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Mark Mon-Williams, Sinead Sheehan, Andrew D. Wilson, Geoffrey P. Bingham; Head-torso coordination and overt shifts in attention. Journal of Vision 2009;9(8):837. doi: 10.1167/9.8.837.
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Background. Overt attention shifts are made through eye, head, and torso rotations or some combination thereof. Many studies have explored eye-head coordination but relatively few studies have investigated head-torso coordination. We explored head-torso coordination using a looking and pointing task. Head-torso coordination involves complex dynamics and we hypothesised that the coordinative behaviour would demonstrate hysteresis (where history influences behaviour) in common with most complex systems.
Methods. Eight right-handed adults sat in a swivel chair and both looked and pointed eight times over a 180° range to eighteen different locations in 10° increments right and left of midline (conditions counter-balanced, target locations randomised). Optoelectronic apparatus recorded head, torso, and hand movements. The positional data were subsequently filtered and differentiated to provide detailed kinematic profiles.
Results. (1) The head, torso, and hand speed profiles unfolded within a common time window enveloped by the head movement duration. Head peak speed had a linear relationship with target angle. Movement time also had a linear relationship with target angle until a plateau around 60°. (2) Even small gaze shifts (10° from the midline) involved changes in head position, which contrasts with previous studies reporting that small gaze shifts only involve the eyes. Whilst participants sometimes pointed at targets on the right hand side without torso rotation, the number of trials with torso rotation increased linearly with angle. There were twice as many trials with torso rotation to the right side targets in the pointing condition when compared to the looking condition.
Conclusion. A reliable relationship exists between speed and amplitude in head movements. A flexible task dependent coordinative relationship exists between the head, torso, and hand. The coordinative relationship cannot be predicted simply from the task - it is necessary to know the history of the system. Thus, the head-torso system exhibits hysteresis as hypothesised.
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