Cognitive Neuroscience Commons^™

Understanding Behavioral And Representational Divergences Of Humans And Machines, Thomas Lasman Botch

Dartmouth College Ph.D Dissertations

Human behavior and cognition are strikingly variable: people differ from one another in their preferences and abilities, and even from themselves across situations. Yet this diversity arises from common neural machinery shaped by the complex environments humans inhabit. A central objective of cognitive neuroscience is to understand how this varied experience emerges from interactions between brains, agents, and environments. In this dissertation, I argue that comparing behavior and neural computation across humans, artificial systems, and contexts is essential for understanding the flexibility of human cognition. Across three chapters, I use this comparative approach to examine how the rich, multimodal contexts …

From Meaning To Memory: Assessing The Capacity And Representational Structure Of Visual Working Memory With Meaningful Stimuli, Yong Hoon Chung

Dartmouth College Ph.D Dissertations

Visual working memory is thought to be strictly limited. Yet we remember meaningful, real-world objects better than abstract stimuli. Here I show that this advantage arises from the semantic structure of meaningful objects, not their perceptual features alone, and that it extends even to memory for associated features such as color. In the brain, meaningful objects elicit greater and more distributed delay activity, consistent with the recruitment of higher-level neural processes during maintenance. I propose that semantic knowledge adds representational dimensions that make items more distinctive, and that these dimensions are organized hierarchically with lower-level visual features. These findings recast …

Neural Patterns Reflect Semantic Representation In Novice Sign Language Learners, Megan E. Hillis

Dartmouth College Ph.D Dissertations

How do novice language learners represent semantic information in their new language? The extent to which languages are supported by distinct or overlapping neural representations in bilinguals has been the topic of much research, but less is known about how new knowledge is integrated into established representational networks, especially at the earliest stages of language acquisition. Furthermore, most investigations have compared languages which share a modality (spoken). Signed languages can provide insight into language unconfounded by perceptual qualities that spoken languages share. Chapter 1 presents an initial study in which hearing English-speaking non-signers learned a set of nouns in American …

Behavioral And Neural Effects Of Distributing Visual Attention Across Location And Feature Space, Mert Özkan

Dartmouth College Ph.D Dissertations

Visual attention refers to the mechanisms by which relevant visual information, such as location, simple features (e.g., color, orientation), and objects, is selected and prioritized for further processing. The current dissertation investigates capacity limitations on spatial and feature–based attention in early visual processing and behavioral performance. Specifically, I examined whether attention could be efficiently tuned across narrow and broad ranges of locations and colors, or even be split across noncontiguous locations in the case of spatial attention. I used several behavioral paradigms and frequency–tagging methods in electroencephalography (EEG) to illustrate the effects of narrowing or broadening the attentional focus on …

Investigating The Human Face Processing Network: Insights From Acquired Prosopagnosia And Hyperfamiliarity For Faces, Marie-Luise Kieseler

Dartmouth College Ph.D Dissertations

Human faces provide essential social cues that we interpret rapidly, allowing us to recognize identities, interpret emotions, and gauge familiarity. This thesis explores face processing disruptions in four case studies, each offering new insights into the brain’s face recognition mechanisms.

Chapter one presents Annie, a 28-year-old woman who acquired prosopagnosia (face blindness) following COVID-19. After recovering from the severe symptoms of the infection, Annie experienced significant difficulty in recognizing familiar faces and navigating familiar environments. Testing confirmed her impairment in face recognition but showed her preserved cognitive and basic visual processing abilities. Annie was still able to recognize objects and …

Behavioral And Neural Evidence For Perceptual Inference Of Position, Sharif Saleki

Dartmouth College Ph.D Dissertations

Extensive neuroscientific research has advanced our knowledge of the mechanisms involved in the detection and recognition of visual stimuli. However, to guide flexible behavior in a changing world, the brain must also construct stable and coherent perceptual representations from retinal images that are often ambiguous. To resolve ambiguities and uncertainties, the visual system combines its input with other sources of information such as context and prior knowledge to infer the most likely interpretation of a scene. Thus, perception is inherently an inferential process that goes beyond simple detection or recognition of stimuli. Although inference has been studied in many areas …

Robust And Generalizable Representations In The Hippocampus, Hung-Tu Chen

Dartmouth College Ph.D Dissertations

An intelligent system must balance generalizing across similar experiences with maintaining the distinctiveness of each experience. This thesis explores how the hippocampus manages this balance through its neural representations to support adaptive behavior. In Chapter 1, I provide an overview of key hippocampal phenomena that contribute to this process, including remapping, splitter signal, and replay. In Chapter 2, I challenge the concept of random remapping by showing that it is possible to predict, better than chance, how a given experience will be encoded in the hippocampus across different subjects. This suggests that encoding of related experiences, which was previously thought …

Integrating Higher-Order Cognition With Sensory Experience: Insights From Cue-Based Expectations Across Diverse Domains, Heejung Jung

Dartmouth College Ph.D Dissertations

Higher-order cognition, such as expectations about the future, cannot be studied in isolation from sensory representations. This thesis explores the dynamic interplay of higher-order cognition and sensory experiences, examining the important role of expectations across multiple domains: sensory, cognitive, and affective. First, a systematic review outlines the origins of higher-order cognitive functions – e.g., social interaction, memory, and attentional control – and how they arise at the convergence of hierarchically organized gradients that extend from primary sensory areas. These convergence zones are rich in information crucial for the human capacity for making projections, such as thinking about another person’s mental …

Target Selection And Enhancement During Attentional Tracking, Marvin R. Maechler

Dartmouth College Ph.D Dissertations

At any waking moment, we are bombarded with more sensory information than we can fully process. Attention is necessary to deal with the dynamic world we live in. One fundamental function of vision and attention is to keep track of moving objects, but what are the targets of attention during tracking?

One of the first theories of attentional tracking predicted that targets would be selected at early processing stages. By employing the double-drift illusion, which dissociates physical and perceived positions of moving objects, we investigated which of these positions is selected for tracking. Contrary to earlier theories and in line …

Unraveling The Neural Basis Of Emotions: Advancing Understanding With Ecologically Valid Paradigms And High-Resolution Intracranial Eeg, Tiankang Xie

Dartmouth College Ph.D Dissertations

Background

Emotion arises from integrating information about the external world with memories of past experiences, current homeostatic states, and future goals. They play a vital role in regulating our thoughts, feelings and behaviors, significantly impacting our mental health. Thus, it is important to understand the neurobiological mechanisms that give rise to emotions. While there has been considerable work investigating the neural basis of emotions, progress has been hampered by several methodological limitations. For example, prior work has relied on relatively simple and isolated stimuli, which often fail to effectively capture the dynamic and multifaceted nature of emotional experiences in real-life …

Accelerated Forgetting In People With Epilepsy: Pathologic Memory Loss, Its Neural Basis, And Potential Therapies, Sarah Ashley Steimel Phd

Dartmouth College Ph.D Dissertations

While forgetting is vital to human functioning, delineating between normative and disordered forgetting can become incredibly complex. This thesis characterizes a pathologic form of forgetting in epilepsy, identifies a neural basis, and investigates the potential of stimulation as a therapeutic tool. Chapter 2 presents a behavioral characterization of the time course of Accelerated Long-Term Forgetting (ALF) in people with epilepsy (PWE). This chapter shows evidence of ALF on a shorter time scale than previous studies, with a differential impact on recall and recognition. Chapter 3 builds upon the work in Chapter 2 by extending ALF time points and investigating the …

Mapping The Malleable Self: How Self-Views Are Represented And Learned Within The Social Brain, Sasha Carmela Brietzke

Dartmouth College Ph.D Dissertations

Humans possess a unique and wide-ranging ability to self-reflect that takes center stage in our everyday cognition. While many people believe their own self to be immutable, different contexts may warp how we perceive the self. The goal of this dissertation is to investigate two lenses through which we may view the self: (1) across time in the past and future, and (2) through the eyes of others via evaluative feedback. In Studies 1-3, I demonstrate that people’s ratings of their own personality become increasingly less differentiated as they consider more distant past and future selves. This effect was preferential …

Genetic Heterogeneity In Schizophrenia And Contribution Of Context To Vowel Recognition, Eva Childers

Dartmouth College Ph.D Dissertations

This dissertation is composed of three chapters that address two distinct topics. Chapter 2 addresses the use of consonantal context in vowel perception. Previous studies have demonstrated that context is important for vowel identification, however, this effect may be an artifact of stimuli production. To address this potential confound, we used stimuli extracted from an audiobook and asked subjects to identify vowels encased in consonants and isolated by themselves. We show that subjects had improved vowel identification when the vowel is presented with a consonantal framing, suggesting there is information contained in the surrounding context that is important for phoneme …

Beyond Homogenous Decision-Making Models: Role Of Brain Areas Interaction And Heterogeneity, Mohsen Rakhshan

Dartmouth College Ph.D Dissertations

Most existing mechanistic models of decision making consider microcircuits within a homogenous brain area and fail to consider the distributed nature of this cognitive process. More specifically, these models do not take into account: a) how different types of information might influence choice in different stages of the process; and b) how interactions and the heterogeneity between circuits across different brain areas might be essential for the process. In this dissertation, I present a combination of experimental and modeling approaches to study distributed nature of the decision-making by examining both the distributed processing of information as well as the interaction …