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Modulation of internal estimates of gravity during and after prolonged roll-tilts.

Tarnutzer AA, Bertolini G, Bockisch CJ, Straumann D, Marti S - PLoS ONE (2013)

Bottom Line: At ± 90° roll-tilt significant increases in absolute adjustment errors were more likely (76%), whereas significant increases (56%) and decreases (44%) were about equally frequent at ± 45°.No significant correlations were found between the drift pattern during and immediately after prolonged roll-tilt.We conclude that the SVV is not stable during and after prolonged roll-tilt and that the direction and magnitude of drift are individually distinct and roll-angle-dependent.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurology, University Hospital Zurich, Zurich, Switzerland.

ABSTRACT
Perceived direction of gravity, as assessed by the subjective visual vertical (SVV), shows roll-angle dependent errors that drift over time and a bias upon return to upright. According to Bayesian observer theory, the estimated direction of gravity is derived from the posterior probability distribution by combining sensory input and prior knowledge about earth-vertical in a statistically optimal fashion. Here we aimed to further characterize the stability of SVV during and after prolonged roll-tilts. Specifically we asked whether the post-tilt bias is related to the drift pattern while roll-tilted. Twenty-nine healthy human subjects (23-56 yo) repetitively adjusted a luminous arrow to the SVV over periods of 5 min while upright, roll-tilted (± 45°, ± 90°), and immediately after returning to upright. Significant (p<0.05) drifts (median absolute drift-amplitude: 10°/5 min) were found in 71% (± 45°) and 78% (± 90°) of runs. At ± 90° roll-tilt significant increases in absolute adjustment errors were more likely (76%), whereas significant increases (56%) and decreases (44%) were about equally frequent at ± 45°. When returning to upright, an initial bias towards the previous roll-position followed by significant exponential decay (median time-constant: 71 sec) was noted in 47% of all runs (all subjects pooled). No significant correlations were found between the drift pattern during and immediately after prolonged roll-tilt. We conclude that the SVV is not stable during and after prolonged roll-tilt and that the direction and magnitude of drift are individually distinct and roll-angle-dependent. Likely sensory and central adaptation and random-walk processes contribute to drift while roll-tilted. Lack of correlation between the drift and the post-tilt bias suggests that it is not the inaccuracy of the SVV estimate while tilted that determines post-tilt bias, but rather the previous head-roll orientation relative to gravity. We therefore favor central adaptation, most likely a shift in prior knowledge towards the previous roll orientation, to explain the post-tilt bias.

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Related in: MedlinePlus

SVV adjustments (filled grey circles) relative to true earth-vertical are plotted against time in a single subject (GB) while roll-tilted (trials interconnected with a grey line) and upon return to upright (trials interconnected with a black line).Baseline recordings (trials interconnected with a black line) of SVV beforehand are shown for comparison. Schematic drawings above the data sets illustrate the subject’s roll orientation as seen from behind. The dashed vertical lines separate sequences with distinct whole-body roll orientations. The dotted horizontal lines indicate true earth-vertical.
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pone-0078079-g001: SVV adjustments (filled grey circles) relative to true earth-vertical are plotted against time in a single subject (GB) while roll-tilted (trials interconnected with a grey line) and upon return to upright (trials interconnected with a black line).Baseline recordings (trials interconnected with a black line) of SVV beforehand are shown for comparison. Schematic drawings above the data sets illustrate the subject’s roll orientation as seen from behind. The dashed vertical lines separate sequences with distinct whole-body roll orientations. The dotted horizontal lines indicate true earth-vertical.

Mentions: A median of 55 trials (± 3; one MAD) was completed within the five-minute recording periods over the entire study population. Figure 1 illustrates drift of the SVV adjustments (raw data) at baseline, while roll-tilted and immediately upon return to upright position in a typical subject. When pooling the SVV data from all subjects, median drift amplitudes were small (see Table 1 for exact numbers) and not significantly different from zero (non-parametric signtest.m, p>0.05) at either ±45° or ±90°, i.e., SVV settings remained stable over time at the group level (Figure 2) during prolonged static roll.


Modulation of internal estimates of gravity during and after prolonged roll-tilts.

Tarnutzer AA, Bertolini G, Bockisch CJ, Straumann D, Marti S - PLoS ONE (2013)

SVV adjustments (filled grey circles) relative to true earth-vertical are plotted against time in a single subject (GB) while roll-tilted (trials interconnected with a grey line) and upon return to upright (trials interconnected with a black line).Baseline recordings (trials interconnected with a black line) of SVV beforehand are shown for comparison. Schematic drawings above the data sets illustrate the subject’s roll orientation as seen from behind. The dashed vertical lines separate sequences with distinct whole-body roll orientations. The dotted horizontal lines indicate true earth-vertical.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3815095&req=5

pone-0078079-g001: SVV adjustments (filled grey circles) relative to true earth-vertical are plotted against time in a single subject (GB) while roll-tilted (trials interconnected with a grey line) and upon return to upright (trials interconnected with a black line).Baseline recordings (trials interconnected with a black line) of SVV beforehand are shown for comparison. Schematic drawings above the data sets illustrate the subject’s roll orientation as seen from behind. The dashed vertical lines separate sequences with distinct whole-body roll orientations. The dotted horizontal lines indicate true earth-vertical.
Mentions: A median of 55 trials (± 3; one MAD) was completed within the five-minute recording periods over the entire study population. Figure 1 illustrates drift of the SVV adjustments (raw data) at baseline, while roll-tilted and immediately upon return to upright position in a typical subject. When pooling the SVV data from all subjects, median drift amplitudes were small (see Table 1 for exact numbers) and not significantly different from zero (non-parametric signtest.m, p>0.05) at either ±45° or ±90°, i.e., SVV settings remained stable over time at the group level (Figure 2) during prolonged static roll.

Bottom Line: At ± 90° roll-tilt significant increases in absolute adjustment errors were more likely (76%), whereas significant increases (56%) and decreases (44%) were about equally frequent at ± 45°.No significant correlations were found between the drift pattern during and immediately after prolonged roll-tilt.We conclude that the SVV is not stable during and after prolonged roll-tilt and that the direction and magnitude of drift are individually distinct and roll-angle-dependent.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurology, University Hospital Zurich, Zurich, Switzerland.

ABSTRACT
Perceived direction of gravity, as assessed by the subjective visual vertical (SVV), shows roll-angle dependent errors that drift over time and a bias upon return to upright. According to Bayesian observer theory, the estimated direction of gravity is derived from the posterior probability distribution by combining sensory input and prior knowledge about earth-vertical in a statistically optimal fashion. Here we aimed to further characterize the stability of SVV during and after prolonged roll-tilts. Specifically we asked whether the post-tilt bias is related to the drift pattern while roll-tilted. Twenty-nine healthy human subjects (23-56 yo) repetitively adjusted a luminous arrow to the SVV over periods of 5 min while upright, roll-tilted (± 45°, ± 90°), and immediately after returning to upright. Significant (p<0.05) drifts (median absolute drift-amplitude: 10°/5 min) were found in 71% (± 45°) and 78% (± 90°) of runs. At ± 90° roll-tilt significant increases in absolute adjustment errors were more likely (76%), whereas significant increases (56%) and decreases (44%) were about equally frequent at ± 45°. When returning to upright, an initial bias towards the previous roll-position followed by significant exponential decay (median time-constant: 71 sec) was noted in 47% of all runs (all subjects pooled). No significant correlations were found between the drift pattern during and immediately after prolonged roll-tilt. We conclude that the SVV is not stable during and after prolonged roll-tilt and that the direction and magnitude of drift are individually distinct and roll-angle-dependent. Likely sensory and central adaptation and random-walk processes contribute to drift while roll-tilted. Lack of correlation between the drift and the post-tilt bias suggests that it is not the inaccuracy of the SVV estimate while tilted that determines post-tilt bias, but rather the previous head-roll orientation relative to gravity. We therefore favor central adaptation, most likely a shift in prior knowledge towards the previous roll orientation, to explain the post-tilt bias.

Show MeSH
Related in: MedlinePlus