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PubMed1996

PET evidence for an amodal verbal working memory system.

Current models of verbal working memory assume that modality-specific representations are translated into phonological representations before entering the working memory system. We report an experiment that tests this assumption. Positron emission tomography measures were taken while subjects performed a verbal working memory task. Stimuli were presented either visually or aurally, and a visual or auditory search tasks, respectively, was used as a control. Results revealed an almost complete overlap between the active memory areas regardless of input modality. These areas included dorsolateral frontal, Broca's area, SMA, and premotor cortex in the left hemisphere; bilateral superior and posterior parietal cortices and anterior cingulate; and right cerebellum. These results correspond well with previous research and suggest that verbal working memory is modality independent and is mediated by a circuit involving frontal, parietal, and cerebellar mechanisms.

Adult↗
PubMed1998

The visuospatial sketchpad for mental images: testing the multicomponent model of working memory.

In the model of Baddeley (Working Memory, Oxford University Press, Oxford, 1986), one function of the visuospatial sketchpad (VSSP) component of working memory is to allow the processing of mental images. Properties of the VSSP were investigated by means of the usual dual-task paradigm (to search for interference from the other components of working memory, i.e., the articulatory loop and the central executive), applied to three distinct subprocesses of mental imagery (Kosslyn, 1994 Image and Brain. MIT Press, Cambridge, MA): image generation (Experiment 1), image maintenance (Experiment 2), and image rotation (Experiment 3). First, in the control condition (no interference task) of each experiment, we replicated the effects of stimulus or task complexity already reported. Second, no interference from the articulatory loop was observed. Third, maintenance of images appeared free from any interference. And fourth, generation and rotation tasks were interfered to a greater extent by the central executive than by the involvement of the VSSP in a secondary task. These observations (a) support the dissociation between the articulatory loop and the VSSP, (b) suggest an important use of central attentional resources in the generation and rotation of mental images, (c) would support the distinction between visual and spatial components in the structure of working memory, and (d) suggest the dissociation of the VSSP into two subcomponents: a passive visuospatial store and an active device for recapitulating visuospatial information.

Adolescent↗
PubMed1999

Verbal working memory and sentence comprehension.

This target article discusses the verbal working memory system used in sentence comprehension. We review the concept of working memory as a short-duration system in which small amounts of information are simultaneously stored and manipulated in the service of accomplishing a task. We summarize the argument that syntactic processing in sentence comprehension requires such a storage and computational system. We then ask whether the working memory system used in syntactic processing is the same as that used in verbally mediated tasks that involve conscious controlled processing. Evidence is brought to bear from various sources: the relationship between individual differences in working memory and individual differences in the efficiency of syntactic processing; the effect of concurrent verbal memory load on syntactic processing; and syntactic processing in patients with poor short-term memory, patients with poor working memory, and patients with aphasia. Experimental results from these normal subjects and patients with various brain lesions converge on the conclusion that there is a specialization in the verbal working memory system for assigning the syntactic structure of a sentence and using that structure in determining sentence meaning that is separate from the working memory system underlying the use of sentence meaning to accomplish other functions. We present a theory of the divisions of the verbal working memory system and suggestions regarding its neural basis.

Cognition↗
PubMed2001

Working memory in schizophrenia: transient "online" storage versus executive functioning.

Working memory has been described as the temporary "online" storage and the subsequent manipulation and retrieval of information. It has been suggested that the prefrontal cortex is a primary site of working memory. Schizophrenia patients, who are thought to have prefrontal cortical dysfunction, have demonstrated inconsistent deficits on a variety of verbal and spatial working memory tests. This has led to questions about how to define and measure working memory, whether these deficits are distinct to one cognitive domain, and what role factors such as intelligence and symptoms play in working memory performance. We compared schizophrenia patients to normal comparison subjects in four separate studies. Based upon the results we recommend that working memory tests be characterized as either transient "online" storage and retrieval tasks (where short-term storage and retrieval of information is required) or executive-functioning working memory tasks (where storage, manipulation, and retrieval of information is required). The importance of clearly identifying which distinct aspects of working memory are assessed is discussed.

Adolescent↗
PubMed1994

Effect of AIT-082, a purine analog, on working memory in normal and aged mice.

Because working memory is the primary type of memory which is disrupted by Alzheimer's disease and stroke and during aging, any therapeutic drug for these conditions should improve and/or restore working memory. The win-shift memory paradigm has been shown to be an excellent model of working memory. In the present study, we examined the effects of a novel purine derivative, 4-[[3-(1,6-dihydro-6-oxo-9-purin-9-yl)-1- oxopropyl]amino]benzoic acid (AIT-082) and physostigmine (PHY) on working memory. Both AIT-082 and PHY improved memory in young mice and restored memory in mice with mild age-induced memory deficits; however only AID-082 was also effective in subjects with moderate deficits. Neither drug improved memory in mice with severe memory deficits. AIT-082 exhibited effectiveness over a broad dose range (0.5-60 mg/kg), and the effects lasted for seven days after a single high-dose drug administration. AIT-082 was devoid of any effects on performance variables and has not shown any toxic side effects, thus making it an interesting potential treatment for working memory deficits associated with aging, strokes, and Alzheimer's disease.

Aging↗
PubMed2003

How conscious experience and working memory interact.

Active components of classical working memory are conscious, but traditional theory does not account for this fact. Global Workspace theory suggests that consciousness is needed to recruit unconscious specialized networks that carry out detailed working memory functions. The IDA model provides a fine-grained analysis of this process, specifically of two classical working-memory tasks, verbal rehearsal and the utilization of a visual image. In the process, new light is shed on the interactions between conscious and unconscious aspects of working memory.

Journal Article↗
PubMed2005

Interactions between attention and working memory.

Studies of attention and working memory address the fundamental limits in our ability to encode and maintain behaviorally relevant information, processes that are critical for goal-driven processing. Here we review our current understanding of the interactions between these processes, with a focus on how each construct encompasses a variety of dissociable phenomena. Attention facilitates target processing during both perceptual and postperceptual stages of processing, and functionally dissociated processes have been implicated in the maintenance of different kinds of information in working memory. Thus, although it is clear that these processes are closely intertwined, the nature of these interactions depends upon the specific variety of attention or working memory that is considered.

Attention↗
PubMed1999

Working memory, short-term memory, and general fluid intelligence: a latent-variable approach.

A study was conducted in which 133 participants performed 11 memory tasks (some thought to reflect working memory and some thought to reflect short-term memory), 2 tests of general fluid intelligence, and the Verbal and Quantitative Scholastic Aptitude Tests. Structural equation modeling suggested that short-term and working memories reflect separate but highly related constructs and that many of the tasks used in the literature as working memory tasks reflect a common construct. Working memory shows a strong connection to fluid intelligence, but short-term memory does not. A theory of working memory capacity and general fluid intelligence is proposed: The authors argue that working memory capacity and fluid intelligence reflect the ability to keep a representation active, particularly in the face of interference and distraction. The authors also discuss the relationship of this capability to controlled attention, and the functions of the prefrontal cortex.

Adult↗
PubMedDate not supplied

Working memory and language: an overview.

Working memory involves the temporary storage and manipulation of information that is assumed to be necessary for a wide range of complex cognitive activities. In 1974, Baddeley and Hitch proposed that it could be divided into three subsystems, one concerned with verbal and acoustic information, the phonological loop, a second, the visuospatial sketchpad providing its visual equivalent, while both are dependent upon a third attentionally-limited control system, the central executive. A fourth subsystem, the episodic buffer, has recently been proposed. These are described in turn, with particular reference to implications for both the normal processing of language, and its potential disorders. The reader will be introduced to the concept of a multi-component working memory. Particular emphasis will be placed on the phonological loop component, and (a) its fractionation into a storage and processing component, (b) the neuropsychological evidence for this distinction, and (c) its implication for both native and second language learning. This will be followed by (d) a brief overview of the visuospatial sketchpad and its possible role in language, culminating in (e) discussion of the higher-level control functions of working memory which include (f) the central executive and its multi-dimensional storage system, the episodic buffer. An attempt throughout is made to link the model to its role in both normal and disordered language functions.

Acoustics↗
PubMed2000

Interactions between visual working memory and selective attention.

The relationship between working memory and selective attention has traditionally been discussed as operating in one direction: Attention filters incoming information, allowing only relevant information into short-term processing stores. This study tested the prediction that the contents of visual working memory also influence the guidance of selective attention. Participants held a sample object in working memory on each trial. Two objects, one matching the sample and the other novel, were then presented simultaneously. As measured by a probe task, attention shifted to the object matching the sample. This effect generalized across object type, attentional-probe task, and working memory task. In contrast, a matched task with no memory requirement showed the opposite pattern, demonstrating that this effect is not simply due to exposure to the sample. These results confirm a specific prediction about the influence of working memory contents on the guidance of attention.

Adult↗
PubMed2002

Dissociation of working memory processing associated with native and second languages: PET investigation.

Verbal working memory plays a significant role in language comprehension and problem-solving. The prefrontal cortex has been suggested as a critical area in working memory. Given that domain-specific dissociations of working memory may exist within the prefrontal cortex, it is possible that there may also be further functional divisions within the verbal working memory processing. While differences in the areas of the brain engaged in native and second languages have been demonstrated, little is known about the dissociation of verbal working memory associated with native and second languages. We have used H2(15)O positron emission tomography in 14 normal subjects in order to identify the neural correlates selectively involved in working memory of native (Korean) and second (English) languages. All subjects were highly proficient in the native language but poorly proficient in the second language. Cognitive tasks were a two-back task for three kinds of visually presented objects: simple pictures, English words, and Korean words. The anterior portion of the right dorsolateral prefrontal cortex and the left superior temporal gyrus were activated in working memory for the native language, whereas the posterior portion of the right dorsolateral prefrontal cortex and the left inferior temporal gyrus were activated in working memory for the second language. The results suggest that the right dorsolateral prefrontal cortex and left temporal lobe may be organized into two discrete, language-related functional systems. Internal phonological processing seems to play a predominant role in working memory processing for the native language with a high proficiency, whereas visual higher order control does so for the second language with a low proficiency.

Adult↗
PubMed2001

Auditory working memory in HIV-1 infection.

We evaluated auditory working memory in 41 HIV-seropositive (HIV+) and 37 HIV-seronegative (HIV-) male drug users, employing a modified version of the Letter-Number Span Task developed by Gold and colleagues. We added a control condition to the standard task in order to evaluate more directly the contribution of the processing component to the working memory deficits with the effects of storage demands minimized. HIV+ subjects performed significantly more poorly compared to controls on an index of working memory processing derived from raw scores obtained under the two testing conditions. These findings are consistent with our previous reports that HIV-related working memory deficits are evident across multiple informational domains; further, the deficit appears to involve multiple-component functions of working memory. Converging findings from recent working memory studies and from primate and neuroimaging investigations suggest that functional abnormalities of prefrontal cortex should receive greater emphasis in models of neurocognitive aspects of HIV-1 infection, which have typically emphasized "subcortical" deficits.

AIDS Dementia Complex↗
PubMed2003

Oculomotor control and the maintenance of spatially and temporally distributed events in visuo-spatial working memory.

Previous studies have demonstrated that working memory for spatial location can be significantly disrupted by concurrent eye or limb movement (Baddeley, 1986; Smyth, Pearson, & Pendleton, 1988). Shifts in attention alone can also interfere with spatial span (Smyth & Scholey, 1994), even with no corresponding movement of the eyes or limbs (Smyth, 1996). What is not clear from these studies is how comparable is the magnitude of effect caused by different forms of spatial disrupter. Recently, it has been demonstrated that limb movements produce as much interference with spatial span as do reflexive saccades (Lawrence, Myerson, Oonk, & Abrams, 2001). In turn this has led to the hypothesis that all spatially directed movement can produce similar effects in visuo-spatial working memory. This paper reports the results of five experiments that have contrasted the effect of concurrent eye movement, limb movement, and covert attention shifts on participants' working memory for sequences of locations. All conditions involving concurrent eye movement produced significantly greater reduction in span than equivalent limb movement or covert attention shifts with eyes fixated. It is argued that these results demonstrate a crucial role for oculomotor control processes during the rehearsal of location-specific representations in working memory.

Adult↗
PubMed1995

Practitioner review: verbal working memory development and its disorders.

Working memory refers to the systems responsible for the temporary storage and manipulation of information during the performance of cognitive tasks. There is a good deal of evidence that verbal short-term memory functions as a working memory system. We review advances in our understanding of the nature and limitations of verbal short-term memory and the reasons for its development with age, and go on to consider the common association between impairments of verbal short-term memory and other impairments of cognitive development. We conclude by considering the relationship between short-term memory development and cognitive development.

Adolescent↗
PubMed2002

The role of stimulus type in age-related changes of visual working memory.

Aging is accompanied by increasing difficulty in working memory associated with the temporary storage and processing of goal-relevant information. Face recognition plays a preponderant role in human behavior, and one might therefore suggest that working memory for faces is spared from age-related decline compared to socially less important visual stimulus material. To test this hypothesis, we performed working memory (n-back) tasks with two different visual stimulus types, namely faces and doors, and compared them to tasks with primarily verbal material, namely letters. Age-related reaction time slowing was comparable for all three stimulus types, supporting hypotheses on general cognitive and motor slowing. In contrast, performance substantially declined with age for faces and doors, but little for letters. Working memory for faces resulted in significantly better performance than that for doors and was more sensitive to on-line manipulation errors such as the temporal order. All together, our results show that even though face perception might play a specific role in visual processing, visual working memory for faces undergoes the same age-related decline as it does for socially less relevant visual material. Moreover, these results suggest that working memory decline cannot be solely explained by increasing vulnerability in prefrontal cortex related to executive functioning, but indicate an age-related decrease in a visual short-term buffer, possibly located in the temporal cortex.

Adult↗
PubMed2000

The role of working memory in analogical mapping.

The impact of a working-memory load on analogical mapping was examined in two experiments, using a dual-task paradigm. In Experiment 1, we used a phonological working-memory load; in Experiment 2, we used a phonological working-memory load and an executive working-memory load. The subjects were required to identify correspondences between visual scenes, either for single objects or for three objects simultaneously. The results indicated that the imposition of either a phonological or an executive working-memory load decreased the frequency with which the subjects identified correspondences between scenes based on relations and increased the frequency with which they identified correspondences based on object attributes. The frequency with which subjects made relational mappings was increased by the instruction to find correspondences for multiple objects in a scene simultaneously, rather than for just one. These results indicate that mapping on the basis of relations places greater demands on both modality-specific buffers and executive components of working memory than does mapping on the basis of object attributes.

Association Learning↗
PubMed2001

Overlapping mechanisms of attention and spatial working memory.

Spatial selective attention and spatial working memory have largely been studied in isolation. Studies of spatial attention have provided clear evidence that observers can bias visual processing towards specific locations, enabling faster and better processing of information at those locations than at unattended locations. We present evidence supporting the view that this process of visual selection is a key component of rehearsal in spatial working memory. Thus, although working memory has sometimes been depicted as a storage system that emerges 'downstream' of early sensory processing, current evidence suggests that spatial rehearsal recruits top-down processes that modulate the earliest stages of visual analysis.

Journal Article↗
PubMedDate not supplied

Physiological characteristics of capacity constraints in working memory as revealed by functional MRI.

A fundamental characteristic of working memory is that its capacity to handle information is limited. While there have been many brain mapping studies of working memory, the physiological basis of its capacity limitation has not been explained. We identified characteristics of working memory capacity using functional magnetic resonance imaging (fMRI) in healthy subjects. Working memory capacity was studied using a parametric 'n-back' working memory task involving increasing cognitive load and ultimately decreasing task performance. Loci within dorsolateral prefrontal cortex (DLPFC) evinced exclusively an 'inverted-U' shaped neurophysiological response from lowest to highest load, consistent with a capacity-constrained response. Regions outside of DLPFC, in contrast, were more heterogeneous in response and often showed early plateau or continuously increasing responses, which did not reflect capacity constraints. However, sporadic loci, including in the premotor cortex, thalamus and superior parietal lobule, also demonstrated putative capacity-constrained responses, perhaps arising as an upstream effect of DLPFC limitations or as part of a broader network-wide capacity limitation. These results demonstrate that regionally specific nodes within the working memory network are capacity-constrained in the physiological domain, providing a missing link in current explorations of the capacity characteristics of working memory.

Adolescent↗