Suboptimality in foraging and its association with age and mental health factors

People constantly decide how much time to invest in more versus less rewarding activities. Foraging tasks, during which participants visit contexts with diminishing reward rates, examine this type of decision-making by measuring when individuals choose to switch contexts. It is widely known that humans and other animals perform suboptimally in these tasks. However, the precise nature of this suboptimality, and its links to other behaviourally relevant traits, remain unclear. Here, we developed a foraging task to disambiguate the impacts of initial reward rates and reward rate changes. We investigated how foraging behaviour differs with age and relates to apathy and depression, which are key factors known to influence reward-based decision-making, while controlling for cognitive factors. In addition to overstaying, we found that participants performed more suboptimally as reward decay rate increased, and that many participants expressed a heuristic preference for staying in the single best condition. Moreover, overstaying was strongly associated with higher scaling of stay durations to each condition, and this overstaying/scaling behaviour was positively associated with age but negatively associated with depressive symptoms. No associations were found between foraging behaviour and apathy. Together, our results suggest that people may counterproductively interpret staying in a patch as persistence in reward extraction, which would explain the tight link between overstaying but high sensitivity to reward conditions, and their association with depressive symptoms.