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Browsing by Author "Thomas, Michael, committee member"

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    Cue competition and feature representation in a category learning task: an fMRI study
    (Colorado State University. Libraries, 2023) Jentink, Kade, author; Seger, Carol, advisor; Burzynska, Agnieszka, committee member; Rojas, Don, committee member; Thomas, Michael, committee member
    During learning, attention is limited, and therefore selecting what feature(s) to attend to in the environment is important. Sometimes, attention is captured by a cue or feature in such a way that other cues or features are not attended to, known as overshadowing. This process is not entirely understood in category learning, with some studies suggesting that it enhances learning of other features (Murphy et al., 2017), while others suggest that it inhibits (Lau et al., 2020). Furthermore, the location and organization of the neural representations that develop for category features during overshadowing has not been previously examined in this context. The present experiment used representational similarity analyses (RSA), a method for interrogating representational structure (Kriegeskorte et al., 2008), in order to examine where and how features were represented during overshadowing in a category learning task. Participants completed a category learning task in which categories were defined based on two informative features, one binary and one continuous. The binary feature was easier to learn (i.e., more salient), and it was hypothesized that it would overshadow learning of the more difficult continuous feature. This was demonstrated behaviorally: participants learned to categorize when the binary feature was present, then performed at chance when it was removed in a transfer task. Three different hypothetical models were fit to the neural data to determine underlying representational structure: a binary category model, an effector-specific motor model, and a model representing the degree of perceptual similarity for the continuous feature. During initial learning when the primary binary feature was present, the category model fit data from both early visual and object-specific areas of visual cortex, while the motor model fit data from motor-related regions including primary somatomotor cortex and the cerebellum. The perceptual similarity model for the continuous feature did not fit any task data during either Training or Transfer. However, there was a trend for the category model to fit activity in the basal ganglia and lateral occipital complex (LOC) during the Transfer task when the only information available for categorization was the continuous feature. Taken together, these results suggest that, although overshadowing inhibits use of the overshadowed continuous feature as the basis of categorization behavior, it might still contribute to activation of neural representations of category membership.
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    Differentiating associations between tasks and outcomes in the human brain
    (Colorado State University. Libraries, 2022) Nelson, Lauren, author; Seger, Carol, advisor; Thomas, Michael, committee member; Anderson, Chuck, committee member; Tompkins, Sara Anne, committee member
    In order to successfully achieve their goals in a noisy and changing environment, organisms must continually learn both Pavlovian (stimulus-outcome or S-O) and instrumental (action-outcome or A-O) associations. A wide range of brain regions are implicated in reinforcement learning and decision-making, including the basal ganglia, medial prefrontal cortex, the dorsolateral prefrontal cortex (dlPFC), and the anterior cingulate cortex (ACC). One possible explanation of disparate findings is that activation depends on the nature of the action or response under consideration. To investigate representations of task-reward associations, subjects switched between an emotional judgement task and a spatial judgement task, combined with either a high or low level of reward. A general linear model (GLM) compared activation for different combinations of task and reward. A cluster in the mid-prefrontal cortex was more active for right versus left response, whereas a cluster in the midbrain near the brainstem was more active for left responses. Performance of the spatial task was associated with activation in the ventral occipital cortex and ventral prefrontal cortex. Clusters in the posterior parietal cortex and lateral prefrontal cortex were more active during the emotion task. Receiving a large reward was accompanied by activation in primary somatosensory cortex and auditory cortex, while receiving a low reward appeared to recruit the anterior cingulate cortex. Comparing trials which yielded a reward versus trials with no reward revealed activation in the dorsal prefrontal cortex. A 2-way ANOVA examining independent contributions of response and reward found an effect of response in cuneus and pre-cuneus, an effect of reward in anterior insula and sensorimotor cortex, and an interaction in the post-central gyrus. A 2-way ANOVA of task and reward found a main effect of task in several clusters in the medial occipital cortex, a main effect of reward in somatosensory cortex and anterior insula, and an interaction in the ventral occipital and anterior prefrontal cortex.
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    Educational attainment polygenic scores, socioeconomic factors, and resting-state functional connectivity in children and adolescents
    (Colorado State University. Libraries, 2024) Hansen, Melissa, author; Merz, Emily, advisor; Thomas, Michael, committee member; Seger, Carol, committee member; Riggs, Nathan, committee member
    Socioeconomic factors, such as family income and parental education, have been associated with resting-state functional connectivity (rsFC) in networks responsible for executive function in children and adolescents. Yet, children's socioeconomic context interacts with the genetics they inherit from their parents, and few studies of socioeconomic context and rsFC in children have considered genetics. Polygenic scores for educational attainment (PGS-EA) derived from genome-wide association studies (GWAS) reflect genetic predisposition to educational attainment. Yet, no studies have examined the associations between PGS-EA and rsFC. The goal of this study was to investigate how socioeconomic factors and PGS-EA jointly predict rsFC in neural networks associated with executive function, including the central executive (CEN), dorsal attention (DAN), salience (SN), and default mode networks (DMN) in children and adolescents. Participants are typically-developing 3- to 21-year-olds (N = 245, 51% female) from the previously-collected Pediatric Imaging, Neurocognition, and Genetics (PING) study. PGS-EA were computed based on the EA3 GWAS of educational attainment. Resting- state fMRI data were acquired, and system-level rsFC was computed. Findings indicated that family income was inversely associated with rsFC in the SN, while PGS-EA was positively associated with rsFC in the CEN. There were family income-by-age interactions for rsFC in the CEN and DAN, such that age was positively associated with rsFC in the CEN and DAN for children from higher income families and inversely associated with rsFC in the CEN for children from lower income families. These findings help to elucidate the independent genetic and socioeconomic contributions to connectivity in intrinsic functional neural networks underlying executive function.
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    Eye've seen this before: building a gaze data analysis tool for déjà vu detection
    (Colorado State University. Libraries, 2022) Seabolt, Logan K., author; Blanchard, Nathaniel, advisor; Anderson, Charles, advisor; Thomas, Michael, committee member
    In order to expand the understanding of the phenomenon known as déjà vu, an investigation into the use of eyetracking was needed. Through the use of an advanced eyetracking device, open-source software, and previous research into déjà vu, this thesis provides a discussion and analysis of the development for a standardized eyetracking set up for general gaze data collection and a novel gaze data conversion pipeline. The tools created for this thesis work in conjunction to collect and convert data into easier to comprehend formats and separates the results into simplified separate text files. This data analysis tool analyzes and formats files en mass in order to make the processing of high volumes of data easier. These tools are designed to be accessible to professionals within and outside of the field of computer science. With these tools researchers can develop their own projects and implement the eyetracking code over theirs and then pass the output data through the data analysis tool to gather all the information needed.
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    Familiarity-detection from different facial feature-types: is the whole greater than the sum of its parts?
    (Colorado State University. Libraries, 2023) Carlaw, Brooke N., author; Cleary, Anne, advisor; Rhodes, Matthew, committee member; Thomas, Michael, committee member; Blanchard, Nathaniel, committee member
    Prior research indicates that perceived familiarity with a cue during cued recall failure can be systematically increased based on the amount of feature overlap between that cue and studied items in memory (Huebert et al., 2022; McNeely-White et al., 2021, Ryals & Cleary, 2012). However, these studies used word or musical stimuli. Faces represent a special class of stimuli, as evidence suggests that unlike other types of stimuli (such as word or musical stimuli), faces may be primarily processed in a holistic fashion. A recent study demonstrated that even when a person's identity was prevented by the presence of a facial occlusion like a surgical mask or sunglasses, familiarity-detection with the occluded face could still occur, suggesting that holistic processing was not a requirement for facial familiarity-detection (Carlaw et al., 2022). However, some researchers have suggested that although faces can be decomposed into component parts when partially occluded, when faces are presented unoccluded in their entirety, the holistic face processing system may then be obligatory (Manley et al., 2019). The present study suggests that this is not the case. Isolating specific feature types at encoding through partial occlusion of faces at study (via a surgical mask or sunglasses), then embedding those familiarized feature sets in otherwise novel whole faces at test, systematically and combinedly increased the perceived familiarity of the otherwise novel whole faces. These results suggest that even whole faces are processed as sets of component parts.
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    Heart rate variability as a biomarker of self-control and its relationship with depression
    (Colorado State University. Libraries, 2021) Darwin, Marielle L., author; Davalos, Deana, advisor; Thomas, Michael, committee member; Rickard, Kathryn, committee member; Tracy, Brian, committee member
    Human behavior is guided by a desire to attain certain goals. Individuals must manipulate the pursuit of multiple goals simultaneously and decide how to navigate their environments to support the desires they most value. Failures of self-control are common and present as psychopathologies characterized by emotional and cognitive dysregulation, namely depression. The relationship between poor self-control and the manifestation of depression is critical to target in order to better predict, understand, diagnose, and treat symptomologies, yet the precise nature of the relationship between self-control and depression is insufficiently understood. The current study employed a novel approach to investigate the relationship between self-control and depression and whether our understanding of that relationship could be improved with the incorporation of heart rate variability (HRV), a robust neurocardiac biomarker of self-control-related abilities. Findings supported the merit of HRV as a biomarker of self-control and revealed that self-control fully mediated the relationship between HRV and depression, although effect sizes indicate that the relationships were weak. It was expected that age played a role in this relationship due to the changing lifespan trajectories of neurocardiac networks interconnected with self-control and depression, although this premise was found to be unsupported. These discoveries deepen our understanding of the neurocognitive and autonomic dynamics of depression and supplicate clinical researchers aiming to decrease dysfunction to entertain approaches supported by a biopsychological perspective.
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    Neural correlates of prospective memory in college students with anxiety
    (Colorado State University. Libraries, 2023) Rice, Michaela S., author; Davalos, Deana, advisor; Thomas, Michael, committee member; Faw, Meara, committee member; Tompkins, Sara Anne, committee member
    Prospective memory is the ability to create and execute future tasks. It is comprised of two components: cue detection and intention retrieval. Prospective memory is essential for successfully performing high-level goals, a proficiency that is of extreme importance in college populations. Previous research has shown that prospective memory is vulnerable to deterioration in individuals with psychological disorders. Anxiety is a psychological disorder that has been associated with various cognitive deficits, including prospective memory impairment, and it is highly prevalent among undergraduate students. To date, no studies have investigated the relationship between prospective memory and anxiety using neurophysiology. The purpose of the present study is to fill this gap in the literature by examining prospective memory performance in college students with anxiety using an electroencephalogram (EEG). After recording anxiety levels via self-reported measures, participants completed a computerized prospective memory task while two types of event-related potentials were recorded from an EEG: the N300 to assess cue detection, and the prospective positivity to assess intention retrieval. The findings indicate that anxiety was not significantly related to prospective memory performance, although the data patterns suggest that accuracy decreased as anxiety increased. Intention retrieval was weakly positively correlated with accuracy, and weakly negatively correlated with state anxiety. Taken together, these results suggest intention retrieval could be a key component in supporting prospective memory for college students with high state anxiety.
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    Neuralator 5000: exploring and enhancing the BOLD5000 fMRI dataset to improve the robustness of artificial neural networks
    (Colorado State University. Libraries, 2023) Pickard, William Augustus, author; Blanchard, Nathaniel, advisor; Anderson, Chuck, committee member; Thomas, Michael, committee member
    Artificial neural networks (ANNs) originally drew their inspiration from biological constructs. Despite the rapid development of ANNs and their seeming divergence from their biological roots, research using representational similarity analysis (RSA) shows a connection between the internal representations of artificial and biological neural networks. To further investigate this connection, human subject functional magnetic resonance imaging (fMRI) studies using stimuli drawn from common ANN training datasets are being compiled. One such dataset is the BOLD5000, which is composed of fMRI data from four subjects who were presented with stimuli selected from the ImageNet, Common Objects in Context (COCO), and Scene UNderstanding (SUN) datasets. An important area where this data can be fruitful is in improving ANN model robustness. This work seeks to enhance the BOLD5000 dataset and make it more accessible for future ANN research by re-segmenting the data from the second release of the BOLD5000 into new ROIs using the vcAtlas and visfAtlas visual cortex atlases, generating representational dissimilarity matrices (RDMs) for all ROIs, and providing a new, biologically-inspired set of supercategory labels specific to the ImageNet dataset. To demonstrate the utility of these new BOLD5000 derivatives, I compare human fMRI data to RDMs derived from the activations of four prominent vision ANNs: AlexNet, ResNet-50, MobileNetV2, and EfficientNet B0. The results of this analysis show that the old, less-advanced AlexNet has a higher neuro-similarity than the much more recent, and technically better-performing models. These results are further confirmed through the use of Fiedler vector analysis on the RDMs, which shows a reduction in the separability of the internal representations of the biologically inspired supercategories.
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    Socioeconomic inequality, amygdala and ventral striatal connectivity, and affective outcomes in children and adolescents
    (Colorado State University. Libraries, 2023) Strack, Jordan, author; Merz, Emily, advisor; Thomas, Michael, committee member; Seger, Carol, committee member; Lucas-Thompson, Rachel, committee member
    Socioeconomic disadvantage has been significantly associated with an increased risk for internalizing problems in children and adolescents. The neural mechanisms underlying these associations, however, are not well understood. Differences in connectivity of the amygdala and ventral striatum with the prefrontal cortex (PFC) may play an important role in these mechanisms. The goals of this study were to examine (1) the associations among socioeconomic factors, amygdala and ventral striatal resting-state functional connectivity (rsFC), and emotional outcomes in children and adolescents, (2) sex differences in associations between socioeconomic factors and amygdala and ventral striatal rsFC, and (3) interactions between socioeconomic factors and familial/genetic risk for anxiety/depression in predicting amygdala and ventral striatal rsFC. Participants were typically-developing 3- to 20-year-olds (50% male, N = 590) from the Pediatric Imaging, Neurocognition, and Genetics (PING) study (Jernigan et al., 2016). Resting-state fMRI, socioeconomic (family income, parental education), and self-reported positive and negative affect data were collected. Measures of familial and genetic risk for anxiety/depression were family history of anxiety/depression and genome-wide polygenic risk scores for major depressive disorder (PRS-MDD), respectively. Whole-brain, seed-based functional connectivity analyses were conducted with the ventral striatum and the amygdala as seeds. Findings indicated significant interactions between socioeconomic factors and PRS-MDD for amygdala rsFC with the frontopolar cortex. Positive and negative affect were associated with amygdala and ventral striatum rsFC with various brain regions. Associations between socioeconomic factors and amygdala and ventral striatal rsFC and sex differences were not significant. These findings can be applied to informing the design of more effective prevention and intervention strategies to facilitate healthy emotional development.