Granit, Ragnar Arthur (1900-1991) was a Finnish-born Swedish neurophysicist who studied the physiology (function) of the eye. He shared the 1967 Nobel Prize in physiology or medicine with the American scientists Haldan Keffer Hartline and George Wald. The prize was awarded for their work on chemical and physiological processes in the eye.

Beginning in the 1920's, Granit's research focused on psychophysics, a branch of psychology dealing with the relations betwen physical stimuli and sensations. Granit used techniques for amplifying the small electrical impulses in the nervous system to study the physiology of the retina, the part of the eye that absorbs light rays. He also conducted many investigations into the responses of individual retinal cells to light of a variety of wavelengths and intensities. His investigations into the retina led to his dominator-modulator theory of color discrimination. According to Granit, some optic nerve fibers (the dominators) respond to the whole spectrum of light, but others (the modulators) are color-specific.

Granit used the recording of electroretinograms (ERG's), charts of the electrical responses of the retina to light. Granit compared the ERG's of various animals, in different light conditions. Granit's later work focused on the role of sensory organs in muscle spindles. Other work conducted by Granit includes research into the spinal cord and related questions of motor control and neuro-physiology.

Granit was born in Helsinki, Finland. He studied medicine at Helsinki University. In 1940, he went to Sweden and became professor of neuro-physiology at Stockholm's Karolinska Institute.