Recent studies indicate that cognitively intact individuals experience frequent rightward collisions while walking through narrow doorways. Such a directional bias has been attributed to an attentional bias in spatial perception. However, these studies did not investigate the involvement of any motor factor that could affect the directional bias in the body. In the present study, three experiments were conducted to quantify the impact of the leading foot when crossing a doorway threshold on the directional bias in the body midpoint when passing through the doorway. Participants walked through the perceived center of a relatively wide doorway. Measurements of the deviation of the upper-body midpoint from the center of the doorway demonstrated that the leading foot had a very strong influence on the directional bias. Some participants showed rightward deviation irrespective of which foot was used to step through the doorway (Experiment 1). However, a consistent rightward bias in the body was not observed in other experiments. Both the movement of one hand (Experiment 2) and covert visual attention to one side of the door (Experiment 3) caused contralateral deviation of the body. It is likely that the movement of the hand and a visual stimulus serve as an attentional cue and are effective to avoid neglect of the ipsilateral side; as a result, the body midpoint is deviated to the contralateral side. From these findings, we conclude that the directional bias in locomotor trajectories while passing through a doorway results from the combination of a motor factor, particularly the leading foot, and attentional/brain factors.

When individuals attempt to walk through the center of a doorway (i.e., spatial bisection), the body's midpoint at crossing can deviate from its true center. Such deviation could result from asymmetry in spatial cognition. However, previous studies failed to find a significant correlation between bisection performance during walking and that during line/spatial bisection. We investigated whether such failure would result from different effectors being used for bisection (i.e., body midpoint or finger/laser pointer). We also investigated whether the difference in an individual's eye dominance would affect the relationship. Thirty-two young adults (16 of them with right-eye dominance) participated. For a walking task, participants walked through the perceived center of a wide doorway. For a spatial bisection task, they observed the same doorway under two distance conditions (about 0.5 and 2 m) and aligned their body midpoint with the perceived center in the sagittal dimension. Both tasks were performed under three visual occlusion conditions (dominant eye, non-dominant eye, and no occlusion). The results showed that, for the spatial bisection task, occluding the dominant eye caused deviation of the bisected point to the contralateral side. However, for the walking task, such an effect was observed only in participants with a dominant right eye. Consequently, directional biases in both tasks were significantly correlated only for right-eye-dominant participants. These results suggest that, for right-eye-dominant individuals only, use of the same effector for both tasks showed a clear relationship between the two tasks. Possible explanations for these findings were discussed.