When a vertebrate retina is stimulated by a short intense flash of light, an almost instantaneous electrical response is generated by the visual receptors. This response has been labeled the early receptor potential (early RP) by Brown and Murakami (1964a) who first observed it as part of the local electroretinogram recorded with an intraretinal micro-electrode. This recently discovered electrical response can also be observed in the conventional electroretinogram (ERG) obtained by placing an electrode on the cornea (Cone, 1964b). Figure 1 shows how the early RP appears in the ERG of the rat (A) and the frog (B) when the a-wave of the ERG has been eliminated. In every animal so far investigated (monkey, rat, cat, squirrel, goldfish, and frog) the response is biphasic, like that of the frog in Fig. 1B. The rat is somewhat unusual in that its response appears to be monophasic at physiological temperatures, but...
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Richard A. Cone (1965) studied this question.