Odum, A. L., & Schaal, D. W. (2000).
The effects of morphine on fixed-interval patterning and temporal discrimination.
Journal of the Experimental Analysis of Behavior,
74, 229-243.
Changes produced by drugs in response patterns under
fixed-interval schedules of reinforcement have been interpreted
to result from changes in temporal discrimination. To examine
this possibility, this experiment determined the effects of
morphine on the response patterning of 4 pigeons during a
fixed-interval 1-min schedule of food delivery with interpolated
temporal discrimination trials. Twenty of the 50 total intervals
were interrupted by choice trials. Pecks to one key color
produced food if the interval was interrupted after a short time
(after 2 or 4.64 s). Pecks to another key color produced food if
the interval was interrupted after a long time (after 24.99 or 58
s). Morphine (1.0 to 10.0 mg/kg) decreased the index of curvature
(a measure of response patterning) during fixed intervals and
accuracy during temporal discrimination trials. Accuracy was
equally disrupted following short and long sample durations.
Although morphine disrupted temporal discrimination in the
context of a fixed-interval schedule, these effects are
inconsistent with interpretations of the disruption of response
patterning as a selective overestimation of elapsed time. The
effects of morphine may be related to the effects of more
conventional external stimuli on response patterning.
Key words: fixed-interval schedule, temporal discrimination,
response patterning, timing, index of curvature, morphine, key
peck, pigeons