Odum, A. L. & Ward, R. D. (2004).
The effects of morphine on the production and discrimination of interresponse times.
Journal of the Experimental Analysis of Behavior, 82, 197-212.
Recent experiments suggest that the effects of drugs of abuse on the discrimination of
the passage of time may differ for experimenter-imposed and subject-produced events.
The current experiment examined this suggestion by determining the effects of morphine
on the discrimination of interresponse times (IRTs). Pigeons pecked a center key on a
random-interval 20-s schedule of matching-to-sample trials. Once the interval had
timed out, a choice trial randomly followed either a short (2- to 3-s) or long
(6- to 9-s) IRT on the center key. Pecking the side key lit one color produced
food after a short IRT, and pecking the side key lit the other color produced
food after a long IRT. Two experimental phases differed in the functional role
of the different key colors. Under control conditions, the IRT distributions had
two modes, one at the lower bound of the short category and a smaller one at the
lower bound of the long category. Pigeons accurately categorized the duration of
the IRTs: One key color was pecked following short IRTs and the other key color
was pecked following long IRTs. Morphine flattened the IRT distribution and
reduced the accuracy of categorizing IRTs. Categorization of long IRTs was
particularly disrupted. Morphine did not produce overestimation of time as
assessed by the production or categorization of IRTs. These results are
similar to those obtained previously for the effects of morphine on the
discrimination of the duration of experimenter-imposed events.
Key words: morphine, timing, temporal discrimination, interresponse time, key peck, pigeons