The influence of rod light and dark adaptation upon rod-cone interaction.

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Abstract
The influence of a rod-detected mask of illuminance (IR) on the threshold illuminance of a cone-detected test flash (ICth) was assessed while rods were recovering from the effects of a bleach and when rods were selectively light adapted. Providing that IR was restricted to within 2 log10 units of rod mask threshold (IRth), results show that ICth/ICo = K(.sqroot.(IR/IRth) + D), where ICo is cone absolute threshold, D is a dark noise term and K is a proportionality constant. The data were used to obtain equivalent background functions or Crawford (1947) transforms (illuminance of a background field plotted against time in the dark). The same Crawford transform was obtained when either IRth or ICth (in the presence of a fixed illuminance IR) were used as equating variables. All these results could be predicted by considering both the influence of light adaptation on rods and the model developed by Bauer, Frumkes and Nygaard (1982). Under dark-adapted conditions, 40'' and 60'' diameter rod masks of equal illuminance have very similar influences on ICth. When rods are selectively light adapted 60'' masks have smaller influences on ICth. Evidently, rod adaptation has a distinct influence on neural loci designated E (the excitatory spatial summator) and I (the inhibitory spatial summator), and E apparently represents a site for both adaptation and spatial summation.

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