Phase-linking and the perceived motion during off-vertical axis rotation

Abstract

Human off-vertical axis rotation (OVAR) in the dark typically produces perceived motion about a cone, the amplitude of which changes as a function of frequency. This perception is commonly attributed to the fact that both the OVAR and the conical motion have a gravity vector that rotates about the subject. Little-known, however, is that this rotating-gravity explanation for perceived conical motion is inconsistent with basic observations about self-motion perception: (a) that the perceived vertical moves toward alignment with the gravito-inertial acceleration (GIA) and (b) that perceived translation arises from perceived linear acceleration, as derived from the portion of the GIA not associated with gravity. Mathematically proved in this article is the fact that during OVAR these properties imply mismatched phase of perceived tilt and translation, in contrast to the common perception of matched phases which correspond to conical motion with pivot at the bottom. This result demonstrates that an additional perceptual rule is required to explain perception in OVAR. This study investigates, both analytically and computationally, the phase relationship between tilt and translation at different stimulus rates-slow (45°/s) and fast (180°/s), and the three-dimensional shape of predicted perceived motion, under different sets of hypotheses about self-motion perception. We propose that for human motion perception, there is a phase-linking of tilt and translation movements to construct a perception of one's overall motion path. Alternative hypotheses to achieve the phase match were tested with three-dimensional computational models, comparing the output with published experimental reports. The best fit with experimental data was the hypothesis that the phase of perceived translation was linked to perceived tilt, while the perceived tilt was determined by the GIA. This hypothesis successfully predicted the bottom-pivot cone commonly reported and a reduced sense of tilt during fast OVAR. Similar considerations apply to the hilltop illusion often reported during horizontal linear oscillation. Known response properties of central neurons are consistent with this ability to phase-link translation with tilt. In addition, the competing "standard" model was mathematically proved to be unable to predict the bottom-pivot cone regardless of the values used for parameters in the model.

Asymmetries and three-dimensional features of vestibular cross-coupled stimuli illuminated through modeling

“…the percent of the 16 possible (4×4) in which a stimulus (head angular, head linear, body angular, body linear) was in the roll direction of cross-coupling in a yaw movement (NUP-to-RED, RED-to-NUP, NUP-to-LED, LED-to-NUP). For linear stimuli, rightward and leftward linear velocities were considered as being in the same direction as rightward and leftward roll, respectively, and similarly for forward and backward linear velocities and pitch, based upon evidence of linear-angular perceptual alignment [13]. …”

“…8], a nonlinearity that holds regardless of whether the angular velocities are of the centrifuge [8] or the head (confirmed though follow-up testing). In addition, perceptions of angular and linear motion affect each other in centrifuges [10, 12] and during off-vertical axis rotation [13]. In other words, there is evidence that a subject’s perception of angular motion may be affected by the linear stimulus, and vice versa.…”

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

“…This is important, since in the absence of vision, perception of vertical is altered by the changing gravito-inertial vector that results from any acceleration not aligned with the constant gravitational background force (i.e., the hilltop illusion) [14], [18], [19], [47]. In this study, no visual tilt is present in the visual input other than the visual tilt directly resulting from self-generated head tilts.…”

“…A switch from visual to vestibular dominance over control of the head is likely related to the slow response times of retinal slip detection involved in the optokinetic reflex (OKR) and the much faster vestibular-ocular reflex (VOR). 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].…”

Sensory conflict compared in microgravity, artificial gravity, motion sickness, and vestibular disorders1

“…The equations for the model are analogous to those previously developed for sinusoidal motion [27, 28]. The variables:…”