An evaluation of the associative strength of a partially reinforced serial CS

Three experiments examined the factors that are responsible for producing a high rate of autoshaped keypecking in pigeons when the conditioned stimulus is followed by varying consequences. In the first experiment, a single group received three serial conditioning schedules presented on different keys. The AB⁺ schedule consisted of trials in which A was followed by B, which, in turn, was followed by food. The CD⁺C° schedule consisted of reinforced CD pairings plus presentations of C alone. The EF^+/0 schedule consisted of a mixture of reinforced and nonreinforced EF pairings. It was found that responding was most rapid during C, slowest during E, and at an intermediate rate during A. In spite of this ordering A was chosen in preference to C, when these stimuli were presented simultaneously. In Experiments 2 and 3 the schedules AB⁺A° and AB^+/0 were presented to separate groups. The rate of responding during A was substantially greater in the former schedule, yet it was found that this stimulus was equally ineffective as a conditioned reinforcer in both groups. We propose that autoshaped keypecking is composed of two types of response, a conditioned response and an orienting response, which are governed by different processes.