Zarcone, T. J., & Ator, N. A. (2000).
Drug discrimination: Stimulus control during repeated testing in extinction.
Journal of the Experimental Analysis of Behavior,
74, 283-294.
Rats were trained, under a two-lever drug-discrimination
procedure, to respond differentially depending upon whether
lorazepam (1.0 mg/kg) or no injection had been administered
before the session. Responses on the appropriate lever produced a
food pellet under a modified fixed-ratio (FR) 10 schedule, in
which the 10 responses had to be emitted consecutively. In
reinforcement tests, completing an FR 10 on either lever produced
a pellet. In extinction tests, stimulus changes paired with
reinforcement occurred but no pellet was delivered. Training
sessions were conducted between test sessions. Each of four
extinction phases consisted of six tests preceded by one stimulus
(e.g., lorazepam). Repeated exposures to extinction reduced
response rates for all rats, but stimulus control, as inferred
from either percentage of total responses or percentage of total
FR 10s on the drug-appropriate lever, remained high. The
percentage of total FR 10s measure was less subject to skewing
under low-rate conditions than was the percentage of total
responses measure and provided an evaluation of stimulus control
in terms of meeting the consecutive response contingency. These
results demonstrate a level of independence between response rate
and stimulus control in drug discrimination, which has positive
implications for the validity of interpreting discriminative
effects of novel test conditions in well-trained animals, even
when overall response rates are low.
Key words: extinction, drug discrimination, stimulus control,
lorazepam, lever press, rats