Verbal Working Memory Task Research Articles

The Effects of Home-Based Cognitive Training on Verbal Working Memory and Language Comprehension in Older Adulthood.

Effective language understanding is crucial to maintaining cognitive abilities and learning new information through adulthood. However, age-related declines in working memory (WM) have a robust negative influence on multiple aspects of language comprehension and use, potentially limiting communicative competence. In the current study (N = 41), we examined the effects of a novel home-based computerized cognitive training program targeting verbal WM on changes in verbal WM and language comprehension in healthy older adults relative to an active component-control group. Participants in the WM training group showed non-linear improvements in performance on trained verbal WM tasks. Relative to the active control group, WM training participants also showed improvements on untrained verbal WM tasks and selective improvements across untrained dimensions of language, including sentence memory, verbal fluency, and comprehension of syntactically ambiguous sentences. Though the current study is preliminary in nature, it does provide initial promising evidence that WM training may influence components of language comprehension in adulthood and suggests that home-based training of WM may be a viable option for probing the scope and limits of cognitive plasticity in older adults.

Verbal working memory and inhibition-concentration in adults with cochlear implants.

ObjectivesNeurocognitive functions contribute to speech recognition in postlingual adults with cochlear implants (CIs). In particular, better verbal working memory (WM) on modality‐specific (auditory) WM tasks predicts better speech recognition. It remains unclear, however, whether this association can be attributed to basic underlying modality‐general neurocognitive functions, or whether it is solely a result of the degraded nature of auditory signals delivered by the CI. Three hypotheses were tested: 1) Both modality‐specific and modality‐general tasks of verbal WM would predict scores of sentence recognition in speech‐shaped noise; 2) Basic modality‐general neurocognitive functions of controlled fluency and inhibition‐concentration would predict both modality‐specific and modality‐general verbal WM; and 3) Scores on both tasks of verbal WM would mediate the effects of more basic neurocognitive functions on sentence recognition.Study DesignCross‐sectional study of 30 postlingual adults with CIs and thirty age‐matched normal‐hearing (NH) controls.Materials and MethodsParticipants were tested for sentence recognition in speech‐shaped noise, along with verbal WM using a modality‐general task (Reading Span) and an auditory modality‐specific task (Listening Span). Participants were also assessed for controlled fluency and inhibition‐concentration abilities.ResultsFor CI users only, Listening Span scores predicted sentence recognition, and Listening Span scores mediated the effects of inhibition‐concentration on speech recognition. Scores on Reading Span were not related to sentence recognition for either group.ConclusionInhibition‐concentration skills play an important role in CI users' sentence recognition skills, with effects mediated by modality‐specific verbal WM. Further studies will examine inhibition‐concentration and WM skills as novel targets for clinical intervention.Level of Evidence4.

Working memory strategies during rational number magnitude processing.

Rational number understanding is a critical building block for success in more advanced mathematics; however, how rational number magnitudes are conceptualized is not fully understood. In the current study, we used a dual-task working memory (WM) interference paradigm to investigate the dominant type of strategy (i.e., requiring verbal WM resources vs. requiring primarily visuospatial WM resources) used by adults when processing rational number magnitudes presented in both decimal and fraction notation. Analyses revealed no significant differences in involvement of verbal and visuospatial WM, regardless of notation (fractions vs. decimals), indicating that adults rely upon a mix of strategies and WM resources when processing rational number magnitudes. However, this pattern interacted with algebra ability such that those performing better on the algebra assessment relied upon both verbal and visuospatial WM when engaging in rational number comparisons, whereas rational number performance by adults with low algebra fluency was affected only by a simultaneous verbal WM task. Together, results support previous work implicating the involvement of WM resources in rational number processing and is the first study to indicate that the involvement of both verbal and visuospatial WM, as opposed to relying primarily on verbal WM, when processing rational number magnitudes may be indicative of higher mathematical proficiency in the domain of algebra. (PsycINFO Database Record (c) 2017 APA, all rights reserved)

Movement Interferes with Visuospatial Working Memory during the Encoding: An ERP Study.

The present study focuses on the functional interactions of cognition and manual action control. Particularly, we investigated the neurophysiological correlates of the dual-task costs of a manual-motor task (requiring grasping an object, holding it, and subsequently placing it on a target) for working memory (WM) domains (verbal and visuospatial) and processes (encoding and retrieval). Thirty participants were tested in a cognitive-motor dual-task paradigm, in which a single block (a verbal or visuospatial WM task) was compared with a dual block (concurrent performance of a WM task and a motor task). Event-related potentials (ERPs) were analyzed separately for the encoding and retrieval processes of verbal and visuospatial WM domains both in single and dual blocks. The behavioral analyses show that the motor task interfered with WM and decreased the memory performance. The performance decrease was larger for the visuospatial task compared with the verbal task, i.e., domain-specific memory costs were obtained. The ERP analyses show the domain-specific interference also at the neurophysiological level, which is further process-specific to encoding. That is, comparing the patterns of WM-related ERPs in the single block and dual block, we showed that visuospatial ERPs changed only for the encoding process when a motor task was performed at the same time. Generally, the present study provides evidence for domain- and process-specific interactions of a prepared manual-motor movement with WM (visuospatial domain during the encoding process). This study, therefore, provides an initial neurophysiological characterization of functional interactions of WM and manual actions in a cognitive-motor dual-task setting, and contributes to a better understanding of the neuro-cognitive mechanisms of motor action control.

Study on object, verbal and space working memory in male patients with alcohol dependence

Objective To explore working memory in male patients with alcohol dependence. Methods 50 male patients with alcohol dependence(AD group) and 50 healthy controls(HC group) were assessed by digit span test, trail making test and verbal fluency test. The visual-object, visual-verbal, visual-space working memory tasks were used to measure the difference of working memory between the two groups. Results Compared with HC group, alcohol dependence group showed significant impairments in performance of error number of visual-object, visual-verbal, visual-space working memory tasks (AD group: (3.76±2.20), 3(2, 5), (3.74±2.40)); (HC group: (2.94±1.60), 2(1, 3), 2(1, 4))(t=2.133, P=0.035; Z=-2.400, P=0.016; Z=-2.654, P=0.008). Moreover, scores of Michigan alcoholism screening test were positively correlated with the error number of verbal working memory task (r=0.371, P=0.008). Conclusion The male patients with alcohol dependence exhibit impairments in all aspects of working memory. Key words: Alcohol drinking; Working memory; Neuropsychology

Load-Dependent Increases in Delay-Period Alpha-Band Power Track the Gating of Task-Irrelevant Inputs to Working Memory.

Studies exploring the role of neural oscillations in cognition have revealed sustained increases in alpha-band power (ABP) during the delay period of verbal and visual working memory (VWM) tasks. There have been various proposals regarding the functional significance of such increases, including the inhibition of task-irrelevant cortical areas as well as the active retention of information in VWM. The present study examines the role of delay-period ABP in mediating the effects of interference arising from on-going visual processing during a concurrent VWM task. Specifically, we reasoned that, if set-size dependent increases in ABP represent the gating out of on-going task-irrelevant visual inputs, they should be predictive with respect to some modulation in visual evoked potentials resulting from a task-irrelevant delay period probe stimulus. In order to investigate this possibility, we recorded the electroencephalogram while subjects performed a change detection task requiring the retention of two or four novel shapes. On a portion of trials, a novel, task-irrelevant bilateral checkerboard probe was presented mid-way through the delay. Analyses focused on examining correlations between set-size dependent increases in ABP and changes in the magnitude of the P1, N1 and P3a components of the probe-evoked response and how such increases might be related to behavior. Results revealed that increased delay-period ABP was associated with changes in the amplitude of the N1 and P3a event-related potential (ERP) components, and with load-dependent changes in capacity when the probe was presented during the delay. We conclude that load-dependent increases in ABP likely play a role in supporting short-term retention by gating task-irrelevant sensory inputs and suppressing potential sources of disruptive interference.

A molecular pathway analysis stresses the role of inflammation and oxidative stress towards cognition in schizophrenia.

Cognitive processes have a genetic component and are impaired in Schizophrenia (SKZ). The exact nature of such impairment escapes definition. The aim of the present contribution was the identification of the molecular pathways enriched with mutations (SNPs) associated with cognitive performance during antipsychotic treatment. 765 individuals from the CATIE study, males=559, mean age 40.93±11.03 were included. Working memory and the verbal memory were the evaluated outcomes. A mixed regression model for repeated measures served in R for clinical and molecular pathway analysis. The analysis of quality was conducted under the following criteria: minor allele frequency >0.01, genotype call rate >95%, missing data frequency <5%, Hardy-Weimberg equilibrium threshold >0.0001. The inflation factor was controlled by lambda values. Input for the pathway analysis was SNPs at a p level <0.05 of association genome-wide. Gender, age, education and the duration of the disease were the clinical and socio-demographic variables associated with the cognitive performance. 4268977 SNPs were available after imputation and quality analysis. Pathways related to inflammation and oxidation were the most strongly associated with verbal memory and working memory at a conservative adjusted p value<0.01. We report that inflammation and in particular the pathway associated with arachidonic acid was enriched in mutations associated with poorer performance at the verbal memory and working memory tasks in SKZ patients.

Verbal and visual-spatial working memory: What develops over a life span?

This study investigates whether age-related changes in the structure of 5 complex working memory (WM) tasks (a) reflect a general or domain specific system, (b) follows a similar trajectory across different age spans, and (c) contribute domain general or domain specific resources to achievement measures. The study parsed the sample (N = 2,471) into 11 age groups (mean ages of 6, 7, 8, 9, 11, 13, 15, 18, 26, 41, and 66 years), and compared their performances on verbal and visuospatial WM measures. Three important findings emerged: (a) a confirmatory factor analysis and Schmid-Leiman transformation to a high-order model solution supported a domain general factor model for the total sample as well as separately for children and adults, (b) performance on visual-spatial WM tasks as a function of age decreased at a faster rate than verbal WM tasks, and (c) both verbal and visual-spatial WM measures in concert with each other uniquely predicted reading and math measures, suggesting that a domain general WM system contributed to performance on achievement measures. The results support the notion that (a) complex WM tasks function as a domain general system and (b) the factor structure for children and adults on complex WM tasks was highly similar, even though there was evidence of differentiation among verbal and visual-spatial WM measures at certain age groups. (PsycINFO Database Record

Brain structure and verbal function across adulthood while controlling for cerebrovascular risks.

The development and decline of brain structure and function throughout adulthood is a complex issue, with cognitive aging trajectories influenced by a host of factors including cerebrovascular risk. Neuroimaging studies of age-related cognitive decline typically reveal a linear decrease in gray matter (GM) volume/density in frontal regions across adulthood. However, white matter (WM) tracts mature later than GM, particularly in regions necessary for executive functions and memory. Therefore, it was predicted that a middle-aged group (MC: 35-45 years) would perform best on a verbal working memory task and reveal greater regional WM integrity, compared with both young (YC: 18-25 years) and elder groups (EC: 60+ years). Diffusion tensor imaging (DTI) and magnetoencephalography (MEG) were obtained from 80 healthy participants. Objective measures of cerebrovascular risk and cognition were also obtained. As predicted, MC revealed best verbal working memory accuracy overall indicating some maturation of brain function between YC and MC. However, contrary to the prediction fractional anisotropy values (FA), a measure of WM integrity, were not greater in MC (i.e., there were no significant differences in FA between YC and MC but both groups showed greater FA than EC). An overall multivariate model for MEG ROIs showed greater peak amplitudes for MC and YC, compared with EC. Subclinical cerebrovascular risk factors (systolic blood pressure and blood glucose) were negatively associated with FA in frontal callosal, limbic, and thalamic radiation regions which correlated with executive dysfunction and slower processing speed, suggesting their contribution to age-related cognitive decline. Hum Brain Mapp 38:3472-3490, 2017. © 2017 Wiley Periodicals, Inc.

Training spatial-simultaneous working memory in individuals with Down syndrome

Recent studies have suggested that the spatial-simultaneous component of working memory (WM), which is involved when stimuli are presented simultaneously, is selectively impaired in individuals with Down syndrome (DS).The main objective of the present study was to examine whether WM performance can be enhanced in individuals with DS by analyzing the immediate and maintenance effects of a training program. For this purpose, 61 individuals with DS were randomly assigned to three groups: one trained on simultaneous components of visuospatial WM; one serving as an active control group, that completed activities on vocabulary; and one serving as a passive control group, that only attended the pre- and post-test and follow-up assessments. The efficacy of the training was analyzed in terms of specific (spatial-simultaneous WM tasks), near transfer (spatial-sequential and verbal WM tasks), far transfer (spatial abilities, everyday competences), and maintenance effects (with a follow-up at 1 month). The results showed an overall significant effect on the WM on the group receiving the training. The benefit was generally specific, however, with some transfer to other WM tasks, but only in the immediate (post-test) assessment.

Gender Differences in Verbal and Visuospatial Working Memory Tasks in Patients with Mild Cognitive Impairment and Alzheimer Disease

Background/Aims: To date, there are few studies on gender differences in patients with mild cognitive impairment (MCI) and Alzheimer disease (AD). In the present study, the existence of differences between sexes in verbal and visuospatial working memory tasks in the evolution of cognitive and pathological aging was examined. Method: Ninety participants took part in this study: 30 AD, 30 MCI, and 30 healthy elderly participants (50% men and 50% women). Results: There were no significant differences between men and women with AD in visuospatial tasks, whereas these differences were found within the MCI group, with the average of men achieving significantly higher results than women. In verbal tasks, there were no differences between sexes for any of the groups. Conclusion: Execution in visuospatial tasks tends to depend on gender, whereas this does not occur for verbal tasks.

Planning sentences while doing other things at the same time: effects of concurrent verbal and visuospatial working memory load.

This study investigated to what extent advance planning during sentence production is affected by a concurrent cognitive load. In two picture-word interference experiments in which participants produced subject-verb-object sentences while ignoring auditory distractor words, we assessed advance planning at a phonological (lexeme) and at an abstract-lexical (lemma) level under visuospatial or verbal working memory (WM) load. At the phonological level, subject and object nouns were found to be activated before speech onset with concurrent visuospatial WM load, but only subject nouns were found to be activated with concurrent verbal WM load, indicating a reduced planning scope as a function of type of WM load (Experiment 1). By contrast, at the abstract-lexical level, subject and object nouns were found to be activated regardless of type of concurrent load (Experiment 2). In both experiments, sentence planning had a more detrimental effect on concurrent verbal WM task performance than on concurrent visuospatial WM task performance. Overall, our results suggest that advance planning at the phonological level is more affected by a concurrently performed verbal WM task than advance planning at the abstract-lexical level. Also, they indicate an overlap of resources allocated to phonological planning in speech production and verbal WM.

Boosting Cognition: Effects of Multiple-Session Transcranial Direct Current Stimulation on Working Memory.

Transcranial direct current stimulation (tDCS) is a promising tool for neurocognitive enhancement. Several studies have shown that just a single session of tDCS over the left dorsolateral pFC (lDLPFC) can improve the core cognitive function of working memory (WM) in healthy adults. Yet, recent studies combining multiple sessions of anodal tDCS over lDLPFC with verbal WM training did not observe additional benefits of tDCS in subsequent stimulation sessions nor transfer of benefits to novel WM tasks posttraining. Using an enhanced stimulation protocol as well as a design that included a baseline measure each day, the current study aimed to further investigate the effects of multiple sessions of tDCS on WM. Specifically, we investigated the effects of three subsequent days of stimulation with anodal (20 min, 1 mA) versus sham tDCS (1 min, 1 mA) over lDLPFC (with a right supraorbital reference) paired with a challenging verbal WM task. WM performance was measured with a verbal WM updating task (the letter n-back) in the stimulation sessions and several WM transfer tasks (different letter set n-back, spatial n-back, operation span) before and 2 days after stimulation. Anodal tDCS over lDLPFC enhanced WM performance in the first stimulation session, an effect that remained visible 24 hr later. However, no further gains of anodal tDCS were observed in the second and third stimulation sessions, nor did benefits transfer to other WM tasks at the group level. Yet, interestingly, post hoc individual difference analyses revealed that in the anodal stimulation group the extent of change in WM performance on the first day of stimulation predicted pre to post changes on both the verbal and the spatial transfer task. Notably, this relationship was not observed in the sham group. Performance of two individuals worsened during anodal stimulation and on the transfer tasks. Together, these findings suggest that repeated anodal tDCS over lDLPFC combined with a challenging WM task may be an effective method to enhance domain-independent WM functioning in some individuals, but not others, or can even impair WM. They thus call for a thorough investigation into individual differences in tDCS respondence as well as further research into the design of multisession tDCS protocols that may be optimal for boosting cognition across a wide range of individuals.

Evidence for cognitive resource imbalance in adolescents with narcolepsy

The study investigated brain activity changes during performance of a verbal working memory task in a population of adolescents with narcolepsy. Seventeen narcolepsy patients and twenty healthy controls performed a verbal working memory task during simultaneous fMRI and EEG acquisition. All subjects also underwent MRS to measure GABA and Glutamate concentrations in the medial prefrontal cortex. Activation levels in the default mode network and left middle frontal gyrus were examined to investigate whether narcolepsy is characterized by an imbalance in cognitive resources. Significantly increased deactivation within the default mode network during task performance was observed for the narcolepsy patients for both the encoding and recognition phases of the task. No evidence for task performance deficits or reduced activation within the left middle frontal gyrus was noted for the narcolepsy patients. Correlation analyses between the spectroscopy and fMRI data indicated that deactivation of the anterior aspect of the default mode in narcolepsy patients correlated more with increased concentrations of Glutamate and decreased concentrations of GABA. In contrast, deactivation in the default mode was correlated with increased concentrations of GABA and decreased concentrations of Glutamate in controls. The results suggested that narcolepsy is not characterized by a deficit in working memory but rather an imbalance of cognitive resources in favor of monitoring and maintaining attention over actual task performance. This points towards dysregulation within the sustained attention system being the origin behind self-reported cognitive difficulties in narcolepsy.

Externally induced frontoparietal synchronization modulates network dynamics and enhances working memory performance.

Cognitive functions such as working memory (WM) are emergent properties of large-scale network interactions. Synchronisation of oscillatory activity might contribute to WM by enabling the coordination of long-range processes. However, causal evidence for the way oscillatory activity shapes network dynamics and behavior in humans is limited. Here we applied transcranial alternating current stimulation (tACS) to exogenously modulate oscillatory activity in a right frontoparietal network that supports WM. Externally induced synchronization improved performance when cognitive demands were high. Simultaneously collected fMRI data reveals tACS effects dependent on the relative phase of the stimulation and the internal cognitive processing state. Specifically, synchronous tACS during the verbal WM task increased parietal activity, which correlated with behavioral performance. Furthermore, functional connectivity results indicate that the relative phase of frontoparietal stimulation influences information flow within the WM network. Overall, our findings demonstrate a link between behavioral performance in a demanding WM task and large-scale brain synchronization.

Hippocampal subfields' volumes are more relevant to fluid intelligence than verbal working memory

The hippocampus plays an important role in learning and memory. Poor segmentation tools of hippocampal subfields, however, have hindered our understanding of their specific roles. Using FreeSurfer 6.0, which provides more accurate segmentation than previous versions (especially for Cornu Ammonis [CA] subfields), the current study examined the 12 hippocampal subfields' contributions to fluid intelligence (measured with Raven's Advanced Progressive Matrices, RAPM) and working memory (measured with n-back visual and verbal working memory tasks) in a sample of 417 healthy young adults. Results showed that RAPM and visual n-back working memory had similar correlations with hippocampal subfields' volumes, but RAPM was more highly correlated with the volumes of the right hippocampus as well as three of its subfields (CA1, molecular layer of the hippocampus, and hippocampal tail) than was verbal n-back working memory (after correcting for multiple comparisons). In addition, sex moderated the correlation between left hippocampal fissure volume and n-back working memory. These results suggest both shared and distinct neural substrates for fluid intelligence and visual and verbal working memory, and highlight the role of CA1 in visuospatial cognition.

Rest Is Still Best.

We examined the impact task interruptions of differing qualitative and quantitative load have on visuospatial vigilance sensitivity. The vigilance decrement and attempts to develop countermeasures to the decrement is one of the most important human factors issues. There is an ongoing debate between those who interpret the increase in the rate of failures to detect signals over time as being due to objective task monotony or task underload and those who interpret this increased failure proneness as being predominately due to cognitive-resource depletion and task overload. Participants were assigned at random to one of six interruptions: Participants were given a complete rest (rest); participants completed a 1-back verbal working-memory (WM) task, a 3-back verbal WM task, a 1-back spatial WM task, or a 3-back spatial WM task; or participants performed the primary vigilance task (continuous). Postinterruption performance was best for rest and worst for continuous. A resource theory perspective led us to make two possible predictions of relative interruption effect orders of the six conditions out of 720 possible orderings. We found one of the two orders. Overall, the vigilance sensitivity decrement appears to be due to the recurring use of particular cognitive resources, and resource theorists should explore this more extensively in the future. Countermeasures for the vigilance decrement should be based on clear cognitive-resource considerations. Rest is the best countermeasure. Intervening tasks should be chosen that minimize resource-demand overlap with the vigilance task.

Aberrant Neuronal Dynamics during Working Memory Operations in the Aging HIV-Infected Brain

Impairments in working memory are among the most prevalent features of HIV-associated neurocognitive disorders (HAND), yet their origins are unknown, with some studies arguing that encoding operations are disturbed and others supporting deficits in memory maintenance. The current investigation directly addresses this issue by using a dynamic mapping approach to identify when and where processing in working memory circuits degrades. HIV-infected older adults and a demographically-matched group of uninfected controls performed a verbal working memory task during magnetoencephalography (MEG). Significant oscillatory neural responses were imaged using a beamforming approach to illuminate the spatiotemporal dynamics of neuronal activity. HIV-infected patients were significantly less accurate on the working memory task and their neuronal dynamics indicated that encoding operations were preserved, while memory maintenance processes were abnormal. Specifically, no group differences were detected during the encoding period, yet dysfunction in occipital, fronto-temporal, hippocampal, and cerebellar cortices emerged during memory maintenance. In addition, task performance in the controls covaried with occipital alpha synchronization and activity in right prefrontal cortices. In conclusion, working memory impairments are common and significantly impact the daily functioning and independence of HIV-infected patients. These impairments likely reflect deficits in the maintenance of memory representations, not failures to adequately encode stimuli.

Working memory load-dependent spatio-temporal activity of single-trial P3 response detected with an adaptive wavelet denoiser

Working memory (WM) refers to the holding and manipulation of information during cognitive tasks. Its underlying neural mechanisms have been explored through both functional magnetic resonance imaging (fMRI) and electroencephalography (EEG). Trial-by-trial coupling of simultaneously collected EEG and fMRI signals has become an important and promising approach to study the spatio-temporal dynamics of such cognitive processes. Previous studies have demonstrated a modulation effect of the WM load on both the BOLD response in certain brain areas and the amplitude of P3. However, much remains to be explored regarding the WM load-dependent relationship between the amplitude of ERP components and cortical activities, and the low signal-to-noise ratio (SNR) of the EEG signal still poses a challenge to performing single-trial analyses. In this paper, we investigated the spatio-temporal activities of P3 during an n-back verbal WM task by introducing an adaptive wavelet denoiser into the extraction of single-trial P3 features and using general linear model (GLM) to integrate simultaneously collected EEG and fMRI data. Our results replicated the modulation effect of the WM load on the P3 amplitude. Additionally, the activation of single-trial P3 amplitudes was detected in multiple brain regions, including the insula, the cuneus, the lingual gyrus (LG), and the middle occipital gyrus (MOG). Moreover, we found significant correlations between P3 features and behavioral performance. These findings suggest that the single-trial integration of simultaneous EEG and fMRI signals may provide new insights into classical cognitive functions.

Frontal activity during a verbal emotional working memory task in patients with Alzheimer's disease: A functional near-infrared spectroscopy study

Emotional working memory (EWM) is suggested as a working memory (WM) type, distinguished to process emotional stimuli, and may or may not be spared in Alzheimer's disease (AD). The aim was to compare patients with AD and healthy older adults (HC) on verbal EWM performance and accompanying prefrontal cortex activity. Twenty AD patients along with 20 HC individuals are required to complete an emotional one-back task in three conditions (neutral, positive and negative word lists). Prefrontal oxyhemoglobin (oxyHb) concentrations were measured simultaneously by a 24- channel functional near infrared spectroscopy device. Correct response rates were similar in two groups in all conditions. Reaction times were comparable in the EWM positive condition but longer in the AD group in EWMneutral and negative conditions. In the HC group, emotional words had no significant effect on WM. On the other hand, positive compared to neutral words led to greater activation in the left ventral prefrontal cortex (VPFC) in AD group. When compared to HCs, activity in the VPFC was significantly higher in AD patients during the positive condition. Positive words facilitated WM performance in participants with AD. Activity in VPFC may be the functional correlate of this phenomenon.