AUTHOR=Tarnutzer Alexander Andrea , Duarte da Costa Vasco , Baumann Denise , Hemm Simone 

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

JOURNAL=Frontiers in Neurology

VOLUME=Volume 13 - 2022

YEAR=2022

URL=https://www.frontiersin.org/journals/neurology/articles/10.3389/fneur.2022.868144

DOI=10.3389/fneur.2022.868144

ISSN=1664-2295

ABSTRACT=Background: After prolonged static whole-body roll-tilt a significant bias of internal estimates of 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 prolonged roll-tilt to either side perceived straight-ahead will be biased as well. 
Methods: Twenty-five healthy participants were asked to rest in three different lying positions (supine, right-ear-down, left-ear-down) for five minutes (“adaptation period”) prior to walking straight-ahead blindfolded for two minutes. Walking was recorded with inertial measurement unit sensors attached to different body locations and with sensor shoe insoles. Raw data was segmented with a gait-event detection method. 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 ob-served in the post-adaptation trials. This bias was identified in both measurement systems and de-creased again over the two-minute walking period.
Conclusions: The bias observed further confirms the influence of prior knowledge on spatial ori-entation 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 not optimally tuned internal estimates of direction of gravity and direction of straight-ahead.