Introduction -- The experiment of Hecht, Schlaer, and Pirenne -- The physics of light -- Quantal fluctuations -- The action of light on rod pigments -- The excitation of rods -- Cones and cone pigment -- Color vision I -- discriminations among wavelenght mixtures -- Color vision II -- retinal color systems -- Color vision III -- the perception of color -- The psychophysiology of brightness I: spatial interaction in the visual system -- The psychophysiology of brightness II: modulation transfer functions -- Brightness and color constancy -- Temporal properties of the visual system -- Stimulus generalization -- Speculations on "Higher Processes" -- Appendix I: Visual Angle -- Appendix II: Filter transmission versus density -- Appendix III: How to build an Ophthalmoscope -- Appendix IV: Demonstration of color contrast (colored shadows).