Savastano, H. I., & Fantino, E. (1996).
Differences in delay, not ratios, control choice in concurrent chains.
Journal of the Experimental Analysis of Behavior,
66, 97-116.
In two experiments, pigeons were trained with concurrent-chains
schedules, wherein responding to equal initial links measured
preference between variable-interval terminal links. Absolute
terminal-link duration was varied by keeping constant the
difference between the terminal-link delays and forcing their
ratio to change. Delay-reduction theory scales value relative to
a common temporal context and requires that delay differences
control choice. Thus, preference should remain invariant. Most
competing accounts, including the matching law and a strong form
of Weber's law, require that preference vary with the delay
ratio. Experiment 1 employed standard concurrent chains, in which
terminal-link position and color were confounded. Although
average preference remained constant, individual preferences were
highly variable and inconsistent, possibly due to carryover of
position biases across conditions. In an attempt to reduce
variability, Experiment 2 used a modified concurrent-chains
procedure. Preference at different terminal-link durations was
assessed simultaneously to prevent order effects, and
terminal-link position was alternated randomly across trials to
minimize the impact of position biases. In Experiment 2, both
individual and mean preferences showed the constant-difference
invariance. Overall, choice was controlled by terminal-link
differences, not ratios.
Key words: choice, concurrent-chain schedules, conditioned
reinforcement, delay-reduction theory, contextual choice model,
matching law, Weber's law, key peck, pigeons