The sunk cost effect in pigeons and humans.
Sunk-cost errors live in pigeons and people; strip the signals that mark past effort and give clean restart choices to keep behavior optimal.
01Research in Context
What this study did
Dagnan et al. (2005) let pigeons and people choose between two keys or buttons.
One option stayed easy. The other started hard, then turned easy or stayed hard.
A light or sound marked when the work rule changed. The team watched who kept pecking or pressing even when the better deal was to switch.
What they found
Both birds and humans stuck with the first choice too long when they had already paid a high cost.
The brighter or louder the signal that marked the change, the deeper the sunk-cost hole.
When the signal was removed, subjects quit sooner and earned more reinforcers overall.
How this fits with other research
Davison et al. (1995) showed that adding a clear stimulus lets you shape pigeons to leave matching and pick the richer schedule. Dagnan et al. (2005) flips that idea: removing the same kind of signal cuts the sunk-cost bias.
Lea (1976) proved pigeons can self-adjust schedules to stay optimal. The new study shows this skill breaks down when past effort is highlighted, extending the same law-of-effect line.
Hopkins et al. (1977) found pigeons love stimuli that tell them a reinforcer is coming. The 2005 data warn that these helpful cues can also lock them into bad choices.
Why it matters
Your client may keep doing a hard task because "I already started." Hide cues that mark the shift from hard to easy, like removing the timer beep or covering the token board. Insert fresh choice points every few minutes so the learner can quit without shame. You will see fewer tears and faster gains.
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02At a glance
03Original abstract
The sunk cost effect is the increased tendency to persist in an endeavor once an investment of money, effort, or time has been made. To date, humans are the only animal in which this effect has been observed unambiguously. We developed a behavior-analytic model of the sunk cost effect to explore the potential for this behavior in pigeons as well as in humans. Each trial started out with a short expected ratio, but on some trials assumed a longer expected ratio part way through the trial. Subjects had the (usually preferable) option of "escaping" the trial if the longer expected ratio had come into effect in order to bring on a new trial that again had a short expected ratio. In Experiments 1 through 3, we manipulated two independent variables that we hypothesized would affect the pigeons' ability to discriminate the increase in the expected ratio within a trial: (a) the presence or absence of stimuli that signal an increase in the expected ratio, and (b) the severity of the increase in the expected ratio. We found that the pigeons were most likely to persist nonoptimally through the longer expected ratios when stimulus changes were absent and when the increase in the expected ratio was less severe. Experiment 4 employed a similar procedure with human subjects that manipulated only the severity of the increase in the expected ratio and found a result similar to that of the pigeon experiment. In Experiment 5, we tested the hypothesis that a particular history of reinforcement would induce pigeons to persist through the longer expected ratios; the results suggested instead that the history of reinforcement caused the pigeons to persist less compared to pigeons that did not have that history.
Journal of the experimental analysis of behavior, 2005 · doi:10.1901/jeab.2005.21-04