The term cognitive enhancers are substances that increase cognitive performance. The stimulant methylphenidate is commonly used as a medication for attention deficit hyperactive disorder and is highly popular as a cognitive enhancer. One of its theorized mechanisms of action is to enhance working memory. This systematic review aims to examine literature that tests the effect of methylphenidate on cognitive performance, specifically working memory, in healthy subjects. Following the PRISMA guidelines, a systematic search was conducted on Web of Science, Scopus, and Medline Ebsco on 1st March 2022. Articles were selected based on the predetermined eligibility criteria. Of the ten selected articles, three found a significant effect of methylphenidate on working memory, and one found a significant effect on spatial working memory. The studies produced varied results due to differential use of working memory tasks and methylphenidate dosage. Further studies on how methylphenidate affects working memory are needed.

Although the effect of working memory (WM) load on the magnitude of distractor interference has been studied extensively, a common characteristic in prior research is that the target and distractors belong to different objects. The present experiments investigate the effect of WM load on distractor interference when the relevant and irrelevant information is part of the same object. In two experiments, participants saw stimulus displays that consisted of a memory set followed by a Stroop color stimulus. The tasks were to respond to the color of the stimulus first and then to a memory probe. The principal manipulations were the relationship between the color and meaning of the Stroop stimulus (neutral vs. incongruent) and the level of WM load (high vs. low). The results show that WM load had little effect on the magnitude of Stroop interference. These results were consistent with previous research which shows that WM load plays a limited role in the efficiency of selective attention when the extent of attentional focus was held constant across different WM load conditions. They also emphasize the importance of stimulus structure in understanding selective attention in general, and distractor processing in particular.

To achieve goal-orientated behaviour, selective attention is often needed to filter out irrelevant information. Past research has shown that working memory (WM) plays a critical role in selective attention, with high WM load leading to more distractor interference than low WM load. However, because WM load is usually manipulated by requiring participants to hold in memory either one or several digits that were presented simultaneously while performing a selective attention task, the extent of attentional focus was not controlled. The present study examined the effect of WM load on distractor inhibition while keeping attentional focus constant by presenting one digit (low load condition) or six digits (high load condition) sequentially. The participants in the high-load condition demonstrated greater distractor interference than the participants in the low-load condition, suggesting that WM load influences distractor inhibition even when the extent of attentional focus was controlled. This result provides converging evidence to Lavie's (1995, 2005) load theory of attention and cognitive control.

A number of models of working memory have been proposed since the seminal work of Baddeley and Hitch (1974) on the Multiple Component Model (MCM). Subsequent MCM research focussed on developing a theoretical framework based on modality-specific stores that can operate in parallel during dual-tasking. The MCM can be contrasted with theories of working memory that assume an attention-based domain-general shared resource responsible for both short term retention as well as on-line cognition, such as the Time-Based Resource Sharing (TBRS) model (Barrouillet, Bernardin, & Camos, 2004; Barrouillet, Bernardin, Portrat, Vergauwe, & Camos, 2007). The TBRS model assumes that short-term memory is dependent on access to attention, and any diversion of attention results in increased forgetting. The model describes ‘refreshing’ as the process of serially bringing memory items briefly into the focus of attention. Barrouillet and colleagues have demonstrated in numerous studies that memory spans lower as the cognitive demand of the secondary task increases - findings that are incompatible with the MCM. However, Camos, Mora, and Oberauer (2011) found that both sub-vocal rehearsal (the verbal maintenance mechanism described in the MCM) and attention-based refreshing can be selectively employed by participants depending on task demands. Since TBRS methodology compares spans measured under different cognitive load levels that are the same for every participant, we were interested in whether ensuring that secondary task demand was set within each participant’s abilities would avoid ‘over-taxing’ the working memory system and reduce dual-task costs. Our initial investigations re-measured memory and processing spans under dual-task conditions with secondary tasks’ demand titrated according to each individual’s measured ability (Experiments 1 and 2, and Doherty & Logie, 2016). We found that memory span was unaffected when processing demand was titrated, but that processing performance was lower when memory load was set above participants’ span. Subsequent experiments (3-8) investigated the effect of setting memory and processing load ‘below span’, ‘at span’, and ‘above span’ on memory and processing accuracy during dual-tasking. Overall it was found that processing resources can be reallocated to support memory performance but memory resources cannot be reallocated to support processing performance. We interpret the results as evidence for specialised memory resources and rehearsal mechanisms that can be supplemented by attention-based processes once storage capacities are exceeded. Experiments 6-8 aimed to encourage the use of phonological- or attention-based rehearsal mechanisms for verbal short term memory by either introducing articulatory suppression (AS) or shortening available encoding time for memory items. It was found that participants exhibited shared-resource effects when they completed the dual-task under AS, suggesting a shift to attention-based rehearsal. When encoding time was limited participants’ memory performance during dual-tasking was unaffected by concurrent processing load, suggesting the use of a rehearsal method which did not require access to attention. Experiment 9 investigated whether participants could dynamically allocate attention to one task or the other, and found that while ‘priority’ tasks received no benefit, non-priority tasks exhibited a marked decrement in performance. We conclude that the perceived incompatibility between the MCM and attention-based theories of working memory such as the TBRS model may be more apparent than real, and suggest that future research should incorporate procedures and methodological considerations that take into account findings from both literatures.

The effectiveness of attention and working memory (A/WM) training programs in improving executive functions (EFs) is heavily debated. The objective of the current study was to evaluate the efficacy of a game-based process-specific cognitive intervention program (Dino Island; DI), on improving attention, working memory (WM), and pre-literacy skills in preschoolers. A secondary objective was to evaluate the feasibility of delivering DI intervention in community settings. Dino Island is an intervention program that consists of five hierarchically structured tasks that target attention and WM. The intervention also involves the teaching of metacognitive strategies to facilitate transfer effects to daily activities. The DI intervention was delivered to preschoolers (ages four to six years) during regular school days. Ten preschoolers were randomly assigned to either an active DI intervention group, or an educational games control group, with five participants in each group. All participants completed 12 hours of intervention over an eight to ten-week period. Children’s attention, EF and school readiness was assessed pre and post intervention using cognitive measures, rating scales and interviews. Non-parametric test results found significant changes in working memory for the DI intervention group (p = .03), however, results did not show significant gains in other abilities. A case study approach was then utilized to further explore outcomes for children in the DI intervention condition. The results suggest that DI training can potentially lead to gains in WM among preschool children, providing preliminary evidence of its efficacy within this age groups. DI is also feasible to be delivered within school settings during regular school hours. / Graduate

The ‘belief bias’ effect is one of the most pervasive findings in the study of syllogistic reasoning. Here, participants respond “valid” to more believable than unbelievable conclusions, regardless of the actual validity of the conclusion. There is also an interaction characteristic of the belief bias effect, in that conclusion believability plays a greater role when conclusions are invalid than when they are valid. The experiments reported in this thesis had two goals: first, to determine how individual differences in working memory (WM) capacity influence belief bias in reasoning; and second, to indentify which WM systems are involved in syllogistic deductive reasoning. To this end, both experiments employed a dual task paradigm. In Experiment 1, participants remembered spatial arrays whilst reasoning through syllogisms in order to load the visuospatial sketchpad. Results demonstrated that performance on the secondary spatial memory task suffered when participants reasoned through syllogisms of which the validity and believability of conclusions were incongruent (i.e., “conflict” problems), indicating that reasoning through conflict problems utilized limited visuospatial WM resources. Also, only participants with high WM capacities showed the typical belief-bias effect, with greater effects of conclusion believability on invalid than on valid conclusions. This interaction was not present for low WM span participants, because they made greater errors on problems with invalid, unbelievable conclusions. In Experiment 2, participants remembered digit sequences whilst reasoning in order to load the phonological loop. Both of the major results from Experiment 1 were replicated. Accuracy on the secondary digit recall task was impaired when participants reasoned through conflict problems, demonstrating that limited verbal WM resources were directed toward reasoning. Again, only high WM span participant showed the interaction between conclusion validity and believability characteristic of the belief bias effect. Effects were additive for low WM span participants because they made more errors on invalid, unbelievable syllogisms. Results from both experiments demonstrate first, that both visuospatial and verbal WM resources are involved in syllogistic reasoning, and second, that individuals with different amounts of available WM resources demonstrate differential belief bias. These results are discussed in terms of the mental models and mental logic theories of reasoning and in terms of dual process accounts of reasoning.

The ‘belief bias’ effect is one of the most pervasive findings in the study of syllogistic reasoning. Here, participants respond “valid” to more believable than unbelievable conclusions, regardless of the actual validity of the conclusion. There is also an interaction characteristic of the belief bias effect, in that conclusion believability plays a greater role when conclusions are invalid than when they are valid. The experiments reported in this thesis had two goals: first, to determine how individual differences in working memory (WM) capacity influence belief bias in reasoning; and second, to indentify which WM systems are involved in syllogistic deductive reasoning. To this end, both experiments employed a dual task paradigm. In Experiment 1, participants remembered spatial arrays whilst reasoning through syllogisms in order to load the visuospatial sketchpad. Results demonstrated that performance on the secondary spatial memory task suffered when participants reasoned through syllogisms of which the validity and believability of conclusions were incongruent (i.e., “conflict” problems), indicating that reasoning through conflict problems utilized limited visuospatial WM resources. Also, only participants with high WM capacities showed the typical belief-bias effect, with greater effects of conclusion believability on invalid than on valid conclusions. This interaction was not present for low WM span participants, because they made greater errors on problems with invalid, unbelievable conclusions. In Experiment 2, participants remembered digit sequences whilst reasoning in order to load the phonological loop. Both of the major results from Experiment 1 were replicated. Accuracy on the secondary digit recall task was impaired when participants reasoned through conflict problems, demonstrating that limited verbal WM resources were directed toward reasoning. Again, only high WM span participant showed the interaction between conclusion validity and believability characteristic of the belief bias effect. Effects were additive for low WM span participants because they made more errors on invalid, unbelievable syllogisms. Results from both experiments demonstrate first, that both visuospatial and verbal WM resources are involved in syllogistic reasoning, and second, that individuals with different amounts of available WM resources demonstrate differential belief bias. These results are discussed in terms of the mental models and mental logic theories of reasoning and in terms of dual process accounts of reasoning.

Memory is an essential component for learning. Deficits in verbal short-term memory (STM) and working memory (WM) are thought to hinder language learning, reading acquisition, and academic achievement. The Children’s Memory Scale (CMS) is an assessment instrument used to identify memory and learning deficits and strengths in children ages five through 16. This study investigated the impact of culture and parent educational level (PEL) on student performance on the Children’s Memory Scale using the CMS standardization data. The major question addressed was: Will CMS subtest performance differ significantly between ethnic groups or as a function of PEL? The results of this study support a relationship between STM and WM performance and culture. Culture as defined by ethnicity minimally impacted student subtest performance on the CMS when PEL was taken into account. In contrast, PEL was significantly associated with student subtest performance within each ethnic group. Student subtest performance improved with each increase in PEL regardless of ethnicity. CMS subtest performance of Hispanic and African American students was most affected by PEL; however, no difference occurred in subtest performance by ethnicity or as a function of PEL for African American and Hispanic students on the Family Pictures subtest which examines visual and auditory memory processes through recall of everyday life tasks in meaningful context. Although statistical significance was found between CMS subtest performance and cultural factors, the effect sizes were mainly in the small range and variance was not specific to any one subtest. Larger effect sizes were found on verbal subtests which in previous studies have been found to be most impacted by quality of schooling and lower PELs. Mean score differences did not exceed one standard deviation with the exception of one subtest. The results of this study provide a better understanding of the effect of culture and PEL on memory and learning.

Chronic exposure to psychostimulants such as amphetamine (AMPH) can induce long-term disruptions in cognition via actions on prefrontal cortex dopamine. Previous work has shown that two types of executive functions, set shifting and working memory (WM), are disrupted by AMPH sensitization and that these cognitive domains are impaired in schizophrenics and stimulant abusers. We assessed the effects of AMPH sensitization on behavioural flexibility using a cross-maze set shifting task and a WM task using the delayed spatial win-shift (SWSh) task in Long Evans (LE) and Sprague Dawley (SD) rats. Rats were exposed to an AMPH sensitization regimen (15 AMPH or saline injections: 1-5 mg/kg every 2nd day, increasing the dose by 1 mg every 3rd injections) following habituation on the mazes. In experiment 1, LE and SD rats were initially trained on a visual cue discrimination. During the set shift, rats were required to shift from the previously acquired visual-cue-based strategy to a response strategy (e.g.; always turn left, ignore the visual cue). For the reversal, rats were trained to reverse their turn direction. AMPH treatment did not impair learning of the initial cue discrimination in either strain. However, AMPH treated rats learned the response discrimination faster than controls during the set shift and AMPH treated LE rats were faster than controls to reach acquisition criterion during the response reversal. AMPH treatment neither impaired nor improved reversal learning in SD rats. In experiment 2, rats were tested on the SWSh task in which spatial information acquired during a training phase was used 30 minutes later during the testing phase in order to retrieve food pellets on the maze. In this task, AMPH treated rats were faster to re-attain criterion than control rats. Correlational analysis further revealed that AMPH sensitized rats that required more days to reach criterion before AMPH treatment (i.e. slow learners) tended to make more errors during re-acquisition of the memory task. Viewed collectively, these results suggest that chronic AMPH treatment can enhance behavioural flexibility and WM assessed in this manner. However, repeated AMPH exposure may have exacerbated pre-existing cognitive deficits in slow learning rats.

The purpose of the current study was to examine the impact of working memory on speech monitoring processes in the primary language of school-age children using the framework of Levelt’s Perceptual Loop Theory of speech production (1983). A community sample of eight children aged 6-8 and fourteen children aged 10-12 completed 4 verbal description tasks under different conditions; control, working memory load, white noise and combined working memory load and white noise. Participants also completed measures of listening span, digit span and spatial span. The results indicate that with increasing working memory load, children make significantly more speech errors, silent pauses and repetitions. No relationship was found between working memory and total repairs per errors or between working memory and total number of editing terms used. Group differences across the conditions were not significant; however, age-related trends were notable. Younger children had greater difficulty monitoring their speech with the introduction of working memory load; whereas, older children had greater difficulty with the introduction of white noise. A revised speech production model incorporating aspects of working memory is recommended and implications for clinical populations are discussed. / Graduate / 0290 / 0620 / 0460 / tlentz@icloud.com