Fig. 4. Spectral sensitivity of curves describing response of monkey cone mechanisms to 25-Hz stimulus under conditions of dark adaptation or in the presence of intense chromatic backgrounds. Sector disc (50% duty cycle) was used to present flickering stimuli (25 Hz). Stimulus subtended visual angle of 45 degrees and was centrally superimposed on 68-degree background. Spectral sensitivity data were based on the log relative quantum flux at the retina necessary to elicit a criterion amplitude in the electroretinogram. Red cone mechanism showed best separation on blue-green adapting field, green cone mechanism on purple adapting field, and blue cone mechanism on yellow adapting field. Data points (circles) are an average of three animals. Vertical lines equal ± 1 SD (average). (Mehaffey L III, Berson EL: Cone mechanisms in the electroretinogram of the cynomolgus monkey. Invest Ophthalmol 13:266, 1974)