THEORY AND MEASUREMENT OF VISUAL MECHANISMS

Abstract

Flicker contours from vertebrates (fishes to man) show that the slope parameter σ'_{log I} in the efficiently descriptive probability summation 100 F/F_max. = ∫_–inf;^{log I} e–(log I/I_i)^{–(log I/I_i)2}/2(σ')^/2(σ')2 ·d log I is distributed bimodally (simple fields, "white" light), from 0.60 to 2.3, with well defined peaks at 0.80 and 1.75. This parameter is independent of F_max., log I_i, temperature, light-time fraction, and in general not greatly influenced by λ. "Rod" components of known visually duplex contours, without exception, and some "cone" contours, are in the first group; an equal number of "cone" curves are in the second group, together with one simplex "rod" contour; purely cone contours are in each group, as well as cone segments of duplex curves. No firm zoological grouping of the "cone" curves can be made, on present evidence,—although the 5 fishes used give high-slope curves, 2 amphibians low slopes, reptiles (5) either high or low, birds (2) and anthropoids (2) low-slope "cone" curves.