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The relationship between motion and posture was investigated from the kinematics of unconstrained head movements. Head movements for visual gazing exhibited an initial component whose amplitude does not exceed 20.3° for target eccentricity up to 120°. This component was truncated by subsequent corrective movements whose occurrence generally increases with target eccentricity, although with a large variability (R2 ≤ 0.46). The head is finally stabilized at 72% of target eccentricity (R2 ≥ 0.92). These results indicate that the final head posture can be achieved through a number of loosely-programmed kinematic variations. Based on these results, unconstrained head movements were simulated, within the context of application to posture prediction for estimation of the visual field.

Where is my head? Knowing head orientation in space is necessary to estimate the extent of the visual field in tasks requiring visual feedback such as driving or manual materials handling. Visually guided tasks are generally dependent on head and eye movements for visual acquisition of the target, and head movements are of significant importance when target eccentricity from the neutral reference point is large. The aim of the present work was to investigate head orientation in space in hand pointing tasks and to model the head response. Standing subjects were required to direct their gaze at one of three targets, equally distributed (vertically) in the sagittal plane. The task was performed while standing a) with the arms next to the body, b) holding a load in a static condition, c) aiming at targets with a heavy or light load held in the hands. Movements of the head and the body segments were recorded by the motion capture systems.