Effects of time between trials on rats' and pigeons' choices with probabilistic delayed reinforcers.
Letting animals quit after non-reinforcement wipes out the usual 'longer wait, safer choice' effect—except in rats.
01Research in Context
What this study did
Lancioni et al. (2011) tested rats and pigeons on a two-key choice task. One key gave food every time after 6 s. The other key gave food after 6 s only half the time.
Trials started every 5, 15, 30, or 60 s. In one condition the bird or rat had to keep picking after no food. In the other they could walk away.
What they found
When forced to keep choosing, both animals picked the sure key more as the wait between trials grew longer.
When they could walk away after no food, only rats still did this. Pigeons stopped caring about the wait time.
How this fits with other research
Tracey et al. (1974) saw the same pigeon pattern but blamed "execution noise." E et al. show the noise story only holds when birds cannot leave the trial.
Byiers et al. (2025) found that after two-day breaks, animal choices look like "spontaneous recovery" but may just be fresh exploration. Short gaps (seconds to minutes) in E et al. give cleaner data because exploration is low.
Sutphin et al. (1998) showed rats skip costly patches by eating fewer, bigger meals. E et al. add that rats also skip risky options when trials are far apart, showing the same cost-saving style.
Why it matters
If your client can leave the task after an error, watch for species-like differences. Humans who bolt after failure may stop noticing timing changes, just like pigeons. Keep sessions short or add brief pauses instead of dragging out inter-trial intervals. For clients who must stay, longer waits can naturally tilt them toward surer rewards—use that when shaping safe, steady responding.
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After an error, let the client stand up for 5 s, then re-present the trial—note if their next choice becomes more cautious.
02At a glance
03Original abstract
Parallel experiments with rats and pigeons examined reasons for previous findings that in choices with probabilistic delayed reinforcers, rats' choices were affected by the time between trials whereas pigeons' choices were not. In both experiments, the animals chose between a standard alternative and an adjusting alternative. A choice of the standard alternative led to a short delay (1 s or 3 s), and then food might or might not be delivered. If food was not delivered, there was an "interlink interval," and then the animal was forced to continue to select the standard alternative until food was delivered. A choice of the adjusting alternative always led to food after a delay that was systematically increased and decreased over trials to estimate an indifference point--a delay at which the two alternatives were chosen about equally often. Under these conditions, the indifference points for both rats and pigeons increased as the interlink interval increased from 0 s to 20 s, indicating decreased preference for the probabilistic reinforcer with longer time between trials. The indifference points from both rats and pigeons were well described by the hyperbolic-decay model. In the last phase of each experiment, the animals were not forced to continue selecting the standard alternative if food was not delivered. Under these conditions, rats' choices were affected by the time between trials whereas pigeons' choices were not, replicating results of previous studies. The differences between the behavior of rats and pigeons appears to be the result of procedural details, not a fundamental difference in how these two species make choices with probabilistic delayed reinforcers.
Journal of the experimental analysis of behavior, 2011 · doi:10.1901/jeab.2011.95-41