Up, Down, Near, Far: An Online Vestibular Contribution to Distance Judgement

PLOS ONE, Dec 2019

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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Up, Down, Near, Far: An Online Vestibular Contribution to Distance Judgement

January Up, Down, Near, Far: An Online Vestibular Contribution to Distance Judgement A 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. - 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)


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Ágoston Török, Elisa Raffaella Ferrè, Elena Kokkinara, Valéria Csépe, David Swapp, Patrick Haggard. Up, Down, Near, Far: An Online Vestibular Contribution to Distance Judgement, PLOS ONE, 2017, Volume 12, Issue 1, DOI: 10.1371/journal.pone.0169990