Differences in delay, not ratios, control choice in concurrent chains.
A fixed delay gap, not the delay ratio, locks in preference—so program schedules by the gap you give, not the math you write.
01Research in Context
What this study did
Dougherty et al. (1996) worked with pigeons in a two-key chamber.
Birds first pecked on either key to enter a terminal link.
In that last link they faced a fixed delay to food.
The team kept the delay difference the same while changing the ratio of delays.
They wanted to know if choice follows the ratio or the flat delay gap.
What they found
Preference stayed put when the delay gap stayed the same.
Changing the ratio of delays did not budge the birds’ choice.
The result says animals track the simple delay difference, not a math ratio.
How this fits with other research
Fantino (1969) first said choice tracks relative expected time.
H et al. keep that idea but narrow it to the raw gap between delays.
Grant (1989) looks like a clash: pigeons picked the key that ended in pecking even when delays matched.
The studies differ by what was held constant.
H et al. locked the delay gap; S locked the delay time and swapped the response form.
Both can be true: delay gap matters when topography is the same, but topography can override when it is not.
Alvarez et al. (1998) later added that local cues, not global rates, steer choice.
Together the papers say: watch the delay gap first, then check what the stimulus and response look like on each side.
Why it matters
When you set up concurrent schedules, think delay difference first.
Keep the gap small if you want balanced responding.
If you must use unlike response forms, test for topography bias before you call the data clean.
This saves you from chasing ratio rules that the learner never sees.
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Join Free →Pick two reinforcers, set the wait time to each at 3 s versus 6 s, and see if response split stays the same when you later try 2 s versus 5 s—gap stays 3 s, ratio changes.
02At a glance
03Original abstract
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.
Journal of the experimental analysis of behavior, 1996 · doi:10.1901/jeab.1996.66-97