The Generality of Working Memory Capacity: A Latent-Variable Approach to Verbal and Visuospatial Memory Span and Reasoning.

A latent-variable study examined whether verbal and visuospatial working memory (WM) capacity measures reflect a primarily domain-general construct by testing 236 participants in 3 span tests each of verbal WM. visuospatial WM, verbal short-term memory (STM), and visuospatial STM. as well as in tests of verbal and spatial reasoning and general fluid intelligence (Gf). Confirmatory' factor analyses and structural equation models indicated that the WM tasks largely reflected a domain-general factor, whereas STM tasks, based on the same stimuli as the WM tasks, were much more domain specific. The WM construct was a strong predictor of Gf and a weaker predictor of domain-specific reasoning, and the reverse was true for the STM construct. The findings support a domain-general view of WM capacity, in which executive-attention processes drive the broad predictive utility of WM span measures, and domain-specific storage and rehearsal processes relate more strongly to domain-specific aspects of complex cognition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effects of smoking and smoking abstinence on verbal and visuospatial working memory capacity.

Several studies have examined the effects of smoking and abstaining from smoking on working memory (WM) but have yielded inconclusive findings. Thus, the authors used a repeated measures design to assess the effects of smoking and abstaining from smoking on both visuospatial and verbal WM capacity (WMC) using highly reliable, well-validated, and theoretically driven WM span tasks. Verbal n-back was also administered to examine its relationship to these complex WM span tasks and to compare this study's results with previous findings. Smokers (n = 23) and nonsmokers (n = 21) participated in 2 sessions separated by 1 week. During 1 session, smokers completed the WM tasks after abstaining from smoking for at least 12 hr, whereas in the other session smokers did not abstain from smoking and were tested immediately after smoking (all WM tasks were completed 45 min or less since last cigarette). Results indicated that smokers' verbal WM span was lower than nonsmokers' and was lower during the nonabstinent session compared with the abstinent session. Smokers' verbal n-back performance was also lower than nonsmokers', although there was no difference in verbal n-back performance between the smoking sessions. In contrast, there was no difference in visuospatial WM span between the smoking sessions or between smokers and nonsmokers. Taken together, these findings demonstrate that (a) smokers' verbal WM is lower than nonsmokers, (b) smokers' verbal WMC is lower during nonabstinence compared with abstinence, and (c) smoking exhibits differential effects on the different WM domains. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Working memory for complex figures: An fMRI comparison of letter and fractal n-back tasks.

n-back letter and fractal tasks were administered to I I participants during functional magnetic resonance imaging to test process specificity theories of prefrontal cortex (PFC) function and assess task validity. Tasks were matched on accuracy, but fractal n-back responses were slower and more conservative. Maintenance (1-back minus O-back) activated inferior parietal and dorsolateral PFC, with additional activation in right ventrolateral PFC during letter n-back and left lingual gyrus during fractal n-back. Maintenance plus manipulation (2-back minus 0-back) activated inferior parietal, Broca's area, insula, and dorsolateral and ventral PFC, with greater right dorsolateral PFC activation for letter n-back. Manipulation only (2-back minus 1-back) produced additional and equivalent dorsolateral PFC and anterior cingulate activation in both tasks. Results support fractal n-back validity and indicate substantial overlap in working memory functions of dorsal and ventral PFC. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The relationship between processing speed and working memory demand in systemic lupus erythematosus: Evidence from a visual n-back task.

Objective: Working memory (WM) deficits have been reported previously in systemic lupus erythematosus (SLE), but the relationship between information processing speed (PS) and WM deficits in SLE is unknown. This study examined whether or not PS slowing could account for the WM deficits observed in SLE. Method: A visual n-back task was used to measure simple and complex PS and WM in 40 SLE patients and 36 healthy controls. Simple PS was defined as reaction time (RT) to correct responses under a very low WM load condition (0-back), while complex PS was defined as RT to correct responses under moderate and high WM load conditions (1 and 2-back). Results: The results showed that SLE patients performed as well as the controls at the lower WM load conditions but had fewer correct responses than controls under the highest WM load condition (2-back). SLE patients had slower RTs than controls under all conditions, but they had relatively greater RT slowing than controls under the higher WM load conditions. Further, when RT for simple PS was subtracted from complex PS, SLE patients still showed slower complex PS for the 1- and 2-back compared with controls. Both simple and complex PS slowing were related to poorer accuracy scores on the 2-back condition, only for the SLE group. Conclusions: The n-back task provides a sensitive measure of PS and WM. The results suggest that PS deficits alone could not account for the WM deficits in SLE. Disease duration, disease activity, and depression did not appear to account for the observed PS and WM deficits. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Changes in Working Memory After Traumatic Brain Injury in Children.

The impact of traumatic brain injury (TBI) on working memory (WM) was studied in 144 children (79 with mild, 23 with moderate, and 42 with severe injuries) who underwent magnetic resonance imaging (MRI) at 3 months and were tested at baseline and at 3, 6, 12, and 24 months postinjury. An n-back WM task for letter identity was administered with memory load ranging from 1- to 3-back and a 0-back condition. A TBI Severity × Quadratic Tune interaction showed that net percentage correct (correct detections of targets minus false alarms) was significantly lower in severe than in mild TBI groups. The Left Frontal Lesions × Age interaction approached significance. Mechanisms mediating late decline in WM and the effects of left frontal lesions are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neural mechanisms of interference control underlie the relationship between fluid intelligence and working memory span.

Fluid intelligence (gF) and working memory (WM) span predict success in demanding cognitive situations. Recent studies show that much of the variance in gF and WM span is shared, suggesting common neural mechanisms. This study provides a direct investigation of the degree to which shared variance in gF and WM span can be explained by neural mechanisms of interference control. The authors measured performance and functional magnetic resonance imaging activity in 102 participants during the n-back WM task, focusing on the selective activation effects associated with high-interference lure trials. Brain activity on these trials was correlated with gF, WM span, and task performance in core brain regions linked to WM and executive control, including bilateral dorsolateral prefrontal cortex (middle frontal gyrus; BA9) and parietal cortex (inferior parietal cortex; BA 40/7). Interference-related performance and interference-related activity accounted for a significant proportion of the shared variance in gF and WM span. Path analyses indicate that interference control activity may affect gF through a common set of processes that also influence WM span. These results suggest that individual differences in interference-control mechanisms are important for understanding the relationship between gF and WM span. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Interference, aging, and visuospatial working memory: The role of similarity.

Objective: Older adults' performance on working memory (WM) span tasks is known to be negatively affected by the buildup of proactive interference (PI) across trials. PI has been reduced in verbal tasks and performance increased by presenting distinctive items across trials. In addition, reversing the order of trial presentation (i.e., starting with the longest sets first) has been shown to reduce PI in both verbal and visuospatial WM span tasks. We considered whether making each trial visually distinct would improve older adults' visuospatial WM performance, and whether combining the 2 PI-reducing manipulations, distinct trials and reversed order of presentation, would prove additive, thus providing even greater benefit. Method: Forty-eight healthy older adults (age range = 60–77 years) completed 1 of 3 versions of a computerized Corsi block test. For 2 versions of the task, trials were either all visually similar or all visually distinct, and were presented in the standard ascending format (shortest set size first). In the third version, visually distinct trials were presented in a reverse order of presentation (longest set size first). Results: Span scores were reliably higher in the ascending version for visually distinct compared with visually similar trials, F(1, 30) = 4.96, p = .03, η2 = .14. However, combining distinct trials and a descending format proved no more beneficial than administering the descending format alone. Conclusions: Our findings suggest that a more accurate measurement of the visuospatial WM span scores of older adults (and possibly neuropsychological patients) might be obtained by reducing within-test interference. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Working memory plasticity in old age: Practice gain, transfer, and maintenance.

Adult age differences in cognitive plasticity have been studied less often in working memory than in episodic memory. The authors investigated the effects of extensive working memory practice on performance improvement, transfer, and short-term maintenance of practice gains and transfer effects. Adults age 20-30 years and 70-80 years practiced a spatial working memory task with 2 levels of processing demands across 45 days for about 15 min per day. In both age groups and relative to age-matched, no-contact control groups, we found (a) substantial performance gains on the practiced task, (b) near transfer to a more demanding spatial n-back task and to numerical n-back tasks, and (c) 3-month maintenance of practice gains and near transfer effects, with decrements relative to postpractice performance among older but not younger adults. No evidence was found for far transfer to complex span tasks. The authors discuss neuronal mechanisms underlying adult age differences and similarities in patterns of plasticity and conclude that the potential of deliberate working memory practice as a tool for improving cognition in old age merits further exploration. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dynamic cortical networks of verbal and spatial working memory: effects of memory load and task practice

Working memory (WM), the ability to briefly retain and manipulate information in mind, is central to intelligent behavior. Here we take advantage of the high temporal resolution of electrophysiological measures to obtain a millisecond timescale view of the activity induced in distributed cortical networks by tasks that impose significant WM demands. We examined how these networks are affected by the type and amount of information to be remembered, and by the amount of task practice. Evoked potentials (EPs) were obtained from eight subjects performing spatial and verbal versions of a visual n-back WM task (n = 1, 2, 3) on each of three testing days. In well-trained subjects, WM tasks elicited transient responses reflecting different subcomponents of task processing, including transient (lasting 0.02-0.3 s) task-sensitive and load-sensitive EPs, as well as sustained responses (lasting 1-1.5 s), including the prestimulus Contingent Negative Variation (CNV), and post-stimulus frontal and parietal Slow Waves. The transient responses, with the exception of the P300, differed between the verbal and spatial task versions, and between trials with different response requirements. The P300 and the Slow Waves were not affected by task version but were affected by increased WM load. These results suggest that WM emerges from the formation of a dynamic cortical network linking task-specific processes with non-specific, capacity-limited, higher-order attentional processes. Practice effects on the EPs suggested that practice led to the development of a more effective cognitive strategy for dealing with lower-order aspects of task processing, but did not diminish demands made on higher order processes. Thus a simple WM task is shown to be composed of numerous elementary subsecond neural processes whose characteristics vary with type and amount of information being remembered, and amount of practice.     

Complex span versus updating tasks of working memory: The gap is not that deep.

How to best measure working memory capacity is an issue of ongoing debate. Besides established complex span tasks, which combine short-term memory demands with generally unrelated secondary tasks, there exists a set of paradigms characterized by continuous and simultaneous updating of several items in working memory, such as the n-back, memory updating, or alpha span tasks. With a latent variable analysis (N = 96) based on content-heterogeneous operationalizations of both task families, the authors found a latent correlation between a complex span factor and an updating factor that was not statistically different from unity (r = .96). Moreover, both factors predicted fluid intelligence (reasoning) equally well. The authors conclude that updating tasks measure working memory equally well as complex span tasks. Processes involved in building, maintaining, and updating arbitrary bindings may constitute the common working memory ability underlying performance on reasoning, complex span, and updating tasks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Individual differences in working memory within a nomological network of cognitive and perceptual speed abilities.

It has become fashionable to equate constructs of working memory (WM) and general intelligence (g). Few investigations have provided direct evidence that WM and g measures yield similar ordering of individuals. Correlational investigations have yielded mixed results. The authors assess the construct space for WM and g and demonstrate that WM shares substantial variance with perceptual speed (PS) constructs. Thirty-six ability tests representing verbal, numerical, spatial, and PS abilities; the Raven Advanced Progressive Matrices; and 7 WM tests were administered to 135 adults. A nomological representation for WM is provided through a series of cognitive and PS ability models. Construct overlap between PS and WM is further investigated with attention to complexity, processing differences, and practice effects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cold pressor stress impairs performance on working memory tasks requiring executive functions in healthy young men.

The current study investigated the effects of cold pressor stress (CPS) on 2 working memory (WM) tasks differing in the demand they put on maintenance and executive processing. For this purpose 72 healthy young men were exposed either to a stress group or a nonstressful control group. Subsequently, WM performance on the O-Span task (Turner & Engle, 1989) and the digit span task was assessed. Salivary cortisol was measured before and 2 times after the treatment as a marker of hypothalamus–pituitary–adrenal (HPA) axis activity. Results revealed a significant performance impairment of the O-Span and the digit span task backward in stressed subjects that correlated negatively with CPS-induced cortisol increases. Digit span forward was neither affected by CPS nor related to the ensuing cortisol increases. These results indicate that acute stress impairs WM performance for tasks requiring executive functions that operate on the stored material but not for WM tasks that only require maintenance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Similarities and differences between working memory and long-term memory: Evidence from the levels-of-processing span task.

Two experiments compared the effects of depth of processing on working memory (WM) and long-term memory (LTM) using a levels-of-processing (LOP) span task, a newly developed WM span procedure that involves processing to-be-remembered words based on their visual, phonological, or semantic characteristics. Depth of processing had minimal effect on WM tests, yet subsequent memory for the same items on delayed tests showed the typical benefits of semantic processing. Although the difference in LOP effects demonstrates a dissociation between WM and LTM, we also found that the retrieval practice provided by recalling words on the WM task benefited long-term retention, especially for words initially recalled from supraspan lists. The latter result is consistent with the hypothesis that WM span tasks involve retrieval from secondary memory, but the LOP dissociation suggests the processes engaged by WM and LTM tests may differ. Therefore, similarities and differences between WM and LTM depend on the extent to which retrieval from secondary memory is involved and whether there is a match (or mismatch) between initial processing and subsequent retrieval, consistent with transfer-appropriate-processing theory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The role of working memory in spatial S-R correspondence effects.

This study investigates the impact of working memory (WM) load on response conflicts arising from spatial (non) correspondence between irrelevant stimulus location and response location (Simon effect). The dominant view attributes the Simon effect to automatic processes of location-based response priming. The automaticity view predicts insensitivity of the Simon effect to manipulations of processing load. Four experiments investigated the role of spatial and verbal WM in horizontal and vertical Simon tasks by using a dual-task approach. Participants maintained different amounts of spatial or verbal information in WM while performing a horizontal or vertical Simon task. Results showed that high load generally decreased, and sometimes eliminated, the Simon effect. It is interesting to note that spatial load had a larger impact than verbal load on the horizontal Simon effect, whereas verbal load had a larger impact than spatial load on the vertical Simon effect. The results highlight the role of WM as the perception-action interface in choice-response tasks. Moreover, the results suggest spatial coding of horizontal stimulus-response (S-R) tasks, and verbal coding of vertical S-R tasks. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

How are visuospatial working memory, executive functioning, and spatial abilities related? A latent-variable analysis.

This study examined the relationships among visuospatial working memory (WM) executive functioning, and spatial abilities. One hundred sixty-seven participants performed visuospatial short-term memory (STM) and WM span tasks, executive functioning tasks, and a set of paper-and-pencil tests of spatial abilities that load on 3 correlated but distinguishable factors (Spatial Visualization, Spatial Relations, and Perceptual Speed). Confirmatory factor analysis results indicated that, in the visuospatial domain, processing-and-storage WM tasks and storage-oriented STM tasks equally implicate executive functioning and are not clearly distinguishable. These results provide a contrast with existing evidence from the verbal domain and support the proposal that the visuospatial sketchpad may be closely tied to the central executive. Further, structural equation modeling results supported the prediction that, whereas they all implicate some degree of visuospatial storage, the 3 spatial ability factors differ in the degree of executive involvement (highest for Spatial Visualization and lowest for Perceptual Speed). Such results highlight the usefulness of a WM perspective in characterizing the nature of cognitive abilities and, more generally, human intelligence. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Working-memory capacity and the control of attention: The contributions of goal neglect, response competition, and task set to Stroop interference.

Individual differences in working-memory (WM) capacity predicted performance on the Stroop task in 5 experiments, indicating the importance of executive control and goal maintenance to selective attention. When the Stroop task encouraged goal neglect by including large numbers of congruent trials (RED presented in red), low WM individuals committed more errors than did high WM individuals on the rare incongruent trials (BLUE in red) that required maintaining access to the "ignore-the-word" goal for accurate responding. In contrast, in tasks with no or few congruent trials, or in high-congruency tasks that followed low-congruency tasks, WM predicted response-time interference. WM was related to latency, not accuracy, in contexts that reinforced the task goal and so minimized the difficulty of actively maintaining it. The data and a literature review suggest that Stroop interference is jointly determined by 2 mechanisms, goal maintenance and competition resolution, and that the dominance of each depends on WM capacity, as well as the task set induced by current and previous contexts. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

COMT val158Met and executive control: A test of the benefit of specific deficits to translational research.

The role of catechol-O-methyltransferase (COMT) val158met in prefrontal cortical deficits associated with the liability to schizophrenia remains controversial. This study evaluated 464 healthy adult participants using three measures of executive functions in working memory: a 3-back version of the N-back continuous performance task (CPT) and two variants of the AX-CPT. The interpretability of N-back performance was confounded by possible generalized deficits, whereas the AX variants included internal controls for uncovering specific deficits. There was no relationship between the COMT genotype and N-back performance, whereas val/val individuals had a specific deficit on a dot-pattern version of the AX-CPT. In this case, a specific executive function known as context processing appeared to be compromised. These data suggest that the interpretability gained by including task manipulations to uncover specific deficits can enhance associations between cognitive and genetic levels of analysis. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Working memory training in older adults: Evidence of transfer and maintenance effects.

Few studies have examined working memory (WM) training-related gains and their transfer and maintenance effects in older adults. This present research investigates the efficacy of a verbal WM training program in adults aged 65–75 years, considering specific training gains on a verbal WM (criterion) task as well as transfer effects on measures of visuospatial WM, short-term memory, inhibition, processing speed, and fluid intelligence. Maintenance of training benefits was evaluated at 8-month follow-up. Trained older adults showed higher performance than did controls on the criterion task and maintained this benefit after 8 months. Substantial general transfer effects were found for the trained group, but not for the control one. Transfer maintenance gains were found at follow-up, but only for fluid intelligence and processing speed tasks. The results are discussed in terms of cognitive plasticity in older adults. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Performance of schizophrenia and bipolar patients on verbal and figural working memory tasks.

Working memory (WM) was studied in 82 healthy volunteers, 43 schizophrenia patients, and 81 bipolar patients. Schizophrenia patients were impaired on verbal and figural WM tasks that possessed similar test discriminating power. Bipolar patients performed similarly to healthy volunteers. A mathematical model of WM performance revealed a primary role for reduced WM span in accounting for the impaired verbal WM of schizophrenia patients and a primary role for diminished attention in accounting for impaired figural WM. Although WM impairment in schizophrenia is due neither to the general effects of severe mental illness nor to the specific type of material studied, the microarchitecture of abnormal WM in schizophrenia may depend on the stimulus material presented. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Fearful faces influence attentional control processes in anxious youth and adults.

This study examined the effects of trait anxiety and age on performance of an emotional working memory task designed to investigate attentional control processes in the context of emotion. Participants included children, adolescents, and adults (8–30 years old). They performed the Emotional Face N-Back (EFNBACK) task, a modified n-back working memory task with four emotional distracter types (no picture, neutral, fearful, and happy) and two memory-load conditions (0-back and 2-back), and completed self-report trait anxiety measures. Results indicated that participants high in trait anxiety had slower reaction times on the fearful 2-back memory-load condition. A significant interaction with age indicated that this effect was greater in the younger participants. These findings suggest that anxious individuals, particularly younger ones, exhibit difficulty resisting interference from threat-related stimuli when greater attentional resources are being recruited. (PsycINFO Database Record (c) 2010 APA, all rights reserved)