Do tufted capuchin monkeys, Sapajus spp., experience regret in decision making under risk?

It is well known that several nonhuman animal species can show negative emotional responses after receiving unfavourable outcomes (i.e. disappointment-like emotions). Previous research, carried out in neurophysiological laboratories, indicates that, when making decisions, nonhuman animals may also experience regret-like emotions (i.e. negative emotional responses arising when comparing the outcome of a chosen option with the outcome they could have obtained if they had chosen differently). However, little is known about whether nonhuman animals housed in less constrained conditions than the typical neurophysiological laboratory also show regret-like emotions, as well as whether and how these emotions influence subsequent choices. Here we assessed whether tufted capuchin monkeys, Sapajus spp., showed behavioural responses compatible with disappointment- and regret-like emotions in a risky decision-making task and whether these responses were related to their subsequent choices. Twelve capuchins were repeatedly offered a choice between a safe option (corresponding to four food units) and a risky option (corresponding to either one or seven food units) with different probabilities of receiving the larger pay-out. We measured scratching behaviour, as well as capuchins' attempts to change their choice (switching behaviour), after the outcome of the chosen option and of the forgone option were revealed. We found that capuchins flexibly chose according to the probability of receiving the larger payout and attempted to modify their initial choice more often after receiving an unfavourable rather than a positive outcome (disappointment-like behaviour) and after seeing that the outcome of the forgone option was better than the outcome of the chosen option (regret-like behaviour). Moreover, males showed more attempts to modify their initial choice than females and capuchins increased their preference for the risky options after showing both disappointment- and regret-like behaviours. These results indicate that capuchins, as other species, show disappointment-like behaviour for receiving a bad outcome and demonstrates, for the first time in a zoo population, the occurrence of regret-like behaviour for not having chosen differently.& COPY; 2023 The Author(s). Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour. This is an open access article under the CC BY license (http://creativecommons.org/licenses/ by/4.0/).