Systematic biases in human heading estimation.

Heading estimation is vital to everyday navigation and locomotion.
Despite extensive behavioral and physiological research on both
visual and vestibular heading estimation over more than two
decades, the accuracy of heading estimation has not yet been
systematically evaluated. Therefore human visual and vestibular
heading estimation was assessed in the horizontal plane using a
motion platform and stereo visual display. Heading angle was
overestimated during forward movements and underestimated during
backward movements in response to both visual and vestibular
stimuli, indicating an overall multimodal bias toward lateral
directions. Lateral biases are consistent with the
overrepresentation of lateral preferred directions observed in
neural populations that carry visual and vestibular heading
information, including MSTd and otolith afferent populations. Due
to this overrepresentation, population vector decoding yields
patterns of bias remarkably similar to those observed behaviorally.
Lateral biases are inconsistent with standard bayesian accounts
which predict that estimates should be biased toward the most
common straight forward heading direction. Nevertheless, lateral
biases may be functionally relevant. They effectively constitute a
perceptual scale expansion around straight ahead which could allow
for more precise estimation and provide a high gain feedback signal
to facilitate maintenance of straight-forward heading during
everyday navigation and locomotion.