Elucidating the Functional Relationship Between Working MemoryCapacity and Psychometric Intelligence: A Fixed-Links Modeling Approach forExperimental Repeated-Measures Designs

Is the n-back task a measure of unstructured working memory capacity? Towards understanding its connection to other working memory tasks

It is well established that measures of reasoning ability and of working memory capacity (WMC) correlate positively. However, the question of what explains this relationship remains open. The purpose of this study was to investigate the capacity hypothesis, which ascribes causality to WMC. This hypothesis holds that people high in WMC are more successful in capacity-demanding cognitive tasks than people lower in WMC because they can temporarily maintain more information in the form of sub-goals, hypotheses, and partial solutions. Accordingly, this hypothesis predicts that the correlation between WMC and reasoning performance should increase as the capacity demands of the reasoning items increase. We tested this prediction using items from Raven's Progressive Matrices and two measures of WMC, complex span and the k estimate from the Visual Arrays task. Neither WMC measure showed the effect predicted by the capacity hypothesis. Furthermore, the results cannot be attributed to restriction of range in performance on the individual reasoning items. This finding adds to existing evidence calling into question the capacity hypothesis, and, more generally, the view that WMC has a causal influence on fluid intelligence.

The purposes of the study were to investigate (a) the task-specific differences in short-term memory (STM) and working memory capacity (WMC) in individuals with mild cognitive impairment (MCI) and normal elderly adults (NEAs), (b) the Stroop interference and facilitation effects, and (c) the relationship of STM and WMC to the Stroop effects. Thirty-two individuals participated in the study (n = 16 for each group). WMC demands were increased using a computerized Stroop-like token task to add more linguistic units. Six STM and WMC measures were administered overall. Digit-related tasks and an alphabet span task sensitively differentiated individuals with MCI from the NEA group. The group with MCI exhibited greater Stroop interference effects than the NEA group, but the 2 groups did not exhibit different Stroop facilitation effects. WMC significantly predicted performance on the response time analyses but not on the error rate analyses. Task-specific differences emerged in the group with MCI, and a reduced WMC accounts for the impaired inhibitory and goal maintenance processes. It is critical that WMC demands be systematically manipulated to tax individuals' WMC in a way that can clearly demonstrate their deficits, especially in individuals who are at risk for clinically demented states.

Intelligence is one of the most studied constructs in psychological research and fascinates scientists and the general public alike. Accordingly, researchers have spent decades trying to identify the processes underlying individual differences in intelligence, eventually proposing two widely accepted candidates: the information processing speed (IPS; also referred to as mental speed) and the working memory capacity (WMC). Research consistently shows that higher intelligence is associated with greater speed of information processing on the one hand, and higher WMC on the other. While this nomological network is well established, recent findings on the measurement of WMC and IPS suggest that further research could refine our understanding of this relationship. Thus, the central aim of this dissertation is to gain insights into the processes underlying individual differences in intelligence by integrating recent findings from different streams of cognitive psychology, neuroscience, and intelligence research. I propose that, in order to gain new insights, we must first improve our understanding of the measures used, in particular WMC and IPS, and secondly examine the boundary conditions under which the respective correlations occur. In line with this agenda, three central research approaches are outlined as part of this dissertation: 1) First, to enhance our understanding of the processes involved in WM, I examined the neurophysiological representation of WM tasks commonly used to measure WMC. 2) Second, to improve the measurement of IPS, I investigated the conditions under which researchers may obtain reliable and valid neurophysiological indicators of IPS. 3) Third, I tested the boundary conditions of the relationship between IPS, WMC, and intelligence. Together, this dissertation provides guidance for intelligence research and allows conclusions to be drawn about the nature of the mechanisms underlying intelligence. In particular, the findings suggest that a) general short-term maintenance may account for the relationship between WMC and intelligence, b) analytical decisions affect the validity and reliability of neurocognitive IPS measurements, supporting the use of latent modeling, and c) the speed of decision-related processes is most likely the driver of the relationship between IPS and intelligence.

The relation between working memory capacity and auditory lateralization in children with auditory processing disorders

Introduction: Working memory is assumed to play a major part in hearing and communication in everyday listening situations. Our working memory stores information, but in suboptimal listening conditions, interfering stimuli can lead to information only being partially stored, or even missed. Research suggests that a high working memory capacity (WMC) might not just be a result of a large store, but in addition good inhibitory control can facilitate working memory, and therefore aid in situations where focus on a target stimulus while ignoring distractors is needed.Objective: The aim of the present study was to investigate how individual WMC, cognitive inhibition, and lexical decision relate to listening to speech under adverse conditions in two separate groups: 46 young normally hearing (NH) and 40 elderly hearing-impaired (HI) individuals.Results: It showed that lexical access was of little importance for young NH individuals in a speech-in-noise test, but that high lexical decision-making was associated with lower signal-to-noise ratios for the elderly HI individuals. The results also showed that WMC was of importance for word recognition in a speech-in-noise test for elderly participants, when the 80% word recognition criterion was targeted, but not for the young NH individuals. Finally, results suggest that cognitive inhibition, as measured with the Hayling task, was important for young NH individuals when listening conditions are suboptimal.Conclusion: In conclusion, hearing loss is a strong contributing factor to declines in the ability to recognize speech in noise, and in order to assess speech-recognition-in-noise performance, individual differences in WMC and cognitive inhibition should be taken into consideration. Future research should include various age groups, with and without hearing loss, as well as measures of WMC, cognitive inhibition, and lexical access when assessing the ability to listen to speech under adverse conditions.

Explaining the high working memory capacity of gifted children: Contributions of processing skills and executive control

BackgroundWorking memory capacity impairment is an early sign of Alzheimer's disease, but the underlying mechanisms remain unclear. Clarifying how working memory capacity is affected will help us better understand the pathological mechanism of Alzheimer's disease. We used the olfactory working memory capacity paradigm to evaluate memory capacity in 3-month-old 5XFAD (an animal model of Alzheimer's disease) mice. Immunofluorescence staining of the prefrontal cortex was performed to detect the number of FOS-positive neurons, calmodulin-dependent protein kinase II-positive neurons, and glutamate decarboxylase-positive neurons in the prelimbic cortex and infralimbic cortex. A chemogenetic method was then used to modulate the inhibition and activation of excitatory neurons in the prelimbic cortex of wild-type and 5XFAD mice and to measure the memory capacity of mice.ResultsWorking memory capacity was significantly diminished in 5XFAD mice compared to littermate wild-type mice. Neuronal activation of the prelimbic cortex, but not the infralimbic cortex, was attenuated in 5XFAD mice performing the olfactory working memory capacity task. Subsequently, the FOS-positive neurons were co-localized with both calmodulin-dependent protein kinase II-positive neurons and glutamate decarboxylase-positive neurons. The results showed that the activation of excitatory neurons in the prelimbic cortex was correlated with working memory capacity in mice. Our results further demonstrate that the chemogenetic inhibition of prelimbic cortex excitatory neurons resulted in reduced working memory capacity in wild-type mice, while the chemogenetic activation of prelimbic cortex excitatory neurons improved the working memory capacity of 5XFAD mice.ConclusionThe diminished activation of prelimbic cortex excitatory neurons in 5XFAD mice during task performance is associated with reduced working memory capacity, and activation modulation of excitatory neurons by chemogenetic methods can improve memory capacity impairment in 5XFAD mice. These findings may provide a new direction for exploring Alzheimer's disease therapeutic approaches.

New insights in implicit sequence learning of adults with traumatic brain injury: As measured by an ocular serial reaction time (O-SRT) task.

It has been suggested that hearing-impaired listeners with a good working memory (WM) should be fitted with a compression system using short time constants (i.e., fast-acting compression [FAC]), whereas those with a poorer WM should be fitted with a longer time constant (i.e., slow-acting compression [SAC]). However, commercial hearing aids (HAs) seldom use a fixed speed of compression. The performance of a variable speed compression (VSC) system relative to a fixed speed compressor (FAC and SAC) on measures of speech intelligibility, recall, and subjective report of listening effort and tolerable time was evaluated. The potential interaction with the listeners' WM capacity (WMC) was also examined. A double-blinded, repeated measures design. Seventeen HA wearers (16 with greater than one year HA experience) with a bilaterally symmetrical, mild to moderately severe sensorineural hearing loss participated in the study. Participants wore the study HAs at three compression speeds (FAC, SAC, and VSC). Each listener was evaluated on the Office of Research in Clinical Amplification-nonsense syllable test (NST) at 50 dB SPL (signal-to-noise ratio [SNR] = +15 dB), 65 dB SPL (SNR = +5 dB), 80 dB SPL (SNR = 0 dB), and a split (80 dB SPL-50 dB SPL) condition. Listeners were also evaluated on a Repeat Recall Test (RRT), where they had to repeat six short sentences (both high- and low-context sentences) after each was presented. Listeners recalled target words in all six sentences after they were presented. They also rated their listening effort and the amount of time they would tolerate listening under the specific condition. RRT sentences were presented at 75 dB SPL in quiet, as well as SNR = 0, 5, 10, and 15 dB. A Reading Span Test (RST) was also administered to assess listeners' WMC. Analysis of variance using RST scores as a covariate was used to examine differences in listener performance among compressor speeds. Listener performance on the NST was similar among all three compression speeds at 50, 65, and 80 dB SPL. Performance with FAC was significantly better than SAC for the split condition; however, performance did not differ between FAC and VSC or between SAC and VSC. Performance on the NST was not affected by listeners' RST scores. On the RRT, there was no effect of compressor speed on measures of repeat, recall, listening effort, and tolerable time. However, VSC resulted in significantly lower (better) speech reception threshold at the 85% correct recognition criterion (SRT85) than FAC and SAC. Listener RST scores significantly affected recall performance on the RRT but did not affect SRT85, repeat, listening effort, or tolerable time. These results suggest that the VSC, FAC, and SAC yield similar performance in most but not all test conditions. FAC outperforms SAC, where the stimulus levels change abruptly (i.e., split condition). The VSC yields a lower SRT85 than a fixed compression speed at a moderately high level with a favorable SNR. There is no interaction between compression speed and the participants' WMC.

Creative idea generation engages complex cognitive functions such as working memory capacity (WMC). The relationship between creativity and WMC has remained inconsistent due to the lack of experimental evidence and the mismatching of WMC tasks and creativity measurements. Therefore, we used both measurements and experiments to explore the effects of WMC on creativity with the matching of task types considered. In Study 1, we conducted multiple measurements to explore the relationship between verbal/visuospatial WMC and verbal/figural creativity and found that participants with higher visuospatial WMC performed better in both types of creativity tasks. Furthermore, we conducted two dual task experiments in Study 2 to explore the causal effects of WMC on creativity. We found only interfering with participants’ visuospatial WMC would significantly decrease their creative performances. Moreover, Study 3 ruled out the potential confounding factor of general attention resources in the visuospatial secondary tasks by using a control dual task experiment. These findings indicated that the creative thinking process is likely to rely on visuospatial processing regardless of the form of the presented information.

Working memory, which accounts for the ability to process information in the face of interference, is critical to second language acquisition (SLA) and use. The interaction of working memory capacity (WMC) with specific pedagogical interventions is a logical place for empirical SLA research, both to examine the cognitive processes underpinning second language performance and to identify instructional treatments that may serve learners differently based on their WMC. This study considers WMC along with two different types of pre-task planning time (guided and unguided) as predictors of the attempted accuracy and fluency of learners’ discourse. Seventy-two intermediate ESL students from seven classes at a community college participated by completing two different working memory span tasks, as well as two different “There-and-Then” oral story-telling tasks. The treatment condition of the story-telling tasks was manipulated so that learners’ performance could be considered in terms of provision of pre-task planning (+/− planning), type of planning (guided vs. unguided), and order of planning (planning first or planning second). Task order had a clear effect on learners’ production, regardless of the provision of planning time. Guided planning time promoted a focus on attempted accuracy and unguided planning time fostered fluency. Finally, this study indicates that task conditions can affect high- and low-WMC learners in different ways: the former are more likely to comply with complex story-telling instructions, requiring them to focus on grammatical form at the expense of fluency, whereas the latter are less likely to comply with the same instructions.

The executive attention theory of working memory capacity (WMC) proposes that measures of WMC broadly predict higher order cognitive abilities because they tap important and general attention capabilities (R. W. Engle & M. J. Kane, 2004). Previous research demonstrated WMC-related differences in attention tasks that required restraint of habitual responses or constraint of conscious focus. To further specify the executive attention construct, the present experiments sought boundary conditions of the WMC-attention relation. Three experiments correlated individual differences in WMC, as measured by complex span tasks, and executive control of visual search. In feature-absence search, conjunction search, and spatial configuration search, WMC was unrelated to search slopes, although they were large and reliably measured. Even in a search task designed to require the volitional movement of attention (J. M. Wolfe, G. A. Alvarez, & T. S. Horowitz, 2000), WMC was irrelevant to performance. Thus, WMC is not associated with all demanding or controlled attention processes, which poses problems for some general theories of WMC.

In a previous study, ) investigated whether pure-tone average (PTA) hearing loss and working memory capacity (WMC) modulate benefit from different binaural noise reduction (NR) settings. Results showed that listeners with smaller WMC preferred strong over moderate NR even at the expense of poorer speech recognition due to greater speech distortion (SD), whereas listeners with larger WMC did not. To enable a better understanding of these findings, the main aims of the present study were (1) to explore the perceptual consequences of changes to the signal mixture, target speech, and background noise caused by binaural NR, and (2) to determine whether response to these changes varies with WMC and PTA. As in the previous study, four age-matched groups of elderly listeners (with N = 10 per group) characterized by either mild or moderate PTAs and either better or worse performance on a visual measure of WMC participated. Five processing conditions were tested, which were based on the previously used (binaural coherence-based) NR scheme designed to attenuate diffuse signal components at mid to high frequencies. The five conditions differed in terms of the type of processing that was applied (no NR, strong NR, or strong NR with restoration of the long-term stimulus spectrum) and in terms of whether the target speech and background noise were processed in the same manner or whether one signal was left unprocessed while the other signal was processed with the gains computed for the signal mixture. Comparison across these conditions allowed assessing the effects of changes in high-frequency audibility (HFA), SD, and noise attenuation and distortion (NAD). Outcome measures included a dual-task paradigm combining speech recognition with a visual reaction time (VRT) task as well as ratings of perceived effort and overall preference. All measurements were carried out using headphone simulations of a frontal target speaker in a busy cafeteria. Relative to no NR, strong NR was found to impair speech recognition and VRT performance slightly and to improve perceived effort and overall preference markedly. Relative to strong NR, strong NR with restoration of the long-term stimulus spectrum and thus HFA did not affect speech recognition, restored VRT performance to that achievable with no NR, and increased perceived effort and reduced overall preference markedly. SD had negative effects on speech recognition and perceived effort, particularly when both speech and noise were processed with the gains computed for the signal mixture. NAD had positive effects on speech recognition, perceived effort, and overall preference, particularly when the target speech was left unprocessed. VRT performance was unaffected by SD and NAD. None of the datasets exhibited any clear signs that response to the different signal changes varies with PTA or WMC. For the outcome measures and stimuli applied here, the present study provides little evidence that PTA or WMC affect response to changes in HFA, SD, and NAD caused by binaural NR. However, statistical power restrictions suggest further research is needed. This research should also investigate whether partial HFA restoration combined with some pre-processing that reduces co-modulation distortion results in a more favorable balance of the effects of binaural NR across outcome dimensions and whether NR strength has any influence on these results.

This paper examines the intricate relationship between working memory (WM) capacity and inhibitory control as a function of both L2 proficiency and age. In both its design and research questions, this study closely follows Gass & Lee’s work, where both L1 and L2 Reading Span Tasks (as measures of WM capacity) and L1 and L2 Stroop interference tasks (to measure inhibitory control) were administered. In this study, the test battery is augmented by both an L1 and L2 C-test of overall language proficiency. Participants were 63 L1 Dutch speakers of L2 English, who had been immersed in an L2 environment for a considerable amount of time. Their data were set off against those of 54 monolingual Dutch speakers and 56 monolingual English speakers. At the time of testing, all the bilingual participants had a near-native command of English and their L1 and L2 WM scores were not found to be significantly different. However, discrepancies did occur in Stroop test scores of inhibition, where the bilinguals performed better in their L2 English than L1 Dutch. These main effects often contradicted the results found in Gass & Lee’s study, who examined less proficient L2 learners. An aging effect was furthermore found: older subjects consistently performed more poorly on WM and inhibition tasks than their younger peers. These results can shed light on how individual factors like WM capacity and inhibitory control interact in successful late bilinguals and how these dynamics shift with advanced age.