Dissertations, Theses, and Capstone Projects

Date of Degree


Document Type


Degree Name





Tony Ro

Committee Members

Robert Duncan

Jay Edelman

Tatiana Emmanouil

Jonathan Levitt

Subject Categories

Cognition and Perception | Cognitive Neuroscience


transcranial magnetic stimulation, vision, visual perception, brain stimulation, phosphenes


While many of us rely on vision to interact with and experience the world, for people with damage or disease to the eye or visual cortex, experience through this modality is extremely limited. Brain and retinal stimulation devices show exciting promise for restoring vision, but little is understood about where and when vision percepts can be induced through stimulation. Using a non-invasive brain stimulation technique called transcranial magnetic stimulation (TMS), we characterized the spatial and temporal dynamics of perception induced through brain stimulation. In the first set of experiments, we explore the importance of higher visual and non-visual areas vs. early visual areas in generating perception. We demonstrate that stimulation of even non-visual areas can evoke percepts in some subjects, but that this perception is likely a consequence of direct or indirect stimulation of early visual regions. In the second set of experiments, we demonstrate that percepts evoked from stimulation of this non-visual area likely arise from excitation of the optic nerve, an early visual structure. This reinforces the importance of early visual areas, not later ones, in generating perception, and suggests that induction of perception must involve activity in early visual structures. In the last set of experiments, we investigated the temporal dynamics of percepts induced through non-invasive stimulation. We show that the latency and duration of percepts evoked through brain stimulation are highly variable across individuals. Furthermore, we demonstrate that perception of these percepts is not instantaneous, but rather requires additional feedback processing for conscious awareness. Together, our results bridge a fundamental gap in our understanding of the some of the most fundamental characteristics of perception induced through non-invasive brain stimulation.