Computing Joint Action Costs: Co-Actors Minimize the Aggregate Individual Costs in an Action Sequence

Abstract

Successful performance in cooperative activities relies on efficient task distribution between co-actors. Previous research found that people often forgo individual efficiency in favor of co-efficiency (i.e., joint-cost minimization) when planning a joint action. The present study investigated the cost computations underlying co-efficient decisions. We report a series of experiments that tested the hypothesis that people compute the joint costs of a cooperative action sequence by summing the individual action costs of their co-actor and themselves. We independently manipulated the parameters quantifying individual and joint action costs and tested their effects on decision-making by fitting and comparing Bayesian logistic regression models. Our hypothesis was confirmed: people weighed their own and their partner’s costs similarly to estimate the joint action costs as the sum of the two individual parameters. Participants minimized the aggregate cost to ensure co-efficiency. The results provide empirical support for behavioral economics and computational approaches that formalize cooperation as joint utility maximization based on a weighted sum of individual action costs.

The multimodal nature of communicative efficiency in social interaction

“…Taken together, these findings provide a novel unifying perspective on studies of language use [11][12][13] and nonlinguistic joint action [8][9][10] . The coordination of joint action minimally involves dynamically updated task representations, monitoring processes, and adjustable behaviors 69 .…”

“…Whether people are moving a couch or having a chat, joint action appears to be organized according to a principle of efficiency or effort minimization [3][4][5][6][7] . Empirical work on joint action shows that this effort minimization appears to target overall joint effort (or coefficiency) rather than individual effort [8][9][10] . Work on spoken language likewise suggests that people work together to minimize the cost for the dyad as a social unit-known as the principle of least collaborative effort [11][12][13] .…”

Infants expect agents to minimize the collective cost of collaborative actions

“…Several explanations may account for the 14-month-olds’ expectations of collective efficiency. In our view, the most plausible explanation is that infants assess the efficiency of a collective action by processing it as a complex action composed of sub-parts that are achieved by physically distinct effectors (Note, though, that adults’ collaborative actions tend to be also collectively efficient when they cannot be divided into components this way 46 ). This view is consistent with theories of team reasoning 47 – 50 , and shared-effort models 20 , and postulates that infants perform efficiency computation on the aggregate of the costs of the two agents’ actions.…”

What makes us act together? On the cognitive models supporting humans’ decisions for joint action

“…In the developmental psychology, utility models have been recently adopted to explain how infants and children understand, compare, and select individual actions in social contexts (Naive Utility Calculus model, Jara-Ettinger et al, 2016 , 2020 ; Liu et al, 2019 ; Bridgers et al, 2020 ; Lucca et al, 2020 ). Although little is known about whether and how adults represent the utility of joint actions, recent work demonstrated that when they are involved in coordinated joint actions with a partner, adults consistently prioritize joint efficiency over individual efficiency, i.e., individuals prefer task solutions that minimize the action costs for both co-actors ( Török et al, 2019 , 2021 ). While this suggests that individuals are capable of computing and comparing individual and joint utility, it is not clear whether individuals expect the same kinds of costs and rewards to be associated with the two action alternatives.…”