Two-key concurrent responding: response-reinforcement dependencies and blackouts.
Post-response blackout length alone can shift choice, so check delay contingencies before adjusting reinforcement rates.
01Research in Context
What this study did
Pigeons pecked two keys. Food came on one side only if a short blackout followed the peck. Food on the other side came after a long blackout.
The birds could switch keys at any time. Researchers watched which key the birds chose as the blackout times changed.
What they found
Birds moved toward the key with the shorter blackout. Their choice numbers followed a negative-exponential curve, not the usual strict matching line.
This shows the delay after the response, not just the food rate, steered the choice.
How this fits with other research
Dougan (1992) later added a twist: pecks could also cancel an upcoming timeout. Birds again shifted their choice, proving one response can be controlled by two contingencies at once.
McSweeney (1975) found classic matching in pigeons on concurrent schedules. The 1970 curve looks like a mismatch, but it isn’t: K used equal blackout times, so only reinforcement rate mattered. McKearney (1970) varied blackout, so delay became the big lever.
Finney et al. (1995) showed longer changeover delays sharpen matching in hens. Same idea—time gates choice—but they used changeover delay while McKearney (1970) used post-response blackout.
Why it matters
When you run concurrent programs, remember the clock after the response. A tiny added wait can swing client preference even if the pay rate stays the same. Check your blackout or transition times before you tweak reinforcement ratios.
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Join Free →Time your changeover or post-response blackout; if one side looks sluggish, shorten its delay before you raise the reinforcer amount.
02At a glance
03Original abstract
Two-key concurrent responding was maintained for three pigeons by a single variable-interval 1-minute schedule of reinforcement in conjunction with a random number generator that assigned feeder operations between keys with equal probability. The duration of blackouts was varied between keys when each response initiated a blackout, and grain arranged by the variable-interval schedule was automatically presented after a blackout (Exp. I). In Exp. II every key peck, except for those that produced grain, initiated a blackout, and grain was dependent upon a response following a blackout. For each pigeon in Exp. I and for one pigeon in Exp. II, the relative frequency of responding on a key approximated, i.e., matched, the relative reciprocal of the duration of the blackout interval on that key. In a third experiment, blackouts scheduled on a variable-interval were of equal duration on the two keys. For one key, grain automatically followed each blackout; for the other key, grain was dependent upon a response and never followed a blackout. The relative frequency of responding on the former key, i.e., the delay key, better approximated the negative exponential function obtained by Chung (1965) than the matching function predicted by Chung and Herrnstein (1967).
Journal of the experimental analysis of behavior, 1970 · doi:10.1901/jeab.1970.14-61