Phonological similarity in working memory

That phonologically similar words in a short-term memory test are more difficult to recall than phonologically dissimilar words is a well-known phenomenon. This effect is the phonological similarity decrement. In the present study, we examined whether this phonological similarity decrement is present when additional semantic information is available, as in a reading span test, as compared with a standard presentation, or in the context of an operation span test. The results revealed a phonological similarity facilitation. Phonologically similar words were remembered better than phonologically dissimilar words.     

Processing and storage in working memory span

Two experiments are reported that address theoretical assumptions as to the nature of working memory involved in working memory span tasks (Daneman & Carpenter, 1980). Experiment 1 used a version of the sentence span task, and Experiment 2 combined arithmetic verification with recall of presented words. In each experiment, working memory processing span was assessed independently of temporary storage span prior to their combination. Combined task performance under high demand for each component resulted in substantial residual performance for both task elements, particularly in Experiment 2. The results do not challenge the utility of the sentence span task as a measure of on-line cognition, but they raise concerns as to how resource might be allocated to processing and storage elements of the task within a single flexible resource pool, or between different resources of a multiple component working memory system. Although both models lack predictive power regarding resource allocation in these tasks, the multiple resource model appears to offer the better account.     

Interference between maintenance and processing in working memory: the effect of item-distractor similarity in complex span

Four experiments examined the effect of phonological similarity between items and distractors on complex span performance. Item-distractor similarity benefited serial recall when distractors followed the items they were similar to, but not when distractors preceded the items they were similar to. These findings are predicted by C-SOB (contextual serial order in a box), a computational model of complex span. The model assumes that distractors are involuntarily encoded into memory, being associated to the preceding item's list position. Distractors interfere with items by superposition of distributed representations that are associated to the same position. Superposition distorts item memory; this distortion is less severe when the distractor is similar to the item. Further support for the assumption that distractors are encoded at the position of the preceding item comes from the finding that intrusions of distractors at recall tended to come from the position of the target item. In addition, intruding distractors tend to replace items to which they are similar, showing that lack of distinctiveness also contributes to interference.     

Proactive interference and item similarity in working memory

Proactive interference (PI) may influence the predictive utility of working memory span tasks. Participants in one experiment (N=70) completed Ravens Advanced Progressive Matrices (RAPM) and multiple versions of operation span and probed recall, modified for the type of memoranda (digits or words). Changing memoranda within- or across-trials released PI, but not doing so permitted PI buildup. Scores from PI-build trials, but not PI-release trials, correlated with RAPM and accounted for as much variance in RAPM as unmodified tasks. These results are consistent with controlled attention and inhibition accounts of working memory, and they elucidate a fundamental component of working memory span tasks.     

On the interpretation of working memory span in adults

Experimental research into children's working memory span has shown that retention duration contributes substantially to span performance, while processing efficiency need not be related to concurrent memory load (Towse, Hitch, & Hutton, 1998). These findings have been used to argue for a model of working memory span that emphasizes time-based forgetting rather than the popular resource-sharing or tradeoff framework. The present paper considers whether adults perform working memory span tasks in a qualitatively different way. Data from reading span and operation span tasks show that adults' performance can be distinguished from that of children, but also that a task-switching model of working memory span can explain some important aspects of performance.     

Mask similarity impacts short-term consolidation in visual working memory

Short-term consolidation is the process by which perceptual representations are stabilized into visual working memory (VWM) representations to prevent interference from subsequent visual input. The present article reports how short-term consolidation is affected by the similarity of the subsequent visual items (i.e., visual masks) by using a color change detection task. In the task, masks were either similar or dissimilar to the memory stimuli and were displayed at varying intervals following the memory array. The similar masks were made up of the same colored squares as the to-be-remembered stimuli, whereas the dissimilar masks were black-and-white grids. The results showed more interference from similar than from dissimilar masks: Similar masks required more time to consolidate and elicited lower overall performance than did dissimilar masks. These results suggest that a simple overwriting process cannot fully account for the impact of mask type on short-term consolidation performance and that other cognitive mechanisms are involved (e.g., controlled attention).     

Evidence for different components in children's visuospatial working memory

There are a large number of studies demonstrating that visuospatial working memory (VSWM) involves different subcomponents, but there is no agreement on the identity of these dimensions. The present study attempts to combine different theoretical accounts by measuring VSWM. A battery composed of 13 tests was used to assess working memory and, in particular, the hypothesized mechanisms involved in the tasks, that is, active processing and passive recall of visual versus sequential‐spatial versus simultaneous‐spatial versus verbal tasks. The battery consisted of a number of tests already used in previous studies and new tests developed to examine specific components of working memory. We analysed the psychometric characteristics of the tests, the correlations amongst measured variables and estimated the measured variables with structural equation modelling in children attending third and fourth grades. Results revealed that the best model was composed of a specific verbal factor, three visuospatial passive factors (sequential‐spatial, simultaneous‐spatial, and visual) and one visuospatial active factor.     

Dissociative style and individual differences in verbal working memory span

Dissociative style is mostly studied as a risk factor for dissociative pathology, but it may also reflect a fundamental characteristic of healthy information processing. Due to the close link between attention and working memory and the previous finding of enhanced attentional abilities with a high dissociative style, a positive relationship was also expected between dissociative style and verbal working memory span. In a sample of 119 psychology students, it was found that the verbal span of the high-dissociative group was about half a word larger than of the medium and low-dissociative groups. It is suggested that dissociative style may be one of only very few individual differences that is directly relevant to consciousness research.     

Mapping the developmental constraints on working memory span performance

This study investigated the constraints underlying developmental improvements in complex working memory span performance among 120 children of between 6 and 10 years of age. Independent measures of processing efficiency, storage capacity, rehearsal speed, and basic speed of processing were assessed to determine their contribution to age-related variance in complex span. Results showed that developmental improvements in complex span were driven by 2 age-related but separable factors: 1 associated with general speed of processing and 1 associated with storage ability. In addition, there was an age-related contribution shared between working memory, processing speed, and storage ability that was important for higher level cognition. These results pose a challenge for models of complex span performance that emphasize the importance of processing speed alone.     

Bilingual working memory span is affected by language skill

A complex span procedure was used to study whether there is a measurable extra load on general working memory (WM) when a not fully automatised language has to be comprehended. Participants verified heard sentences in relation to simultaneously shown pictures and memorised the last word of each sentence. The sentences were presented in growing set sizes and recall of all the last words was required after each set. The largest number of sentences that could be processed in combination with successful recall of their last words determined the participant's WM span. Sentences were either in the participants' native language or a well-mastered second language, English. Participants were psychology and English students. WM span and decision accuracy were better for native-language than foreign-language sentences, especially for the psychology students. A second experiment ascertained that the difference between participant groups could not be explained by variables related to phonological shortterm memory or word processing. A third experiment controlled for systematic trade-off differences between languages and groups. We conclude that aspects of sentence comprehension in foreign language develop with practice so that they require less WM resources.     

Short-term memory and working memory as indices of children's cognitive skills

In the current literature, empirical and conceptual distinctions have been drawn between a more or less passive short-term memory (STM) system and a more dynamic working memory (WM) system. Distinct tasks have been developed to measure their capacity and research has generally shown that, for adults, WM, and not STM, is a reliable predictor of general cognitive ability. However, the locus of the differences between the tasks has received little attention. We present data from children concerning measures of matrices reasoning ability, reading, and numerical skill along with forward and backward order serial recall of WM, STM, and STM with articulatory suppression tasks. As indices of children's cognitive skills, STM and WM are shown to be rather similar in terms of memory per se. Neither the opportunity for rehearsal nor task complexity provides satisfactory explanations for differences between memory tests.     

Short-term memory and working memory as indices of children's cognitive skills

In the current literature, empirical and conceptual distinctions have been drawn between a more or less passive short-term memory (STM) system and a more dynamic working memory (WM) system. Distinct tasks have been developed to measure their capacity and research has generally shown that, for adults, WM, and not STM, is a reliable predictor of general cognitive ability. However, the locus of the differences between the tasks has received little attention. We present data from children concerning measures of matrices reasoning ability, reading, and numerical skill along with forward and backward order serial recall of WM, STM, and STM with articulatory suppression tasks. As indices of children's cognitive skills, STM and WM are shown to be rather similar in terms of memory per se. Neither the opportunity for rehearsal nor task complexity provides satisfactory explanations for differences between memory tests.     

The Gestalt principle of similarity benefits visual working memory

Visual working memory (VWM) is essential for many cognitive processes, yet it is notably limited in capacity. Visual perception processing is facilitated by Gestalt principles of grouping, such as connectedness, similarity, and proximity. This introduces the question, do these perceptual benefits extend to VWM? If so, can this be an approach to enhance VWM function by optimizing the processing of information? Previous findings have demonstrated that several Gestalt principles (connectedness, common region, and spatial proximity) do facilitate VWM performance in change detection tasks (Jiang, Olson, & Chun, 2000; Woodman, Vecera, & Luck, 2003; Xu, 2002, 2006; Xu & Chun, 2007). However, one prevalent Gestalt principle, similarity, has not been examined with regard to facilitating VWM. Here, we investigated whether grouping by similarity benefits VWM. Experiment 1 established the basic finding that VWM performance could benefit from grouping. Experiment 2 replicated and extended this finding by showing that similarity was only effective when the similar stimuli were proximal. In short, the VWM performance benefit derived from similarity was constrained by spatial proximity, such that similar items need to be near each other. Thus, the Gestalt principle of similarity benefits visual perception, but it can provide benefits to VWM as well.     

The influence of similarity on visual working memory representations

In verbal memory, similarity between items in memory often leads to interference and impaired memory performance. The present study sought to determine whether analogous interference effects would be observed in visual working memory by varying the similarity of the to-be-remembered objects in a colour change detection task. Instead of leading to interference and impaired performance, increased similarity among the items being held in memory led to improved performance. Moreover, when two similar colours were presented along with one dissimilar colour, memory performance was better for the similar colours than for the dissimilar colour. Similarity produced better performance even when the objects were presented sequentially and even when memory for the first item in the sequence was tested. These findings show that similarity does not lead to interference between representations in visual working memory. Instead, similarity may lead to improved task performance, possibly due to increased stability or precision of the memory representations during maintenance.     

Individual and developmental differences in working memory across the life span

The effects of secondary tasks on verbal and spatial working memory were examined in multiple child, young adult, and older adult samples. Although memory span increased with age in the child samples and decreased with age in the adult samples, there was little evidence of systematic change in the magnitude of interference effects. Surprisingly, individuals who had larger memory spans when there was no secondary task showed greater interference effects than their age-mates. These findings are inconsistent with the hypothesis that age and individual differences in working memory are due to differences in the ability to inhibit irrelevant information, at least as this hypothesis is currently formulated. Moreover, our results suggest that different mechanisms underlie developmental and individual differences in susceptibility to interference across the life span. A model is proposed in which memory span and processing speed both increase with development but are relatively independent abilities within age groups.     

Children's working memory: investigating performance limitations in complex span tasks

Three experiments investigated the roles of resource-sharing and intrinsic memory demands in complex working memory span performance in 7- and 9-year-olds. In Experiment 1, the processing complexity of arithmetic operations was varied under conditions in which processing times were equivalent. Memory span did not differ as a function of processing complexity. In Experiment 2, complex memory span was assessed under three conditions designed to vary both processing and intrinsic storage demands: mental arithmetic (significant attentional demands-requires storage), odd/even judgments (significant attentional demands-no storage required), and articulatory suppression (minimal attentional demands--no storage required). The highest memory spans were found in the articulatory suppression task. Span was at an intermediate level with arithmetic processing and was lowest for processing involving odd/even judgments. This difference in memory span for processing tasks involving arithmetic processing and odd/even judgments was eliminated in Experiment 3 when the pacing requirements of the arithmetic and odd/even processing tasks were equated. The results are consistent with the view that complex memory span performance is disrupted by processing activities that divert attentional resources from storage.     

Modeling working memory: An interference model of complex span

This article introduces a new computational model for the complex-span task, the most popular task for studying working memory. SOB-CS is a two-layer neural network that associates distributed item representations with distributed, overlapping position markers. Memory capacity limits are explained by interference from a superposition of associations. Concurrent processing interferes with memory through involuntary encoding of distractors. Free time in-between distractors is used to remove irrelevant representations, thereby reducing interference. The model accounts for benchmark findings in four areas: (1) effects of processing pace, processing difficulty, and number of processing steps; (2) effects of serial position and error patterns; (3) effects of different kinds of item-distractor similarity; and (4) correlations between span tasks. The model makes several new predictions in these areas, which were confirmed experimentally.     

Stimulus similarity and order as factors in visual short-term memory in nonhuman primates.

The short-term retention of nonhuman primates for a single sample or for two successively presented samples was assessed in four delayed matching-to-sample experiments with delays of .03, 4, 8, 16, and 32 sec. The single sample tasks included one (Experiment 1) or two (Experiment 4) distractor stimuli in the choice set (matching test). In the two successive samples tasks, the animals matched (reconstructed) the order of presentation of two samples with (Experiment 3) and without (Experiment 2) a distractor stimulus. Also, the possible combinations of eight stimuli (four colors and four shapes) were arranged to test the effects of sample set and choice set similarity. Taken together, analyses of the errors indicated that both sample and choice set similarity were significant sources of confusions in delayed matching. Order errors occurred independently of similarity but were a source of forgetting primarily at the longest delays (16 and 32 sec). Two exceptions to the similarity effect (second response errors in Experiment 3 and errors of an inexperienced group in Experiment 4) were observed. Possible reasons for the exceptions and several implications of these findings for theories of short-term memory are discussed.     

Dopamine D2 agonist affects visuospatial working memory distractor interference depending on individual differences in baseline working memory span

The interplay of dopaminergic striatal D1–D2 circuits is thought to support working memory (WM) by selectively filtering information that is to be remembered versus information to be ignored. To test this theory, we conducted an experiment in which healthy participants performed a visuospatial working memory (VSWM) task after ingesting the D2-receptor agonist cabergoline (or placebo), in a randomized, double-blinded, crossover design. Results showed greater interference from distractors under cabergoline, particularly for individuals with higher baseline dopamine (indicated by WM span). These findings support computational theories of striatal D1–D2 function during WM encoding and distractor-filtering, and provide new evidence for interactive cortico-striatal systems that support VSWM capacity and their dependence on WM span.     

Proactive interference and practice effects in visuospatial working memory span task performance

In the current study the influence of proactive interference (PI) and practice on recall from a visuospatial working memory (WM) task was examined. Participants completed a visuospatial WM span task under either high-PI conditions (a traditional span task) or low-PI conditions (a span task with breaks between trials). Trials of each length (i.e., two to five to-be-remembered items) were equally distributed across three blocks in order to examine practice effects. Recall increased across blocks to a greater extent in the low-PI condition than in the high-PI condition, indicating that reducing PI increased recall from WM. Additionally, in the final block the correlation between fluid intelligence and WM recall was stronger for the high-PI condition than the low-PI condition, indicating that practice reduced the strength of the correlation between span task recall and fluid intelligence, but only in the low-PI condition. These results support current theories that propose that one source of variability in recall from WM span task is the build-up of PI, and that PI build-up is an important contributing factor to the relation between visuospatial WM span task recall and higher-level cognition.