Motion perceptions induced by off-vertical axis rotation (OVAR) at small angles of tilt

Abstract

Off-vertical axis rotation in darkness induces a perception of body motion which lasts as long as rotation continues. Perceived body motion is the combination of two simultaneous displacements. The most easily perceived is a translation without rotation along a conical path, at the frequency of the actual rotation. Meanwhile, the subjects feel as if they were always facing towards the same direction. The summit of the cone is generally below the head, from the waist to below the feet, and subjects have a sense of progression in the direction opposite to actual spinning. Some subjects feel, on the contrary, the summit of the cone above their heads, and the progression in the direction of spinning. Subjects also perceived another body motion, although it was faint for some of them. It consists of a rotation at low velocity in the same direction as progression along the cone. The axis of the cone is perceived as slowly rotating along a larger cone. These motion perceptions increase with tilt angle and rotation velocity. They probably result from the analysis by the Central Nervous System of the acceleration acting on the otoliths. The perceived trajectory would be reconstructed from estimates of gravity, and kinematic variables such as head translational acceleration and velocity, and head rotational velocity. The same variables would account for OVAR-induced nystagmus. Motion sickness would result from the impossibility of reconstructing a consistent body movement from most sets of values of these variables.

Verticality Perception During Off-Vertical Axis Rotation

“…Because of the tilted axis, head orientation changes continuously with respect to gravity, as the body alternates between roll and pitch tilt. In a recent study (Vingerhoets et al 2006), following up on earlier investigations by Denise et al (1988) and Guedry (1974), we showed that the initially veridical rotation percept during prolonged OVAR decays gradually (Fig. 2B) and that a percept of circular head translation against the actual direction of movement emerges concurrently (Fig.…”

“…In an earlier OVAR study, Denise et al (1988) reported that their subjects felt being in the nose-up position 0 to 50°before they actually reached this position, which indicates a perceptual phase lead. By contrast, as shown in Fig.…”

“…Mittelstaedt (1983) attributes this apparent disparity to the tendency to use the body axis as a partial reference for verticality judgments in the context of the SVV task, but not in the perception of body tilt. A possible indication that body-tilt percepts during OVAR may differ from SVV results comes from experiments from Denise et al (1988), who asked subjects to verbally estimate the cone angle during OVAR. Denise and coworkers reported that subjects perceived a cone angle greater than the actual tilt angle.…”

Tilt and translation motion perception during off-vertical axis rotation

“…Verbal reports of the perceived motion path were consistent across CW and CCW directions of rotation, and are therefore combined in Table 1. During OVAR at 10° tilt, all subjects reported the pattern of body motion previously described by Denise et al (1988): progression along a conical path while facing the same direction. For 20° tilt at 0.125 Hz, 79% of subjects continued to perceive a conical path.…”

“…A tilt angle of 10° was also tested during 0.125 Hz rotation, which allowed a direct comparison of our motion perception results with those previously obtained by Denise et al (1988).…”