UC Berkeley

Interaction with our environment involves a constant influx of visual inputs. There has been significant investigation into the complex neural transformations that reflect sensory input as a series of neural activity patterns. However, a paucity of human studies have captured the canonical early and late neural activity patterns that occur across stages of visual processing. Thus, we leverage the millimeter spatial and millisecond temporal resolution of invasive recordings in neurosurgical patients to explore how visual information is rapidly represented in the human brain over time. Chapter 1 investigates visual repetition suppression, the phenomenon where repeated presentations of a stimulus produce a decreased neural response. Repetition suppression occurs ubiquitously across sensory modalities and has been widely studied using non-human primate electrophysiology and human neuroimaging. Here, we investigate the temporal profile of repetition suppression in humans when images are repeated over long time lags. We find robust repetition suppression associated with smaller peak magnitudes, lower total responses, and earlier peak responses. We discuss these findings in the context of theoretical models of repetition suppression and the early and late temporal windows of perception. Chapter 2 explores visual perception using binocular rivalry, a unique experience in which different images are simultaneously presented to each eye, and perception dynamically alternates between the two images. This provides a rare opportunity to disentangle conscious perception and sensory inputs since perception alternates between the two possible percepts, while the stimulus remains static. Significant debate surrounds whether binocular rivalry is the result of competitive interactions between populations in visual areas, top-down influence from associative cortices, or a combination of the two. Chapter 2 attempts to resolve these disagreements using intracranial recordings across the human brain. The first portion explores the initial perception of an ambiguous binocular image. We compare neural responses to ambiguous and unambiguous images and explore their temporal profile across regions. We find that early neural activity predicts subsequent perception. The latter portion investigates changes in perception by studying the neural correlates of endogenous switching from seeing one percept to the other. We find that associative cortices initiate changes in perception and precede sensory reactivation in visual cortices. We find a bi-directional relationship distributed across visual and associative cortices that i) encode and represent ambiguous percepts and ii) are engaged at temporally distinct periods across perception. Overall, this dissertation reports several novel findings in studying sensory networks supporting perception. It aims to bridge the literature in nonhuman primates and human neuroimaging with novel data in human electrophysiology to further understand how the human brain supports visual perception.