Fig. 9.

Minimum-rotation strategy observed during the head-gaze dissociation task. A, Head facing upward targets. B, Head facing forward targets.C, Head facing downward targets. Eachpanel shows two oppositely elongated (one upward and one downward) angular velocity loops, for one leftward and one rightward head movement, respectively. Each point along these loops defines the instantaneous axis and speed of head rotation, as a vector emanating from the origin. Vectors pointing rightward (i.e., forward for the subject) show the facing direction of the head during the rightward (hatched line) and leftward (dotted line) movements. Corresponding vertical linesshow the perpendiculars to these facing vectors, which aligned closely with the angular velocity loops. Thus, as indicated by thecaricatures, the vertical axis of head rotation remained orthogonal to head-facing direction, in contrast to the space-fixed vertical axes observed during normal random gaze shifts.