Discriminative stimulus control and the effects of concurrent operants.
Richer reinforcement on one choice flattens stimulus discrimination, so equalize payoff rates to sharpen discrimination.
01Research in Context
What this study did
Pigeons pecked two keys under different colored lights. The lights were the signals, or discriminative stimuli.
The birds could switch keys at any time. One schedule paid off twice as often as the other. The team also added short pauses, called changeover delays, after a switch.
They tracked how sharp the birds’ discrimination was between the colors under each payoff ratio.
What they found
When the richer side paid double, the birds’ discrimination gradients flattened. They responded almost the same to both colors.
When both sides paid equally, the gradients grew steep. The birds sharply favored the color tied to the key they liked best.
Adding a pause after a switch had only a small effect on the shape of the gradients.
How this fits with other research
Schwarz et al. (1970) saw U-shaped gradients when birds could hop between colors on their own. The 1987 study shows that payoff size, not just hop control, sculpts the slope.
Neuringer et al. (1968) found that birds still matched their time to payoff ratios even when pecks did not matter. Leigland (1987) adds that those same ratios also mold how well signals control behavior.
Krägeloh et al. (2003) later showed that adding a changeover delay plus signals doubled choice sensitivity. Leigland (1987) had already hinted that the delay itself tweaks control, just more gently.
Why it matters
Your client may look inattentive, but the real issue could be payoff imbalance. If one task pays far more, stimulus control will flatten and errors rise. Balance reinforcement rates first, then add prompts or delays.
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02At a glance
03Original abstract
Discriminative-stimulus-control functions were investigated in a concurrent operant context. Variable-interval reinforcement schedules were arranged for pigeons on two response keys. One key, illuminated with a white vertical line on green background (position irrelevant), was programmed with a given schedule value across groups. For different groups of pigeons, the alternative key, illuminated with green alone, was programmed with twice, the same, or half the reinforcement frequency of the other key. Stimulus-control gradients were collected from both keys as line orientation was varied. On the green-plus-line alternative, flattest gradients were observed when twice the reinforcement frequency was concurrently programmed and the steepest were observed when equal values were concurrently programmed. Also examined were the effects of a programmed changeover delay, important in maintaining the independence of concurrent operants. The changeover delay was found to have relatively minor effects upon stimulus control, despite its typical and marked effects upon steady-state responding.
Journal of the experimental analysis of behavior, 1987 · doi:10.1901/jeab.1987.47-213