The limits imposed in primate vision by transduction in cone photoreceptors
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Experientially, our ability to visually perceive the world seems extraordinary, yet we keep asking ourselves: "could perception be better?" This dissertation centers around this question, exploring how the biophysics of photoreceptors impose constraints on the visual system and dictate certain aspects of perception. The first chapter explores the sources of noise in cone phototransduction and identifies open-close transitions of the cGMP-gated channels as a dominant source of noise. This noise source also escapes the light-adaptation mechanisms that control gain, establishing a particular scenario that determines the shape of threshold-vs.-intensity curves in single cones and ultimately in humans. The second chapter investigates how cones adapt during eye movements, uncovering that adaptation has at least two different time scales that influence the encoding of mean luminance and modulation around the mean luminance separately. This will lead to the construction of a biophysical model that only when endowed with two separate light-adaptation mechanisms is able to reproduce responses to a wide array of stimuli. It is my hope that this model can be used as a tool to explore the constraints imposed by cone signals on the rest of the retinal circuitry and that it can help clarify how computations are implemented in downstream neural circuits.