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Abstract:
During walking the behavior of the head and trunk are closely coupled. This becomes particularly clear while taking a turn. Here, we investigate this coupling during two phases of turning,
before and during. Before a turn people make anticipatory orientations of the head into the
direction of the turn. Previous research suggests that this anticipation occurs at a constant
distance before the curve for different walking speeds. However, in most studies participants
only performed 90 turns. We tested whether anticipation distance is invariant across different
turn angles. As the turn progresses the head continues to look further into the turn than the
trunk, and slowly converging towards the end of turn. An additional question here is the dependence
of relative yaw between head and trunk on the turn angle. To answer these questions
we measured head-trunk angles across a range of different turn angles. Participants followed
predefined paths around obstacles with the radius of turn indicated by circles drawn on the
floor. Turning angles ranged from 45 to 180 in steps of 45. The position and orientation of
both the head and trunk were measured using an optical tracking system. Two parameters were
calculated from the data: head anticipation and maximum relative yaw. Head anticipation is the
distance in space where the head starts to look into the upcoming turn. Maximum relative yaw
is the maximum difference occurring between the yaw angle of the head and the trunk during
a turn. Both head anticipation and maximum relative yaw increased with turn angle, although
maximum relative yaw leveled off after 135. In a second experiment, participants followed
the same paths as in Experiment 1, but were not constrained in the turn radius. Results showed
that turn radius decreased with increasing turn angle. Nevertheless, we found the same pattern
of results as in Experiment 1. In conclusion, the relation between head and trunk both before
and during a turn is dependent on the angle of turn one is about to make.
