Increase In Working Memory Load Research Articles

Age differences in the recruitment of syntactic analysis and semantic plausibility during sentence comprehension

Syntactic analysis and semantic plausibility provide important cues to build the meaningful representation of sentences. The purpose of this research is to explore the age-related differences in the use of syntactic analysis and semantic plausibility during sentence comprehension under different working memory load conditions. A sentence judgment task was implemented among a group of older and younger adults. Semantic plausibility (plausible, implausible) and syntactic consistency (consistent, inconsistent) were manipulated in the experimental stimuli, and working memory load (high, low) was varied by manipulating the presentation of the stimuli. The study revealed a stronger effect of semantic plausibility in older adults than in younger adults when working memory load was low. But no significant age difference in the effect of syntactic consistency was discovered. When working memory load was high, there was a stronger effect of semantic plausibility and a weaker effect of syntactic consistency in older adults than in younger adults, which suggests that older adults relied more on semantic plausibility and less on syntactic analysis than younger adults. The findings indicate that there is an age-related increase in the use of semantic plausibility, and a reduction in the use of syntactic analysis as working memory load increases.

Working Memory Load Impact on Effective Connectivity: a Dynamic Causal Modeling Study

This study aims to examine the roles of the brain regions in working memory (WM) processing and the modulatory effects of WM load. Electroencephalogram (EEG) signals were recorded when participants perform a letter-version n-back task with three different levels of WM load. The directional causal connections between brain regions were estimated using Dynamic Causal Modeling (DCM). The directions and strengths of the connections were compared for different WM load conditions. The results showed a right-lateralized, backward-only connection pattern for the high WM load condition. The results also showed changes in the roles of the brain regions when the WM load increases. These findings of the modulatory effects of WM load may be utilized in measuring cognitive states, and designing adaptive automation in augmented cognition programs.

Unconscious priming shares a common resource pool with the manipulation subsystem.

BackgroundWorking memory can be subdivided into two relatively independent subordinate systems, the maintenance subsystem and the manipulation subsystem. Although the two subsystems are quite heterogeneous, research thus far has not adequately distinguished the resource pools of the two subsystems. Additionally, previous research on the relationship between working memory and unconscious priming is paradoxical. Different subsystems leading to different effects on unconscious priming might be the reason for the paradoxical research. Therefore, the current article aimed to distinguish the resource pools among two working-memory subsystems and to investigate the relationship between the two subsystems and unconscious priming.MethodsTo address these issues, a maintenance dual-task and a manipulation dual-task program were developed. Each participant had to separately perform the two dual tasks in a balanced order. In each dual task, participants first completed a masked priming task accompanied by working-memory load. As a control, participants completed a prime identification test to confirm that the processing of the masked prime was at the unconscious level. The maintenance dual task comprised sandwich masking trials accompanied by Sternberg trials, while the manipulation dual task comprised sandwich masking trials accompanied by N-back trials.ResultsThe results of the prime identification test indicated that the participants could not consciously perceive the masked prime of both dual tasks. The results of the working-memory task of both dual tasks indicated that the load manipulation was successful for both dual tasks. Most importantly, the results of the masking task of both dual tasks showed that an increase in working-memory load decreased the magnitude of unconscious priming in the manipulation dual task, whereas an increase in working-memory load did not decrease unconscious priming in the maintenance dual task. These observations demonstrate that the manipulation subsystem, rather than the maintenance subsystem, interferes with unconscious priming. Together with previous research, we propose a two-pool attention resource model to explain the modulation of working memory on unconscious priming by dissociating the executive resource pool of the manipulation system from the retention resource pool of the maintenance system. Thus, the current work confirms and extends the extant literature about the dependence of unconscious processing on attention resources by suggesting that unconscious priming shares a common resource pool with the manipulation subsystem.

The number of objects determines visual working memory capacity allocation even for complex items

article i nfo Article history: The goal of the present study was to examine whether visual working memory (WM) capacity allocation is determined solely by complexity, with the number of objects being redundant, as suggested by flexible resource models. Participants performed the change detection task with random polygons as stimuli, while we monitored the contralateral delay activity (CDA), an electrophysiological marker whose amplitude rises as WM load increases. In Experiment 1, we compared the WM maintenance of one whole polygon to a single half of the polygon, equating the number of items but varying the complexity level. Additionally, we compared the whole polygon to two halves of a polygon, thus roughly equating perceptual complexity but manipulating the number of items. The results suggested that only thenumberof objectsdetermined WMcapacity allocation: theCDA was identicalwhen comparing one wholepolygonto onepolygon half,eventhoughtheseconditions differedincom- plexity. Furthermore, the CDA amplitude was lower in the whole polygon condition relative to the two halves condition, even though both contained roughly the same amount of information. Experiment 2 extended these results by showing that two polygon halves that moved separately but then met and moved together were gradually integrated to consume similar WM capacity as one polygon half. Additionally, in both experiments we found an object benefit in accuracy, corroborating the important role of objects in WM. Our results demon- strate that WM capacity allocation cannot be explained by complexity alone. Instead, it is highly sensitive to objecthood, as suggested by discrete slot models.

The number of objects determines visual working memory capacity allocation for complex items

The goal of the present study was to examine whether visual working memory (WM) capacity allocation is determined solely by complexity, with the number of objects being redundant, as suggested by flexible resource models. Participants performed the change detection task with random polygons as stimuli, while we monitored the contralateral delay activity (CDA), an electrophysiological marker whose amplitude rises as WM load increases. In Experiment 1, we compared the WM maintenance of one whole polygon to a single half of the polygon, equating the number of items but varying the complexity level. Additionally, we compared the whole polygon to two halves of a polygon, thus roughly equating perceptual complexity but manipulating the number of items. The results suggested that only the number of objects determined WM capacity allocation: the CDA was identical when comparing one whole polygon to one polygon half, even though these conditions differed in complexity. Furthermore, the CDA amplitude was lower in the whole polygon condition relative to the two halves condition, even though both contained roughly the same amount of information. Experiment 2 extended these results by showing that two polygon halves that moved separately but then met and moved together were gradually integrated to consume similar WM capacity as one polygon half. Additionally, in both experiments we found an object benefit in accuracy, corroborating the important role of objects in WM. Our results demonstrate that WM capacity allocation cannot be explained by complexity alone. Instead, it is highly sensitive to objecthood, as suggested by discrete slot models.

The processing of syntactic islands – An fMRI study

Abstract The aim of this study was to investigate whether LIFG activation was sensitive to increases in syntactic working memory load triggered by multiple extractions from an embedded clause, so-called island violations, and whether there was any difference between argument and adjunct extraction. Event-related fMRI (n = 30) was used to measure the cortical effects of the differences in acceptability between ungrammatical sentences and three types of wh-movement in Danish: short movement (to the front of an embedded clause), long movement (to the beginning of the matrix clause), and movement across another wh-phrase. The neural activation in LIFG was predicted to correlate negatively with the level of acceptability. Ungrammatical sentences were predicted to engage LIFG, potentially overlapping with the effects of acceptability. The behavioral results replicated the findings from an earlier study showing that acceptability correlates negatively with demands on syntactic working memory. Short movement is more acceptable than long movement, which is more acceptable than movement across another wh-phrase. Contrary to prediction, the imaging data showed no significant difference between long movement and movement across another wh-phrase, while both induced a significant increase in activation in LIFG compared to short movement. It is argued that the clause itself, rather than movement as such, is an important factor. Movement out of an embedded clause increases syntactic complexity, which in turn increases neural activation. Short movement per se is not complex enough to have a significant effect on the BOLD signal. There was no effect of ungrammaticality, but this absence is argued to be due to the nature of the anomaly. The activation in LIFG correlated with the crossing of a clause boundary, not with increases in working memory load or decreases in acceptability due to island violations.

From distributed resources to limited slots in multiple-item working memory: a spiking network model with normalization.

Recent behavioral studies have given rise to two contrasting models for limited working memory capacity: a "discrete-slot" model in which memory items are stored in a limited number of slots, and a "shared-resource" model in which the neural representation of items is distributed across a limited pool of resources. To elucidate the underlying neural processes, we investigated a continuous network model for working memory of an analog feature. Our model network fundamentally operates with a shared resource mechanism, and stimuli in cue arrays are encoded by a distributed neural population. On the other hand, the network dynamics and performance are also consistent with the discrete-slot model, because multiple objects are maintained by distinct localized population persistent activity patterns (bump attractors). We identified two phenomena of recurrent circuit dynamics that give rise to limited working memory capacity. As the working memory load increases, a localized persistent activity bump may either fade out (so the memory of the corresponding item is lost) or merge with another nearby bump (hence the resolution of mnemonic representation for the merged items becomes blurred). We identified specific dependences of these two phenomena on the strength and tuning of recurrent synaptic excitation, as well as network normalization: the overall population activity is invariant to set size and delay duration; therefore, a constant neural resource is shared by and dynamically allocated to the memorized items. We demonstrate that the model reproduces salient observations predicted by both discrete-slot and shared-resource models, and propose testable predictions of the merging phenomenon.

Neural correlates of working memory in Temporal Lobe Epilepsy — An fMRI study

It has traditionally been held that the hippocampus is not part of the neural substrate of working memory (WM), and that WM is preserved in Temporal Lobe Epilepsy (TLE). Recent imaging and neuropsychological data suggest this view may need revision. The aim of this study was to investigate the neural correlates of WM in TLE using functional MRI (fMRI). We used a visuo-spatial ‘n-back’ paradigm to compare WM network activity in 38 unilateral hippocampal sclerosis (HS) patients (19 left) and 15 healthy controls. WM performance was impaired in both left and right HS groups compared to controls. The TLE groups showed reduced right superior parietal lobe activity during single- and multiple-item WM. No significant hippocampal activation was found during the active task in any group, but the hippocampi progressively deactivated as the task demand increased. This effect was bilateral for controls, whereas the TLE patients showed progressive unilateral deactivation only contralateral to the side of the hippocampal sclerosis and seizure focus. Progressive deactivation of the posterior medial temporal lobe was associated with better performance in all groups. Our results suggest that WM is impaired in unilateral HS and the underlying neural correlates of WM are disrupted. Our findings suggest that hippocampal activity is progressively suppressed as the WM load increases, with maintenance of good performance. Implications for understanding the role of the hippocampus in WM are discussed.

Effects of Working Memory Load on Performance and Cardiovascular Activity in Younger and Older Workers

Working memory (WM) declines with ageing, and this may cause problems in older workers who have to do complex work requiring WM. We tested the assumption that an increase in WM load negatively affects performance and results in impaired cardiovascular adaptation to changing task demands in older workers relative to younger ones. Thirty-three younger (29 ± 3years) and 32 older (55 ± 3years) workers had to perform a visual 0-back (low WM load) and 2-back (high WM load) task. Heart rate (HR), heart rate variability (HRV), beat-to-beat blood pressure (BP) and baroreflex were registered. In the high WM load condition, older adults responded more slowly and less accurately than younger adults, while no age effects in the low WM load condition were found. Older workers showed a higher systolic blood pressure (SBP) reactivity to high WM load as well as a diminished post-task recovery of SBP and HRV than younger workers. Factor analysis demonstrated a close relationship between HR, baroreflex and HRV and their modulation by a common factor ("vagal tone") in the younger group. By contrast, HR was more related to the "sympathetic" factor in the older group. The data suggest that older workers as compared with younger ones are impaired in tasks requiring WM, which is accompanied by enhanced cardiovascular "costs" in terms of increased SBP and reduced vagal control over HR.

Encoding/retrieval dissociation in working memory for human body forms

The present study was conducted to investigate the effect of working memory (WM) load on body processing mechanisms by using event-related potentials (ERPs). It is well known that WM load modulates the P3b (amplitude decreases as WM load increases). Additionally, WM load for faces modulates earlier ERPs like the N170. The present study aimed to investigate the effect of WM load for bodies on the P3b which is associated with WM. Additionally, we explored the effect of WM load on the N170, which is thought to be associated with configural processing, and P1, which has been observed in body as well as in face processing. Effects were analyzed during the encoding and retrieval phases. WM load was modulated by presenting one to four unfamiliar bodies simultaneously for memory encoding. The present study showed that early encoding processes (reflected by the P1 and N170) might not be modulated by WM load, whereas during the retrieval phase, early processes associated with structural encoding (N170) were affected by WM load. A possible explanation of the encoding/retrieval differences might be that subjects used distinct processing strategies in both phases. Parallel encoding of the simultaneously presented bodies might play an important role during the encoding phase where one to four bodies have to be stored, whereas serial matching might be used to compare the probe with the stored pictures during the retrieval phase. Additionally, WM load modulations were observed in later processing steps, which might be associated with stimulus identification and matching processes (reflected by the early P3b) during the encoding but not during the retrieval phase. The current findings further showed for both the encoding and the retrieval phase that the late P3b amplitude decreased as WM load for body images increased indicating that the late P3b is involved in WM processes which do not appear to be category-specific.

The role of working memory in dichotic-listening studies of auditory laterality

We present data related to the role of working memory in dichotic-listening studies of speech lateralization using consonant–vowel syllable stimuli. A working-memory procedure was actually used in the pioneering dichotic-listening studies by Doreen Kimura in 1960, a fact that was forgotten in later dichotic-listening studies, exclusively focusing on the perceptual aspects of speech sound lateralization. Capitalizing on the original Kimura (1961a, 1961b) studies, we hypothesized that an increase in working-memory load leads to an amplified right-ear advantage (REA) in the dichotic-listening task. A total of 30 participants completed a dichotic-listening task including three working-memory load conditions, each consisting of trials of 3, 4, and 5 dichotically presented letter pairs. Results confirmed an enhanced REA as working-memory load increased. This right-ear effect increased significantly from 3 to 4 stimulus pairs and leveled off with the 5th pair. In addition, the assumption was tested that, within a single load condition, the REA appears mainly in late serial input positions. A detailed analysis of the results revealed that only late positions contributed to the overall REA. However, the highest load condition (5 letter pairs) also produced significant ear differences in the early part of the input position curve. The mechanisms likely to be responsible for these results are discussed in terms of top-down and bottom-up processes in hemispheric asymmetry.

Working memory related gamma oscillations in schizophrenia patients

Recent reports show that the capability of neural networks supporting high-frequency synchronization is reduced in the brain of schizophrenia patients. Specifically, deficits in gamma activity have been shown in schizophrenia patients during perception and simple cognitive tasks. However little is known about alterations in gamma responses during complex and higher cognitive processing. The main objective of this study was to investigate modulation of event-related gamma responses in tasks varying working memory (WM) load in schizophrenia patients ( N = 10) and healthy controls ( N = 10). Gamma amplitude values were obtained for a simple choice reaction task, a low WM demand task, and a high WM demand task. During all three tasks schizophrenia patients showed significantly slower reaction times and higher error rates than controls. A gradual increase of gamma amplitudes after stimulus onset was associated with increase of WM load in controls. In contrast, high amplitude gamma oscillations remained constant regardless of task difficulty in patients. These results suggest that healthy subjects used various cognitive strategies depending on task difficulty, while schizophrenia patients needed to initiate complex cognitive processes similar to those used during processing of novel contexts or stimuli even for the simple choice reaction task with low cognitive demand.

Chronic nicotine improves working and reference memory performance and reduces hippocampal NGF in aged female rats

The cholinergic system is involved in cognition and several forms of dementia, including Alzheimer's disease, and nicotine administration has been shown to improve cognitive performance in both humans and rodents. While experiments with humans have shown that nicotine improves the ability to handle an increasing working memory load, little work has been done in animal models evaluating nicotine effects on performance as working memory load increases. In this report, we demonstrate that in aged rats nicotine improved the ability to handle an increasing working memory load as well as enhanced performance on the reference memory component of the water radial arm maze task. The dose required to exert these effects (0.3 mg/kg/day) was much lower than doses shown to be effective in young rats and appears to be a lower maintenance dose than is seen in light to moderate smokers. In addition, our study reports a nicotine-induced reduction in nerve growth factor (NGF) protein levels in the hippocampus of the aged rat. The effects of nicotine on hippocampal NGF levels are discussed as a potential mechanism of nicotine-induced improvements in working and reference memory.

The neurophysiological basis of word order variations in German

This paper aims to dissociate grammatical and general cognitive (e.g., working-memory based) accounts of the processing costs elicited by word order variations in German. To this end, we present a study using event-related brain potentials (ERPs), in which dislocated arguments were instantiated either by non-pronominal or by pronominal noun phrases. This manipulation allows for a dissociation of the two competing accounts, since only a dislocation of non-pronominal arguments gives rise to a non-canonical structure. The results show that (a) in sentences with non-pronominal arguments, the determiner of a non-canonical noun phrase elicited a broadly distributed negativity, and (b) in sentences with pronominal arguments, no differences were observed for object- vs. subject-initial word orders. These findings show that the human parser is sensitive to fine-grained grammatical regularities. We therefore argue that the negativity is a reflection of a local syntactic mismatch, rather than of an increase in working-memory load.

Estradiol facilitates performance as working memory load increases.

A water-escape version of the radial-arm maze was used to assess rat spatial working memory performance. Intact females and ovariectomized females receiving a physiologically low dose, physiologically moderate dose or no estradiol replacement were studied. Subjects were given seven trials a day for 12 days. Females receiving moderate dose estradiol made fewer errors than the other three groups during the latter portion of testing. As trials progressed within a session, the elements of information to be remembered increased. Assessment of individual trials revealed that when the demand on an animal's working memory system was limited to one to four elements of information, the three groups with estrogen (including intact females) maintained successful performance, whereas the ovariectomized females made more errors. However, when the demand on an animal's working memory system was increased to six elements of information, only the moderate dose estradiol females maintained successful performance. These data suggest that, although moderate levels of estradiol replacement are the most beneficial for working memory function, even low-dose estradiol replacement can act to protect working memory systems from the decline seen with the removal of ovarian hormones.