The time constant of the somatogravic illusion

Abstract

Humans perceive tilt when experiencing a sustained acceleration.This tilt illusion is commonly referred to as the somatogravic illusion. Although the physiological basis of the illusion seems to be well understood, the dynamic behavior is still subject to discussion. In this study the dynamic behavior of the illusion was modeled and the time constant was measured experimentally. Subjects were exposed to pure centripetal accelerations in the lateral direction and were asked to indicate their tilt percept by means of a joystick. Variable radius centrifugation during constant angular rotation was used to generate three different motion profrles. Results showed that the time constant of the somatogravic illusion is in the order of two seconds contradicting the high time constant found in fixed radius centrifugation studies. The model fit was not improved when using an otolith model sensitive to high frequency accelerations. Apart from the fundamental importance, these results also have practical consequences for the simulation of sustained accelerations in motion simulators.

Causal Inference in Multisensory Heading Estimation

“…In contrast, perceptions of translation resulting from inertial stimulation are consistent with segregation based on high-pass frequency filtering of otolith afferents (e.g., [49–54]): the high frequency component of the gravito-inertial acceleration is attributed to translation, whereas the low-frequency component is attributed to body tilt relative to gravity. The cut-off frequencies of the inertial high-pass filter [51, 53–57], and the visual low-pass filter [49] are estimated to be approximately 0.5Hz –although the exact value of the estimates varies between studies and individuals, from approximately 0.1 to 1Hz. The cut-off frequency indicates a boundary above or below which the output of a filter begins to be attenuated (for a low-pass and high-pass filter, respectively).…”

Perception of rotation, path, and heading in circular trajectories

“…Similarly, perceived linear velocity has also been shown to decay over time when the linear velocity is constant (Seidman 2008 ). In addition, prolonged linear acceleration in darkness is known to induce a feeling of tilt (i.e., somatogravic illusion, Guedry 1974 ; Merfeld et al 2001 ; Clement et al 2002 ; Correia Grácio et al 2013 ). This occurs because at low-frequency motions the response of the SCCs is attenuated, which impedes the separation of tilt and translation.…”

Moving in a Moving World: A Review on Vestibular Motion Sickness

“…The basic assumption is that gravity is the only know constant acceleration. Accordingly, segregation of the gravity vector from the inertial vector can be obtained by separation of the slow- and fast-changing component of the gravitoinertial acceleration with the first representing gravity and the second the inertial acceleration [frequency segregation hypothesis ( 89 – 91 )]. This estimate of the direction of gravity, considered by the brain highly reliable, is also combined with the perceived head rotation derived from the semicircular canals ( 49 , 92 ), and the agreement of both inputs is essential for a correct estimation of the head orientation in space ( 93 – 95 ).…”

“…The picture becomes clearer when recalling that the conflicts of the sensory mismatch theory are defined as a discrepancy between the brain expectation and the actual arrangement of sensory inputs ( 2 , 42 – 46 ). To understand how sensory inputs are processed during linear oscillation, one must take into account that the otolith signal is normally low pass filtered to separate the gravity vector, expected to undergo relatively slow variations in direction and the inertial component of the sensed gravitoinertial vector (frequency segregation hypothesis) ( 89 – 91 ). Accelerations during linear oscillations below a specific frequency are, therefore, added to gravity as the brain fails to identify them correctly and perceives an unexpected change of the gravity vector, unmatched by other sensory signals.…”