Travel Distance and Stimulus Duration on Observing Responses by Rats

establishment of an operant when its only consequence was the presentation of discrimina-tive stimuli. He used an experimental chamber equipped with a response key, a food tray, and a pedal located on the floor below the response key. Key pecking was reinforced on an analog to a mixed fixed interval (FI) 30 s extinction (EXT) 30 s in which both components of the schedule alternated randomly. The response key was il-luminated with a white light during both FI and EXT unless the pigeons stepped on the pedal that changed the light to red during FI (S+) and to green during EXT (S-). Whenever the pigeons stepped off the pedal the response key light changed back to white. Wyckoff reported that the pigeons produced the discriminative stimuli during more of the session time when the color of the response key correlated with the components of the mixed schedule than when it did not. Wyckoff named the responses that were sustained by the production of the discrimina-tive stimuli observing responses and concluded that the discriminative stimuli functioned as conditioned reinforcers. Given that the emission of observing re-sponses does not affect the rate of the primary reinforcer, the observing-response procedure has become an useful technique to study the phenomenon of conditioned reinforcemen