Towards validation of delay discounting in the pigeon
Key pecks give clean delay-discounting data in pigeons, so you can swap out treadles for a simpler setup.
01Research in Context
What this study did
Holt and team worked with four pigeons in a lab chamber.
Birds could peck a lit key or press a small treadle.
Each response started a delay, then food arrived.
Delays ranged from 1 to 30 seconds across sessions.
The goal was to see if simple key pecks give clean delay-discounting curves.
What they found
Key pecks produced smooth, hyperbolic curves for every bird.
The same shape appeared when birds used the treadle.
Each pigeon kept its own steep or flat curve across days.
Orderly data mean key pecks are a valid measure of delay discounting.
How this fits with other research
Corrigan et al. (1998) saw key pecks drop when delays were hidden.
Their delays were unsignaled, so birds stared at the feeder instead.
Holt used lit-key signals, so birds kept pecking.
The studies differ only in signaled versus hidden delays, not a true clash.
McKerchar et al. (2019) later repeated the hyperbolic shape with adult humans online.
Nickerson et al. (2015) also found the same curve when people waited for hypothetical money.
Together, the pattern spans pigeons, people, and many response forms.
Why it matters
You can trust a simple key-peck procedure for discounting assays.
No need for bulky treadles or special equipment.
Use the same hyperbolic model to compare pigeon and human data.
Signal the delay with a stimulus to keep response rates steady.
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02At a glance
03Original abstract
A series of procedures were conducted in an attempt to assess various forms of validity related to the use of pigeons in research on delay discounting. In separate experimental arrangements, pigeons pressed a treadle, pecked a lit key, pecked a darkened key, or pecked a lit key with a hold as the required response. First, the obtained results were consistent with what would be necessary if the construct of delay discounting were being measured, which provides evidence of face validity. Second, criterion validity was assessed by comparing individual differences in rates of discounting across procedures. Third, to assess internal validity, each pigeon repeated the Treadle, Key Peck, and Dark Key procedures. Again, at both the aggregate and individual levels, the obtained indifference points did not differ systematically between replications. Finally, to assess external validity, discounting was observed regardless of the procedure, where the patterns of data at the aggregate level, and generally at the individual level, were orderly and well described by a hyperbolic function. In addition, rates of discounting were similar when pigeons pecked a lit key, a dark key, or a key with a hold; and each of those rates of discounting tended to be steeper than when treadle pressing. Generally speaking, pigeons that discounted relatively steeply on one procedure also tended to discount relatively steeply on the other procedures. The procedures evidence some of the necessary elements involved with the use of pigeons in research on delay discounting.
Journal of the Experimental Analysis of Behavior, 2018 · doi:10.1002/jeab.470