Variations in working memory capacity:From cognition to brain networks

Werkgeheugen (WG) voorspelt ons vermogen om kennis te vergaren en nieuwe vaardigheden te leren, en is een betere voorspeller van academisch succes dan IQ. Het onderzoek zoals beschreven in deze thesis is gemotiveerd door een van de cognitieve theorieën van WG- de executive-aandacht theorie van WG. De theorie suggereert een nauwe relatie tussen individueel werkgeheugen en aandachtvermogen tijdens interferentie van gewone handelingspatronen, afleidende factoren an de omgeving, of gedachten die niet relevant zijn voor de bewuste taak (i.e. niet-taakgeralateerde gedachten of afwalende gedachten) zijn. In deze thesis kijken we naar de vaak geziene relatie tussen werkgeheugen en prestatie tijdens respons-conflict taken (e.g., Simon taak, Eriksen flanker taak), die een uitdaging vormen voor iemands vermogen om taken uit te voeren terwijl ze worden afgeleid. Door de relatie tussen het WG en cognitief vermogen te karakteriseren zoeken we de verbreding van WG-onderzoek van het cognitieve tot het neurale niveau. Daarbij combineren we diverse analyses en experimentele benaderingen. Tot slot, de resultaten zoals in dit proefschrift beschreven, wijzen op de noodzaak om de bestaande cognitieve theorieën van het WG te vernieuwen met neurofysiologische bevindingen uit fMRI en EEG onderzoek, omdat bestaande beschrijvende cognitieve modellen tekort schieten om de rijkdom en complexiteit van de verschijnselen in combinatie met individuele variaties in het WG te verklaren.Working memory capacity (WMC) predicts our ability to acquire knowledge and develop new skills, and is a better predictor of academic achievement than IQ. The research described in this thesis was motivated by one of the cognitive theories of WM – the executive-attention theory of WMC. The theory suggests a close relationship between individual’s WMC and attention control abilities in the face of interference from habitual action routines, environmental distractors, or thoughts that are irrelevant for the task at hand (i.e. task-unrelated thoughts or mind wandering). In this thesis, we exploited the often-observed relationship between WMC and performance in response-conflict tasks (e.g., Simon task, Eriksen flanker task), which challenge one’s ability to maintain task goals in the face of distraction. By characterizing the relationship between WMC and cognitive control abilities combining different analyses and experimental approaches we sought to extend WMC research from cognitive to the neural level. In summary, results described in this thesis point to the need to update existing cognitive theories of WMC with neurophysiological findings from fMRI and EEG, as existing descriptive cognitive models are too under-specified to explain the richness and complexity of phenomena related to individual variations in WMC

Fronto-parietal network oscillations reveal relationship between working memory capacity and cognitive control

Executive-attention theory proposes a close relationship between working memory capacity (WMC) and cognitive control abilities. However, conflicting results are documented in the literature, with some studies reporting that individual variations in WMC predict differences in cognitive control and trial-to-trial control adjustments (operationalized as the size of the congruency effect and congruency sequence effects, respectively), while others report no WMC-related differences. We hypothesized that brain network dynamics might be a more sensitive measure of WMC-related differences in cognitive control abilities. Thus, in the present study, we measured human EEG during the Simon task to characterize WMC-related differences in the neural dynamics of conflict processing and adaptation to conflict. Although high- and low-WMC individuals did not differ behaviorally, there were substantial WMC-related differences in theta (4-8 Hz) and delta (1-3 Hz) connectivity in fronto-parietal networks. Group differences in local theta and delta power were relatively less pronounced. These results suggest that the relationship between WMC and cognitive control abilities is more strongly reflected in large-scale oscillatory network dynamics than in spatially localized activity or in behavioral task performance

Dissociable mechanisms underlying individual differences in visual working memory capacity

Individuals scoring relatively high on measures of working memory tend to be more proficient at controlling attention to minimize the effect of distracting information. It is currently unknown whether such superior attention control abilities are mediated by stronger suppression of irrelevant information, enhancement of relevant information, or both. Here we used steady-state visual evoked potentials (SSVEPs) with the Eriksen flanker task to track simultaneously the attention to relevant and irrelevant information by tagging target and distractors with different frequencies. This design allowed us to dissociate attentional biasing of perceptual processing (via SSVEPs) and stimulus processing in the frontal cognitive control network (via time–frequency analyses of EEG data). We show that while preparing for the upcoming stimulus, high- and low-WMC individuals use different strategies: High-WMC individuals show attentional suppression of the irrelevant stimuli, whereas low-WMC individuals demonstrate attentional enhancement of the relevant stimuli. Moreover, behavioral performance was predicted by trial-to-trial fluctuations in strength of distractor-suppression for high-WMC participants. We found no evidence for WMC-related differences in cognitive control network functioning, as measured by midfrontal theta-band power. Taken together, these findings suggest that early suppression of irrelevant information is a key underlying neural mechanism by which superior attention control abilities are implemented

The effects of verbal and spatial memory load on children's processing speed

Examining the impact of maintenance on processing speed allows us to test whether storage and processing resources are shared. Comparing these relationships in children of different ages allows further insight into whether one or multiple resources for these operations must be assumed and whether remembering is proactive throughout childhood. We tested 185 4-6 and 8-10 year-old children using adaptive complex span tasks, in which simple judgments were interleaved between to-be-remembered items. The adaptiveness of our tasks ensured that all participants frequently correctly recalled the items. If storage and processing require a single resource, and if participants serially reactivate the memoranda in between processing episodes, processing response times should increase with serial position of the processing judgment within lists. We observed different within-list dynamics for each age group. Older children’s processing judgments slowed gradually when more than two memory items were maintained. In contrast, younger children showed no evidence of slower processing with increasing memory load. Our results support models of working memory that assume that some common resource is responsible for verbal and spatial storage and processing. They also support the notion that remembering becomes more proactive as children mature

The Ganzflicker experience:High probability of seeing vivid and complex pseudo-hallucinations with imagery but not aphantasia

There are considerable individual differences in visual mental imagery ability across the general population, including a “blind” mind's eye, or aphantasia. Recent studies have shown that imagery is linked to differences in perception in the healthy population, and clinical work has found a connection between imagery and hallucinatory experiences in neurological disorders. However, whether imagery ability is associated with anomalous perception–including hallucinations–in the general population remains unclear. In the current study, we explored the relationship between imagery ability and the anomalous perception of pseudo-hallucinations (PH) using rhythmic flicker stimulation (“Ganzflicker”). Specifically, we investigated whether the ability to generate voluntary imagery is associated with susceptibility to flicker-induced PH. We additionally explored individual differences in observed features of PH. We recruited a sample of people with aphantasia (aphants) and imagery (imagers) to view a constant red-and-black flicker for approximately 10 min. We found that imagers were more susceptible to PH, and saw more complex and vivid PH, compared to aphants. This study provides the first evidence that the ability to generate visual imagery increases the likelihood of experiencing complex and vivid anomalous percepts