Function Of Working Memory Load Research Articles

Depth benefits now loading: Visual working memory capacity and benefits in 3-D.

The present studies explored how performance in multidimensional displays varies as a function of visual working memory load, item distribution across depths, and individual capacity differences. In Experiment 1, the benefit of depth information (one depth vs. two depths) was examined across seven set sizes within a change-detection paradigm. Multiple depth planes engendered performance benefits with five items, but elicited performance decrements with three items. These effects were associated with working memory capacity, such that benefits were only observed when the working memory load exceeded an individual's max capacity. Experiment 2 evaluated how the distribution of items in depth aids working memory performance. Equal distribution of items across depths produced higher accuracy compared with when the target was isolated in depth. Lastly, Experiment 3 explored how differences in working memory capacity affect an individual's ability to use depth information to improve their performance. The results indicate that both low-capacity and high-capacity individuals can benefit from depth information, but this may vary as a function of working memory load. Overall, the results indicate that multidimensional displays can improve performance with sufficient working memory load, possibly through some sort of depth tag.

Testing the efforts model of simultaneous interpreting: An ERP study.

We utilized the event-related potential (ERP) technique to study neural activity associated with different levels of working memory (WM) load during simultaneous interpretation (SI) of continuous prose. The amplitude of N1 and P1 components elicited by task-irrelevant tone probes was significantly modulated as a function of WM load but not the direction of interpretation. Furthermore, the latency of the P1 increased significantly with WM load. The WM load effect on N1 latency, however, did not reach significance. Larger negativity under lower WM loads suggests that more attention is available to process the source message, providing the first electrophysiological evidence in support of the Efforts Model of SI. Relationships between the direction of interpretation and median WM load are also discussed.

Functional brain organization of working memory in adolescents varies in relation to family income and academic achievement.

Working memory (WM) capacity reflects executive functions associated with performance on a wide range of cognitive tasks and education outcomes, including mathematics achievement, and is associated with dorsolateral prefrontal and parietal cortices. Here we asked if family income is associated with variation in the functional brain organization of WM capacity among adolescents, and whether that variation is associated with performance on a statewide test of academic achievement in mathematics. Participants were classified into higher-income and lower-income groups based on family income, and performed a WM task with a parametric manipulation of WM load (N-back task) during functional magnetic resonance imaging (fMRI). Behaviorally, the higher-income group had greater WM capacity and higher mathematics achievement scores. Neurally, the higher-income group showed greater activation as a function of WM load in bilateral prefrontal, parietal, and other regions, although the lower-income group exhibited greater activation at the lowest load. Both groups exhibited positive correlations between parietal activations and mathematics achievement scores, but only the higher-income group exhibited a positive correlation between prefrontal activations and mathematics scores. Most of these findings were maintained when higher- and lower-income groups were matched on WM task performance or nonverbal IQ. Findings indicate that the functional neural architecture of WM varies with family income and is associated with education measures of mathematics achievement.

Acetylcholine modulates human working memory and subsequent familiarity based recognition via alpha oscillations

Working memory (WM) can be defined as the ability to maintain and process physically absent information for a short period of time. This vital cognitive function has been related to cholinergic neuromodulation and, in independent work, to theta (4–8Hz) and alpha (9–14Hz) band oscillations. However, the relationship between both aspects remains unclear. To fill this apparent gap, we used electroencephalography (EEG) and a within-subject design in healthy humans who either received the acetylcholinesterase inhibitor galantamine (8mg) or a placebo before they performed a Sternberg WM paradigm. Here, sequences of sample images were memorized for a delay of 5s in three different load conditions (two, four or six items). On the next day, long-term memory (LTM) for the images was tested according to a remember/know paradigm. As a main finding, we can show that both theta and alpha oscillations scale during WM maintenance as a function of WM load; this resembles the typical performance decrease. Importantly, cholinergic stimulation via galantamine administration slowed down retrieval speed during WM and reduced associated alpha but not theta power, suggesting a functional relationship between alpha oscillations and WM performance. At LTM, this pattern was accompanied by impaired familiarity based recognition. These findings show that stimulating the healthy cholinergic system impairs WM and subsequent recognition, which is in line with the notion of a quadratic relationship between acetylcholine levels and cognitive functions. Moreover, our data provide empirical evidence for a specific role of alpha oscillations in acetylcholine dependent WM and associated LTM formation.

Dissociation of working memory impairments and attention-deficit/hyperactivity disorder in the brain.

Prevailing neuropsychological models of attention-deficit/hyperactivity disorder (ADHD) propose that ADHD arises from deficits in executive functions such as working memory, but accumulating clinical evidence suggests a dissociation between ADHD and executive dysfunctions. This study examined whether ADHD and working memory capacity are behaviorally and neurobiologically separable using functional magnetic resonance imaging (fMRI). Participants diagnosed with ADHD in childhood who subsequently remitted or persisted in their diagnosis as adults were characterized at follow-up in adulthood as either impaired or unimpaired in spatial working memory relative to controls who never had ADHD. ADHD participants with impaired spatial working memory performed worse than controls and ADHD participants with unimpaired working memory during an n-back working memory task while being scanned. Both controls and ADHD participants with unimpaired working memory exhibited significant linearly increasing activation in the inferior frontal junction, precuneus, lingual gyrus, and cerebellum as a function of working-memory load, and these activations did not differ significantly between these groups. ADHD participants with impaired working memory exhibited significant hypoactivation in the same regions, which was significantly different than both control participants and ADHD participants with unimpaired working memory. These findings support both a behavioral and neurobiological dissociation between ADHD and working memory capacity.

Nonlinear Effects of Noxious Thermal Stimulation and Working Memory Demands on Subjective Pain Perception.

A bidirectional relationship between working memory (WM) and acute pain has long been assumed, but equivocal evidence exists regarding this relationship. This study characterized the relationship between WM and acute pain processing in healthy individuals using an adapted Sternberg WM task. Participants completed a Sternberg task while receiving noxious thermal stimulation. Participants received a pseudorandom presentation of four different temperatures (baseline temperatures and individually determined low-, medium-, and high-temperature stimuli) and four levels of Sternberg task difficulty (0-, 3-, 6-, and 9-letter strings). Twenty-eight healthy participants were recruited from Stanford University and the surrounding community to complete this study. A nonlinear interaction between intensity of thermal stimulation and difficulty of the Sternberg task was noted. Increased cognitive load from the Sternberg task resulted in increased perception of pain in low-intensity thermal stimulation but suppressed pain perception in high-intensity thermal stimulation. Thermal stimulation had no significant effect on participants' response time or accuracy on the Sternberg task regardless of intensity level. Pain perception appears to decrease as a function of WM load only for sufficiently noxious stimuli. However, increasing noxious stimuli did not affect cognitive performance. These complex relationships may reflect a shared cognitive space that can become "overloaded" with input of multiple stimuli of sufficient intensity.

Dopaminergic stimulation facilitates working memory and differentially affects prefrontal low theta oscillations

We used electroencephalography (EEG) together with psychopharmacological stimulation to investigate the role of dopamine in neural oscillations during working memory (WM). Following a within-subjects design, healthy humans either received the dopamine precursor l-Dopa (150mg) or a placebo before they performed a Sternberg WM paradigm. Here, sequences of sample images had to be memorized for a delay of 5s in three different load conditions (two, four or six items). On the next day, long-term memory (LTM) for the images was tested. Behaviorally, l-Dopa improved WM and LTM performance as a function of WM load. More precisely, there was a specific drug effect in the four-load condition with faster reaction times to the probe in the WM task and higher corrected hit-rates in the LTM task. During the maintenance period, there was a linear and quadratic effect of WM load on power in the high theta (5–8Hz) and alpha (9–14Hz) frequency range at frontal sensors. Importantly, a drug by load interaction – mimicking the behavioral results – was found only in low theta power (2–4Hz). As such, our results indicate a specific link between prefrontal low theta oscillations, dopaminergic neuromodulation during WM and subsequent LTM performance.

Working memory deficits in multiple sclerosis: Comparison between then-back task and the Paced Auditory Serial Addition Test

Working memory (WM) deficits are common in multiple sclerosis (MS). The Paced Auditory Serial Addition Test (PASAT) is used frequently to measure WM in clinical settings. The n-back paradigm is used often in experimental studies of WM. One unique component of the n-back task is that it provides a measure of reaction time (RT), an additional behavioral index of processing speed and task difficulty. Despite the use of both tasks to measure WM, their common variance has not been documented. We tested 32 MS patients and 20 controls; performance measures were obtained for both tasks. Compared with controls, MS patients generally had poorer performance on both the PASAT and n-back task. MS patients also had slower RTs on the n-back than controls and showed more slowing than controls as a function of WM load. Correlational analyses showed a high correspondence between performance measures on the PASAT and n-back. Principal components analysis pointed to a common feature of the PASAT, n-back, and specific other neuropsychological measures, that is, processing speed. Although the PASAT and n-back were shown to have a significant amount of shared variance, each test has specific advantages and disadvantages for use in clinical populations.

The influence of increased working memory load on semantic neural systems: a high-resolution event-related brain potential study

The effects of working memory (WM) on the semantic N400 response were studied using high-resolution event-related brain potentials (ERPs). Participants were presented with semantically related sentence pairs and the terminal word congruence was varied in the second sentence. WM load was varied for the sentence pairs using a modified fan procedure [J.R. Anderson, Retrieval of propositional information from long-term memory. Cogn. Psychol., 6 (1974) 451–474; J.R. Anderson, A spreading activation theory of memory. J. Verbal Learn. Verbal Behav., 22 (1983) 261–295]. ERPs were recorded to the onset of the terminal word (Congruent and Incongruent) for sentence pairs at two levels of WM load (WML1 and WML2). Behavioral data analysis revealed that reaction times (RTs) increased as a function of WM load (i.e., the fan effect). Semantically incongruent words elicited an N400 response. Increased WM load reduced the congruency effect and, importantly, resulted in a significant delay in N400 peak latency (∼50 ms). Moreover, the latency delay was correlated with a neuropsychological measure of individual WM capacity. WM load effects on the N400 were interpreted as a result of competing activation in WM, both modulating semantic expectancies and delaying semantic integration. Exploratory source analysis revealed activation in occipital, temporal, and parietal regions. Consistent with prior reports on the N400 and semantic processing, equivalent current dipoles were modeled in the left perisylvian region. Increased WM load led to novel source activation in the left inferior parietal region as well as increased activation levels in anterior temporal sources. The source modeling results were in agreement with the functional roles typically ascribed to these areas and confirmed that the scalp-recorded WM load effects on the N400 were present within the intracranial generators.