The specific objective of this proposal is to compare the response of the first cell in the visual system (the receptor) to the response of the last cell, or output of the retina (the ganglion cell). The functional problem of interest is the adjustment, or adaptation, to the wide range of ambient lights that confronts the vertebrate visual system. Receptor activity is measured using gross electrodes and the aspartate-treated isolated frog retina. Most of the proposed experiments deal with ganglion cell activity which is measured using microelectrodes and frog isolated retinas and eyecups. Comparisons of these data to receptor data allow the testing of models that deal with the loci and mechanisms of adaptation. In addition, an attempt is made to uncover more general principles of retinal organization and visual function.