Timing and distance characteristics of interpersonal coordination during locomotion.

Most studies about human locomotion only tend to consider single subjects walking alone in a stationary environment. Nevertheless, human subjects have often to plan and generate their locomotor trajectories according to one another's displacements. Therefore, in the present study we address the question of the interpersonal coordination when pairs of subjects walk simultaneously. Six pairs of subjects walking face to face, backwards and forwards on a 8 m x 2 m track were involved in our experiment. Within each pair, the leader (L) was required to break the initial interpersonal distance whereas the follower (F) had to maintain this distance constant (1, 2 or 3 m). We measured their position and analyzed their travelled distance, the time course of their linear displacement, and the kinematics parameters of their steps. Our results show that F travels smaller distances than L and that even if they are highly correlated, some temporal delays exist between displacements of L and F with greater values when the interpersonal distance increases (from 1 to 3 m). These results are discussed in terms of high level imitation, i.e. bidirectional interactions with mutual influences of each subject on one another.