Phonological working memory (PWM) is the mind's capacity for maintaining and manipulating representations of the sounds important for speech when they are not actively being perceived. It is believed to be a critical component supporting typical language acquisition and vocabulary development, as well as second-language learning. Despite the success of the theoretical framework traditionally used to conceptualize PWM, consensus on its instantiation in the brain remains elusive. In this thesis, I will describe a series of studies designed to interrogate the functionality of the brain regions supporting PWM. In Chapter 1, we compare activation patterns from a canonical PWM task, nonword repetition, to nonword discrimination, a matched task designed to engage core PWM functions, but for the purpose of comparing stimuli, not repeating them. We replicate the findings that PWM during nonword repetition engages speech cortices and show that these cortical regions are also reliably engaged in nonword discrimination, in individual subjects. In Chapter 2, we directly assess the extent to which conjunctive activation between language and working memory paradigms can be interpreted as shared functionality. We find that despite the ability to localize regions in which the majority of subjects show conjunction of significant activation between tasks, the pattern similarity between tasks within those regions vary. We find no pattern similarity between language and spatial working memory, and marginal similarities between language and verbal working memory. Verbal working memory and spatial working memory conjunctions localize a similar network to the multiple demand network and find highly similar patterns of activation in these regions across working memory tasks. Finally, in Chapter 3, we investigate the functional properties of brain areas supporting PWM by comparing activation between nonword repetition, language, verbal working memory, and spatial working memory tasks. We find that PWM shares support with areas involved in spoken language perception, as well as regions engaged by working memory tasks that lie outside of the core language network. Taken together, these studies give a detailed account of the neural bases of PWM, through the lens of shared functionality between this capacity, language, and other domains of working memory.

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.

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.

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.

Research has revealed a relation between phonological working memory (PWM) and language abilities, showing that children with language-learning impairments have poorer PWM than their typically-developing peers (Montgomery et al., 2010). Limited work has examined PWM in relation to sentence production abilities in school-aged children. We hypothesized that PWM abilities would predict performance on the Formulated Sentences (FS) subtest of the Clinical Evaluation of Language Fundamentals – IV, of typically-developing and language-learning impaired school-aged children (N=273). Additionally, we hypothesized that the children's PWM abilities would correlate with characteristics of their correct formulated sentences, measured by lexical diversity, length, and complexity (hypothesis 2), and that PWM would correlate with processing fluency, measured by mazes (hypothesis 3) and pauses (hypothesis 4). For our fifth hypothesis, we predicted there would be group differences in PWM and sentence characteristics when comparing the typically-developing children to children with language-learning impairment. We examined these hypotheses with data from a subset of 27 children with language-learning impairment and 27 typically-developing peers. Results support our first and third hypotheses and partially support our fifth hypothesis but not our second or fourth hypotheses. These results suggest that PWM can be used to predict FS scores and that PWM may be more closely related to the types of errors in children’s sentences. Furthermore, results from our fifth hypothesis suggest that deficits in PWM and sentence production may simply co-occur but not interact in children with language-learning impairment.

The purpose of the current investigation was to explore the effects of aphasia on working memory (WM) in bilingual adults. Available research supports the notion that there are strong positive correlations between WM capacity and language function in monolingual adults with aphasia and that aphasic adults' ability to comprehend language may be predicted by WM capacity. The relationship between WM capacity and auditory comprehension, as measured by the Token Test, was investigated in bilingual adults with and without aphasia. Additional areas of investigation included examination of the influence of aphasia on bilingualism and language proficiency as measured by differential performance in both languages on the Boston Naming Test (BNT); relationships between severity of aphasia, as measured by the Bilingual Aphasia Test (BAT); and WM, as measured by listening span. Sixteen participants between the ages of 26 and 91 were included in this study (mean age for women was 61.3; men was 52.8; 37% of the sample population was male, 63% was female). Eight participants were non-aphasic bilingual adults, the remaining 8 participants were bilingual aphasic adults. Results of the study indicated that both groups yielded relatively equivalent findings for the two languages on WM measures. Highly significant and strong positive correlations were observed between WM and auditory comprehension for both groups in both languages. There were no significant differences between English and Spanish results relative to auditory comprehension in the group with aphasia. There was, however, more variability on the BNT for the group with aphasia. Moreover, a significant difference between English and Spanish on the BNT was observed for the non-aphasic group. Significant relationships were found between language proficiency and aphasia severity for both languages; however, no significant differences were found between English and Spanish on the BAT. Nonetheless, moderate to strong positive linear relationships were observed between WM and aphasic severity (BAT) and strong positive relationships were found between language proficiency and aphasia severity for both languages for the group with aphasia. In conclusion, results suggest that the impact of bilingualism on WM for aphasic adults may be similar to what has been observed for monolingual aphasic individuals. Further research is needed relative to the nature of WM in bilingual adults with aphasia.