Date of Graduation


Document Type


Degree Type



Eberly College of Arts and Sciences



Committee Chair

David W. Schaal.


The present experiments tested the effects of d-amphetamine and morphine on pigeons' responding during conventional and clocked FI schedules of food reinforcement. The first experiment compared performance between FI 5-min and continuously clocked FI 5-min components of a multiple schedule in which the rate of the houselight flashing increased in a continuous manner. The second experiment examined the differences between keypecking maintained by FI 5-min, response-dependent clocked FI 5-min, and response-independent clocked FI 5-min components of a multiple schedule. In the response-dependent clocked FI component, each peck produced a stimulus change that was correlated with the passage of time, while the response-independent clocked FI component provided the stimulus change without a peck requirement. The main effect of both d-amphetamine and morphine was an increase in early-interval responding in all FI components. This result was not consistent with previous studies in that usually behavior under the control of clock stimuli is resistant to the early rate-increasing effects of these drugs. While attending to time in the interval is beneficial in FI schedules, added clock stimuli may remove this importance allowing for drugs to have their effect by causing the pigeons to fail to attend to the relevant stimuli such that other factors control responding.