Heading Direction Is Significantly Biased by Preceding Whole-Body Roll-Orientation While Lying

Alexander Andrea Tarnutzer; Vasco Duarte da Costa; Denise Baumann; Simone Hemm

doi:10.3389/fneur.2022.868144

Heading Direction Is Significantly Biased by Preceding Whole-Body Roll-Orientation While Lying

Front Neurol. 2022 Apr 18:13:868144. doi: 10.3389/fneur.2022.868144. eCollection 2022.

Authors

Alexander Andrea Tarnutzer^{1

2}, Vasco Duarte da Costa³, Denise Baumann³, Simone Hemm³

Affiliations

¹ Department of Neurology, Cantonal Hospital of Baden, Baden, Switzerland.
² Faculty of Medicine, University of Zurich, Zurich, Switzerland.
³ School of Life Sciences, Institute for Medical Engineering and Medical Informatics, University of Applied Sciences and Arts Northwestern Switzerland, Muttenz, Switzerland.

Abstract

Background: After a prolonged static whole-body roll-tilt, a significant bias of the internal estimates of the direction of gravity has been observed when assessing the subjective visual vertical.

Objective: We hypothesized that this post-tilt bias represents a more general phenomenon, broadly affecting spatial orientation and navigation. Specifically, we predicted that after the prolonged roll-tilt to either side perceived straight-ahead would also be biased.

Methods: Twenty-five healthy participants were asked to rest in three different lying positions (supine, right-ear-down, and left-ear-down) for 5 min ("adaptation period") prior to walking straight-ahead blindfolded for 2 min. Walking was recorded with the inertial measurement unit sensors attached to different body locations and with sensor shoe insoles. The raw data was segmented with a gait-event detection method. The Heading direction was determined and linear mixed-effects models were used for statistical analyses.

Results: A significant bias in heading into the direction of the previous roll-tilt position was observed in the post-adaptation trials. This bias was identified in both measurement systems and decreased again over the 2-min walking period.

Conclusions: The bias observed further confirms the influence of prior knowledge on spatial orientation and navigation. Specifically, it underlines the broad impact of a shifting internal estimate of direction of gravity over a range of distinct paradigms, illustrating similar decay time constants. In the broader context, the observed bias in perceived straight-ahead emphasizes that getting up in the morning after a good night's sleep is a vulnerable period, with an increased risk of falls and fall-related injuries due to non-availability of optimally tuned internal estimates of the direction of gravity and the direction of straight-ahead.

Keywords: inertial measurement unit; perceived straight-ahead; post-tilt bias; prior knowledge; sensor shoe insoles; spatial orientation and navigation.