This year we plan to study the effects of bleaching and background adaptation on intensity discrimination in the rod system in much the same way as in the previous year. In particular, increment-threshold functions will be obtained (1) at various times during dark adaptation following full bleaches, (2) in the presence of steady adapting backgrounds, and (3) in the presence of adapting backgrounds that are extinguished during presentation of the flashed backgrounds. Also we hope to begin extending these experiments to examine the effects of bleaches and backgrounds on perceived brightness. We have been able to account for the fairly wide range of data obtained in the studies listed above with models consisting of a cascade of linear and static nonlinear transforms. We have developed and plan to continue developing efficient computer programs, based on digital-filtering techniques, to test and explore models of this type. Finally, there are several new experiments, not presented in the original proposal, which we have designed to test specific hypotheses suggested by results of the four studies completed last year.