Knealing, T. W., & Schaal, D. W. (2002).
Disruption of temporally organized behavior by morphine.
Journal of the Experimental Analysis of Behavior,
77, 157-169.
Four pigeons pecked keys in two different procedures commonly
used in the study of timing, or temporal discrimination. Sessions
consisted of 40 trials. During half of the trials, two keys were
presented for 50 s. Left-key pecks were reinforced according to
a variable-interval 67.86-s schedule during the first 25 s of the
trial, and right-key pecks were not reinforced. During the second
25 s of the trial, right-key pecks were reinforced according to
the same schedule, and left-key pecks were not reinforced. In the
other half of the 40-trial session, the center key was presented.
The majority of these trials arranged fixed-interval 25-s
schedules. Occasionally a probe, or peak-interval, trial was
presented. These trials were 100 s in duration and terminated
without reinforcement. These two procedures were used to examine
the effects of morphine on indexes of timing and on patterns of
responding. Morphine altered behavior in a rate- dependent manner
in both procedures. Low baseline (saline) response rates were
increased following morphine administration, and high baseline
rates were either unaffected or decreased slightly.
Rate-dependent effects appeared as leftward shifts in the timing
index for two-key trials and decreases in the index of curvature
for fixed-interval trials. Despite large changes in response
rates, no consistent shift of the peak time was observed during
peak-interval trials. These results are discussed primarily in
terms of rate dependency; that is, rates of responding following
drug administration tend to be determined in large part by rates
of responding under baseline conditions.
Key words: morphine, fixed-interval schedules, peak procedure,
temporal discrimination, timing, key peck, pigeons