The development of working memory: further note on the comparability of two models of working memory

This paper is a set of reflections on Kemps, De Rammelaere, and Desmet's article (2000, this issue), in which the two models by Baddeley and Pascual-Leone are compared. First, some of the similarities and differences between the two models which we identified in a 1994 paper (de Ribaupierre & Bailleux, 1994) are briefly summarized and reexamined in the light of more recent work. Second, we debate the issue of whether each model makes a specific contribution to the explanation of some of Kemps et al.'s results, that is, of whether they can be considered to be complementary. Third, we argue for the necessity of theoretical task analyses, in view of the divergent results obtained in the two tasks used (the Corsi and the Peanut tasks), notably different developmental profiles, and an overall higher level of performance in the Corsi task. Finally, we briefly summarize a very similar study in which we also used Mr. Peanut with concurrent tasks in children and in young adults and in which we obtained rather different results. By comparing the experimental procedures used in the two studies, we contribute some exploratory hypotheses, while raising issues that can easily be generalized to other visuo-spatial working memory tasks.     

The development of visuo-spatial working memory

Children's performance on tests of visuo-spatial working memory improves with age, although relatively little is known about why this happens. One explanation concerns the development of the ability to recode visually presented information into phonological form. This process appears to be used from around 8 years of age and is a major contributor to tasks in which stimuli can be verbally labelled. However, evidence suggests that phonological recoding cannot account for all of the age-related change in performance on visuo-spatial working memory tasks. In this review, four other mechanisms (knowledge, processing strategies, processing speed, and attentional capacity) are considered in terms of their contribution to children's visuo-spatial working memory development.     

Access to information in working memory: exploring the focus of attention

Participants memorized briefly presented sets of digits, a subset of which had to be accessed as input for arithmetic tasks (the active set), whereas another subset had to be remembered independently of the concurrent task (the passive set). Latencies for arithmetic operations were a function of the setsize of active but not passive sets. Object-switch costs were observed when successive operations were applied to different digits within an active set. Participants took 2 s to encode a passive set so that it did not affect processing latencies (Experiment 2). The results support a model distinguishing 3 states of representations in working memory: the activated part of long-term memory, a capacity limited region of direct access, and a focus of attention.     

Olfactory working memory: exploring the differences in n-back memory for high and low verbalisable odorants

ABSTRACT

We describe four experiments each examining n-back performance for high and low verbalisable odorants. Participants were presented with a sequence of odorants and were required to state if the current odorant was the same or different to the odorant presented two items earlier. Experiment 1 reported superior performance for high, relative to low, verbalisable odorants and was evident despite above-chance memory performance for the low verbalisable odorants. Experiment 2 showed that such superiority persisted with a concurrent articulation condition, suggesting that the memory benefit was not a consequence of verbal recording and rehearsal. Experiment 3 employed metacognitive judgments and showed that correct 2-back responses for high verbalisable odorants received more recollection responses compared to low verbalisable odorants. Experiment 4 compared n-back performance across different stimulus types and showed that, for high verbalisable odorants, performance correlated with both letters and abstract shapes, but such correlations were absent for low verbalisable odorants. Taken together, these findings show differences in n-back performance between high and low verbalisable odorants, and show that high verbalisable odorants exhibit performance similarities with both verbal and visual stimuli. We further argue that n-back performance for low verbalisable odorants operates differently to that of high verbalisable odorants.     

Computational models of working memory: putting long-term memory into context

Detailed computational modeling of human memory has typically been aimed at either short-term (working) memory or long-term memory in isolation. However, recent research highlights the importance of interactions between these systems for both item and order information. At the same time, computational models of both systems are beginning to converge onto a common framework in which items are associated with an evolving "context" signal and subsequently compete with one another at recall. We review some of these models, and discuss a common mechanism capable of modelling working memory and its interaction with long-term memory, focussing on memory for verbal sequences.     

What you say matters: exploring visual-verbal interactions in visual working memory

The aim of this study was to explore whether the content of a simple concurrent verbal load task determines the extent of its interference on memory for coloured shapes. The task consisted of remembering four visual items while repeating aloud a pair of words that varied in terms of imageability and relatedness to the task set. At test, a cue appeared that was either the colour or the shape of one of the previously seen objects, with participants required to select the object's other feature from a visual array. During encoding and retention, there were four verbal load conditions: (a) a related, shape-colour pair (from outside the experimental set, i.e., "pink square"); (b) a pair of unrelated but visually imageable, concrete, words (i.e., "big elephant"); (c) a pair of unrelated and abstract words (i.e., "critical event"); and (d) no verbal load. Results showed differential effects of these verbal load conditions. In particular, imageable words (concrete and related conditions) interfered to a greater degree than abstract words. Possible implications for how visual working memory interacts with verbal memory and long-term memory are discussed.     

The phonological-similarity effect differentiates between two working memory tasks

Working memory is a set of interactive cognitive processes that maintain information on–line and available for analysis. Part of the system is specialized for maintaining verbal information, a core component of which is thought to be a phonological store. On the basis of the study of patients with acquired brain lesions, this store has been localized to the supramarginal and angular gyri of the speech–dominant hemisphere, and some functional neuroimaging studies support this localization. However, other imaging studies localize the phonological store in a more dorsal region of the parietal lobe. To reconcile these findings, we examined the phonological–similarity effect in two different tasks. A phonological–similarity effect was observed only in the task that involved sequential presentation and explicit verbal rehearsal. We conclude that at least one possible source of the differences in brain activation between different working memory tasks may be differences in phonological processing.     

The role of working memory in the development of emotion comprehension

This study investigated the relationship between emotion comprehension, grammar comprehension, and working memory capacity in children between 5 and 11 years (n= 130), testing the hypothesis that working memory has a role in the development of emotion comprehension. We replicated the correlation between emotion comprehension and grammar comprehension, and found that working memory capacity correlates with both of these variables (also with age statistically controlled). The significant effect of age on emotion comprehension was eliminated when working memory capacity was co‐varied. In a regression analysis of emotion comprehension scores, when working memory capacity was entered as a predictor, no additional variance was significantly accounted for by grammar comprehension, gender, or age. A structural relations model, in which the paths from working memory capacity to emotion comprehension and from working memory capacity to grammar comprehension account fully for the correlation between grammar and emotion comprehension, fit the data well. However, working memory capacity was not equally related to all components of the Test of Emotion Comprehension (TEC) ( Pons & Harris, 2000 ), the relationship being significant only for some of them. In particular, working memory capacity has a decisive role in the transition from understanding external to mental aspects of emotions. It is concluded that the development of working memory has a considerable impact on the development of emotion comprehension.     

Concurrent performance of two memory tasks: evidence for domain-specific working memory systems

Previous studies of dual-task coordination in working memory have shown a lack of dual-task interference when a verbal memory task is combined with concurrent perceptuomotor tracking. Two experiments are reported in which participants were required to perform pairwise combinations of (1) a verbal memory task, a visual memory task, and perceptuomotor tracking (Experiment 1), and (2) pairwise combinations of the two memory tasks and articulatory suppression (Experiment 2). Tracking resulted in no disruption of the verbal memory preload over and above the impact of a delay in recall and showed only minimal disruption of the retention of the visual memory load. Performing an ongoing verbal memory task had virtually no impact on retention of a visual memory preload or vice versa, indicating that performing two demanding memory tasks results in little mutual interference. Experiment 2 also showed minimal disruption when the two memory tasks were combined, although verbal memory (but not visual memory) was clearly disrupted by articulatory suppression interpolated between presentation and recall. These data suggest that a multiple-component working memory model provides a better account for performance in concurrent immediate memory tasks than do theories that assume a single processing and storage system or a limited-capacity attentional system coupled with activated memory traces.     

The development of visual working memory capacity during early childhood

The change detection task has been used in dozens of studies with adults to measure visual working memory capacity. Two studies have recently tested children in this task, suggesting a gradual increase in capacity from 5 years to adulthood. These results contrast with findings from an infant looking paradigm suggesting that capacity reaches adult-like levels within the first year. The current study adapted the change detection task for use with children younger than 5 years to test whether the standard version of the task was too difficult and may have underestimated children's capacity. Results showed that 3- and 4-year-olds could successfully complete this modified task and that capacity increased roughly linearly, from 2 or 3 items during this period to 3 or 4 items between 5 and 7 years. Furthermore, performance did not differ significantly between the modified version and a replication of the standard version with 5- and 7-year-olds. Thus, there is no evidence that previous research with the change detection task underestimated children's capacity. Further research is needed to understand how performance relates across the infant looking task and change detection to provide a more complete picture of visual working memory capacity over development.     

On the independence of short-term memory and working memory in cognitive development

We report some experiments that were concerned with the now familiar hypothesis that short-term memory and information processing draw upon a common pool of scarce resources. The results of two series of experiments were more consistent with the hypothesis that the resources that support short-term memory and information processing do not overlap and develop independently of each other. In Experiments 1–4, children's performance on four reasoning problems (class inclusion, conservation, probability judgment, and transitive inference) was found to be stochastically independent of their short-term memory for the critical background facts on these problems. Age changes in reasoning and short-term memory also proved to be independent. It was found in the second series of experiments that certain manipulations which affect the accuracy of children's reasoning do not affect short-term memory, and conversely. In Experiments 5–7, manipulations that affected the difficulty of information processing on class-inclusion and transitivity tasks did not affect short-term memory on these same tasks. In Experiments 8 and 9, manipulations that affected short-term retention of the background facts on conservation and probability-judgment tasks did not affect reasoning on these same tasks.     

The development of verbal and visual working memory processes: a latent variable approach

Working memory (WM) processing in children has been studied with different approaches, focusing on either the organizational structure of WM processing during development (factor analytic) or the influence of different task conditions on WM processing (experimental). The current study combined both approaches, aiming to distinguish verbal and visual processing in order to investigate WM development. We investigated recall performance under different task conditions in a sample of 5- to 13-year-olds, applying latent class regression analysis. In this analysis, we examined latent classes (subgroups) within the sample that differed in terms of processing type. The interpretations of the latent classes were validated internally using characteristics of the latent classes and externally using recall performance of words and figures. The results showed that children of different developmental stages used the same type of processing under the same conditions. However, due to developmental differences, their overall performances differed, showing groups of children who were successful in verbal or visual processing and groups of children who were not. This study shows and discusses the importance of disentangling the influence of task conditions from the influence of WM development when interpreting recall performance in children.     

Focused attention improves working memory: implications for flexible-resource and discrete-capacity models

Performance in working memory (WM) tasks depends on the capacity for storing objects and on the allocation of attention to these objects. Here, we explored how capacity models need to be augmented to account for the benefit of focusing attention on the target of recall. Participants encoded six colored disks (Experiment 1) or a set of one to eight colored disks (Experiment 2) and were cued to recall the color of a target on a color wheel. In the no-delay condition, the recall-cue was presented after a 1,000-ms retention interval, and participants could report the retrieved color immediately. In the delay condition, the recall-cue was presented at the same time as in the no-delay condition, but the opportunity to report the color was delayed. During this delay, participants could focus attention exclusively on the target. Responses deviated less from the target’s color in the delay than in the no-delay condition. Mixture modeling assigned this benefit to a reduction in guessing (Experiments 1 and 2) and transposition errors (Experiment 2). We tested several computational models implementing flexible or discrete capacity allocation, aiming to explain both the effect of set size, reflecting the limited capacity of WM, and the effect of delay, reflecting the role of attention to WM representations. Both models fit the data better when a spatially graded source of transposition error is added to its assumptions. The benefits of focusing attention could be explained by allocating to this object a higher proportion of the capacity to represent color.     

The personalisation method applied to a working memory task: Evidence of long-term working memory effects

Ericsson and Kintsch (1995) proposed that, in situations of expertise, individuals can overcome working memory limitations by using long-term working memory. It allows a greater capacity than working memory thanks to long-term memory encoding and retrieving. To test this characteristic, an adaptation of Daneman and Carpenter's (1980) reading span was used. To operationalise expertise, the personalisation method (Guida & Tardieu, 2005) was employed. In Experiment 1, a personalised group, which read reading span sentences that mentioned familiar locations, was compared to a nonpersonalised group, which read sentences with unfamiliar locations. In Experiment 2, a personalised group, which read reading span sentences with neutral locations, was encouraged to mentally personalise these locations by thinking about known locations. This group was compared to a nonpersonalised group, which was encouraged to think about unknown locations. The personalised groups were expected to store and retrieve information in long-term memory via long-term working memory more easily than the nonpersonalised groups, which had to count massively on working memory. The results showed that personalisation enhanced reading span and confirmed one implication of the long-term working memory theory: high- and low-reading-span differences could also be due to long-term memory retrieval. Finally, these results are interpreted in terms of interaction between working memory size and long-term memory knowledge, showing that participants with a lower reading span benefited more from high domain knowledge than participants with a higher reading span.     

The development of strategy use in elementary school children: working memory and individual differences

The current study tested the development of working memory involvement in children's arithmetic strategy selection and strategy efficiency. To this end, an experiment in which the dual-task method and the choice/no-choice method were combined was administered to 10- to 12-year-olds. Working memory was needed in retrieval, transformation, and counting strategies, but the ratio between available working memory resources and arithmetic task demands changed across development. More frequent retrieval use, more efficient memory retrieval, and more efficient counting processes reduced the working memory requirements. Strategy efficiency and strategy selection were also modified by individual differences such as processing speed, arithmetic skill, gender, and math anxiety. Short-term memory capacity, in contrast, was not related to children's strategy selection or strategy efficiency.     

The primate working memory networks

Working memory has long been associated with the prefrontal cortex, since damage to this brain area can critically impair the ability to maintain and update mnemonic information. Anatomical and physiological evidence suggests, however, that the prefrontal cortex is part of a broader network of interconnected brain areas involved in working memory. These include the parietal and temporal association areas of the cerebral cortex, cingulate and limbic areas, and subcortical structures such as the mediodorsal thalamus and the basal ganglia. Neurophysiological studies in primates confirm the involvement of areas beyond the frontal lobe and illustrate that working memory involves parallel, distributed neuronal networks. In this article, we review the current understanding of the anatomical organization of networks mediating working memory and the neural correlates of memory manifested in each of their nodes. The neural mechanisms of memory maintenance and the integrative role of the prefrontal cortex are also discussed.     

The development of memory maintenance: Children’s use of phonological rehearsal and attentional refreshment in working memory tasks

Past research suggests that children begin to phonologically rehearse at around 7 years of age. Less is known regarding the development of refreshment, an attention-based maintenance mechanism. Therefore, the use of these two maintenance methods by 6- and 8-year-olds was assessed using memory span tasks that varied in their opportunities for maintenance activity. Experiment 1 showed that nonverbal processing impaired both groups’ performance to similar extents. Experiment 2 employed phonologically similar or dissimilar memory items and compared the effects of verbal versus nonverbal processing on recall. Both groups showed evidence of phonological maintenance under nonverbal processing but not under verbal processing. Furthermore, nonverbal processing again impaired recall. Verbal processing was also more detrimental to performance in 8-year-olds than in 6-year-olds. Together, the results suggest that nonverbal processing impairs recall by obstructing refreshment and that developmental change in maintenance between 6 and 8 years of age consists primarily of an increase in phonological rehearsal.     

Selective attention,filtering, and the development of working memory

Selective attention is fundamental for learning across many situations, yet it exhibits protracted development, with young children often failing to filter out distractors. In this research, we examine links between selective attention and working memory (WM) capacity across development. One possibility is that WM is resource‐limited, with development resulting in an increase in the amount of resources available for processing information. However, it is also possible that development results in greater efficiency of using available resources. In the current research, we explore the latter possibility by examining the developmental trajectory of selectivity and filtering in relation to WM capacity. We report that filtering efficiency of adults (N = 30), 7‐year‐olds (N = 29), and 4‐year‐olds (N = 28) was uniquely predictive of WM capacity. We also report that filtering efficiency continues to develop after 7 years of age, whereas WM capacity may reach an asymptote around 7 years of age. The latter finding suggests that selective attention plays a critical role in developmental and individual differences in visual working memory capacity.     

Effect of articulatory suppression on task-switching performance: implications for models of working memory

In a series of experiments, we examine some effects of articulatory suppression in task switching. The results from Experiments 1a and 2a showed that switch costs in the articulatory suppression condition were larger than those in the control and tapping conditions when the switching cues were not provided. On the other hand, articulatory suppression did not have any effect on switch costs in Experiments 1b and 2b, where the switching cues were provided. In Experiment 3, using a computer-assisted experimentation, this pattern of data was replicated in a two-factor design with articulatory suppression and switching cues factors. The results indicate that a specific component in working memory, the phonological loop, might contribute to the performance in task switching, at least in situations where the external task cues were not available. The data reported here suggest that the phonological loop plays an important role in one of the executive control processes, and challenge the traditional idea that the slave systems are simply governed by the central executive in the working memory.