The Wyckoff observing response-a reappraisal.

Pigeons were trained on a Wyckoff observing response procedure in which key responses were reinforced on a mixed schedule consisting of fixed-interval and extinction components. In Experiment 1, stepping on a pedal (a) converted the mixed schedule to a multiple schedule, (b) replaced the mixed-schedule stimulus with an unlit key (or, in different phases, a blackout), or (c) had no consequence. In Experiment 2, pedal standing removed the mixed-schedule stimulus that was physically similar to the multiple-schedule stimuli or one that was less similar. In Experiment 3, Wyckoff's differential and nondifferential discrimination procedure was repeated. The results of Experiments 1 and 2 showed that the Wyckoff pedal response was controlled by neither the removal of the mixed-schedule stimulus nor the production of discriminative stimuli. The results indicated a correlation between key-response rates and pedal-standing time. Experiment 3 showed that high response rates to mixed-schedule stimuli were correlated with little pedal-standing time while high key-response rates to multiple-schedule stimuli were correlated with considerable pedal standing time. The correlation between key-response rates and pedal-standing time was related to the physical arrangement between the key and pedal operanda.