Failure to find a distance effect in pigeon choice: Manipulating amount and delay of reinforcement
Pigeons decide just as fast when reinforcers are almost equal, so latency is a poor probe of value distance.
01Research in Context
What this study did
Sanabria et al. (2020) tested whether pigeons slow down when two food choices are almost equal in value. They gave pigeons two keys. One key delivered a small amount of milo right away. The other key delivered more milo after a short wait.
The team made the two choices closer in value by tweaking amount and delay. They watched how long the birds took to pick a key. If pigeons act like monkeys, latency should grow as value difference shrinks.
What they found
Choice speed stayed flat. Even when the options were nearly equal, birds pecked just as fast. They still tracked amount and delay changes, but closeness alone did not slow decisions.
In short, pigeons showed no distance effect. Primates hesitate when values get close; pigeons do not.
How this fits with other research
The result lines up with earlier pigeon work. Kydd et al. (1982) also found that pigeons ignore relative immediacy once total delay is equal. Both studies show pigeons miss cues that sway primate choice.
Vasconcelos et al. (2007) failed to replicate the pigeon 'work ethic' effect, another case where birds skip value subtleties. Together, the three papers suggest pigeons use simpler choice rules than primates.
Azrin et al. (1967) did show pigeons follow the matching law with delay. Sanabria does not contradict this; matching tracks allocation, not latency. The new paper adds that choice time, not choice share, is immune to value distance.
Why it matters
If you run preference assessments with clients who have IDD, remember that response latency may not tell you how close the reinforcers are in value. Use allocation data (how often each option is picked) rather than timing data to judge preference strength. Flat latency does not mean flat preference; it may just mean the learner, like a pigeon, decides quickly even when values are near equal.
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02At a glance
03Original abstract
The choice behavior of primates, including humans, displays a distance effect: Latency to choose between alternatives appears to increase with smaller differences in value. There is, so far, no demonstration of this effect in birds. Tests of distance effects in birds have been conducted in binary choice situations with a dominant alternative, where one alternative is superior to the other in all aspects that meaningfully contribute to value (e.g., provides access to the same reinforcer, but with a shorter delay). The present study considers the possibility that including dominant alternatives in choice tests precludes distance effects. Four pigeons were presented with binary choices between alternatives that varied in amount and delay. Some choices had a dominant alternative (smaller-sooner or larger-later vs. smaller-later) and some did not (smaller-sooner vs. larger-later). Across phases, only the delay to the smaller-sooner reinforcer varied. Distance effects were expected to be expressed as longer latencies as choice between smaller-sooner and larger-later reinforcers approached indifference. Despite the sensitivity of choice to differences in amount and delay, no distance effect was observed. Alternative explanations for the failure to find a distance effect in pigeon choice, including the Sequential Choice Model (SCM), are discussed.
Journal of the Experimental Analysis of Behavior, 2020 · doi:10.1002/jeab.627