Date of Award
Spring 2023
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Interdepartmental Neuroscience Program
First Advisor
Nandy, Anirvan
Abstract
The ability of humans and other animals to perceive and understand stimuli in the visual world is substantially modulated by internal and external states. Internal states, such as arousal and attention, influence how we can perceive stimuli even when the physical characteristics of that stimulus are constant. Additionally, external configuration of objects in the visual world can influence our perceptual abilities, even when other characteristics remain unchanged. We first studied internal state-dependent modulation of perception by examining what states were associated with accurate perception at threshold, a condition in which the physical properties of a stimulus remain constant, and a subject has an equal chance of perceptual success or failure. We show that a state of elevated arousal and perceptual stability contributes to accurate perception at threshold. This brain state is associated with activity patterns in visual area V4 that likely reflect higher fidelity stimulus representations. Target stimuli evoke higher firing rates in V4 in hits compared to misses. Additionally, before the target is presented, V4 neurons exhibit firing patterns that are associated with improved stimulus encoding ability. This improved representational fidelity may allow successful perception at threshold. We next designed a project to study how the state of visual stimuli in the external world influence stimulus representations in the primary visual cortex (V1). Visual crowding, the inability to recognize a target object among distractor stimuli surrounding it, is a critical bottleneck in our visual perception. Crowding effects are anisotropic, with radial-out distractors more substantially impacting perception than other stimulus configurations. We identified the first evidence that crowding impacts stimulus representations in V1 in an anisotropic manner. Radial-out crowding more strongly impairs the ability to decode the identity of a target stimulus compared to other stimulus configurations. Radial-out crowding broadens the tuning curves of V1 neurons through untuned facilitation and tuned suppression, leading to this impairment in decoding performance. These anisotropic modulations are specific to the V1 subpopulations involved in the feed-forward pathway. These anisotropic interactions in V1 explain and reflect differences seen in perceptual experiments on visual crowding. Together, the results in this thesis present a substantial advance in our understanding of how internal and external states influence our ability to process visual information, which ultimately reflects in our perceptual abilities.
Recommended Citation
Morton, Mitchell Paul, "Internal and External State-Dependent Modulation of Visual Perception and Cortical Processing" (2023). Yale Graduate School of Arts and Sciences Dissertations. 965.
https://elischolar.library.yale.edu/gsas_dissertations/965
