Double branched flicker fusion curves from the all-rod skate retina.

Electrical responses from the skate retina will only follow flicker up to frequencies of 5 hertz when intensities are below rod saturation. At greater luminances, the eye responds to rates as high as 30 hertz. As a result, a plot of critical flicker fusion as a function of intensity is a double branched curve. It seems that prolonged stimulation of skate rods, at high intensities, permits them to change their temporal response characteristics so that they follow high frequencies much as cones do in the duplex retina.