Postural Perceptions and Eye Displacements During the Variation of A Force Field Acting in the Mid-Frontal Plane

Abstract

Applying a previously described centrifuge-test method, the changes of position in space along three axes of an observed target in an otherwise dark room were recorded. Ten subjects were positioned heading forwards (HF) with their left sides to the centre of the centrifuge. In order to separate directional and magnitudinal factors inherent in the produced force field, the procedure was repeated with the same subject in three positions of tilt in the frontal plane (erect = HF 0° tilt; tilted 50° inwards = HF 50° inw.; tilted 50° outwards = HF 50° outw.). Using an infrared (IR) technique, one eye was filmed, and its torsional position evaluated concurrently along the same three axes, simultaneously with the subjective data recorded. The increase in the angle formed between resultant force and physical vertical (angle Φ) generally produced an apparent clockwise rotation of the phenomenal horizontal in the two positions HF 50° inw. and HF 0° tilt, in a clear positive relation to the relative direction and also to the magnitude of the force field. The great uncertainty of reports in position HF 50° outw. did not permit the same conclusions. Simultaneously, a countertorsion of the eye was detected around its line of sight, in the opposite direction to the initial tilt and to the angular displacement of the horizontal. The amount of countertorsion was much inferior in size to the angle of tilt and to the subjective phenomenon, and—at least in the erect and inward tilted positions—in a definite relation to both directional and magnitudinal factors. Certain discrepancies in the patterns of subjective and ocular response registered both in the rolling plane (Z axis) and along the two other axes investigated (X and Y) suggest that the two types of response may be distinctly separated reactions to the same mechanical stimulus.