Denis Baylor was an American neurobiologist notable for his exceptional contribution to uncovering fundamental processes of vision. Over several decades, his pioneering studies of cells in the retina revealed the mechanisms of light detection and established the physiological basis for many aspects of human sight.

Vertebrates rely on rod and cone photoreceptor cells to mediate image-forming vision. Denis developed now-common techniques to record electrical activity within individual cells when they are exposed to light. He showed that rod cells are specialised for low-light vision, partly through proving their ability to respond to individual photons of light. He also delineated the sensitivity of cone cells to light of different wavelengths.

Over his career, Denis clarified the mechanisms by which retinal rods and cones encode light stimuli. His achievements were recognised by numerous international awards and prizes as well as election to the US National Academy of Sciences.

Professor Denis Baylor ForMemRS died on 16 March 2022.