ABSTRACT
We studied the contribution of vestibular and somatosensory/proprioceptive stimulation to the perception of the apparent zenith (AZ). Experiment 1 involved rotation on a centrifuge and settings of the AZ. Subjects were supine on the centrifuge, and their body position was varied in relation to the rotation axis so that the gravitoinertial resultant force at the otoliths was 1 or 1.2 g with the otolith organs positioned 50 or 100 cm from the axis of rotation. Their legs were also positioned in different configurations, flexed and elevated or extended, to create different distributions of blood and lymph. Experiment 2 involved (a) settings of the AZ for subjects positioned supine with legs fully extended or legs flexed and elevated to create a torsoward shift of blood and (b) settings of the subjective visual vertical for subjects horizontally positioned on their sides with legs extended or bent. Experiment 3 had subjects in the same body configurations as in Experiment 2 indicate when they were horizontal as they were rotated in pitch or roll about an inter-aural or naso-occipital axis. The experimental results for all three experiments demonstrated that both visual localization and apparent body horizontal are jointly determined by multimodal combinations of otolithic and somatosensory/proprioceptive stimulation. No evidence was found for non-overlapping or exclusive mechanisms determining one or the other. The subjective postural horizontal and AZ were affected in similar ways by comparable manipulations.
Subject(s)
Gravitation , Touch/physiology , Acceleration , Adult , Centrifugation , Cues , Data Interpretation, Statistical , Female , Humans , Leg/physiology , Male , Orientation/physiology , Otolithic Membrane/physiology , Photic Stimulation , Physical Stimulation , Proprioception/physiology , Rotation , Supine Position/physiology , Young AdultABSTRACT
The present paper aims at critically reviewing the most outstanding and recent studies regarding the control of body orientation in the vertical space. A first part defines the general concepts used throughout this manuscript. The second part investigates the vertical perception and the main factors which affect it, while trying to overcome the five areas of theoretical and experimental controversies we have identified in the literature. The third part of this review presents the different theoretical models of the vertical perception and body orientation in space. Finally, the last part focuses on the functional coupling between perception of the vertical and orientation of the body in space. It considers more particularly how these two dimensions interact for explaining the observed behaviors.