Choosing among different options typically entails weighing their anticipated costs and benefits. Previous research has predominantly focused on situations, where the costs and benefits of choices are known before an action is effectuated. Yet many decisions in daily life are made on the fly, for instance, making a snack choice while walking through the grocery store. Notably, the costs of actions change dynamically while moving. Therefore, in this study we examined whether the concurrent action dynamics of gait form part of and affect value-based decisions. In three experiments, participants had to decide which lateral (left vs. right) target (associated with different rewards) they would go to, while they were already walking. Results showed that the target choice was biased by the alternating stepping behavior, even at the expense of receiving less reward. These findings provide evidence that whole-body action dynamics affect value-based decisions.

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A main objective in bipedal walking is controlling the whole body to stay upright. One strategy that promotes this objective is to direct the ground reaction forces (GRFs) to a point above the center of mass (COM). In humans, such force patterns can be observed for unperturbed walking, but it is not known whether the same strategy is used for a walkway that changes in height. In this study, 11 volunteers stepped down off a visible (0, 10 and 20 cm) and a camouflaged (0 or 10 cm) curb while walking at two different speeds (1.2±0.1 and 1.7±0.1 m s −1). The results showed that in all conditions the GRFs pointed predominantly above the COM. Vectors directed from the center of pressure (COP) to the intersection point (IP) closely fitted the measured GRF direction not only in visible conditions (R 2 >97.5%) but also in camouflaged curb negotiation (R 2 >89.8%). Additional analysis of variables included in the calculation of the IP location showed considerable differences for the camouflaged curb negotiation: compared with level walking, the COP shifted posterior relative to the COM and the vertical GRFs were higher in the beginning and lower in later parts of the stance phase of the perturbed contact. The results suggest that IP behavior can be observed for both visible and camouflaged curb negotiation. For further regulation of the whole-body angle, the asymmetrical vertical GRFs could counteract the effect of a posterior shifted step.

Research on embodied decision-making only recently started to examine whether and how concurrent actions influence value-based decisions. For instance, during walking humans preferably make decisions that align with a turn towards the side of their current swing leg, sometimes resulting in unfavorable choices (e.g., less rewards). It is suggested that concurrent movements influence decision-making by coincidental changes in motor costs. If true, systematic manipulations of motor costs should bias decisions. To test this, participants had to accumulate rewards (i.e., points) by walking and turning towards left and right targets displaying rewards across three experiments. In Exp. 1a and 1b, we manipulated turning cost based on the current swing leg by applying different symmetrical turning magnitudes (i.e., same angles for left and right targets). In Exp. 2, we manipulated the turning cost by administering asymmetrical turning magnitudes (i.e., different angles for left and right targets). Finally, in Exp. 3, we increased the cost of walking by adding ankle weights. Altogether, the experiments support the claim that differences in motor costs influenced participants' decisions: Exp. 1a and 1b revealed that the swing leg effect and stepping behavior was moderated by turning magnitude. In Exp. 2, participants showed a preference for less costly, smaller turning magnitudes. Exp. 3 replicated the swing leg effect when motor costs were increased by means of ankle weights. In conclusion, these findings provide further evidence that value-based decisions during ongoing actions seem to be influenced by dynamically changing motor costs, thereby supporting the concept of 'embodied decision-making'.

In everyday life, action and decision-making often run in parallel. Action-based models argue that action and decision-making strongly interact and, more specifically, that action can bias decision-making. This embodied decision bias is thought to originate from changes in motor costs and/or cognitive crosstalk. Recent research confirmed embodied decision biases for different tasks including walking and manual movements. Yet, whether such biases generalize within individuals across different tasks remains to be determined. To test this, we used two different decision-making tasks that have independently been shown to reliably produce embodied decision biases. In a within-participant design, participants performed two tasks in a counterbalanced fashion: (i) a walking paradigm for which it is known that motor costs systematically influence reward decisions, and (ii) a manual movement task in which motor costs and cognitive crosstalk have been shown to impact reward decisions. In both tasks, we successfully replicated the predicted embodied decision biases. However, there was no evidence that the strength of the biases correlated between tasks. Hence, our findings do not confirm that embodied decision biases transfer between tasks. Future research is needed to examine whether this lack of transfer may be due to different causes underlying the impact of motor costs on decisions and the impact of cognitive crosstalk or task-specific differences.