Responding is not constant across the experimental session when animals respond on operant-conditioning procedures. Instead, responding often begins slowly, increases to a peak and then decreases through the rest of the session. The present experiments will begin to determine under what conditions these within-session changes in responding occur. They will also begin to determine why these changes occur. In particular, the experiments will try to separate the contribution of factors related to reinforcement, such as satiation, from factors related to responding, such as fatigue. They will try to separate the contribution of central factors, such as focusing of attention, from factors at the periphery, such as interference from competing responses. They will try to separate the effect of factors that accumulate over the session, such as fatigue, from the anticipation of things to come, such as the return to the home cage at the end of the session. These experiments are theoretically important because rate of responding averaged over the session is one of the primary dependent variables in operant psychology. Finding systematic changes in responding within sessions suggests that this measure ignores important changes in behavior at a more fine-grained level. The research is methodologically important because many experiments are not designed so that their data can be interpreted if such within-session changes in responding occur. Improving theory and methodology in operant psychology is important for applied reasons. Operant techniques are used as methods for determining the effects of physiological variables and as the basis for some forms of therapy for human behavioral problems.
