Swanson, Link2023-01-042023-01-042022-10https://hdl.handle.net/11299/250433University of Minnesota Ph.D. dissertation. 2022. Major: Neuroscience. Advisors: Daniel Kersten, Michael-Paul Schallmo. 1 computer file (PDF); 236 pages.The visual effects of psychedelic drugs are well-known but not well understood. In this dissertation, I investigate psychedelic visual phenomenology. I provide evidence and analysis to argue that psychedelics selectively impact contextual modulation at multiple levels of mental function. I report preliminary results of two experiments from a pilot study, in which we measured contrast surround suppression in humans under the psychedelic drug psilocybin, using psychophysical and EEG event-related potential (ERP) methods. We found that psilocybin enhanced perceptual surround suppression, and strengthened surround suppression of neural responses, compared with placebo. The results support the hypothesis that psychedelics enhance contextual modulation in visual processes, which has theoretical as well as practical implications for psychedelic therapy, cognitive neuroscience, and philosophy.encontextual modulationillusionpsilocybinpsychedelic drugssurround suppressionvisualThesis or Dissertation