Up, Down, Near, Far: An Online Vestibular Contribution to Distance Judgement
January
Up, Down, Near, Far: An Online Vestibular Contribution to Distance Judgement
AÂ goston ToÈ roÈ k 1 2 3
Elisa Raffaella Ferrè 0 1 3
Elena Kokkinara 1 3
Vale ria Cse pe 1 2 3
David Swapp 1 3 4
Patrick Haggard 1 3
These authors are co-first authors on this work. 1 3
1 3
0 Department of Psychology, Royal Holloway University of London , Egham , United Kingdom , 4 Department of Personality, Assessment and Psychological Treatments, University of Barcelona , Barcelona , Spain
1 Community's Research Infrastructure Action 262044 Mr. Agoston Torok and Elena Kokkinara; Magyar TudomaÂnyos AkadeÂmia (HU) Young Researcher Fellowship Mr. Agoston Torok; European Union Seventh Framework Programme (EU FP7) vere wp1 Dr. Elisa Raffaella Ferre and Prof. Patrick Haggard; BIAL 269/14 Dr. Elisa Raffaella Ferre and Prof. Patrick Haggard
2 Brain Imaging Centre, Research Centre for Natural Sciences, Hungarian Academy of Sciences , Budapest , Hungary , 2 Institute of Cognitive Neuroscience, University College London , London , United Kingdom
3 Editor: Chung-Lan Kao, Taipei Veterans General Hospital , TAIWAN
4 Department of Computer Science, University College London , London , United Kingdom
Whether a visual stimulus seems near or far away depends partly on its vertical elevation. Contrasting theories suggest either that perception of distance could vary with elevation, because of memory of previous upwards efforts in climbing to overcome gravity, or because of fear of falling associated with the downwards direction. The vestibular system provides a fundamental signal for the downward direction of gravity, but the relation between this signal and depth perception remains unexplored. Here we report an experiment on vestibular contributions to depth perception, using Virtual Reality. We asked participants to judge the absolute distance of an object presented on a plane at different elevations during brief artificial vestibular inputs. Relative to distance estimates collected with the object at the level of horizon, participants tended to overestimate distances when the object was presented above the level of horizon and the head was tilted upward and underestimate them when the object was presented below the level of horizon. Interestingly, adding artificial vestibular inputs strengthened these distance biases, showing that online multisensory signals, and not only stored information, contribute to such distance illusions. Our results support the gravity theory of depth perception, and show that vestibular signals make an on-line contribution to the perception of effort, and thus of distance.
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Data Availability Statement: All relevant data are
within the paper and its Supporting Information
files.
Introduction
Perceiving how far away an object is from one's own body is essential for interacting with the
environment. Distance can be inferred directly from visual information, using accommodation
[
1
] and binocular cues such as vergence [
2
] and disparity [
3
]. However, distance perception is
dramatically biased if the target objects are presented above or below the level of horizon. For
example, a mountain refuge seems farther or closer depending on whether we look up at it from
below or down at it from above [
4
]. Hence, purely visual information about distance may be
affected by non-visual factors [
5,6
], such as fear of heights [4] or perceived effort of access [
7
].
Economic and Social Research Council
Professorial Fellowship Prof. Patrick Haggard;
European Research Council Advanced Grant
HUMVOL Prof. Patrick Haggard.
Contrasting explanations have been proposed for non-visual distance biases. On the one
hand, the gravity theory claims that distance perception is based on the estimated motor effort
of navigating to the perceived object [
7,8
]. Accordingly upward distances are overestimated
[9]. On the other hand, the evolved navigation theory posits an evolutionary advantage in
overestimating the risk of falling [
10,11
]. On this view, contrary to gravity theory, downward
distances are overestimated. Both theories assume that current head and gaze elevations are
combined with internally-stored information in order to compute distance. Gravity theories
require stored information about previous motor efforts [8], while evolved navigation theories
require internal information about potential risks of falling [
12
]. Critically, removing the fear
of falling by experimenting in low detail Virtual Reality [
13
] or reducing the expected effort of
access by e.g. not wearing any heavy backpacks [
9
] reportedly diminishes these elevation
distance biases.
In principle, the influence of upward/downward head inclination on distance perception
could be based on online information, rather than stored information. In particular, under
terrestrial conditions, the vestibular system constantly provides signals relating current head
orientation to the direction of gravity. Combining a vestibular sig (...truncated)