Effects of d-amphetamine and pentobarbital under concurrent fixed-ratio schedules.
Reinforcement history can lock in response biases that outlast schedule changes and even pharmacological challenges.
01Research in Context
What this study did
Pigeons pecked two keys under concurrent fixed-ratio schedules.
One key required more pecks than the other.
The birds had a year-and-a-half history with this setup.
Researchers then gave d-amphetamine or pentobarbital to see if the birds would still favor the key they had always preferred.
What they found
The pigeons kept favoring the key that had paid off more in the past.
Speed-up drug d-amphetamine made the bias a little stronger.
Slow-down drug pentobarbital flipped the bias for a short while.
Even when the drug wore off, the old favorite key still won out.
How this fits with other research
Garcia (1974) first showed that these drugs change response rate in opposite ways depending on how fast the bird was already pecking.
Louie (1980) moves that idea to a two-key world and shows history can lock the bird in even when the drug tries to push it out.
WALLETHOMAS et al. (1963) mapped an upside-down U curve for pentobarbital on a single key: low doses speed birds up, high doses slow them down.
Louie (1980) finds the same drug can reverse a side bias, revealing that the curve now plays out across two choices, not just one.
McMillan et al. (1999) later used the same two-key setup to teach birds to tell pentobarbital from saline, proving the schedule can shape drug signals too.
Why it matters
Old reinforcement patterns can outrank new contingencies and even drug effects.
When you see a client stuck on one response even after you change the pay-off, think history first, not defiance.
Run a quick probe: swap the richer schedule to the other option and watch if the bias holds—if it does, plan extra trials to re-balance the history before you expect change.
Want CEUs on This Topic?
The ABA Clubhouse has 60+ free CEUs — live every Wednesday. Ethics, supervision & clinical topics.
Join Free →Switch the richer schedule to the less-preferred option for one session and count responses to see if history still rules.
02At a glance
03Original abstract
Pigeons were studied under a two-key concurrent fixed-ratio schedule of food presentation. During the first five sessions, the fixed-ratio requirements were 30 responses on one key (major key) and 120 responses on the other key (minor key): responding occurred almost exclusively on the major key. When the fixed-ratio requirements were then made equal at 30 responses on both keys, responding continued to predominate on the major key. The asymmetric distribution of responses persisted when the concurrent fixed-ratio fixed-ratio schedule was interrupted with periods during which the major key was associated with extinction while the other key remained associated with a fixed-ratio schedule. Additionally, in some subjects the fixed-ratio requirements were increased. These schedule modifications decreased the asymmetry in responding but did not eliminate it. d-Amphetamine decreased rates on both keys and slightly increased the asymmetric distribution of responses, while pentobarbital reversed the distribution of responses by increasing low rates and decreasing high rates. The pigeons maintained their original asymmetric distribution of responses during the 1 1/2-year-long study, despite schedule alterations and drug administrations.
Journal of the experimental analysis of behavior, 1980 · doi:10.1901/jeab.1980.34-107