On the Duplexity Theory of Visual Response in Vertebrates

Abstract

The absence of rods from the retina of the turtle Pseudemys scripta is correlated with the absence of a rod portion in the curve for response to visual flicker. This gives a proof for the validity of the essence of the duplexity doctrine. It permits the logical correlation of the occurrence of rods in diverse retinas with the presence of a presumptive rod contribution to the measured contours of visual performance. For this turtle the flicker frequency vs. log critical intensity curve is a smooth probability integral over its whole determinable range; this justifies the method of analytical dissection which has been employed with the composite F-log I curves of other vertebrates.