  Human and humanoid posture control models usually rely on single or multiple
degrees of freedom inverted pendulum representation of upright stance
associated with a feedback controller. In models typically focused on the
action between ankles, hips, and knees, the control of head position is often
neglected, and the head is considered one with the upper body. However, two of
the three main contributors to the human motion sensorium reside in the head:
the vestibular and the visual system. As the third contributor, the
proprioceptive system is distributed throughout the body. In human
neurodegenerative brain diseases of motor control, like Progressive
Supranuclear Palsy PSP and Idiopathic Parkinson's Disease IPD, clinical studies
have demonstrated the importance of head motion deficits. This work
specifically addresses the control of the head during a perturbed upright
stance. A control model for the neck is proposed following the hypothesis of a
modular posture control from previous studies. Data from human experiments are
used to fit the model and retrieve sets of parameters representative of the
behavior obtained in different conditions. The result of the analysis is
twofold: validate the model and its underlying hypothesis and provide a system
to assess the differences in posture control that can be used to identify the
differences between healthy subjects and patients with different conditions.
Implications for clinical pathology and application in humanoid and assistive
robotics are discussed.
