Rod-cone interaction through flicker detection and the course of critical flicker frequency during dark adaptation

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Virginia Polytechnic Institute and State University

Critical flicker fusion (CFF) functions are reported during the course of dark adaptation under various states of cone and rod adaptation. Also, measurements were made of the stimulus intensity necessary to just perceive flicker for a wide range of frequencies. The resulting data clearly demonstrate a rod-cone interaction causing a suppression of the threshold.

Our results reproduce the familiar rod and cone branches of the CFF function, and confirm the assertion that CFF is dependent upon state of retinal adaptation. Intensities necessary for flicker detection were recorded at various frequencies during the cone plateau. However, the very same frequencies required as much as 1.5 Log units more intensity when recorded after complete rod recovery. We were able to detect the cone-rod interference only at the time when the rods begin to significantly contribute to the threshold. Our data suggest a channel whereby the rods have an accessible mechanism of directly influencing the cone signal as well as the total contribution to a threshold. The probable retinal area of this interaction is also discussed. Results are reported from a rod monochromat and six color normals. This study discusses other stimulus properties which could also reveal the rod-cone suppression.