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 …

Identifying A Neural Signature That Predicts Self-Focus, Danika Jean Geisler

Dartmouth College Master’s Theses

BACKGROUND AND AIM: People are remarkably self-focused, choosing to think and talk about themselves at disproportionately high levels. When people are instructed to think about the self in a task, activation occurs in the core subsystem of the default network, in particular the medial prefrontal cortex (MPFC). We hypothesize this tendency to “default back” to the core subsystem and MPFC as soon as we have a mental break sets our self-focus in motion. PROCEDURE: Participants completed a three-phase scanning session. In phase 1, they completed a resting state scan in which they intermittently answered questions about their thoughts. In phase …

No Fixed Limit For Storing Simple Visual Features: Realistic Objects Provide An Efficient Scaffold For Holding Features In Mind, Yong Hoon Chung

Dartmouth College Master’s Theses

Prominent theories of visual working memory postulate that the capacity to maintain a particular visual feature is fixed. In contrast to these theories, recent studies have demonstrated that meaningful objects are better remembered than simple, non-meaningful stimuli. Here, we test whether this is solely because meaningful stimuli can recruit additional features — and thus more storage capacity — or whether simple visual features that are not themselves meaningful can also benefit from being part of a meaningful object. Across five experiments (each N=30) we demonstrate that visual working memory capacity for color is increased when colors are part of recognizable …

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 …

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 …

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 …

Application Of Cycle-By-Cycle Analysis To Eeg Data From Individuals With Phelan-Mcdermid Syndrome, Naomi Miller

ENGS 88 Honors Thesis (AB Students)

This study aimed to analyze a novel method of processing data from electroencephalography (EEG) recordings, which implements time-domain cycle-by-cycle analysis. This "bycycle" method, developed by the Cole & Voytek laboratory, was implemented on a EEG dataset of children with and without Phelan-McDermid Syndrome in the hopes of uncovering network-level explanations for the genetic disorder. A supplemental Python pipeline was developed to organize and visualize the data. This led to the discovery of group-level differences in measures of cycle symmetry in alpha band waves over the sensorimotor electrodes. Through the same pipeline, the bycycle tool was validated as a sound EEG …

Acth Prevents Deficits In Fear Extinction Associated With Early Life Seizures, Andrew T. Massey, David K. Lerner, Gregory L. Holmes, Rod C. Scott, Amanda Hernan

Dartmouth Scholarship

Objective: Early life seizures (ELS) are often associated with cognitive and psychiatric comorbidities that are detrimental to quality of life. In a rat model of ELS, we explored long-term cognitive outcomes in adult rats. Using ACTH, an endogeneous HPA-axis hormone given to children with severe epilepsy, we sought to prevent cognitive deficits. Through comparisons with dexamethasone, we sought to dissociate the corticosteroid effects of ACTH from other potential mechanisms of action.

Results: Although rats with a history of ELS were able to acquire a conditioned fear learning paradigm and controls, these rats had significant deficits in their ability to extinguish …

Cosmomvpa: Multi-Modal Multivariate Pattern Analysis Of Neuroimaging Data In Matlab/Gnu Octave, Nikolaas N. Oosterhof, Andrew C. Connolly, James V. Haxby

Dartmouth Scholarship

Recent years have seen an increase in the popularity of multivariate pattern (MVP) analysis of functional magnetic resonance (fMRI) data, and, to a much lesser extent, magneto- and electro-encephalography (M/EEG) data. We present CoSMoMVPA, a lightweight MVPA (MVP analysis) toolbox implemented in the intersection of the Matlab and GNU Octave languages, that treats both fMRI and M/EEG data as first-class citizens. CoSMoMVPA supports all state-of-the-art MVP analysis techniques, including searchlight analyses, classification, correlations, representational similarity analysis, and the time generalization method. These can be used to address both data-driven and hypothesis-driven questions about neural organization and representations, both within and …

Reconstructing Representations Of Dynamic Visual Objects In Early Visual Cortex, Edmund Chong, Ariana M. Familiar, Won Mok Shim

Dartmouth Scholarship

As raw sensory data are partial, our visual system extensively fills in missing details, creating enriched percepts based on incomplete bottom-up information. Despite evidence for internally generated representations at early stages of cortical processing, it is not known whether these representations include missing information of dynamically transforming objects. Long-range apparent motion (AM) provides a unique test case because objects in AM can undergo changes both in position and in features. Using fMRI and encoding methods, we found that the “intermediate” orientation of an apparently rotating grating, never presented in the retinal input but interpolated during AM, is reconstructed in population-level, …

Axonal Activity In Vivo: Technical Considerations And Implications For The Exploration Of Neural Circuits In Freely Moving Animals, Jeremy M. Barry

Dartmouth Scholarship

While extracellular somatic action potentials from freely moving rats have been well characterized, axonal activity has not. We have recently reported extracellular tetrode recordings of short duration waveforms (SDWs) with an average peak-trough duration less than 172μs. These waveforms have significantly shorter duration than somatic action potentials and tend to be triphasic. The present review discusses further data that suggests SDWs are representative of axonal activity, how this characterization allows for more accurate classification of somatic activity and could serve as a means of exploring signal integration in neural circuits. The review also discusses how axons may function as more …

Dissociation Between Face Perception And Face Memory In Adults, But Not Children, With Developmental Prosopagnosia, Kirsten A. Dalrymple, Lúcia Garrido, Brad Duchaine

Dartmouth Scholarship

Cognitive models propose that face recognition is accomplished through a series of discrete stages, including perceptual representation of facial structure, and encoding and retrieval of facial information. This implies that impaired face recognition can result from failures of face perception, face memory, or both. Studies of acquired prosopagnosia, autism spectrum disorders, and the development of normal face recognition support the idea that face perception and face memory are distinct processes, yet this distinction has received little attention in developmental prosopagnosia (DP). To address this issue, we tested the face perception and face memory of children and adults with DP. By …

Online Tracking Of The Contents Of Conscious Perception Using Real-Time Fmri, Christoph Reichert, Robert Fendrich, Johannes Bernarding, Claus Tempelmann, Hermann Hinrichs, Jochem W. Rieger

Dartmouth Scholarship

Perception is an active process that interprets and structures the stimulus input based on assumptions about its possible causes. We use real-time functional magnetic resonance imaging (rtfMRI) to investigate a particularly powerful demonstration of dynamic object integration in which the same physical stimulus intermittently elicits categorically different conscious object percepts. In this study, we simulated an outline object that is moving behind a narrow slit. With such displays, the physically identical stimulus can elicit categorically different percepts that either correspond closely to the physical stimulus (vertically moving line segments) or represent a hypothesis about the underlying cause of the physical …

Movement-Based Embodied Contemplative Practices: Definitions And Paradigms, Laura Schmalzl, Mardi A. Crane-Godreau, Peter Payne

Dartmouth Scholarship

Over the past decades, cognitive neuroscience has witnessed a shift from predominantly disembodied and computational views of the mind, to more embodied and situated views of the mind. These postulate that mental functions cannot be fully understood without reference to the physical body and the environment in which they are experienced. Within the field of contemplative science, the directing of attention to bodily sensations has so far mainly been studied in the context of seated meditation and mindfulness practices. However, the cultivation of interoceptive, proprioceptive and kinesthetic awareness is also said to lie at the core of many movement-based contemplative …

Normal Acquisition Of Expertise With Greebles In Two Cases Of Acquired Prosopagnosia, Constantin Rezlescu, Jason J. S. Barton, David Pitcher, Bradley Duchaine

Dartmouth Scholarship

Face recognition is generally thought to rely on different neurocognitive mechanisms than most types of objects, but the specificity of these mechanisms is debated. One account suggests the mechanisms are specific to upright faces, whereas the expertise view proposes the mechanisms operate on objects of high within-class similarity with which an observer has become proficient at rapid individuation. Much of the evidence cited in support of the expertise view comes from laboratory-based training experiments involving computer-generated objects called greebles that are designed to place face-like demands on recognition mechanisms. A fundamental prediction of the expertise hypothesis is that recognition deficits …

Network Structure And Dynamics Of The Mental Workspace, Alexander Schlegel, Peter J. Kohler, Sergei V. Fogelson, Prescott Alexander

Dartmouth Scholarship

The conscious manipulation of mental representations is central to many creative and uniquely human abilities. How does the human brain mediate such flexible mental operations? Here, multivariate pattern analysis of functional MRI data reveals a widespread neural network that performs specific mental manipulations on the contents of visual imagery. Evolving patterns of neural activity within this mental workspace track the sequence of informational transformations carried out by these manipulations. The network switches between distinct connectivity profiles as representations are maintained or manipulated.

What Can The Organization Of The Brain’S Default Mode Network Tell Us About Self-Knowledge?, Joseph. M. Moran, William M. Kelley, Todd F. Heatherton

Dartmouth Scholarship

Understanding ourselves has been a fundamental topic for psychologists and philosophers alike. In this paper we review the evidence linking specific brain structures to self-reflection. The brain regions most associated with self-reflection are the posterior cingulate and medial prefrontal (mPFC) cortices, together known as the cortical midline structures (CMSs). We review evidence arguing that self-reflection is special in memory, while noting that these brain regions are often engaged when we think about others in our social worlds. Based on the CMSs’ patterns of connectivity and activity, we speculate about three possible interpretations of their role in supporting self-reflection that are …

Imaging Prior Information In The Brain, Scott Gorlin, Ming Meng, Jitendra Sharma, Hiroki Sugihara

Dartmouth Scholarship

In making sense of the visual world, the brain's processing is driven by two factors: the physical information provided by the eyes (“bottom-up” data) and the expectancies driven by past experience (“top-down” influences). We use degraded stimuli to tease apart the effects of bottom-up and top-down processes because they are easier to recognize with prior knowledge of undegraded images. Using machine learning algorithms, we quantify the amount of information that brain regions contain about stimuli as the subject learns the coherent images. Our results show that several distinct regions, including high-level visual areas and the retinotopic cortex, contain more information …

The Neurobiology Of Decision-Making And Responsibility: Reconciling Mechanism And Mindedness, Michael N. Shadlen, Adina L. Roskies

Dartmouth Scholarship

This essay reviews recent developments in neurobiology which are beginning to expose the mechanisms that underlie some elements of decision-making that bear on attributions of responsibility. These “elements” have been mainly studied in simple perceptual decision tasks, which are performed similarly by humans and non-human primates. Here we consider the role of neural noise, and suggest that thinking about the role of noise can shift the focus of discussions of randomness in decision-making away from its role in enabling alternate possibilities and toward a potential grounding role for responsibility.

Data Sharing In Neuroimaging Research, Jean-Baptiste Poline, Janis L. Breeze, Satrajit Ghosh, Krzysztof Gorgolewski, Yaroslav O. Halchenko

Dartmouth Scholarship

Significant resources around the world have been invested in neuroimaging studies of brain function and disease. Easier access to this large body of work should have profound impact on research in cognitive neuroscience and psychiatry, leading to advances in the diagnosis and treatment of psychiatric and neurological disease. A trend toward increased sharing of neuroimaging data has emerged in recent years. Nevertheless, a number of barriers continue to impede momentum. Many researchers and institutions remain uncertain about how to share data or lack the tools and expertise to participate in data sharing. The use of electronic data capture (EDC) methods …