Do walkers follow their heads? Investigating the role of head rotation in locomotor control.

Eye and head rotations are normally correlated with changes in walking direction; however, it is unknown whether they play a causal role in the control of steering. The objective of the present study was to answer two questions about the role of head rotations in steering control when walking to a goal. First, are head rotations sufficient to elicit a change in walking direction? Second, are head rotations necessary to initiate a change in walking direction or guide steering to a goal? To answer these questions, participants either walked toward a goal located 7 m away or were cued to steer to the left or right by 37°. On a subset of trials, participants were either cued to voluntarily turn their heads to the left or right, or they underwent an involuntary head perturbation via a head-mounted air jet. The results showed that large voluntary head turns (35°) yielded slight path deviations (1°-2°) in the same or opposite direction as the head turn, depending on conditions, which have alternative explanations. Involuntary head rotations did not elicit path deviations despite comparable head rotation magnitudes. In addition, the walking trajectory when turning toward an eccentric goal was the same regardless of head orientation. Steering can thus be decoupled from head rotation during walking. We conclude that head rotations are neither a sufficient nor a necessary component of steering control, because they do not induce a turn and they are not required to initiate a turn or to guide the locomotor trajectory to a goal.