The effect of reinforcement differences on choice and response distribution during stimulus compounding.
In a compound cue, the element with the stronger payoff history dominates, even if it is weaker in size or volume.
01Research in Context
What this study did
Clark et al. (1977) worked with pigeons in a small lab chamber.
A tone or a light told the bird which schedule was active.
Sometimes both cues came on together. The team then changed how much food each cue promised.
What they found
When tone and light overlapped, the cue that had delivered the most food won control.
Even if that cue was dim or quiet, it still guided most pecks.
The birds did not add the cues; they picked the richer one.
How this fits with other research
Shull (1971) first showed that mixing sight and sound boosts responding. Clark et al. (1977) added the rule: the richer element, not the louder or brighter one, drives the boost.
Thrailkill et al. (2025) later repeated the idea with probability instead of amount. Pigeons still looked longer at the element that had paid off more. The core finding held across decades.
Huguenin et al. (1980) moved the test to adults with intellectual disabilities. Again, the part of the compound that matched the current payoff grabbed attention. The effect extends beyond pigeons and grain.
Why it matters
When you put two cues together, the client will lock onto the one that has paid the best. If you want joint control, balance the reinforcement history first. Otherwise, plan for the richer cue to win.
Want CEUs on This Topic?
The ABA Clubhouse has 60+ free CEUs — live every Wednesday. Ethics, supervision & clinical topics.
Join Free →Before pairing a picture card with a spoken word, give each the same rate of reinforcement so neither steals control.
02At a glance
03Original abstract
In Experiments I and II, rats were trained to respond on one lever during light and another during tone. The absence of tone and light controlled response cessation. In the multiple schedule of Experiment I, all reinforcements were received for responding in tone or light; in the chain schedule of Experiment II, all reinforcements were received in no tone + no light for not responding. Experiment I subjects, for which tone and light were associated with response and reinforcement increase, responded significantly more to tone-plus-light than to tone or light alone (additive summation). Experiment II subjects, for which tone and light were associated with response increase and reinforcement decrease, responded comparably to tone, light, and tone + light. Thus, additive summation was observed when stimulus-response and stimulus-reinforcer associations in tone and light were both positive, but not when they were conflicting. All subjects in both experiments responded predominantly on the light-correlated lever during tone + light, even when light intensity was reduced in testing. Furthermore, when a light was presented to a subject engaged in tone-associated responding, all subjects immediately switched the locus of responding to the light-correlated lever. No change in locus occurred when a tone was presented to a subject engaged in light-associated responding, irrespective of the stimulus-reinforcer association conditioned to tone. The light-lever preference in tone + light indicates that the heightened responding observed in Experiment I was not the summation of tone-associated behavior with light-associated behavior. Rather, it appears to be the result of a facilitation of one operant (light-associated responding) by the reinforcement-associated cue for the other.
Journal of the experimental analysis of behavior, 1977 · doi:10.1901/jeab.1977.27-351