Spatial Orientation Modeling: Position-Motion Paradox in Hypergravity

Spatial orientation models are often used to predict perceived orientation under conditions of unusual acceleration experienced in the aerospace environment. Until 2014, the models were exclusively based upon vestibular modeling of the semicircular canals and otolith organs for angular and linear acceleration. Newman (2014) expanded the model by adding some basic visual components. A well-known visual-vestibular illusion is the oculogravic illusion in which an isolated object located in front of a subject appears to move upwards as the gravitoinertial force level is increased and the head is in a normal upright position. Much of the data for the vestibular portion of the model has been conducted on ground-based devices such as centrifuges. However, some experiments can only be carried out in-flight as in the case of examining the dynamics of the oculogravic illusion during head movements. Head movements performed in hypergravity on a centrifuge produce cross coupled Coriolis (CCC) effects that confound the perceptions. Tests using high speed aircraft (0.8 Mach) banking to create hypergravity (1.8 G) but with low angular velocity reduced the CCC effects below perceptual threshold. Subjects were flown at 0.87 Mach at various G levels maintained for several minutes (banked turns in KC-135 slowly ascending/descending to avoid jet wash). A consistent report across all subjects was the perceived upward illusionary motion of the faint light positioned directly in front of the subject with a slowly decreasing velocity but continuing vertical paradoxical motion after becoming “fixed in space”. Dynamic perceptions during head movements although not consistent, were never in the direction predicted by cross coupling. Several low-level mishaps have been attributed to this hypergravity or “g-excess effect”. Thus the time course and dynamics of this illusion are important from the perspective of. characterizing these illusions and will contribute to expanding the envelope of the model. We suggest that multisensory cueing techniques can be used to minimize the G-excess illusion and possibly resolve the issue of SD mishaps.