able to account for relatively simple memory-based tasks than more complex cognitive activities. More recent elaborations of the model are, however, able to throw new light on the processes underlying cognitive development, offering a better account than that provided by existing neo-Piagetian interpretations. Meanwhile, the addition of a fourth component to the model, namely the episodic buffer, offers a way of dealing with more complex cognitive activities. Given the major differences between our own model and that of Pascual-Leone in basic assumptions, and in theoretical style, we suggest that any attempt to combine the two would be premature.

Visual similarity effects in immediate verbal serial recall.

The role of visual working memory in temporary serial retention of verbal information was examined in four experiments on immediate serial recall of words that varied in visual similarity and letters that varied in the visual consistency between upper and lower case. Experiments 1 and 2 involved words that were either visually similar (e.g. fly, cry, dry; hew, new, few) or were visually distinct (e.g. guy, sigh, lie; who, blue, ewe). Experiments 3 and 4 involved serial recall of both letter and case from sequences of letters chosen such that the upper- and lower-case versions were visually similar, for example Kk, Cc, Zz, Ww, or were visually dissimilar, for example Dd, Hh, Rr, Qq. Hence in the latter set, case information was encoded in terms of both the shape and the size of the letters. With both words and letters, the visually similar items resulted in poorer recall both with and without concurrent articulatory suppression. This visual similarity effect was robust and was replicated across the four experiments. The effect was not restricted to any particular serial position and was particularly salient in the recall of letter case. These data suggest the presence of a visual code for retention of visually presented verbal sequences in addition to a phonological code, and they are consistent with the use of a visual temporary memory, or visual "cache", in verbal serial recall tasks.

Improvement or simply practice? The effects of twenty repeated assessments on people with and without brain injury.

Measuring recovery of function may mean testing the same individual many times, a procedure that is inevitably open to improvement due to learning on the specific tests rather than recovery per se. This is particularly likely to be an issue with measures of memory performance. We therefore studied the performance of normal and brain-injured people across 20 successive test sessions on measures of orientation, simple reaction time, forward and backward digit span, visual and verbal recognition, word list learning and forgetting, and on three semantic memory measures, namely, letter and category fluency and speed of semantic processing. Differences in overall performances between the two groups occurred for all tests other than orientation, digit span forward, and simple reaction time, although the tests differed in their degree of sensitivity. The tests varied in the presence or absence of practice effects and in the extent to which these differed between the two groups. Data are presented that should allow investigators to select measures that are likely to optimize sensitivity while minimizing possible confounding due to practice effects.

Verbal short-term memory deficits in Down syndrome: a consequence of problems in rehearsal?

Individuals with Down syndrome suffer from relatively poor verbal short-term memory. Previous explanations of this deficit have been framed in terms of inefficient or absent rehearsal of verbal material in Down syndrome within the phonological loop component of Baddeley and Hitch's (1974) working memory model. Two experiments are presented which test this explanation by looking for the markers of rehearsal in children with Down syndrome and verbal mental age matched controls. Both experiments confirm that individuals with Down syndrome show poorer verbal short-term memory performance than controls. However, they rule out rehearsal as an explanation of these deficits because the evidence suggests that neither individuals with Down syndrome nor matched controls are engaging in spontaneous subvocal rehearsal. Other explanations of poor verbal short-term memory performance in Down syndrome, in terms of impairments both within and outside of the phonological loop system, are discussed. Practical implications for intervention strategies aimed at improving verbal short-term memory skills in Down syndrome are also outlined.

Working memory and the vividness of imagery.

The working memory framework was used to investigate the factors determining the phenomenological vividness of images. Participants rated the vividness of visual or auditory images under control conditions or while performing tasks that differentially disrupted the visuospatial sketchpad and phonological loop subsystems of working memory. In Experiments 1, 2, and 6, participants imaged recently presented novel visual patterns and sequences of tones; ratings of vividness showed the predicted interaction between stimulus modality and concurrent task. The images in experiments 3, 4, 5, and 6 were based on long-term memory (LTM). They also showed an image modality by task interaction, with a clear effect of LTM variables (meaningfulness, activity, bizarreness, and stimulus familiarity), implicating both working memory and LTM in the experience of vividness.

Do two separate speech measures constrain verbal short-term memory in children?

Previous research has indicated that 2 processing rates may constrain verbal short-term memory performance. These have been linked to individual differences in (a) the time taken to articulate spoken words and (b) the duration of pauses that occur between words in the output responses to memory tasks. Two experiments examined whether evidence for these effects on memory can be obtained for measures taken from a single speech sample. Children articulated pairs of words as rapidly as possible. In both experiments, the spoken duration of words and the length of the pauses between them predicted significant variance in verbal short-term memory performance. It is argued that the duration of words is linked to memory performance through the processes underlying time-based forgetting in short-term memory. In contrast, the duration of pauses in speeded articulation may index individual differences in speech planning processes.

Measuring recovery from post traumatic amnesia.

Three groups of participants were assessed. Each participant was tested on 20 occasions. The groups comprised people (i) in post traumatic amnesia (PTA) following severe head injury (n=9), (it) with severe head injury but not in PTA (n=10), and (iii) with no history of head injury or other neurological condition (n=13). Subjects were given several tests of memory, attention and learning in order to determine which tests were good at (a) distinguishing people in PTA from those not in PTA, and (b) monitoring recovery over time. The results indicate that people in PTA have a wide range of deficits and their cognitive recovery is a gradual process rather than an all-or-none phenomenon. In terms of measurement, the study suggests that a good test of PTA should include orientation questions, together with a reaction time measure, a visual recognition test and a speed of information processing measure. Most of the tests administered were good at distinguishing between brain-injured and nonbrain-injured people, although only two tests distinguished between the two brain-injured groups, i.e. those in PTA and those out of PTA. Almost all tests were good at monitoring recovery from PTA.

Genetically dissociated components of working memory: evidence from Down's and Williams syndrome.

Wang and Bellugi [J clin exp Neuropsychol 1994;16:317 22] have suggested that Down's and Williams syndrome might be associated with specific and contrasting working memory deficits; with impaired verbal short-term memory in Down's syndrome, and a visuo-spatial short-term memory deficit in Williams syndrome. In two studies we examine whether these apparent deficits might simply be a consequence of the general pattern of learning difficulties associated with these disorders. Experiment 1 compared verbal and visuo-spatial short-term memory abilities in these groups, using analysis of covariance to control for mental age differences. In Experiment 2 individuals with Williams syndrome were matched to control groups for non-verbal mental age, and the short-term memory abilities of these matched groups were compared. The results of both experiments are broadly consistent with those reported by Wang and Bellugi, and support the view that working memory can be dissociated into separate subsystems.

Down syndrome and the phonological loop: the evidence for, and importance of, a specific verbal short-term memory deficit.

Individuals with Down syndrome are thought to perform poorly on tests of verbal short-term memory, such as measures of word span or digit span. This review critically examines the evidence for a specific deficit in verbal short-term memory in Down syndrome, and outlines a range of possible explanations for such a deficit. The potential implications of a verbal short-term memory impairment for broader aspects of development are outlined, in particular with respect to vocabulary development. Possible intervention strategies, which might improve verbal short-term memory performance in Down syndrome are also considered. However, we argue that further research is needed to fully clarify the nature of a verbal short-term memory deficit in Down syndrome, before the merits of these various intervention approaches can be properly evaluated.

Verbal and nonverbal abilities in the Williams syndrome phenotype: evidence for diverging developmental trajectories.

One commonly cited feature of Williams syndrome is a characteristic dissociation between relatively spared language skills and severely impaired nonverbal abilities. However, the actual evidence for a dissociation between verbal and nonverbal abilities in Williams syndrome is equivocal. In two separate studies we examined these abilities in 16 individuals showing the Williams syndrome phenotype. When considered as a whole, the group did have significantly superior verbal abilities, but this difference was caused by a large discrepancy in abilities in only a small number of individuals. In both studies there was a clear, linear relation between individuals' verbal ability, and the magnitude of their verbal-nonverbal discrepancy. We suggest that these results are best explained in terms of verbal ability developing at a faster rate than nonverbal ability in this disorder. We discuss how this model of differential rates of development has the potential to reconcile the apparently inconsistent findings in this area.

Short-term Memory for Verbal and Visuospatial Information in Down's Syndrome.

Short-term memory for verbal and visuospatial information was examined in a group of children and teenagers with Down's syndrome. Performance on the verbal task was impaired relative to matched control groups, but there were no group differences on the visuospatial task. Relatedly, the Down's syndrome group showed inferior short-term memory for verbal as opposed to visuospatial information, whereas controls showed the opposite pattern. These findings did not appear to result from a general superiority of nonverbal abilities in the Down's syndrome group, or from hearing difficulties that might have impacted on the verbal short-term memory task, in which material was presented auditorily. The results are consistent with the suggestion that Down's syndrome is associated with a selective impairment of the phonological loop component of Baddeley and Hitch's (1974) working memory model.

Editorial cognition, neurology, psychiatry: golden triangle or bermuda triangle?

Cognitive neuropsychiatry occupies the comparatively neglected research region that lies between neurology, psychiatry, and cognitive psychology. Reasons for this neglect are discussed, together with arguments as to why it may be timely to focus on this intellectual no man's land.

Analysis of the episodic memory deficit in early Alzheimer's disease: evidence from the doors and people test.

Anterograde episodic memory was assessed in a cohort of 33 patients with early dementia of Alzheimer type (DAT) and 30 matched controls using immediate and delayed prose recall, the CERAD word learning test and the recently developed doors and people test of visual and verbal recall and recognition. DAT patients showed markedly impaired learning on all three measures, with little evidence of cumulation of information across trials. Patients showed more forgetting than controls on prose recall and the CERAD word list, but more detailed analysis suggested that this differential loss was attributable to the contribution of primary memory to immediate but not delayed recall. No differences in forgetting rate were observed on the doors and people test. Scaled scores were used to derive a recall-recognition index, together with a measure of material-specific memory based on the ratio of verbal to visual memory deficits. There was no evidence for differential sensitivity of recall over recognition, implying that the episodic memory deficit is one of learning, rather than of the retrieval of learned material. Although individuals varied in the relative degree of impairment of verbal and visual memory, there was no general tendency for material-specificity. It was concluded that the episodic memory deficit in DAT is general in nature and primarily reflects impaired learning rather than accelerated forgetting or disrupted retrieval.