Discrimination of methadone and cocaine by pigeons without explicit discrimination training.
Internal drug states can turn into cues that guide behavior even without direct teaching.
01Research in Context
What this study did
Researchers gave pigeons methadone or cocaine before each session. The birds simply pecked a key for food. No one told them to act different when high.
After many drug-food pairings, the team tested the birds during withdrawal. They watched how much the pigeons pecked when no food was given.
What they found
Birds pecked more after higher methadone doses and less after higher cocaine doses. The pattern showed up even though they had never been trained to notice the drugs.
When normal discrimination training was added later, the dose-response curves became even cleaner.
How this fits with other research
CHUNG (1965) first showed pigeons can learn to tell stimuli apart even when reward is delayed. McGrother et al. (1996) push that idea further—no reward delay, no extra cues, just the drug state itself.
Wilkie et al. (1981) used the same autoshaping setup to show that new responses can emerge without direct teaching. The new study swaps drug states for key color, but the mechanism—stimulus control without explicit training—is the same.
Blanchard et al. (1979) found that weak parts of a cue gain control only when they signal food. Likewise, methadone and cocaine became cues only because they were repeatedly present when food arrived.
Why it matters
You can build stimulus control simply by pairing a state with reinforcement. For clients who take daily medication, the med itself may become an Sᴰ for skill use or problem behavior. Check if behaviors track dose days versus skip days. If they do, you can program alternative responses to the same internal cue.
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02At a glance
03Original abstract
Pigeons were trained to peck a key on a variable-interval 2-min schedule of food reinforcement. Prior to each session, either 2.0 mg/kg methadone (n = 3), 3.0 mg/kg cocaine (n = 4), or 5.6 mg/kg cocaine (n = 2) was administered. When each pigeon's rate of pecking was stable, a range of doses of the training drug and saline were administered prior to 20-min extinction sessions separated by at least four training sessions. Rate of pecking during these extinction tests was generally an increasing function of dose, with the lowest rates obtained following saline and low doses and the highest rates obtained following doses near the training doses. Dose functions from pigeons trained with 5.6 mg/kg cocaine were steeper than those from pigeons trained with 3.0 mg/kg cocaine. Pigeons trained with methadone or 3.0 mg/kg cocaine were then given discrimination training, in which food reinforcement followed drug administration and 20-min extinction sessions followed saline administration. Rates of pecking under these conditions quickly diverged until near-zero rates were obtained following saline and high rates were obtained following drug. Discrimination training steepened dose functions for the training drugs, and the effects of several other substituted drugs depended on the pharmacology of the training drug. The pigeons trained with 5.6 mg/kg cocaine were tested with d-amphetamine, methadone, and morphine prior to discrimination training. d-Amphetamine increased rates dose dependently, and methadone and morphine did not. The results suggest that discriminative control by methadone and cocaine was established without explicit discrimination training.
Journal of the experimental analysis of behavior, 1996 · doi:10.1901/jeab.1996.66-193