Williams, B. A. (1997).
Conditioned reinforcement dynamics in three-link chained schedules.
Journal of the Experimental Analysis of Behavior,
67, 145-159.
In two experiments rats were trained on three-link
concurrent-chains schedules of reinforcement. In Experiment 1,
additional entries to one terminal link were added during one of
the middle links to a baseline schedule that was otherwise equal
for the two chains, and, depending on the condition, these
additional terminal-link presentations ended either in food or in
no food. When food occurred, preference was always in favor of
the chain with the additional terminal-link presentations (which
also entailed a higher rate of reinforcement). When no food
occurred at the end of the additional terminal links, the outcome
depended on the nature of the stimuli associated with these
additional terminal links. When stimuli different from the
reinforced baseline terminal links were used for the no-food
terminal links, preference was against the choice alternative
that led to the extra periods of extinction. When the same
stimulus was used for the two kinds of terminal links, preference
was near indifference, that is, significantly greater than when
different stimuli were used. In Experiment 2, rats learned
repeated reversals of a simultaneous discrimination under a
three-link concurrent-chains schedule, in which the food or
no-food choice outcomes were delayed until the end of the chain.
Different conditions were defined by the point in the chain at
which differential stimuli occurred. When the middle and terminal
links provided no differential stimuli, discrimination was
acquired more slowly than when differential stimuli occurred in
both links. When differential stimuli occurred in the m iddle but
not the terminal links, acquisition rates were intermediate. Both
experiments together show that the effects of stimuli in a chain
schedule are due partly to the time to food correlated with the
stimuli and partly to the time to the next conditioned reinforcer
in the sequence.
Key words: chained schedules, conditioned reinforcement, lever
press, rats