The present study was designed to investigate whether an intervention during which participants were involved in mental rotation (MR) of a foot stimulus would have immediate beneficial effects on postural stability (Experiment 1) and to confirm whether it was the involvement of MR of the foot, rather than simply viewing foot stimuli, that could improve postural stability (Experiment 2). Two different groups of participants ( in each group) performed MR intervention of foot stimuli in each of the two experiments. Pre- and postmeasurements of postural stability during unipedal and bipedal standing were made using a force plate for the intervention. Consistently, postural sway values for unipedal standing, but not for bipedal standing, were decreased immediately after the MR intervention using the foot stimuli. Such beneficial effects were not observed after the MR intervention using car stimuli (Experiment 1) or when participants observed the same foot stimuli during a simple reaction task (Experiment 2). These findings suggest that the MR intervention using the foot stimuli could contribute to improving postural stability, at least when it was measured immediately after the intervention, under a challenging standing condition (i.e., unipedal standing). 1. Introduction A mental rotation (MR) task using a visual stimulus of a pictured body part, typically a hand or foot, asks participants to judge whether the stimulus is the right or left hand/foot (i.e., laterality judgment). The time required for judging (i.e., reaction time) increased as the linear function of angle rotation [1, 2]. Even if a stimulus was presented with no rotation, the reaction time was delayed when participants kept their right hand behind their back so that the orientation of the hand was far from that of the stimulus [3]. The reaction time was nearly equivalent to the time of the actual body movement to the orientation of the stimulus; for example, the reaction time at 90 degrees is similar to the time it would actually take to move the hand 90 degrees [2]. Moreover, neuroimaging studies showed that the brain regions in the posterior parietal cortex and the precentral cortex, which are involved in motor planning [4, 5], were activated while performing the MR of body parts [6, 7]. Based on these findings, it has been generally considered that MR of a body part involves cognitive processes used for both motor imagery and motor execution [1, 2, 8]. The present study was designed to investigate with two experiments whether the intervention during which participants were involved in MR
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