EVIDENCE FOR 2 SITES OF ADAPTATION AFFECTING THE DARK-ADAPTED ERG OF CATS AND PRIMATES

The present study compared the effects of full-field steady adapting b ackgrounds on the sensitivity of the scotopic threshold response (STR) of the dark-adapted ERG and scotopic PII (b-wave and d.c.-component) to Ganzfeld flashes in cats (n = 4), macaque monkeys (n = 2), and one human subject. In cats, the sensitivity of the STR was reduced by a fa ctor of 2 by backgrounds that were 500 times weaker than backgrounds r educing PII; and for the primates, the STR was reduced by backgrounds almost 100 times weaker than those reducing PII. Since the STR is gene rated more proximally in the retina than PII, these results provide ev idence for proximal and more distal retinal sites of postreceptoral li ght adaptation. A practical implication is that dim scattered room lig ht can remove the STR from the ERG while hardly affecting PII.