Relative sensitivity to reinforcer amount and delay in a self-control choice situation.
Time outweighs amount in choice, and the break-even delay grows faster than the reward size.
01Research in Context
What this study did
The team let rats pick between one pellet right away or six pellets after a wait.
They kept the food ratio at 6:1 and changed the delay ratio in tiny steps.
The goal was to find the exact delay where the rat acted as if both choices were equal.
What they found
When the short delay stayed at five seconds, rats picked six pellets only if the long delay was near fifty-five seconds.
At five versus thirty seconds the rats already flipped to the single pellet, showing time matters more than amount.
The indifference point slid with the absolute delay, not just the ratio.
How this fits with other research
Sanford et al. (1980) saw the same shift sixteen years earlier, but used wider delay jumps.
Haynes et al. (2022) later showed rats reverse their choice mid-session as delays grow, backing the non-constant sensitivity found here.
Gowen et al. (2013) got within-session reversals in pigeons, proving the effect crosses species.
Why it matters
When you build token boards or DRO schedules, remember that a big reward needs a much longer wait to feel 'equal' to a small immediate one. If the client can already wait five seconds, offering ten seconds may kill the deal even though the payoff is six times bigger. Start with tiny delay bumps and watch for the flip point instead of trusting a fixed ratio.
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02At a glance
03Original abstract
Rats were exposed to concurrent-chains schedules in which a single variable-interval schedule arranged entry into one of two terminal-link delay periods (fixed-interval schedules). The shorter delay ended with the delivery of a single food pellet; the longer day ended with a larger number of food pellets (two under some conditions and six under others). In Experiment 1, the terminal-link delays were selected so that under all conditions the ratio of delays would exactly equal the ratio of the number of pellets. But the absolute duration of the delays differed across conditions. In one condition, for example, rats chose between one pellet delayed 5 s and six pellets delayed 30 s; in another condition rats chose between one pellet delayed 10 s and six pellets delayed 60 s. The generalized matching law predicts indifference between the two alternatives, assuming that the sensitivity parameters for amount and delay of reinforcement are equal. The rats' choices were, in fact, close to indifference except when the choice was between one pellet delayed 5 s and six pellets delayed 30 s. That deviation from indifference suggests that the sensitivities to amount and delay differ from each other depending on the durations of the delays. In Experiment 2, rats chose between one pellet following a 5-s delay and six pellets following a delay that was systematically increased over sessions to find a point of indifference. Indifference was achieved when the delay to the six pellets was approximately 55 s. These results are consistent with the possibility that the relative sensitivities to amount and delay differ as a function of the delays.
Journal of the experimental analysis of behavior, 1996 · doi:10.1901/jeab.1996.66-219