Flicker Response Contours for T H E Sparrow, and T H E Theory of the Avian Pecten by W. J. Crozier and Ernst Wolf

For image-forming animals generally it has been found that reduction of the light-time fraction in the light/dark cycle results in enlargement of the F-log I contour for response to flicker and in movement of the curve to lower flash intensities. 1 The asymptotic maximum of the curve is directly proportional to the percentage dark-time, and the abscissa of inflection (T') of the F-log I probability integral is inversely proportional to this quantity; so that r ' and F ~ . are related rectilinearly. With man, reduction of image area reduces the. effect of the light-time fraction on F . . . . , but does not greatly change the dependence of r I on t,., if area, wave-length composition, and retinal location are constant. The theoretical bases for these findings have been discussed. 1 '/'his general description applies to the properties of simplex flicker contours and of the photopic ("cone") portions of duplex contours. The scotopic ("rod") ,'~gments of duplex contours are the resultants of interaction between "cone" and "rod" neural effects, and the properties of the "rod" F,,, , . as a function of tL are therefore complex. 1 In birds one has typically to do with a visual system in which there is cast upon the retina the serrated shadow of a large and complexly developed pecten. 2 Correlated with this we have shown 3 that, using the rotating striped cylinder technic, x there arises in a bird a novel effect of the light-time fraction upon the form and position of the flicker contour. That the correlation is a causal one is indicated by the fact that homologous changes are induced in the human F-log I contours when, with the same method of producing flicker, an artificial "pecten shadow" is placed on the retina. 8 The unique feature of these cases is in the fact that, for bird and man ("cone" curve), the increase of tz to 0.750.90 makes the curve much steeper, in ,eases its F . . . . , and greatly reduces r ' with respect to the values these parameters would have if there were no "pecten effect." The nature of these changes is such as to assist materially in the analytical understanding of the flicker contours, and the effect itself can be shown to have a number of consequences in other directions as well.