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Gravity-dependence of subjective visual vertical variability - Zurich Open Repository and Archive


Tarnutzer, A A; Bockisch, C J; Straumann, D; Olasagasti, I (2009). Gravity-dependence of subjective visual vertical variability. Journal of Neurophysiology, 102(3):1657-1671.

Abstract

The brain integrates sensory input from the otolith organs, the semicircular canals, and the somatosensory and visual systems to determine self-orientation relative to gravity. Only the otoliths directly sense the gravito-inertial force vector and therefore provide the major input for perceiving static head-roll relative to gravity, as measured by the subjective visual vertical (SVV). Intra-individual SVV variability increases with head roll, which suggests that the effectiveness of the otolith signal is roll-angle dependent. We asked whether SVV variability reflects the spatial distribution of the otolithic sensors and the otolith-derived acceleration estimate. Subjects were placed in different roll orientations (0 to 360 degrees , 15 degrees steps) and asked to align an arrow with perceived vertical. Variability was minimal in upright, increased with head-roll peaking around 120-135 degrees , and decreased to intermediate values at 180 degrees . Otolith-dependent variability was modeled by taking into consideration the non-uniform distribution of the otolith afferents and their non-linear firing rate. The otolith-derived estimate was combined with an internal bias shifting the estimated gravity-vector towards the body-longitudinal. Assuming an efficient otolith estimator at all roll angles, peak variability of the model matched our data; however, modeled variability in upside-down and in upright position was very similar, which is at odds with our findings. By decreasing the effectiveness of the otolith estimator with increasing roll, simulated variability matched our experimental findings better. We suggest that modulations of SVV precision in the roll plane are related to the properties of the otolith sensors, and to central computational mechanisms that are not optimally tuned for roll-angles distant from upright.

Abstract

The brain integrates sensory input from the otolith organs, the semicircular canals, and the somatosensory and visual systems to determine self-orientation relative to gravity. Only the otoliths directly sense the gravito-inertial force vector and therefore provide the major input for perceiving static head-roll relative to gravity, as measured by the subjective visual vertical (SVV). Intra-individual SVV variability increases with head roll, which suggests that the effectiveness of the otolith signal is roll-angle dependent. We asked whether SVV variability reflects the spatial distribution of the otolithic sensors and the otolith-derived acceleration estimate. Subjects were placed in different roll orientations (0 to 360 degrees , 15 degrees steps) and asked to align an arrow with perceived vertical. Variability was minimal in upright, increased with head-roll peaking around 120-135 degrees , and decreased to intermediate values at 180 degrees . Otolith-dependent variability was modeled by taking into consideration the non-uniform distribution of the otolith afferents and their non-linear firing rate. The otolith-derived estimate was combined with an internal bias shifting the estimated gravity-vector towards the body-longitudinal. Assuming an efficient otolith estimator at all roll angles, peak variability of the model matched our data; however, modeled variability in upside-down and in upright position was very similar, which is at odds with our findings. By decreasing the effectiveness of the otolith estimator with increasing roll, simulated variability matched our experimental findings better. We suggest that modulations of SVV precision in the roll plane are related to the properties of the otolith sensors, and to central computational mechanisms that are not optimally tuned for roll-angles distant from upright.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:04 Faculty of Medicine > University Hospital Zurich > Clinic for Otorhinolaryngology
04 Faculty of Medicine > University Hospital Zurich > Ophthalmology Clinic
04 Faculty of Medicine > Neuroscience Center Zurich
04 Faculty of Medicine > Center for Integrative Human Physiology
04 Faculty of Medicine > University Hospital Zurich > Clinic for Neurology
Dewey Decimal Classification:570 Life sciences; biology
610 Medicine & health
Language:English
Date:1 September 2009
Deposited On:14 Jul 2009 15:54
Last Modified:28 May 2017 20:46
Publisher:American Physiological Society
ISSN:0022-3077
Publisher DOI:https://doi.org/10.1152/jn.00007.2008
PubMed ID:19571203

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