Compounding of discriminative stimuli that maintain responding on separate response levers.
Put two reinforcer cues together and responding jumps, but you can steer which behavior wins by tweaking light levels or payoff rates.
01Research in Context
What this study did
Macdonald (1973) worked with lab rats that had two levers. Each lever paid off on its own fixed-interval schedule. One lever had a tone cue. The other had a light cue.
Next, the team put both cues on at the same time. The rat could now press either lever. The study asked: would the rat press more, and would it pick one lever?
What they found
When both cues came on together, total presses went up. The rise looked like the sum of the two single rates. Most rats also showed a favorite lever.
Dimming the room lights or making one schedule richer could flip that favorite. The compound cue was not just louder; it could be tuned.
How this fits with other research
Schwarz et al. (1970) first saw this add-up effect, but with only one lever. The 1973 paper moves the same idea to two levers and shows choice, not just speed.
Davis et al. (1972) got summation too, yet with shock-avoidance instead of food. The plus stays the same even when the reinforcer flips from good to bad.
Dove et al. (1974) later found that summation can turn into suppression in chained links. The 1973 study helps explain why: stimulus order and schedule type set the final shape of the curve.
Why it matters
If you run two programs at once—say, DTT and a group game—each with its own cue, the cues may merge and boost responding. Watch for one skill stealing responses from the other. You can rebalance by dimming one cue, enriching the schedule, or moving the stronger cue to a quieter part of the room.
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02At a glance
03Original abstract
In Experiment 1, rats' responses were reinforced on a fixed-interval 30-sec schedule in the presence of either a light or a tone and were not reinforced in their absence. Each stimulus was correlated with its own response lever, with only one lever present during a session. When light and tone were compounded in the presence of the tone-correlated lever, no change in responding occurred. However, when tone was compounded with light in the presence of the light-correlated lever, level of responding was greater than to light alone (response summation). Summation was also found when each stimulus was correlated with the same lever. Next, light and tone were again correlated with separate levers, but both levers were always simultaneously present. Compounding produced both summation and emission of most responses on the light-correlated lever. This prepotency of light was reduced (1) by leaving a houselight on throughout the session; and (2) by correlating each stimulus with a different schedule (either fixed-interval 4.7-sec or fixed-interval 30-sec). With a medium- and high-intensity houselight and with the different reinforcement schedules, similar results were obtained during compounding, regardless of whether compounding occurred in the presence of the light- or tone-correlated lever.
Journal of the experimental analysis of behavior, 1973 · doi:10.1901/jeab.1973.20-57