Frontiers in Neurology

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

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

Department of Neurology, Cantonal Hospital of Baden, Baden


prior knowledge, spatial orientation and navigation, post-tilt bias, perceived straight-ahead, inertial measurement unit, sensor shoe insoles


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.

Moticon's Summary

In this study researchers aimed to investigate post-tilt bias, which is a bias affecting the graviception of the human body following a prolonged whole-body roll-tilt. Patients were instructed to rest in different lying positions and subsequently performed a blindfolded 2 min walking task to assess directional bias. IMUs and Moticon sensor insoles were employed for data collection. The investigators found a bias of heading in the direction of the previous roll-tilt position.

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