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Updated: Jun 16, 2026

Three Laboratory Procedures for Assessing Different Manifestations of Impulsivity in Rats
Published on: March 17, 2019
The importance of the reinforcer as a time marker
David M Freestone1, Russell M Church
1Brown University, United States. David Freestone@brown.edu
Abstract:
Shifts in the psychometric function in the Free Operant Psychophysical Procedure (FOPP) have traditionally been explained by suggesting the pacemaker rate is proportional to the reinforcement rate (Behavioral Theory of Timing; BeT), or by direct associative competition between the two responses (Learning to Time; LeT). The application of these models assumes that the stimulus onset is the relevant time marker. Head-entries were reinforced in the second half of a stimulus (s1) and in the first half of a different stimulus (s2). During extinction, response times shifted earlier in s2 only, contrary to BeT. Competition between responses is an unlikely cause of the shift, contrary to LeT. We found a single-cycle correlation between the last food delivery and the time the rat stopped responding on s2. This correlation was also present in FOPP data. These results are consistent with the interpretation that the reinforcer, more than the stimulus onset, acted as the relevant time marker on this task.
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