The Flicker Response Curve for Fundulus by W. J. Crozier and Ernst Wolf

A number of vertebrates have been examined by us as to the form of the interdependence of flash frequency (F) and flash intensity (I) for reaction to visual flicker. The technic, apparatus, and procedure have been uniform in all these cases. There has been used, except in special experiments, a flash cycle in which light time and dark time are equal, and the temperature is the same (21.5°). We know, for several forms, that the shape of the F-log I curve (the flicker response contour) is not a function of temperature, 1 nor of the fraction of the flash cycle occupied by light. ~ Its position on the log I axis is governed by the temperature; its position and the magnitude of the F-scale units are dependent upon the light time fraction of the cycle time. Its shape is, however, a function of the nature of the animal tested. 8 For typical vertebrates the flicker response contour comprises two parts or segments, so that the curve is a doubly inflected S. 4 The association of the smaller, low intensity part with the functional activity of retinal rods and of the larger, upper portion with that of retinal cones 5 is consistent with a large body of speculation and systematized information in visual physiology. 6 In keeping with this conception, an animal which exhibits no histologically recognizable retinal rods, the turtle Pseuden~ys, and another with no cones, the gecko Spha~roda~tylus, give flicker response curves which follow a