There is evidence that language ability is related to a number of cognitive processes, including memory. As children become more proficient language-users, they develop the ability to use language as a memory attribute. This study used EEG coherence to investigate the extent to which verbal encoding strategies account for individual differences in two short-term recognition memory tasks in 50 3-year-olds. Children with better expressive and receptive language performed better on the picture memory task (which contains stimuli that can easily be labeled) but not the abstract memory task, indicating that language may support memory processes for some types of stimuli more than for others. Analyses of EEG coherence at the hypothesized electrode pairs (F7-T3 and F8-T4) at baseline and encoding were not significant, indicating that verbal encoding does not account for individual differences in short-term memory performance. When these electrode pairs were examined at baseline and retrieval for the picture memory task, EEG coherence analyses indicated that it may be the use of language as a retrieval cue rather than an encoding strategy that explains individual differences in short-term recognition memory. / Ph. D.

The present study examined source memory development in a sample of 4 and 6 year children. Patterns of brain electrical (EEG) activity were examined in order to provide a neural basis for the role of prefrontal cortex functioning during source monitoring. Children were taught a series of novel facts from two difference sources (either an experimenter or puppet) and their memory for both item and source information was later tested. Results demonstrated that, after controlling for language, patterns of frontal brain activity predicted 6 year item recall performance, and trends toward significance were observed for temporal brain activity predicting 6 year source recall performance. No associations between frontal or temporal EEG activity and episodic memory judgments were observed among 4-year-old children. Future investigations should examine how source memory, and on a more general level contextual memory binding, influence the development of episodic memory in early childhood. / Master of Science

Previous literature has suggested an apparent P300 sensitivity to self-relevant stimuli. To further explore this relationship, we asked participants to submit 10 photos, each of a particular category (e.g. footwear, plants), to be used as either targets or distractors in a given condition of an oddball task. Furthermore, we attempted to see whether the effect of self-relevance on the P300 could be induced in a participant by allowing them to study a set of unique photos which would then be used as targets. Our analysis suggested that P300 amplitude elicited in response to self-relevant stimuli used as targets was statistically significantly greater than all other conditions’ targets. This effect was not correlated with the participant sentiment toward their own photos as assessed by the Revised Personal Involvement Inventory. In light of this, we suggest a generalized effect of self-relevance on the P300. Limitations and future directions are discussed.

Our memory system is highly complex and contains numerous features ranging from fine-grained, event-specific details through high-level conceptual knowledge. With immense amounts of constant incoming information, limitations on our memory system do not allow us to encode every detail into long-term memory. Thus, memory is prioritized for the information that is most valuable or important to our current or future goals (Adcock et al., 2006; Murty & Adcock, 2017). While this literature has shown a link between motivation and memory in general, our recent work has begun to characterize how motivation targets different aspects of memory, with evidence suggesting a focus on higher-level features (Horwath et al., 2023; Horwath & Murty, in-prep). Yet, investigating the neural bases of this process will further our understanding of the structure of memory. We tackled this question using representational similarity analysis (RSA) to first characterize the granularity at which reward is represented categorically or continuously in the brain, and then measure how those representations relate to subsequent memory. We measured pattern similarity in the medial temporal lobe (MTL) and a larger network containing anterior temporal (AT) regions, which supports conceptual information, and posterior medial (PM) regions, which support event-specific details. Results showed hippocampal (HPC) and AT involvement in representing categorical aspects of motivation, while PM tracked continuity across value. The AT and PM networks also revealed an important role in supporting successful memory for high- and low-value information, respectively. Together, this work highlights the importance of understanding the neural processes underlying the complexities of motivated memory. / Psychology

Coordinating our actions with others changes how we behave and feel. Here, we provide evidence that interacting with others rests on a balance between self-other integration and segregation. Using a group walking paradigm, participants were instructed to synchronize with a metronome while listening to the sounds of 8 virtual partners. By manipulating the similarity and synchronicity of the partners’ steps to the participant’s own, our novel auditory task disentangles the effects of synchrony and self-other similarity and examines their contribution to both collective and individual awareness. We measured temporal coordination (step timing regularity and synchrony with the metronome), gait patterns, and subjective reports about sense of self and group cohesion. The main findings show that coordination is best when participants hear distinct but synchronous virtual others, leading to greater subjective feelings of agency, strength, dominance, and happiness.

Seventy-three children participated in an investigation of inhibitory control (IC) at 3 years of age. Child IC was measured under various conditions in order to determine the impact that nonverbal and/or motivational task demands had on child IC task performance. Furthermore, task performance was examined with respect to measures of language, temperament, and psychophysiology. Tasks showed different patterns of relations to each of these variables. Furthermore, performance on the Hand Game, our measure of nonverbal IC, was explained by frontal EEG activity and, surprisingly, by language abilities. In contrast, performance on two other IC tasks, Day-Night and Less is More, was not related to measures of language or frontal EEG, perhaps because children performed at chance level on these tasks, indicating that these tasks may be too difficult for 3-year-old children. Implications of these findings are discussed. / Master of Science

Many decisions require us to actively interrogate the world using our senses. Based on what we perceive, we may commit to an immediate course of action or plan for future actions. The neuroscience of perceptual decision-making examines how the brain gathers sensory information and uses it to guide behavior. A widely accepted model represents this decision process as the gradual accumulation of sensory evidence until a threshold or criterion is reached. For decisions about the direction of random-dot motion (RDM) stimuli, extensive research has described the mechanisms of evidence accumulation in association areas such as the lateral intraparietal area (LIP). Recent studies have also made progress in identifying the biological basis of the decision threshold. For overt decisions marked by an immediate saccadic response, neurons in the superior colliculus (SC) are thought to set this threshold by initiating eye movements when LIP activity is sufficiently elevated. Additionally, reversible inactivation of SC neurons has been shown to prolong evidence accumulation in LIP, suggesting that SC neurons play a causal role in terminating the decision process. However, it remains unknown whether SC neurons also contribute to covert decision termination, where commitment results in a planned, rather than an immediate, eye movement. To address this gap, I recorded neural activity from two rhesus macaques as they performed a RDM discrimination task, where I varied the length of the stimulus and delay periods from trial to trial. This design required the animals to make a covert commitment to a choice on each trial, which they later reported with a saccade following the delay period. Using high channel-count electrodes, I recorded simultaneously from large populations of neurons in SC, LIP, and the dorsal pulvinar of the thalamus (dPul) unilaterally. In a majority of trials, SC neurons exhibited non-saccadic bursts — bursts of activity not associated with eye movements or specific trial events. The timing of these non-saccadic bursts suggested they might signal the moment of decision termination. Testing this hypothesis, I found that non-saccadic bursts effectively divided each trial into an early deliberation phase, where sensory evidence informed the decision, and a later commitment phase, where further sensory evidence was ignored. Additionally, the timing of non-saccadic bursts in the SC corresponded with the end of evidence accumulation in LIP. Finally, I identified a population of neurons in dPul that may relay this termination signal from SC to LIP. This study advances our understanding of perceptual decision-making by broadening the function of the SC in decision termination. Beyond its established role in terminating overt decisions with an immediate saccadic report, these findings suggest that the SC also contributes to decision termination following covert commitments, where the saccade occurs after a delay. The results have important implications for systems neuroscience by offering a clear example of serial computations occurring across dedicated cortical and subcortical areas to guide flexible behavior. While the path from sensation to deliberation to commitment is far from fully understood, these results lay the groundwork for future research — both to explore the role of additional nodes in the decision-making network and to investigate the local circuits that give rise to distinct functions within each node. In Chapter 1, I provide historical context on the neurobiology of perceptual decision-making, introduce the bounded evidence accumulation model, and discuss its application to both overt and covert decisions. I also motivate the present study by introducing the superior colliculus and its known role in the decision-making network. In Chapter 2, I investigate physiological markers of decision commitment in the SC. I describe non-saccadic bursts, which are physiological events that occur on single trials, and demonstrate how these events relate to covert decision termination. In Chapter 3, I examine how non-saccadic bursts in the SC might be involved in terminating the process of evidence accumulation in LIP and show how neurons in dPul might mediate this effect. Chapter 4 presents closing considerations and outlines directions for future research.

<p>Thank you to all who were involved in this research including Drs. Benicio Frey,<br />Sue Becker, Margaret McKinnon, Luciano Minuzzi, and Lauren Cudney and Marg Coote. I would like to express my very great appreciation to the midwives at Community Midwives of Hamilton for enabling me to visit the clinic and recruit their pregnant clients. Finally, I would like to thank Lorenda Williams, John Williams, and Eric Johnson for their continued support.</p> / <p>Postpartum depression (PPD) is a serious disorder associated with debilitating effects on mothers and their infants. A previous history of depression appears to be the strongest risk factor for PPD. Previous studies showed that individuals with history of depression accurately recall more negative compared to positive content. The objective of this study was to compare emotional memory for negative and positive images between pregnant women with previous depressive episodes and pregnant women with no lifetime depression. This is the first study to investigate emotional memory in pregnant women with or without previous history of Major Depressive Disorder (MDD). A total of 77<br />participants between the ages of 18 - 44 (mean age: 27.3  6.2yo) completed the study (14 pregnant women with previous depressive episodes, 30 pregnant women with no lifetime depression, 13 non-pregnant women with previous depressive episodes, and 20 non-pregnant healthy). Participants took part in an emotional encoding task consisting of positive, negative, and neutral images from the International Affective Picture System (IAPS) where they were asked to rate these images based on perceived emotional intensity. Participants returned a week later for a surprise incidental recognition memory task. A multivariate general linear model revealed a significant main effect of group (F(1,71)= 8.04, p=.01). Women with history of MDD demonstrated poorer memory performance than women with no history for negative images, but the two groups did not<br />differ on memory for positive images. This suggests that having a history of depression selectively impaired the memory recognition of negative images.</p> / Master of Science (MSc)

The current thesis explores the complex relationship between cognitive control and memory. A series of experiments combined task-switching paradigms with recognition memory tests to measure how switching between tasks influences effective control over long-term memory. In these experiments, participants were presented with compound stimuli consisting of a picture and an overlaid word, and were cued in each trial whether the word or the picture was relevant (attended) or irrelevant (unattended). Participants were then tested for their memory of items presented during task switching. Experiments 1-2 indicated that switching between tasks reduces the selectivity of processing: Switching was associated with impaired task performance as well as more similar memory ratings for attended and unattended items. Experiments 3-5 extended these findings by showing that enhanced top-down control positively affected task-performance as well as memory, in both cases by increasing the selectivity of processing toward task-relevant information. Experiments 6-7 replicated key effects with simple switches of visual attention, and explored the neural correlates of successful task performance and encoding using EEG. The key finding here was that previously observed ―subsequent memory‖ effects reflect, at least in part, selective encoding processes. The last chapter extended the focus of the investigation to explore the role of control in long-term memory retrieval. FMRI meta- analyses indicated considerable overlap in neural activation found during task switching and during the adoption of different retrieval sets. The results of Experiment 8 indicated that switching during task performance and later memory retrieval were both associated with decreased selectivity of processing. Collectively, the results of this thesis suggest that selectivity of processing is a critical factor in effective task performance and successful memory, with potentially very similar mechanisms underlying the two. This work demonstrates the fruitfulness of combining research on cognitive control and memory to study questions relevant for both fields.

The physical properties of the distal stimuli activating our senses are often correlated in nature; it would therefore be advantageous to exploit such correlations to better process sensory information. Stimulus correlations can be contingent and readily available to the senses (like the temporal correlation between mouth movements and vocal sounds in speech), or can be the results of the statistical co-occurrence of certain stimulus properties that can be learnt over time (like the relation between the frequency of acoustic resonance and the size of the resonator). Over the last century, a large body of research on multisensory processing has demonstrated the existence of compatibility effects between individual features of stimuli from different sensory modalities. Such compatibility effects, termed crossmodal correspondences, possibly reflect the internalization of the natural correlation between stimulus properties. The present dissertation assesses the effects of crossmodal correspondences on multisensory processing and reports a series of experiments demonstrating that crossmodal correspondences influence the processing rate of sensory information, distort perceptual experiences and lead to stronger multisensory integration. Moreover, a final experiment investigating the effects of contingent signals’ correlation on multisensory processing demonstrates the key role of temporal correlation in inferring whether two signals have a common physical cause or not (i.e., the correspondence problem). A Bayesian framework is proposed to interpret the present results whereby stimulus correlations, represented on the prior distribution of expected crossmodal co-occurrence, operate as cues to solve the correspondence problem.