Newton (1675) had rightly presumed that light signals were transformed in the retina, and that the information about the visual world was conveyed to the brain by the optic nerve. His suggestion that visual information was transmitted by a vibration code, however, proved to be wrong. Thus, early in the twentieth century it had become generally accepted that the optic nerve fibres reacted to light by discharging a series of brief electrical action potentials. With increasing light intensity, the fibres tended to increase their firing rate, but the size of the discharge remained constant. (For a review of how our knowledge about the electrical nature of nerve impulses emerged, see Boring, 1957, pp. 30, 39–43 and Granit, 1947.)

THE ELECTRICAL RESPONSES TO LIGHT STIMULI IN SINGLE OPTIC NERVE FIBRES

H. K. Hartline was the first to make a thorough investigation of the electrical responses to light stimuli in single optic nerve fibres. A small bundle of fibres dissected from the optic nerve was split successively until only a single fibre remained. Thereafter, the electrical activity of the fibre, generated by a light stimulus, was recorded by means of an oscillograph capable of registering small, rapid voltage fluctuations. The recordings were made under conditions where the eye was illuminated by light of various intensities, durations and wavelengths (see Hartline, 1940, for a review).