Conjunctive schedules of reinforcement. I. Rate-dependent effects of pentobarbital and d-amphetamine.
Pentobarbital and d-amphetamine change pigeons’ key-pecking in opposite directions depending on baseline rate and key arrangement.
01Research in Context
What this study did
Garcia (1974) gave pigeons two keys. Birds had to peck under a conjunctive schedule: finish a fixed ratio and then wait through a fixed interval.
The team injected pentobarbital or d-amphetamine. They watched how fast the birds pecked on one-key versus two-key setups.
What they found
Both drugs boosted low pecking rates and cut high rates. The pattern flipped when the schedule changed from one key to two keys.
In short, drug effect depended on how fast the bird was pecking before the shot, and on the key layout.
How this fits with other research
McKearney (1970) saw the same rate-dependency with amobarbital under a simple fixed-interval. E added a ratio piece and a second key, showing the rule holds even when the schedule is more complex.
Louie (1980) used concurrent fixed-ratio schedules with the same two drugs. They also saw low-rate pecking rise, but the birds kept a strong side bias that drugs barely touched. The studies look opposite—one says layout matters, the other says bias persists. The gap is in the schedule type: conjunctive blends ratio and interval, while concurrent keeps them separate.
Yoon et al. (2009) later kept the conjunctive FI-FR frame but swapped cocaine for the old drugs. They found tolerance built evenly across FI lengths, echoing E’s hint that ratio requirements drive the main drug effect, not the interval size.
Why it matters
Rate-dependency is still true when schedules mix ratio and interval. If you run a chained or conjunctive program with clients, expect that any drug (prescribed or illicit) could raise low-rate acts and suppress high-rate ones. Watch the task layout—single response set versus multiple options—because it can tilt the outcome.
Want CEUs on This Topic?
The ABA Clubhouse has 60+ free CEUs — live every Wednesday. Ethics, supervision & clinical topics.
Join Free →Graph each client’s pre-med response rate; flag low-rate targets that might spike after medication changes.
02At a glance
03Original abstract
Key pecking of pigeons was maintained under conjunctive schedules of food presentation in which both a fixed-interval and a fixed-ratio schedule had to be completed before a peck produced food. For two pigeons, pecks on a single key completed both schedule requirements (fixed-interval 3-min, fixed-ratio 50 for one bird, fixed-interval 5-min, fixed-ratio 50 for the second). For two other pigeons, each requirement was scheduled on a separate key. On the two-key schedule, a peck after 5 min on the key scheduling the fixed-interval requirement produced food if at least 10 pecks had occurred on the ratio key (conjunctive fixed-interval 5-min, fixed-ratio 10). When each requirement was scheduled on a separate key, response rates on the fixed-ratio key were generally higher in the early portion of the interval and declined as the interval progressed; responding on the fixed-interval key, once initiated, typically remained at a constant rate throughout the interval. Responding under the single-key schedule was characterized by a high rate early in the interval; this then changed to a lower rate that continued until a peck produced food. For all pigeons, increases in response rates with pentobarbital and d-amphetamine were inversely related to the control rate of responding. When equivalent rates on each key of the two-key schedule were compared, both drugs increased rates on the fixed-ratio key less. Although the effects of both drugs were rate dependent, each drug differentially modified the pattern of responding under the single-key schedule.
Journal of the experimental analysis of behavior, 1974 · doi:10.1901/jeab.1974.22-561