Postural strategy for two potential targets considering motor costs for postural stabilization and probabilistic information.

When an intended action has multiple potential goals, individuals should consider multiple possibilities about future events to react successfully. Previous studies on arm reaching using a "go-before-you-know" paradigm have found that hand trajectories under multiple potential targets were spatially averaged between targets and biased based on probabilistic information about the targets. Using a target-stepping task while standing, we recently observed that a pre-step posture was planned more advantageously for stepping to the target with higher motor costs for postural stabilization. The present study aimed to examine whether such a postural strategy would be selected when the probability of a potential target with higher motor costs to be selected as the true target was low. Fourteen participants (mean age 23.2±4.6 years) initiated stepping movements knowing only the probability of two potential targets and took a step onto a target revealed after step initiation. The results showed that the participants prepared their mediolateral posture state more advantageously to take a step onto the target with higher costs, even when it was selected with a lower probability. Pre-step postures were also affected by the probability information, although the effects were small. Our simulations demonstrated that the postural strategy prioritizing motor costs was mechanically beneficial for affording time to take a step toward the true target while maintaining an upright posture. These findings suggest that, when maintaining postural stability is critical, the central nervous system considers the motor costs for postural stabilization in addition to probability information under multiple potential targets.