Sensitivity to "sunk costs" in mice, rats, and humans - PubMed (original) (raw)

Comparative Study

Sensitivity to "sunk costs" in mice, rats, and humans

Brian M Sweis et al. Science. 2018.

Abstract

Sunk costs are irrecoverable investments that should not influence decisions, because decisions should be made on the basis of expected future consequences. Both human and nonhuman animals can show sensitivity to sunk costs, but reports from across species are inconsistent. In a temporal context, a sensitivity to sunk costs arises when an individual resists ending an activity, even if it seems unproductive, because of the time already invested. In two parallel foraging tasks that we designed, we found that mice, rats, and humans show similar sensitivities to sunk costs in their decision-making. Unexpectedly, sensitivity to time invested accrued only after an initial decision had been made. These findings suggest that sensitivity to temporal sunk costs lies in a vulnerability distinct from deliberation processes and that this distinction is present across species.

Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

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Conflict of interest statement

Competing interests: The authors have no confuting interests.

Figures

Fig. 1.

Fig. 1.. Task schematics.

(A) In the Restaurant Row task, food-restricted rodents were trained on a maze in which they encountered serial offers for flavored rewards in four “restaurants.” Each restaurant contained a separate offer zone and wait zone. Tones sounded in the offer zone; a fixed tone pitch indicated the delay for which rodents would have to wait in the wait zone (1 to 30 s. random on offer entry). Tone pitch descended in the wait zone during the delay “countdown.” Rodents could quit the wait zone for the next restaurant during the countdown, terminating the trial. (B) In the web Surf task, humans performed an analogous 30-min computer-based foraging paradigm in which they encountered serial offers for short entertaining videos from four “galleries.” A static “download bar” appeared in the offer phase indicating delay length (1 to 30 s. random on offer entry), which did not begin downloading until after entering the wait phase. Downloads could be quit during the wait phase. Humans were also asked to rate each video on a scale from 1 (least enjoyable) to 4 (most enjoyable) after viewing and to rank the genres at the end of the session.

Fig. 2.

Fig. 2.. The amount of time spent waiting increases commitment to continuing reward pursuit in mice, rats, and humans.

(A to C) Probability of earning a reward in the wait zone as a function of countdown time remaining in (A) mice, (B) rats, and (C) humans. Black data points indicate trials in which subjects had just entered the wait zone. Colored data points indicate time remaining in the countdown after subjects had already waited varying times (fig. S3). Linear regressions are plotted with 95% confidence interval shadings. (D to F) Slopes calculated from each linear regression in (A) to (C) (‘‘observed”) and slopes recalculated iteratively from black data points to match colored data ranges in (A) to (C) (“adjusted controls”) (fig. S5) are plotted ±1 SEM. The colored tick on the x axis indicates time in the wait zone until the first significant sunk cost effect was observed. ANOVAs were used to compare slopes of linear regression models, testing for interactions with sunk cost conditions and controls, correcting for multiple comparisons. Not significant (n.s.), P > 0.05; *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001.

Fig. 3.

Fig. 3.. Resources spent while deliberating do not contribute to the sunk cost effect.

(A to C) Amount of time spent in the offer zone choosing to skip versus to enter did not influence the probability of earning versus quitting once in the wait zone after subjects chose to enter (fig. S6). Linear regressions are plotted with 95% confidence interval shadings. (D) Slopes calculated from linear regressions are plotted ±1 SEM and are not significantly different from each other or zero in mice (F = 1.545, P = 0.229), rats (F = 0.767, P = 0.392). or humans (F = 0.117. P = 0.737), on the basis of an ANOVA with post-hoc comparisons against zero. n.s., P > 0.05.

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References

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