Stimulus similarity decrements in children's working memory span

Two experiments investigated the impact of the relationship between processing and storage stimuli on the working memory span task performance of children aged 7 and 9 years of age. In Experiment 1, two types of span task were administered (sentence span and operation span), and participants were required to recall either the products of the processing task (sentence-final word, arithmetic total) or a word or digit unrelated to the processing task. Experiment 2 contrasted sentence span and operation span combined with storage of either words or digits, in tasks in which the item to be remembered was not a direct product of the processing task in either condition. In both experiments, memory span was significantly greater when the items to be recalled belonged to a different stimulus category from the material that was processed, so that in sentence span tasks, number recall was superior to word recall, and in operation span tasks, word recall was superior to number recall. Explanations of these findings in terms of similarity-based interference and response competition in working memory are discussed.     

Individual differences in sentence memory

Results from an experiment with two parts are presented in this paper. In part one, participants listened to sentences containing two, three, four, or five clauses, and were asked questions about the content of the sentences. The results of part one demonstrate that an important unit of representation in sentence memory is the clause, and not some other component of discourse structure. In part two, the same group of participants performed eight different short-term storage/working memory tasks. A composite complex span score was computed for each participant based on three working memory tasks closely based on Daneman & Carpenter's (1980) reading span task. This working memory measure was significantly correlated with the participants' performance on the sentence memory task in part one. A second working memory measure—N-back—was also significantly correlated with the participants' performance on the sentence memory task, and there was no correlation between their performance on the complex span task and the N-back task. It is therefore concluded that (i) working memory consists of a number of dissociable components; and (ii) memory for sentences taps into more than one of these working memory components. Furthermore, the high correlations of sentence memory with the complex span and the N-back tasks (neither of which are language processing tasks) suggests that memory for sentences is not simply a result of linguistic experience; rather, it is likely that an independent working memory component contributes to participants' performance on the sentence memory task.     

The Measurement of Verbal Working Memory Capacity and Its Relation to Reading Comprehension

Ninety-four subjects were tested on the Daneman and Carpenter (1980) reading span task, four versions of a related sentence span task in which reaction times and accuracy on sentence processing were measured along with sentence-final word recall, two number generation tasks designed to test working memory, digit span, and two shape-generation tasks designed to measure visual-spatial working memory. Forty-four subjects were retested on a subset of these measures at a 3-month interval. All subjects were tested on standard vocabulary and reading tests. Correlational analyses showed better internal consistency and test-retest reliability of the sentence span tasks than of the Daneman-Carpenter reading span task. Factor analysis showed no factor that could be related to a central verbal working memory; rotated factors suggested groupings of tests into factors that correspond to digitrelated tasks, spatial tasks, sentence processing in sentence span tasks, and recall in sentence span tasks. Correlational analyses and regression analyses showed that the sentence processing component of the sentence span tasks was the best predictor of performance on the reading test, with a small independent contribution of the recall component. The results suggest that sentence span tasks are unreliable unless measurements are made of both their sentence processing and recall components, and that the predictive value of these tasks for reading comprehension abilities lies in the overlap of operations rather than in limitations in verbal working memory that apply to both.     

Presentation format and its effect on working memory

In three experiments, we examined the separate cognitive demands of processing and storage in working memory and looked at how effective the coordination was when items for storage varied in format/modality. A sentence verification task involving arithmetic facts was combined with a span task involving two to six items presented in picture, printed word, or spoken word format. The first two experiments were the same, except for the added requirement of articulation of the math sentence in Experiment 2. Experiment 3 varied the length of the span item and compared recall with recognition performance. The results showed that both spoken words and picture produced superior recall and recognition, as compared with printed words, and are consistent with Baddeley and Logie's (1999) and Mayer's (2001) models of working memory. Also, the differences in processing performance across spans varied with the difficulty of the task but showed the strongest support for the resource allocation model (Foos 1995).     

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.     

Children's working-memory processes: a response-timing analysis

Recall response durations were used to clarify processing in working-memory tasks. Experiment 1 examined children's performance in reading span, a task in which sentences were processed and the final word of each sentence was retained for subsequent recall. Experiment 2 examined the development of listening-, counting-, and digit-span task performance. Responses were much longer in the reading-and listening-span tasks than in the other span tasks, suggesting that participants in sentence-based span tasks take time to retrieve the semantic or linguistic structure as cues to recall of the sentence-final words. Response durations in working-memory tasks helped to predict academic skill and achievement, largely separate from the contributions of the memory spans themselves. Response durations thus are important in the interpretation of span task performance.     

Asymmetric interference between domains: evidence from the stimulus order effect in complex span tasks

The stimulus order effect refers to the finding that recall in complex span tasks is better when span lists begin with a longer processing task and end with a shorter task than when these processing tasks are presented in the reverse order. This study independently manipulated processing time and processing difficulty between Long-final and Short-final lists. The processing task required participants to solve arithmetic problems with either verbal (Experiment 1) or visuospatial (Experiment 2) materials. The memory items used in the storage task were either digits (verbal material) or dots-in-matrices (visuospatial materials). Storage of both verbal and visuospatial materials was sensitive to the change in processing difficulty, but not processing time. Furthermore, this study provides further evidence for the asymmetry of domain interference in working memory. The similarities and differences between verbal and visuospatial storage in working memory are discussed.     

Exploring the forgetting mechanisms in working memory: Evidence from a reasoning span test

In working memory (WM) span tests participants have to maintain to-be-remembered information while processing other, potentially distracting, information. Previous studies have shown that WM span scores are greater when span lists start with a long processing task and end with a short processing task than when these processing tasks are presented in the reverse order (e.g., Towse, Hitch, & Hutton, 2000). In Experiment 1, we obtained a similar stimulus order effect in a reasoning span test, using reasoning sentences that were equated for length in terms of the number of constituent words, but which differed in processing complexity; span scores were greater when lists began with a complex sentence and ended with a simple sentence than when this stimulus order was reversed. In Experiment 2, the stimulus order effect was not found when processing duration was held constant while sentence complexity was varied using a computer-paced moving window presentation paradigm. These results suggest that duration-based constraints can affect degree of forgetting independently of the load generated during processing phases in WM span performance and therefore imply that time-related forgetting can occur in WM span tests, particularly when the difficulty of the processing component blocks active maintenance of to-be-remembered material.     

Differential constraints on the working memory and reading abilities of individuals with learning difficulties and typically developing children

This study examined the factors that constrain the working memory span performance and reading ability of individuals with generalized learning difficulties. In the study, 50 individuals with learning difficulties (LD) and 50 typically developing children (TD) matched for reading age completed two working memory span tasks. Participants also completed independent measures of the processing and storage operations involved in each working memory span task and Raven's Coloured Progressive Matrices. The results showed that despite an equivalent level of working memory span, the relative importance of the constraints on working memory differed between the groups. In addition, working memory span was not closely related to word recognition or sentence comprehension performance in the LD group. These results suggest that the working memory span performance of LD and TD individuals may reflect different working memory limitations and that individuals with generalized learning difficulties may approach cognitive tasks in a qualitatively different way from that of typically developing individuals.     

The influence of story context on a working memory span task

The purpose of the present study was to examine factors that could influence whether recall performance in the reading span task (Daneman & Carpenter, 1980 ) would benefit from the contextual information from the sentences in the processing component of the task. More specifically, we investigated whether people would benefit from sentence sets that formed short stories or when the entire span task was one continuous story. Overall, there was a clear benefit for contextually related sentence sets (i.e., the story span tasks) compared to the traditional reading span task. However, the benefit was eliminated when the entire set formed one continuous story. These results support the recall reconstruction hypothesis for working memory (Towse, Cowan, Hitch, & Horton, 2008 ), which suggests that people may strategically use the content of the sentences from the processing component of the reading span task as memorial cues to reconstruct the target words of the storage component. However, this benefit is constrained to scenarios when the contextual cues are unique to a specific set.     

What's working in working memory: a role for the Central Executive

Two experiments are reported which seek to explore the nature of the Central Executive of Baddeley's (Baddeley and Hitch, 1974) model of working memory. Experiment 1 uses a dual task methodology to compare performance on two storage tasks, making use of the two slave systems, the Phonological Loop (PL) and the Visuo-Spatial Scratch Pad (VSSP). Results suggest that storage can be thought of as based on the use of slave system independent resources. Experiment 2 uses a similar approach to compare performance on 2 processing tasks, again one PL based, the other VSSP based. These results suggest that processing is based on a central, shared set of resources. The two experiments support both a multiple resources model of working memory and more specifically identify a role for the Central Executive.     

The complexities of complex span: explaining individual differences in working memory in children and adults

Two studies are presented that investigated the constraints underlying working memory performance in children and adults. In each case, independent measures of processing efficiency and storage capacity are assessed to determine their relative importance in predicting performance on complex span tasks,which measure working memory capacity. Results show that complex span performance was independently constrained by individual differences in domain-general processing efficiency and domain-specific storage capacity. Residual variance, which may reflect the ability to coordinate storage and processing, also predicted academic achievement. These results challenge the view that complex span taps a limited-capacity resource pool shared between processing and storage operations. Rather, they are consistent with a multiple-component model in which separate resource pools support the processing and storage functions of working memory.     

A Dissociation Between Simple and Complex Span Impairment in Alcoholics

We investigated whether the surprisingly good memory performance of alcoholics may result from simple memory performance being spared while performance in complex memory tasks is impaired. Simple word span was contrasted with a complex word span task involving concurrent monitoring and re-organisation of items for recall. To control for disruption of rehearsal in the complex word span task, performance on two additional tasks with disrupted rehearsal but no additional processing components was studied. As hypothesised, the alcoholics showed a deficit in the complex but not the simple word span task. They were also impaired, compared to controls, on both tasks with disrupted rehearsal. The difference between groups remained in the complex span task when scores in simple span and either of the two other tasks were used as covariates. Thus, both executive processes necessary for coping with disrupted rehearsal and additional processes scheduling processing and storage in a complex task may play a role in accounting for working memory deficits found in alcoholics.     

The influence of levels of processing on recall from working memory and delayed recall tasks

Recent research in working memory has highlighted the similarities involved in retrieval from complex span tasks and episodic memory tasks, suggesting that these tasks are influenced by similar memory processes. In the present article, the authors manipulated the level of processing engaged when studying to-be-remembered words during a reading span task (Experiment 1) and an operation span task (Experiment 2) in order to assess the role of retrieval from secondary memory during complex span tasks. Immediate recall from both span tasks was greater for items studied under deep processing instructions compared with items studied under shallow processing instructions regardless of trial length. Recall was better for deep than for shallow levels of processing on delayed recall tests as well. These data are consistent with the primary-secondary memory framework, which suggests that to-be-remembered items are displaced from primary memory (i.e., the focus of attention) during the processing phases of complex span tasks and therefore must be retrieved from secondary memory.     

Naturalistic memory in learning-disabled and skilled readers

Three experiments compared learning-disabled and skilled readers' performance on naturalistic memory measures, as well as investigated the relationship between memory performance on everyday and laboratory tasks. In Experiment 1, the laboratory task (sentence span task) and everyday memory measures were correlated moderately for both ability groups. Compared to skilled readers, disabled readers performed poorly on the sentence span task, and were less likely than skilled readers to remember information related to common objects and consequential events. Disabled readers were also less likely to rely on external prompts to help them recall everyday information. Experiment 2 extended the previous findings to older subjects and found that the majority of significant correlations between the laboratory (word span task) and everyday memory tasks were isolated to disabled readers. When compared to chronological-age-matched subjects, disabled readers were inferior in recency performance on the laboratory (word span) and natural serial recall (e.g., recall of U.S. presidents) tasks. Experiment 3 showed that under conditions that facilitate item accessibility, ability group differences in recall were comparable. Taken together, the findings indicate that disabled readers' memory deficits are pervasive across naturalistic and laboratory measures at the younger age, but these deficits diminish for older students. Further, the deficits that occur at the older age are due to problems in accessing knowledge.     

Storage and processing in visuo-spatial working memory

Visuo-spatial working memory has been used to account for performance in a wide range of visuo-spatial tasks, including perceptuo-motor tracking and immediate recall of visually presented patterns. However a developing body of evidence points to a fractionation of the concept into visuo-spatial processing that calls on general purpose executive resources, and a visual 'cache' memory for temporary storage in on-line cognition. Two related experiments are described which address whether processing and temporary memory draw on overlapping or on distinct resources in working memory. Experiment 1 demonstrates that participants can accurately respond to a series of targets appearing in random locations whether or not they have the additional load of retaining and subsequently recalling the appearance of each target. Memory for target appearance likewise is largely unaffected by the additional load of requiring a response to each target. Experiment 2 demonstrates similar findings when verbal labeling of the patterns is inhibited through the use of articulatory suppression. Results are interpreted as consistent with a multiple component working memory system.     

Attentional resources in timing: Interference effects in concurrent temporal and nontemporal working memory tasks

Three experiments examined interference effects in concurrent temporal and nontemporal tasks. The timing task in each experiment required subjects to generate a series of 2- or 5-sec temporal productions. The nontemporal tasks were pursuit rotor tracking (Experiment 1), visual search (Experiment 2), and mental arithmetic (Experiment 3). Each nontemporal task had two levels of difficulty. All tasks were performed under both single- and dual-task conditions. A simple attentional allocation model predicts bidirectional interference between concurrent tasks. The main results showed the classic interference effect in timing. That is, the concurrent nontemporal tasks caused temporal productions to become longer (longer productions represent a shortening of perceived time) and/or more variable than did timing-only conditions. In general, the difficult version of each nontemporal task disrupted timing more than the easier version. The timing data also exhibited a serial lengthening effect, in which temporal productions became longer across trials. Nontemporal task performance showed a mixed pattern. Tracking and visual search were essentially unaffected by the addition of a timing task, whereas mental arithmetic was disrupted by concurrent timing. These results call for a modification of the attentional allocation model to incorporate the idea of specialized processing resources. Two major theoretical frameworks—multiple resource theory and the working memory model—are critically evaluated with respect to the resource demands of timing and temporal/ nontemporal dual-task performance.     

Working memory as a predictor of verbal fluency

This study investigated whether working memory capacity could account for individual differences in verbal fluency. Working memory was assessed by the speaking span test (Daneman & Green, 1986) that taxes the processing and storage functions of working memory during sentence production. Verbal fluency was assessed by (1) a speech generation task in which subjects made a speech about a picture; (2) an oral reading task in which subjects read aloud a prose passage; and (3) a Baars, Motley, and MacKay (1975) task for eliciting oral slips of the tongue (e.g.,wet gun forget one). Speking span was significantly correlated with performance on all three tasks; individuals with small speaking spans were less fluent and more prone to making speech errors. Whereas speaking span was related to individual differences in verbal fluency on the speech and reading tasks, reading span, a measure included to assess working memory capacity during sentence comprehension, was only significantly related to individual differences in verbal fluency on the reading task. The methodology proved useful for revealing whether a particular kind of oral reading error reflected a reading failure or an articulatory failure.This research was supported by a grant from the Natural Sciences and Engineering Research Council of Canada.     

Attention switching and working memory spans

Barrouillet and Camos () concluded from their developmental study on working memory that when performing complex span tasks, individuals maintain memory items by switching rapidly their attention from processing to storage while performing the concurrent task. Thus, a processing component that would require a continuous attentional focusing should have a highly detrimental effect on span. The present study verifies two predictions issuing from this hypothesis by comparing the classical self‐paced reading and operation span tasks with new computer‐paced tasks in adults. First, any increase in the pace at which the processing component of a working memory span task has to be performed impedes switching and then leads to lower spans. Second, when presented at a fast pace, even simple activities such as reading letters or adding and subtracting 1 to small numbers have an effect on spans as detrimental as complex activities like reading and understanding sentences or solving complex equations.     

Interference with visual short-term memory

Working memory (Baddeley and Hitch 1974) incorporates the notion of a visuo-spatial sketch pad; a mechanism thought to be specialized for short-term storage of visuo-spatial material. However, the nature and characteristics of this hypothesized mechanism are as yet unclear. Two experiments are reported which examined selective interference in short-term visual memory. Experiment 1 contrasted recognition memory span for visual matrix patterns with that for visually presented letter sequences. These two span tasks were combined with concurrent arithmetic or a concurrent task which involved manipulation of visuo-spatial material. Results suggested that although there was a small, significant disruption by concurrent arithmetic of span for the matrix patterns, there was a substantially larger disruption of the letter span task. The converse was true for the secondary visuo-spatial task. Experiment 2 combined the span tasks with two established tasks developed by Brooks (1967). Span for matrix patterns was disrupted by a visuo-spatial task but not by a secondary verbal task. The converse was true for letter span. These results suggest that the impairment in short-term visual memory resulting from secondary arithmetic reflects a small general processing load, but that the selective interference due to mode of processing is by far the stronger effect. Results are interpreted as being entirely consistent with the notion of a specialized visuo-spatial mechanism in working memory.