Strict and random alternation in concurrent variable-interval schedules.
Random alternation sharpens matching; signals shift choice only if they change local reinforcement.
01Research in Context
What this study did
Elliffe et al. (2003) tested how two ways of switching between schedules change behavior.
Pigeons pecked on concurrent variable-interval (VI) schedules. The key alternated every 30 s.
In one condition the switch was random. In another it was strict A-B-A-B order. Sometimes a light signaled the next schedule, sometimes it did not.
What they found
Random alternation made response allocation match reinforcement rate more closely.
Signaling the next key created bias and faster switches, but only when the local reinforcer rate also changed. When each side kept its own rate, the signal had no effect.
How this fits with other research
Pliskoff et al. (1978) showed that a 2-s changeover delay keeps post-switch pecking high for 3 s. Douglas holds the delay constant and shows alternation timing, not just delay length, shapes choice.
Krägeloh et al. (2003) ran a similar 2003 study. They found signaling doubled sensitivity. Douglas finds the boost vanishes if local rates stay separate. The two papers together say: signals help only when they carry new rate information.
Harrison et al. (1975) found signaled reinforcers raised response rate on the other key. Douglas shows the same signals can bias choice, but the effect is wiped out by how you count reinforcers.
Why it matters
If you run concurrent schedules in a lab or clinic, use random alternation to get cleaner matching. Add signals only when the next option truly changes the payoff. Otherwise the signal is noise and may mislead your learner.
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02At a glance
03Original abstract
Six pigeons responded on pairs of concurrent variable-interval schedules with, in different parts, four different arrangements of alternation between schedules. Following a single switching-key response, alternation was either strict or random, and the alternative presented after a switch (the postswitch alternative) was either signaled by the location of the switching key or unsignaled. Generalized-matching analyses showed little difference in behavior among the different alternation arrangements, except the usual finding of lower sensitivity of response allocation than time allocation was eliminated by arranging random alternation. Patterns of interchangeover times were similar for all arrangements except signaled random alternation. Differences in behavior preceding the different postswitch alternatives were found in the signaled random alternation procedure. Preference was biased towards the color of the signaled postswitch alternative and showed increased sensitivity when the postswitch alternative was to be the one with the higher reinforcer rate. Interchangeover times were substantially shorter when the postswitch alternative was signaled to be different from the current alternative than when it was signaled to be the same. However, when separate reinforcer ratios were calculated for the different postswitch alternatives, those effects were eliminated or greatly reduced. We suggest that, although behavior is indeed influenced by the postswitch alternative, the mechanism is indirect. That is, the distributions of reinforcers between alternatives obtained before each postswitch alternative differ when those alternatives are signaled, and those distributions are discriminated, but the same relations between choice and relative reinforcement hold irrespective of which postswitch alternative is signaled.
Journal of the experimental analysis of behavior, 2003 · doi:10.1901/jeab.2003.79-65