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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

Comparison of individual adjustment errors in the SVV paradigm (squares) and the SHV paradigm (circles) during prolonged roll-tilt for two of the four roll-tilt conditions studied (panels A and B: 45RED; panels C and D: 90LED) in those six subjects (S1-S6) that completed both paradigms.All runs are plotted against time starting at time t0 seconds (t0s) and ending at time t300s (as shown in the inlet in panel A). Runs with significant exponential drift are presented with dark grey symbols, while those runs with non-significant exponential drift are shown in light grey. The solid black lines indicate the fit of the exponential decay function (Eq. 2).
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pone-0078079-g010: Comparison of individual adjustment errors in the SVV paradigm (squares) and the SHV paradigm (circles) during prolonged roll-tilt for two of the four roll-tilt conditions studied (panels A and B: 45RED; panels C and D: 90LED) in those six subjects (S1-S6) that completed both paradigms.All runs are plotted against time starting at time t0 seconds (t0s) and ending at time t300s (as shown in the inlet in panel A). Runs with significant exponential drift are presented with dark grey symbols, while those runs with non-significant exponential drift are shown in light grey. The solid black lines indicate the fit of the exponential decay function (Eq. 2).

Mentions: From the 24 runs obtained during prolonged roll-tilt, significant drift could be found in 15 (63%), with median absolute drift amplitudes ranging between 6.4 to 14.4° (see Figure 10). Error increases over time were noted in 6 runs (90LED and 45LED 1 each, 45RED and 90RED 2 each), while in the remaining 9 runs with significant drift adjustment errors decreased over time (90LED: 4, 45LED: 2, 45RED: 1, 90RED: 2). Median Tc of drift (using the exponential fit) for the four roll-tilted positions studied ranged between 66 and 879 seconds.


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)

Comparison of individual adjustment errors in the SVV paradigm (squares) and the SHV paradigm (circles) during prolonged roll-tilt for two of the four roll-tilt conditions studied (panels A and B: 45RED; panels C and D: 90LED) in those six subjects (S1-S6) that completed both paradigms.All runs are plotted against time starting at time t0 seconds (t0s) and ending at time t300s (as shown in the inlet in panel A). Runs with significant exponential drift are presented with dark grey symbols, while those runs with non-significant exponential drift are shown in light grey. The solid black lines indicate the fit of the exponential decay function (Eq. 2).
© Copyright Policy
Related In: Results  -  Collection

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

pone-0078079-g010: Comparison of individual adjustment errors in the SVV paradigm (squares) and the SHV paradigm (circles) during prolonged roll-tilt for two of the four roll-tilt conditions studied (panels A and B: 45RED; panels C and D: 90LED) in those six subjects (S1-S6) that completed both paradigms.All runs are plotted against time starting at time t0 seconds (t0s) and ending at time t300s (as shown in the inlet in panel A). Runs with significant exponential drift are presented with dark grey symbols, while those runs with non-significant exponential drift are shown in light grey. The solid black lines indicate the fit of the exponential decay function (Eq. 2).
Mentions: From the 24 runs obtained during prolonged roll-tilt, significant drift could be found in 15 (63%), with median absolute drift amplitudes ranging between 6.4 to 14.4° (see Figure 10). Error increases over time were noted in 6 runs (90LED and 45LED 1 each, 45RED and 90RED 2 each), while in the remaining 9 runs with significant drift adjustment errors decreased over time (90LED: 4, 45LED: 2, 45RED: 1, 90RED: 2). Median Tc of drift (using the exponential fit) for the four roll-tilted positions studied ranged between 66 and 879 seconds.

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