The concurrent reinforcement of two interresponse times: absolute rate of reinforcement.
Response rate and short-IRT bias climb fast until pay hits ~20/h, then flat-line even if pay keeps rising.
01Research in Context
What this study did
Killeen (1970) worked with pigeons in a small lab space.
The birds could peck one key.
The key paid off for two different wait-times: a short pause and a long pause.
Pay-outs came on mixed schedules: variable-interval for the short pause, every-time for the long pause.
The team slowly raised the overall rate of pay from low to high and watched what happened.
What they found
When pay climbed toward 20 treats per hour, pecking speed shot up.
The birds also leaned hard on the short-pause option.
After 20 treats per hour, extra pay no longer pushed speed higher.
At that point the split between short and long pauses stayed about the same.
How this fits with other research
One year earlier Killeen (1969) had shown that birds match their pause split to the harmonic pay split.
The 1970 paper keeps that rule but adds a ceiling: once pay tops 20 per hour, the rule still holds, yet total pecks stop rising.
Shimp (1974) later re-framed the same ceiling as a time-budget problem: birds simply run out of seconds to allocate.
Bradshaw et al. (1978) and Wilkie et al. (1981) kept the curve shape but showed weaker sugar water or smaller drops slide the same curve to the right.
Together the set says: rate sets the height, reinforcer size sets the left-right spot, and 20-ish per hour is where gains level off.
Why it matters
When you shape new skills on thin schedules, expect big gains only until the learner earns about 20 reinforcers per hour.
Past that point, save your chips: more pay will not speed the response further.
Instead, boost quality or add novelty if you need extra snap.
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02At a glance
03Original abstract
Three pigeons obtained food on a one-key schedule of reinforcement for two concurrent, discriminated interresponse times. The overall rate of reinforcement was determined by a family of variable-interval schedules and by a continuous reinforcement schedule. The average frequency of reinforcement varied from 1.1 to 300 reinforcements per hour; the relative frequency of reinforcement for each of the two interresponse times was 0.5 throughout the experiment. The number of responses per minute increased sharply as the number of reinforcements per hour increased from 1 to 20. Beyond 30 reinforcements per hour, the curve was approximately flat, although it sometimes decreased slightly at the highest reinforcement rates. The relative frequency of the shorter interresponse time also increased sharply as the number of reinforcements per hour increased from 1 to 20. The asymptote of the relative frequency function approximately equalled the relative reciprocal of the length of the shorter interresponse time for reinforcement rates greater than 30 or 40 reinforcements per hour. This approximation was obscured by the response-rate function.
Journal of the experimental analysis of behavior, 1970 · doi:10.1901/jeab.1970.13-1