Head movements produced during linear translations in unexpected directions

Abstract

Passive translation of the body in space elicits a complex combination of directionally-specific torques that are exerted on the neck. The inertial torques that are produced by linear translation are counteracted by linear vestibular and proprioceptive reflexes that maintain head stability. A novel experimental apparatus was used in this study to translate human subjects in a random and unpredictable direction in order to quantify the head's 3-D movement with respect to the direction of translation. Head movements were found to be produced in systematic patterns as a function of stimulus direction. Roll and yaw head movements were produced in proportion to the magnitude of the lateral component of the translation. Pitch head movements were proportionate to the magnitude of the fore-aft component of the translation. One surprising observation was that head movements produced during lateral translations were, on average, 17% smaller than those produced during fore-aft translations. This suggests that linear vestibular reflexes that stabilize the head may be directionally-specific and more active during lateral whole body translations.

Head Movements Evoked in Alert Rhesus Monkey by Vestibular Prosthesis Stimulation: Implications for Postural and Gaze Stabilization

“…Accordingly, our approach allowed the dissociation between input (i.e., semicircular canal activation) and output (neck motion) in a manner that is not possible using natural stimuli where extracting the vestibularly evoked motion depends on the biomechanical properties of the head/neck plant. Regardless of whether motion is transiently (e.g., [46]) or continually [8,11] applied. Here, electrical stimulation was applied via metal electrodes implanted within the labyrinth using an approach similar to that of recent studies by several groups [18,47,48].…”

Head Stabilization Shows Visual and Inertial Dependence During Passive Stimulation: Implications for Virtual Rehabilitation

“…Moreover, creating a VE that matches the actual testing room, as we have done in our experiment, has been shown to increase immersion and vection [51]. However, head stabilizing reflexes are directionally specific and lateral head movements are usually smaller than pitch head movements during A/P translation [5], which biased the response toward greater A/P head motion in this experiment. The effects of this bias diminished at the lowest frequency when and jerk were lowest, and as a result the gains of pitch, yaw, and roll were closer in magnitude.…”

“…The cutoff frequency of these sensory systems transitioning from visual to vestibular dominance has been reported to be in the bandwidth of 0.2-0.5 Hz [2], [19], [24], [34]. Another driving factor that may affect how important visual versus inertial inputs are for head stabilization relates to the visual system's ability to remain sensitive to constant velocity cues, while the vestibular system relies on velocity change, i.e., acceleration [5]. However, these systems are highly interdependent.…”