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Sensitivity to “sunk costs” in mice, rats, and humans

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Science  13 Jul 2018:
Vol. 361, Issue 6398, pp. 178-181
DOI: 10.1126/science.aar8644

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The impact of time wasted

The amount of time already spent on a task influences human choice about whether to continue. This dedicated time, known as the “sunk cost,” reduces the likelihood of giving up the pursuit of a reward, even when there is no indication of likely success. Sweis et al. show that this sensitivity to time invested occurs similarly in mice, rats, and humans (see the Perspective by Brosnan). All three display a resistance to giving up their pursuit of a reward in a foraging context, but only after they have made the decision to pursue the reward.

Science, this issue p. 178; see also p. 124

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.

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