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The extent of visual space inferred from perspective angles
Dr. Casper Erkelens
Monday, February 09, 2015, 12:00pm - 07:00pm
Universiteit Utrecht, Helmholtz Institute and Chair, Department of Physics and Astronomy
Retinal images are perspective projections of the visual environment. Despite this, it is not selfevident that visual space is a perspective representation of physical space. Analysis of underlying spatial transformations shows that visual space is perspective only if physically parallel lines vanish at finite distance in visual space. Perspective angles, i.e. the angle perceived between parallel lines in physical space, were estimated for rails of a straight railway track. Perspective angles were also estimated from pictures taken from the same point of view. Perspective angles between rails ranged from 27% to 83% of their angular size in the retinal image. Perspective angles prescribe the distance of vanishing points of visual space. Computed distances were shorter than six meters. This distance of a hypothetical space inferred from perspective angles does not match the depth of visual space. Incongruity between the perceived shape of a railway line on the one hand and the experienced ratio between width and length of the line on the other hand is huge, but apparently so unobtrusive that it has remained unnoticed. The mismatch casts doubt on the existence of a visual space that is consistent for distances and angles.