Abstract

Pigeons responded on concurrent-chains schedules with equal variable-interval schedules as initial links.
One terminal link delivered a single reinforcer after a fixed delay, and the other terminal link delivered
either three or five reinforcers, each preceded by a fixed delay. Some conditions included
a postreinforcer delay after the single reinforcer to equate the total durations of the two terminal
links, but other conditions did not include such a postreinforcer delay. With short initial links,
preference for the single-reinforcer alternative decreased when a postreinforcer delay was present, but
with long initial links, the postreinforcer delays had no significant effect on preference. In conditions
with a postreinforcer delay, preference for the single-reinforcer alternative frequently switched from
above 50% to below 50% as the initial links were lengthened. This pattern of results was consistent with
delay-reduction theory (Squires & Fantino, 1971), but not with the contextual-choice model (Grace,
1994) or the hyperbolic value-added model (Mazur, 2001) as they have usually been applied. However,
the hyperbolic value-added model could account for the results if its calculations were expanded to
include reinforcers delivered in later terminal links. The implications of these findings for models of
concurrent-chains performance are discussed.