RELATION OF VISUAL LATENCY TO INTENSITY

Abstract

THE RESPONSE of an organism to light is invariably preceded by a latent period. It has been shown for the clam siphon,¹ for the electrical activity of a single photoreceptor of the limulus,² and for the electroretinograms of a large number of animals³ (and man⁴) that the duration of the latent period is inversely related to the intensity of the photic stimulus. It is reasonable to suppose that some such relationship could be demonstrated for human vision. Hence, if two neighboring flashes of light of the same duration but of slightly differing intensities were exposed simultaneously, they might appear as if the brighter flash preceded the dimmer one. Asynchronous neighboring flashes of light within certain limits show apparent movement, and the foregoing speculations lead to the expectation that so would simultaneous light flashes of different intensities. Preliminary experiments roughly verified this prediction, although the observation was