Abstract:
Pigeons and other animals soon learn to wait (pause) after food delivery on periodic-food schedules
before resuming the food-rewarded response. Under most conditions the steady-state duration of the
average waiting time, t, is a linear function of the typical interfood interval. We describe three
experiments designed to explore the limits of this process. In all experiments, t was associated with
one key color and the subsequent food delay, T, with another. In the first experiment, we compared
the relation between t (waiting time) and T (food delay) under two conditions: when T was held
constant, and when T was an inverse function of t. The pigeons could maximize the rate of food
delivery under the first condition by setting t to a consistently short value; optimal behavior under the
second condition required a linear relation with unit slope between t and T. Despite this difference
in optimal policy, the pigeons in both cases showed the same linear relation, with slope less than one,
between t and T. This result was confirmed in a second parametric experiment that added a third
condition, in which T + t was held constant. Linear waiting appears to be an obligatory rule for
pigeons. In a third experiment we arranged for a multiplicative relation between t and T (positive
feedback), and produced either very short or very long waiting times as predicted by a quasi-dynamic
model in which waiting time is strongly determined by the just-preceding food delay.
