Directional bias in the body while walking through a doorway: its association with attentional and motor factors.

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.