Biomedical subjects

K Jaggi-Schwarz

Publications and source records attributed to K Jaggi-Schwarz.

4 recordsLinked to original sources

PubMed2004

Direction specific error patterns during continuous tracking of the subjective visual vertical.

The aim of this study was to characterize the error pattern of continuously tracking the perceived earth-vertical during roll rotations from upright to right or left ear-down and from right or left ear-down to upright. We compared the tracking responses of two paradigms, which either continuously activated the otoliths organs alone (constant velocity tilt) or both the otolith organs and the semicircular canals (constant acceleration tilt). The tracking responses of the subjective visual vertical showed characteristic differences depending on starting position and tilt direction relative to gravity. The error patterns in the constant-velocity and constant-acceleration tilt paradigm were reversed. Estimations during tracking, when otolith information was continuously changing, were more precise compared to estimations following fast tilts to fixed roll tilt positions. We conclude that the central processing underlying these perceptual tracking responses requires, besides the otolith input, information from the vertical semicircular canals.

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PubMed2003

Reciprocal error behavior in estimated body position and subjective visual vertical.

This study investigated the reciprocal relation between estimation of body tilt and visual vertical by using self-controlled passive body tilts at constant velocity (slow tilts with no semicircular canal activation) or constant acceleration (rapid tilts with canal activation). In both conditions, the visual vertical was overestimated in the luminous line setting paradigm, whereas body tilt was underestimated in the position estimation paradigm. These errors were larger after slow than rapid tilts. During slow tilts, the range of actually reached positions was on average underestimated by about 25% with respect to the desired positions. Interestingly, there were no significant differences in the estimated positions for tilts in the roll and pitch plane. Most remarkably, in the range of +/-45 degrees the resulting means of position and luminous line setting errors of the velocity and acceleration paradigms as a function of the desired roll positions were close to zero. Furthermore, the resulting means of the two paradigms showed a high correlation in the tested range of +/-90 degrees. We conclude that: (a). the otoliths provide the main information for the spatial reference for both the estimation of body positions and the luminous line settings, at least in the range of about +/-45 degrees where the resulting mean errors between the two paradigms are close to zero, and (b). coactivation of semicircular canals improves the estimations.

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PubMed2003

Common reference system for estimation of the postural and subjective visual vertical.

When tilted subjects are asked to set a luminous line to the perceived earth-vertical in a dark surrounding, they systematically underestimate the true direction of earth-vertical at large tilt angles, a phenomenon first described by Aubert (A-phenomenon). At small tilt angles, subjects usually overestimate the direction of earth-vertical. Overestimation has been first reported by Müller, who termed the notion of E-phenomenon. Since these first reports, this rather remarkable error behavior has been studied extensively. The prevailing notion in most earlier studies was that the erroneous estimation of verticality results from otolith signals, which are thought to represent the major input for spatial orientation, and their interaction with somatosensory signals. To bring the subjects into tilted positions, most investigators used slow tilt velocities or waited for some time to prevent interaction with semicircular canal activity. Here, we tested the hypothesis that vestibular cues about self-orientation relative to gravity are most reliable when both the semicircular canals and the otolith organs are optimally activated. To compare the error behavior in estimations of the visual vertical and perceived body position, we used self-controlled passive tilts at constant velocity or acceleration.

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PubMed2000

Canal-otolith interactions after off-vertical axis rotations I. Spatial reorientation of horizontal vestibuloocular reflex.

We examined the three-dimensional (3-D) spatial orientation of postrotatory eye velocity after horizontal off-vertical axis rotations by varying the final body orientation with respect to gravity. Three rhesus monkeys were oriented in one of two positions before the onset of rotation: pitched 24 degrees nose-up or 90 degrees nose-up (supine) relative to the earth-horizontal plane and rotated at +/-60 degrees /s around the body-longitudinal axis. After 10 turns, the animals were stopped in 1 of 12 final positions separated by 30 degrees. An empirical analysis of the postrotatory responses showed that the resultant response plane remained space-invariant, i.e., accurately represented the actual head tilt plane at rotation stop. The alignment of the response vector with the spatial vertical was less complete. A complementary analysis, based on a 3-D model that implemented the spatial transformation and dynamic interaction of otolith and lateral semicircular canal signals, confirmed the empirical description of the spatial response. In addition, it allowed an estimation of the low-pass filter time constants in central otolith and semicircular canal pathways as well as the weighting ratio between direct and inertially transformed canal signals in the output. Our results support the hypothesis that the central vestibular system represents head velocity in gravity-centered coordinates by sensory integration of otolith and semicircular canal signals.

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