The somatosensory and vestibular interaction in human postural control

Tezin Türü: Doktora

Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Mühendislik Fakültesi, Mühendislik Bilimleri Bölümü, Türkiye

Tezin Onay Tarihi: 2015




Human upright posture is essential for people during daily activities. Upright posture is a skill, which is acquired before walking during the human development. Classically defined five senses (as the sense of kinesthesia is not included) are not enough to obtain this difficult and important skill. Thus, the humans need another group of senses; i.e., proprioception, vestibular sensor, joint receptors etc. to achieve the upright posture. In this thesis, two distinct stimulations were given to the subjects to identify the two different kinematic frames of reference. The first perturbation was above the vestibular threshold (high angular velocity) so gravity vertical has been expected to be the reference frame. The second stimulation was below the vestibular threshold thus, the somatosensory system has been proposed to dominate the postural behavior where the reference frame was hypothesized to be the platform normal. A tilt platform was developed and manufactured to check this hypothesis. The experiments were performed in complete darkness. We have shown that the subjects demonstrated a vestibular dominated postural behavior for the high frequency perturbation (kinematics data revealed that postural corrections were performed with respect to gravity vertical) whereas, subjects’ behavior for the low frequency perturbation presented a habitual postural sway-like behavior on the platform. The findings were mathematically modeled by using a 3-DoF inverted pendulum including vestibular and somatosensory dynamics (optimizing the system parameters), where joint control torque compensated for gravity vertical for the high frequency whereas, control strategy used for the low frequency depended on compensation for CoP deviations.