Working Memory Demands Research Articles

Complementary topology of maintenance and manipulation brain networks in working memory

Working memory (WM) is assumed to consist of a process that sustains memory representations in an active state (maintenance) and a process that operates on these activated representations (manipulation). We examined evidence for two distinct, concurrent cognitive functions supporting maintenance and manipulation abilities by testing brain activity as participants performed a WM alphabetization task. Maintenance was investigated by varying the number of letters held in WM and manipulation by varying the number of moves required to sort the list alphabetically. We found that both maintenance and manipulation demand had significant effects on behavior that were associated with different cortical regions: maintenance was associated with bilateral prefrontal and left parietal cortex, and manipulation with right parietal activity, a link that is consistent with the role of parietal cortex in symbolic computations. Both structural and functional architecture of these systems suggested that these cognitive functions are supported by two dissociable brain networks. Critically, maintenance and manipulation functional networks became increasingly segregated with increasing demand, an effect that was positively associated with individual WM ability. These results provide evidence that network segregation may act as a protective mechanism to enable successful performance under increasing WM demand.

Perceptual biases during cued task switching relate to decision process differences between children and adults.

Previous work suggests that children engage preparatory processing differently than adults in cued task switching. One potential consequence is that they are differentially biased by visual properties of the stimuli, for example, target-choice similarity. We tested this possibility in 215 children and young adults ranging from 6 to 27 years of age. Participants played a cue-target game with varying levels of working memory and attentional demand where they matched multidimensional stimuli according to a cued dimension. Younger age, low working memory demand, and matching fine grained dimensions (i.e., pattern) increased the bias of target-choice similarity on task performance. Older age, high working memory, and matching global dimensions (i.e., shape) mitigated the bias. Developmental transitions to adult performance differed by task demands but generally occurred during adolescence. A drift diffusion analysis revealed age and task differences in decision making strategies consistent with how similarity impacted task performance, indicating that, especially with low working memory demand, children made impulsive, similarity-driven decisions. Our findings support the idea that children engage in preparation strategies that exacerbate perceptual biases on task performance; improvements are observed with age or through changes in task structure and stimuli. These results have implications for interpreting cognitive control performance in children. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

A secondary task is not always costly: Context-based guidance of visual search survives interference from a demanding working memory task.

Repeatedly encountering a visual search display with the target located at a fixed position relative to the distractors facilitates target detection, relative to novel displays – which is attributed to search guidance by (acquired) long‐term memory (LTM) of the distractor ‘context’ of the target. Previous research has shown that this ‘contextual cueing’ effect is severely impeded during learning when participants have to perform a demanding spatial working memory (WM) task concurrently with the search task, though it does become manifest when the WM task is removed. This has led to the proposal that search guidance by LT context memories critically depends on spatial WM to become ‘expressed’ in behaviour. On this background, this study, of two experiments, asked: (1) Would contextual cueing eventually emerge under dual‐task learning conditions if the practice on the task(s) is extended beyond the short training implemented in previous studies? and given sufficient practice, (2) Would performing the search under dual‐task conditions actually lead to an increased cueing effect compared to performing the visual search task alone? The answer is affirmative to both questions. In particular, Experiment 1 showed that a robust contextual cueing effect emerges within 360–720 dual‐task trials as compared to some 240 single‐task trials. Further, Experiment 2 showed that when dual‐ and single‐task conditions are performed in alternating trials blocks, the cueing effect for the very same set of repeated displays is significantly larger in dual‐task blocks than in single‐task blocks. This pattern of effects suggests that dual‐task practice eventually leads to direct, or ‘automatic’, guidance of visual search by learnt spatial LTM representations, bypassing WM processes. These processes are normally engaged in single‐task performance might actually interfere with direct LTM‐based search guidance.

Temporal visual statistical learning is enhanced by increasing working memory demands related to sequence members

Temporal visual statistical learning is enhanced by increasing working memory demands related to sequence members

Evaluating decision making in a multi-objective route planning-task

The present study is an initial investigation of complex decision making performance. Specifically, this work investigated how individuals make decisions involving risk and uncertainty within a spatially focused route planning task involving multiple simulated unmanned vehicles and objectives. Forty-three participants were instructed to create twenty-four route plans, half of which included a combination of risky route suggestions and enhanced icons. Given the high working memory demands of developing a route for multiple vehicles, it was expected that enhanced visualizations, which provided redundant information on target priority, uncertainty, and deadline, would reduce demands on working memory and improve performance. Additionally, it was predicted that providing risky route suggestions would negatively impact performance, yet enhanced visualizations would reduce the effect of risky route suggestions. However, findings supported neither hypothesis; there was no performance difference in providing enhanced visualizations, and risky sub-optimal route suggestions actually improved the expected value of the submitted route. These results could have occurred due to multiple factors, including the multi-objective route planning task being too complex, or the scenarios lacking sufficient variability in expected value. An additional interpretation of these findings is that humans are really poor at performing these complex multi-objective tasks, and failed to comprehend the uncertainty and risk inherent in their decisions.

Abnormal neural response to phonological working memory demands in persistent developmental stuttering.

Persistent developmental stuttering is a neurological disorder that commonly manifests as a motor problem. Cognitive theories, however, hold that poorly developed cognitive skills are the origins of stuttering. Working memory (WM), a multicomponent cognitive system that mediates information maintenance and manipulation, is known to play an important role in speech production, leading us to postulate that the neurophysiological mechanisms underlying stuttering may be associated with a WM deficit. Using functional magnetic resonance imaging, we aimed to elucidate brain mechanisms in a phonological WM task in adults who stutter and controls. A right-lateralized compensatory mechanism for a deficit in the rehearsal process and neural disconnections associated with the central executive dysfunction were found. Furthermore, the neural abnormalities underlying the phonological WM were independent of memory load. This study demonstrates for the first time the atypical neural responses to phonological WM in PWS, shedding new light on the underlying cause of stuttering.

Impaired neural mechanism for online novel word acquisition in dyslexic children

Developmental dyslexia is characterised as an inability to read fluently. Apart from literacy problems, dyslexics have other language difficulties including inefficient speech encoding and deficient novel word learning. Yet, the neural mechanisms underlying these impairments are largely unknown. We tracked online formation of neural memory traces for a novel spoken word-form in dyslexic and normal-reading children by recording the brain’s electrophysiological response dynamics in a passive perceptual exposure session. Crucially, no meaning was assigned to the new word-form nor was there any task related to the stimulus, enabling us to explore the memory-trace formation of a purely phonological form in the absence of any short-term or working memory demands. Similar to previously established neural index of rapid word learning in adults, the control children demonstrated an early brain response enhancement within minutes of exposure to the novel word-form that originated in frontal cortices. Dyslexic children, however, lacked this neural enhancement over the entire course of exposure. Furthermore, the magnitude of the rapid neural enhancement for the novel word-form was positively associated with reading and writing fluency. This suggests that the rapid neural learning mechanism for online acquisition of novel speech material is associated with reading skills. Furthermore, the deficient online learning of novel words in dyslexia, consistent with poor rapid adaptation to familiar stimuli, may underlie the difficulty of learning to read.

Frequency of finger looking during finger counting is related to children's working memory capacities

ABSTRACTFinger counting can be useful in solving arithmetic problems, noticeably because it reduces the working memory demand of mental calculations. However, proprioceptive information might not be sufficient to keep track of the number of fingers raised during problem solving, and visual input may play an important role in this process. The present study was designed to address this question and shows that 8-year-old children look at their fingers in 60% of the trials during finger counting when solving additive problems. Moreover, our results reveal that the frequency of finger looking is negatively correlated with working memory capacities and is higher for more difficult problems. These findings suggest that finger looking is recruited in managing the cognitive demand of the arithmetic task, probably by providing additional external cues to monitor the number of steps that have to be incremented during finger counting.

Impaired recruitment of dopamine neurons during working memory in mice with striatal D2 receptor overexpression

The dopamine (DA) system plays a major role in cognitive functions through its interactions with several brain regions including the prefrontal cortex (PFC). Conversely, disturbances in the DA system contribute to cognitive deficits in psychiatric diseases, yet exactly how they do so remains poorly understood. Here we show, using mice with disease-relevant alterations in DA signaling (D2R-OE mice), that deficits in working memory (WM) are associated with impairments in the WM-dependent firing patterns of DA neurons in the ventral tegmental area (VTA). The WM-dependent phase-locking of DA neurons to 4 Hz VTA-PFC oscillations is absent in D2R-OE mice and VTA-PFC synchrony deficits scale with their WM impairments. We also find reduced 4 Hz synchrony between VTA DA neurons and selective impairments in their representation of WM demand. These results identify how altered DA neuron activity—at the level of long-range network activity and task-related firing patterns—may underlie cognitive impairments.

Non-adaptive strategy selection in adults with high mathematical anxiety

Participants with mathematical anxiety (MA) tend to show particular difficulty in mathematical operations with high working memory (WM) demands compared to operations with lower WM demands. Accordingly, we examined strategy selection to test the cognitive mechanism underlying the observed weakness of high MA participants in mathematical operations with high WM demands. We compared two groups of college students with high or low MA, in the solution of simple non-carry addition problems (e.g., 54 + 63) and complex carryover addition problems (e.g., 59 + 63). The results indicated that high MA participants showed particular difficulty in the harder carry condition. Testing the strategy selection mechanism among high MA participants, we found in the carry condition 1) they used the common strategy less often compared to low MA participants and 2) employed unusual strategies more often compared to low MA participants. Therefore, high MA participants were less efficient in their strategy selection, which may be due to weaker spatial representations, numerical difficulties, or less experience solving complex problems. These primitive representations are not adaptive, and can negatively impact performance in math tasks with high WM demands.

Effects of Working Memory Load and Age on the Comprehension of Passive Sentences

The ability of older adults to comprehend sentences may decline due to the cognitive changes in working memory. Therefore, an increase in working memory demands during sentence comprehension would result in poorer performance among older adults. To test this hypothesis, the present study explored sentence comprehension as a result of manipulations of age and working memory loads using a sentence-picture matching task. 35 older adults and 35 younger adults were required to match Mandarin passive sentences (high working memory load) and active sentences (low working memory load) with pictures. Passive sentences were found to be more difficult than active sentences for all participants. Older adults responded to passive sentences more slowly than younger adults. However, no significant age difference was found in accuracy of responses. Accuracy on passive sentence comprehension was marginally correlated with syntactic complexity effect among older adults. Compared with younger adults, older adults seem to be more disrupted by the increased WM load in passive sentence comprehension, but they can compensate for the decline in the accuracy of comprehension by spending extra time on sentences with high WM load.

Atypical White Matter Connectivity in Dyslexic Readers of a Fairly Transparent Orthography.

Atypical structural properties of the brain’s white matter bundles have been associated with failing reading acquisition in developmental dyslexia. Because these white matter properties may show dynamic changes with age and orthographic depth, we examined fractional anisotropy (FA) along 16 white matter tracts in 8- to 11-year-old dyslexic (DR) and typically reading (TR) children learning to read in a fairly transparent orthography (Dutch). Our results showed higher FA values in the bilateral anterior thalamic radiations of DRs and FA values of the left thalamic radiation scaled with behavioral reading-related scores. Furthermore, DRs tended to have atypical FA values in the bilateral arcuate fasciculi. Children’s age additionally predicted FA values along the tracts. Together, our findings suggest differential contributions of cortical and thalamo-cortical pathways to the developing reading network in dyslexic and typical readers, possibly indicating prolonged letter-by-letter reading or increased attentional and/or working memory demands in dyslexic children during reading.

Time-based prospective memory in children and adolescents with traumatic brain injury: Impact of working memory demands.

Difficulties with prospective memory are frequently reported following pediatric traumatic brain injury (TBI), but rarely researched. We aimed to (i) investigate time-based prospective memory post-pediatric TBI; (ii) examine whether time-based prospective memory is differentially impacted by the demand placed on working memory; and (iii) explore which components of working memory (viz., central executive, phonological loop, and visuospatial sketchpad) are involved in time-based prospective memory under low and high cognitive load following pediatric TBI. Thirty-nine children and adolescents (20 survivors of moderate-severe TBI and 19 healthy controls) completed (i) a newly developed time-based prospective memory task (TBPMT), embedded in an ongoing lexical-decision task, with two conditions: low and high working memory load; and (ii) tests of working memory components from the Automated Working Memory Assessment. Compared to controls, participants with TBI had significantly lower prospective memory accuracy on the TBPMT across working memory loads (low, high). In contrast, the groups did not differ in time monitoring or accuracy on the ongoing task. In the TBI group, higher scores on tests of the central executive (but not phonological loop or visuospatial sketchpad) were associated with higher prospective memory accuracy and time monitoring (controlling for age). Time-based prospective memory is impaired following moderate-severe pediatric TBI, irrespective of the level of working memory demand. Our findings suggest that children and adolescents with TBI may be at risk of failing to perform future intentions at the right time in daily life, especially for individuals identified as having deficits in central executive functioning. (PsycINFO Database Record

Do Working Memory Deficits Underlie Reading Problems in Attention-Deficit/Hyperactivity Disorder (ADHD)?

Reading problems are common in children with ADHD and show strong covariation with these children's underdeveloped working memory abilities. In contrast, working memory training does not appear to improve reading performance for children with ADHD or neurotypical children. The current study bridges the gap between these conflicting findings, and combines dual-task methodology with Bayesian modeling to examine the role of working memory for explaining ADHD-related reading problems. Children ages 8-13 (M = 10.50, SD = 1.59) with and without ADHD (N = 78; 29 girls; 63% Caucasian/Non-Hispanic) completed a counterbalanced series of reading tasks that systematically manipulated concurrent working memory demands. Adding working memory demands produced disproportionate decrements in reading comprehension for children with ADHD (d = -0.67) relative to Non-ADHD children (d = -0.18); comprehension was significantly reduced in both groups when working memory demands were increased. These effects were robust to controls for foundational reading skills (decoding, sight word vocabulary) and comorbid reading disability. Concurrent working memory demands did not slow reading speed for either group. The ADHD group showed lower comprehension (d = 1.02) and speed (d = 0.69) even before adding working memory demands beyond those inherently required for reading. Exploratory conditional effects analyses indicated that underdeveloped working memory overlapped with 41% (comprehension) and 85% (speed) of these between-group differences. Reading problems in ADHD appear attributable, at least in part, to their underdeveloped working memory abilities. Combined with prior cross-sectional and longitudinal findings, the current experimental evidence positions working memory as a potential causal mechanism that is necessary but not sufficient for effectively understanding written language.

Electrophysiological repetition effects in persons with mild cognitive impairment depend upon working memory demand

Forms of implicit memory, including repetition effects, are preserved relative to explicit memory in clinical Alzheimer's disease. Consequently, cognitive interventions for persons with Alzheimer's disease have been developed that leverage this fact. However, despite the clinical robustness of behavioral repetition effects, altered neural mechanisms of repetition effects are studied as biomarkers of both clinical Alzheimer's disease and pre-morbid Alzheimer's changes in the brain. We hypothesized that the clinical preservation of behavioral repetition effects results in part from concurrent operation of discrete memory systems. We developed two experiments that included probes of emotional repetition effects differing in that one included an embedded working memory task. We found that neural repetition effects manifested in patients with amnestic mild cognitive impairment, the earliest form of clinical Alzheimer's disease, during emotional working memory tasks, but they did not manifest during the task that lacked the embedded working memory manipulation. Specifically, the working memory task evoked neural repetition effects in the P600 time-window, but the same neural mechanism was only minimally implicated in the task without a working memory component. We also found that group differences in behavioral repetition effects were smaller in the experiment with a working memory task. We suggest that cross-domain cognitive challenge can expose “defunct” neural capabilities of individuals with amnestic mild cognitive impairment.

General Slowing and Education Mediate Task Switching Performance Across the Life-Span.

Objective: This study considered the potential role of both protective factors (cognitive reserve, CR) and adverse ones (general slowing) in modulating cognitive flexibility in the adult life-span.Method: Ninety-eight individuals performed a task-switching (TS) paradigm in which we adopted a manipulation concerning the timing between the cue and the target. Working memory demands were minimized by using transparent cues. Additionally, indices of cognitive integrity, depression, processing speed and different CR dimensions were collected and used in linear models accounting for TS performance under the different time constraints.Results: The main results showed similar mixing costs and higher switching costs in older adults, with an overall age-dependent effect of general slowing on these costs. The link between processing speed and TS performance was attenuated when participants had more time to prepare. Among the different CR indices, formal education only was associated with reduced switch costs under time pressure.Discussion: Even though CR is often operationalized as a unitary construct, the present research confirms the benefits of using tools designed to distinguish between different CR dimensions. Furthermore, our results provide empirical support to the assumption that processing speed influence on executive performance depends on time constraints. Finally, it is suggested that whether age differences appear in terms of switch or mixing costs depends on working memory demands (which were low in our tasks with transparent cues).

Effects of Age and Working Memory Load on Syntactic Processing: An Event-Related Potential Study.

Cognitive changes in aging include working memory (WM) decline, which may hamper language comprehension. An increase in WM demands in older adults would probably provoke a poorer sentence processing performance in this age group. A way to increase the WM load is to separate two lexical units in an agreement relation (i.e., adjective and noun), in a given sentence. To test this hypothesis, event-related potentials (ERPs) were collected from Spanish speakers (30 older adults, mean age = 66.06 years old; and 30 young adults, mean age = 25.7 years old) who read sentences to detect grammatical errors. The sentences varied with regard to (1) the gender agreement of the noun and adjective, where the gender of the adjective either agreed or disagreed with the noun, and (2) the WM load (i.e., the number of words between the noun and adjective in the sentence). No significant behavioral differences between groups were observed in the accuracy of the response, but older adults showed longer reaction times regardless of WM load condition. Compared with young participants, older adults showed a different pattern of ERP components characterized by smaller amplitudes of LAN, P600a, and P600b effects when the WM load was increased. A smaller LAN effect probably reflects greater difficulties in processing the morpho-syntactic features of the sentence, while smaller P600a and P600b effects could be related to difficulties in recovering and mapping all sentence constituents. We concluded that the ERP pattern in older adults showed subtle problems in syntactic processing when the WM load was increased, which was not sufficient to affect response accuracy but was only observed to result in a longer reaction time.

F156. LONGITUDINAL WORKING MEMORY FUNCTIONAL DYSCONNECTIVITY REFLECTS HETEROGENEITY IN INDIVIDUALS AT ULTRA HIGH RISK FOR PSYCHOSIS

BackgroundVariation in trajectories of Ultra high-risk (UHR) psychosis mental state posts challenge to schizophrenia prevention or onset delay intervention. Our previous work described the heterogeneity at this prodromal stage of schizophrenia in both brain structure changes and resting-state functional network differences. Functional dysconnectivity can be one of the altered brain substrates underlying clinical symptoms. Lower resting-state functional connectivity (FC) within the salience network (SN) in schizophrenia was detectable at the UHR stage. FC between the frontoparietal network (FPN) and the SN was disrupted when network integration fell apart in the UHR state.FPN and SN are important for working memory (WM), which is largely compromised in schizophrenia and lesser in UHR group. Our previous work showed that WM task-related activation in the FPN and SN differed between the UHR and controls. Importantly, such differences varied with WM demands. Evidence has demonstrated that compared to resting-state FC, task-based FC may better predict behavioral performance. However, the WM-related FC in UHR group and its longitudinal changes are still largely unknown.To cover the gap, we sought to examine the heterogeneity in the WM task-related FC changes in a group of UHR participants over time. We expected WM-related FC would link to individual differences in clinical trajectories.MethodsBased on the longitudinal changes of UHR state within 2 years, participants were divided into 3 groups: 42 controls, 34 UHR remitters (UHR-R) and 42 UHR non-remitters (UHR-NR). We acquired fMRI (TR/TE = 2000/30 ms, 3 x 3 x 4 mm3, 28 slices) when participants performed WM task at different WM demands, varying from information maintenance alone (low) to requiring both maintenance and manipulation (high). We used seed-based approach (gPPI) to compare task-related FC of the FPN and the SN among groups. Voxel-wise FC with six seeds (bilateral anterior insula, parietal, and dorsal lateral prefrontal cortex, identified based on task activation) was regressed on WM demands and groups, controlling for age, gender, education, ethnicity, handedness and task accuracy. Linear mixed modeling methods were used to test longitudinal FC changes and the association between FC and clinical syndromes.ResultsTask performance was worse at high WM demand as expected, but no significant difference was found between groups or over time. Compared to controls, higher FC between the FPN (superior parietal gyrus) and the SN (insula) at low demand was observed in the UHR-NR group at baseline. Within the SN, WM-demand related FC between right insula and thalamus varied among 3 groups: low FC at low demand and high FC at high demand in controls; high FC at low demand but low FC at high demand in the UHR-R group. In contrast, UHR-NR group had high thalamus-insula FC in both WM demands.Moreover, longitudinal FC increase only occurred within the SN at high WM demand in the UHR-R group, while other task-related baseline group differences of FC remained stable over time. Importantly, the rate of intra-SN increase of FC over time at higher WM demand was associated with decline of the positive psychosis syndromes in the UHR-R group.DiscussionIn support of the functional dysconnectivity hypothesis, our study indicated that UHR state was accompanied by altered brain FC during WM task performance. In contrast to lower SN FC at rest, UHR state showed SN hyper-connectivity in task with low WM demand, suggesting the importance of studying UHR both at resting and in task. Importantly, intra-SN FC increase at high WM demand was linked to positive psychosis syndrome reduction in remitters, while no FC changes if UHR state persisted. We argued that task FC could reflect the clinical heterogeneity of the UHR group.

Effects of working memory demands on sentence production in aphasia

Abstract The purpose of the study was to investigate the effects of task demands on sentence production and their relation to working memory (WM) capacity in people with aphasia using a verb-final language. The current study manipulated the WM loads on the sentence production tasks by varying the following three factors: task type (syntactic priming vs. sentence completion), sentence type (active vs. passive), and canonicity (canonical vs. noncanonical word order). Task type and word order canonicity were related to individual differences in WM capacity in both people with aphasia and their normal controls.

Combinations of Simple Mechanisms Explain Diverse Strategies in the Freehand Writing of Memorized Sentences.

Individual differences in the strategies that control sequential behavior were investigated in an experiment in which participants memorized sentences and then wrote them by hand, in a non-cursive style. Thirty-two participants each wrote eight sentences, which had hierarchical structures with five levels. The dataset included over 31,000 letters. Despite the deliberately constrained nature of the task and stimuli, 23 patterns of behavior were identified from the durations of pauses that occurred before the inscription of letters at four chunk levels, spanning letters, words, phrases, and sentences. A critical path task analytic model, Graphical Production of Memorized Sentences (GPoMS), shows that the control of writing relies on cues that continuously switch between motor actions and chunk retrievals in a just-in-time fashion at the level of letter information. GPoMS explains the individual differences in terms of variants of a motor production mechanism and variants of a chunk retrieval mechanism, which involve varying degrees of parallelism between cognitive actions and motor actions. A graphical technique for constructing GPoMS models was developed that enabled the estimation of ongoing working memory demands during production.