Photoreceptors

Abstract

This chapter is limited to a discussion of the photo-chemico-electrical transduction, which is the first step in the flow of the information in the visual pathway. Recent reports dealing with vertebrate photoreceptors agree in the somewhat startling disclosure that darkness is the positive stimulus, whereas light inhibits the excitatory state of the receptors. This is no more the case with the neurons further down the line of information transmission, where cells come in two kinds: light-detector and shade-detectors; however, the discussion of neuronal processes of the retina belongs to the province of the central code, and will follow in Chapter 14. A description of the trichromatic theory of color vision is, properly, given here.