Effects of the discriminability of alternatives in three-alternative concurrent-schedule performance.
A third concurrent choice can push pigeons into overmatching, so plan for bigger-than-expected swings in response ratios.
01Research in Context
What this study did
Researchers ran pigeons on three-key concurrent VI schedules. Each key gave grain on its own timer. A color light on the third key acted as a signal.
They added a short blackout after every switch. This tiny pause worked like a mini-punisher. The team wanted to see how the third key changed choices on the other two.
What they found
Birds showed overmatching. Response ratios were more extreme than reinforcer ratios. The third key’s payoff rate pulled sensitivity up or down on the remaining pair.
An extended matching model fit the data. It added terms for signal clarity and the blackout cost.
How this fits with other research
Macdonald et al. (1973) and Frederiksen et al. (1978) found clean matching or slight under-matching with two keys. Adding a third key flipped the curve upward, creating overmatching instead.
Bron et al. (2003) also tweaked discriminability. They used food type, not light color, and still saw bias. Together the papers show that any hard-to-notice difference can bend the matching line.
Katz et al. (2003) later showed that pigeons can track ratios that change every few seconds. Dougherty et al. (1994) used steady ratios, but both studies confirm that choice stays flexible even when the setup grows more complex.
Why it matters
If you run concurrent schedules with three or more options, expect the extra alternative to warp response splits. Watch for overmatching in your data. You may need to adjust reinforcer rates or make each option easier to tell apart. A brief timeout after switching can also act as a mild punisher that steers behavior.
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Join Free →Graph response and reinforcer ratios for each pair of options; if the line is steeper than 1.0, lower the richest schedule’s rate or add clearer signals.
02At a glance
03Original abstract
Six pigeons were trained on two- and three-alternative concurrent schedules in which the alternatives were signaled by different wavelengths of light on the main pecking key. The schedules were arranged according to a switching-key procedure in which pecks on a white side key produced a 3-s blackout and, intermittently, a change in the variable-interval schedule of food programmed on the main (center) key after the blackout. In Part 1, a two-alternative concurrent variable-interval schedule was arranged in which the alternatives were signaled by 560 nm and 630 nm. Parts 2 and 3 arranged three-alternative concurrent variable-interval schedules with the alternatives signaled by 560 nm, 600 nm, and 630 nm (Part 2) and 560 nm, 623 nm, and 630 nm (Part 3). Within each part, the relative rate of food reinforcers available on the alternatives was varied across a wide range. In all parts of the experiment, the ratios of responses emitted between pairs of alternatives were more extreme than the ratios of reinforcers obtained on the pairs of alternatives, a result termed overmatching. In Parts 2 and 3, generalized matching sensitivities between pairs of alternatives were found to be higher when the reinforcer rate on the third alternative was low than when it was high-an apparent failure of the constant-ratio rule. The data were well described by an extension of the Davison and Jenkins (1985) model, which assumes differing discriminabilities between concurrent-schedule alternatives in combination with a punishing effect of blackout following changeovers.
Journal of the experimental analysis of behavior, 1994 · doi:10.1901/jeab.1994.61-45