Ito, M., Takatsuru, S., & Saeki, D. (2000).
Choice between constant and variable alternatives by rats: Effects of different reinforcer amounts and energy budgets.
Journal of the Experimental Analysis of Behavior,
73, 79-92.
Two experiments, using rats as subjects, investigated the effect
of different reinforcer amounts and energy budgets on choice
between constant and variable alternatives under a closed
economy. Rats were housed in the chamber and were exposed to a
modified concurrent-chains schedule in which the choice phase was
separated from a rest phase during which the rats could engage in
other activities. In the choice phase, a single variable-interval
schedule arranged entry into one of two equal terminal links
(fixed-interval schedules). The constant terminal link ended with
the delivery of a fixed number of food pellets (two or three,
depending on the condition), whereas the variable terminal link
ended with a variable number of food pellets (means of two or
three, depending on the condition). Energy budget was defined as
positive when body weights were over 90% of free- feeding
weights, and as negative when they were under 80% of free-
feeding weights. The different body weights were produced by
varying the duration of the equal terminal-link schedules within
daily 3-hr sessions. In Experiment 1, rats chose between a
constant and a variable three pellets under both energy budgets.
Rats preferred the constant three pellets more under the positive
energy budget, whereas they were indifferent under the negative
energy budget. In Experiment 2, rats chose between a constant
three pellets and a variable two pellets, and chose between a
constant two pellets and a variable three pellets under both
energy budgets. The rats strongly preferred the constant three
pellets over the variable two pellets under both energy budgets.
In contrast, rats preferred the variable three pellets over the
constant two pellets only under the negative energy budget,
whereas they were indifferent under the positive energy budget.
These results indicate that rats' choices are sensitive to the
difference in reinforcer amounts and to the energy budgets
defined by the level of body weight. The present results are
consistent with those obtained with small granivorous birds as
well as with the predictions of a recent risk-sensitive foraging
theory.
Key words: choice, risk, energy budgets, body weights, reinforcer
amounts, lever press, rats