Evidence against a constant-difference effect in concurrent-chains schedules.
Keeping the delay gap the same does not keep choice steady; absolute delay still matters.
01Research in Context
What this study did
The team worked with pigeons on concurrent-chains schedules.
They kept the gap between two final delays at 10 seconds every time.
Then they watched if the birds stayed equally picky across different delay lengths.
What they found
The birds did not stay picky.
When both delays got longer, the birds cared less about the 10-second gap.
So the constant-difference rule failed.
How this fits with other research
Schmitt (1984) saw similar shifts when delay and number of reinforcers changed.
Gowen et al. (2013) also showed choice flipping as delays grew inside one session.
These studies line up: absolute delay size, not just the gap, drives choice.
Why it matters
When you set up choice tasks, remember that longer waits weaken preference even if the wait gap stays the same. Check absolute delay, not just the difference.
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02At a glance
03Original abstract
Savastano and Fantino (1996) reported that in concurrent-chains schedules, initial-link choice proportions remained constant as terminal-link durations increased as long as the subtractive difference between the two terminal-link schedules remained constant. Two experiments with pigeons were conducted to examine this constant-difference effect. Both experiments used equal variable-interval schedules as initial links. The terminal links were fixed delays to reinforcement in Experiment 1 and variable delays to reinforcement in Experiment 2. The durations of the terminal links were varied across conditions, but the difference between pairs of terminal links was always 10 s. In both experiments, preference for the shorter terminal link became less extreme as terminal-link durations increased, so a constant-difference effect was not found. It is argued, however, that this choice situation does not provide clear evidence for or against delay-reduction theory versus other theories of choice.
Journal of the experimental analysis of behavior, 2002 · doi:10.1901/jeab.2002.77-147