Date of Graduation


Document Type


Degree Type



Eberly College of Arts and Sciences



Committee Chair

Elizabeth G E Kyonka

Committee Co-Chair

Karen Anderson

Committee Member

Jim Belanger

Committee Member

Michael Perone

Committee Member

Miranda Reed.


Time markers are events that are predictive of when future events will occur. Different events can serve as time markers that initiate intervals in schedules of reinforcement. Pigeons were exposed to fixed-interval (FI) schedules in which the onset of the interval was signaled by the illumination of a key light, initiated by a peck to a lighted key, or a combination of both events. In these variations of fixed-interval schedules, food was delivered contingent on the first response after the interval elapsed. In Experiment 1, three pigeons were exposed to a multiple schedule. One component was a standard FI schedule; key light illumination signaled the onset of the interval. The other component was a response-initiated fixed-interval (RIFI) schedule; the first key-peck response determined the onset of the interval. In Experiment 2, three pigeons were exposed to a multiple FI-RIFI schedule of reinforcement and on occasional trials food was not delivered (i.e., "no-food" or "peak trials"). A yoking procedure equated reinforcement rates between the schedule types in both Experiments 1 and 2. First-response latencies were longer and absolute response rates early in the schedules were higher in the RIFI schedules in Experiments 1 and 2. Normalized response-rate gradients, ogive fits, and breakpoints were equivalent for the schedule types in Experiment 1, indicating no differences in temporal discrimination. However, the duration of responding at a high rate was longer in no-food trials of RIFI schedules than no-food trials of FI schedules in Experiment 2, which suggests that temporal discrimination precision was reduced in the RIFI schedules. In Experiment 3, three pigeons were exposed to FI, RIFI, and Signaled-RIFI schedules of reinforcement. In Signaled-RIFI schedules, the interval-initiating response was associated with a key-light color and location change. First-response latencies were shorter in the Signaled-RIFI schedules than in the FI and RIFI schedules. Reinforcement rates were highest in the FI schedules, and higher in the Signaled-RIFI schedules than the RIFI schedules---a result of the relatively shorter first-response latencies. Normalized response-rate gradients, ogive fits, and breakpoints revealed no significant differences in temporal discrimination between the schedule types. However, response-rate gradients and breakpoints in the Signaled-RIFI schedules were more similar to those obtained in the FI than RIFI schedules. Although current models of interval timing do not include parameters for the dimension of time markers, the results of Experiment 2 indicate that time marker dimension may affect temporal discrimination precision and that responses may be less efficacious time markers than exteroceptive stimuli.