. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. Photoreception 425 efficients obtained by Hecht and the above values are in fair agreement with the theoretical value of RECIPROCITY LAW DETERMINED FROM ELECTRICAL MEASUREMENTS OF RETINAL ACTIVITY. Numerous measurements^^-- ^'^^' ^"' ^^- ^*' ^'^ relate the mag- nitude of the retinal action potential to the stimulating intensity, employ- ing a constant flash duration (Fig. 129). The data of Hartline, ^'^ presented in Figure 130, are particularly instructive. He has measured the magnitude of the retinal
. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. Photoreception 425 efficients obtained by Hecht and the above values are in fair agreement with the theoretical value of RECIPROCITY LAW DETERMINED FROM ELECTRICAL MEASUREMENTS OF RETINAL ACTIVITY. Numerous measurements^^-- ^'^^' ^"' ^^- ^*' ^'^ relate the mag- nitude of the retinal action potential to the stimulating intensity, employ- ing a constant flash duration (Fig. 129). The data of Hartline, ^'^ presented in Figure 130, are particularly instructive. He has measured the magnitude of the retinal action potential in relation to intensity of illumination, em- ploying diff^erent exposure periods. These data reveal that over a wide range the intensity and duration of flash to produce a response of constant magnitude are inversely related, , for longer durations the intensity needed is less, and vice versa. Computa- tion of the intensity-time product necessary to elicit a response of constant magnitude is equal to a constant. Here, then, is a duplication of the applic- l£0 £.0 'f seconds c o ^l^^a-o^^ Log ao .0 Fig. 130. A family of curves relating magnitude of the retinal action potential to log intensity for different periods of exposure. The measurements were obtained from the eye of a grasshopper. From Hartline.** ability of the reciprocity law to photoreception, an earlier application having been made by Hecht (see page 406). Again it should be pointed out that the above relation is valid only for constant response levels. The over-all relation between E and It for the photoreceptor of the grasshopper is apparent from inspection of the data in Figure 130, and is the same as the relation between magnitude of the retinal action potential and logarithm of the intensity. RELATION BETWEEN INTENSITY AND MAGNITUDE OF ELECTRIC RESPONSE. Inspection of the curves in Figure 129 and in Figure 130 indicates that the relation b
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