Partition of perceived space within the fusional area on the basis of apparent fronto-parallel plane criterion

The relationship between visual space and physical space was investigated by means of the apparent fronto-parallel plane percept. A set of curves in physical space, corresponding to fronto-parallel planes perceived in front or behind a given fixation point, was determined. The curvature at the apex of these curves follows a hyperbolic law that depends on the distance between the perceived plane and the fixation point. Our results are interpreted by distinguishing absolute disparity, which sets the position of the perceived plane, from relative disparity measured by adjusting in this plane eccentric vertical lines. We show that Foley's model, which interprets the shape of the apparent fronto-parallel planes on the mis-evaluation of egocentric distance, works for absolute disparity judgements, but seems to be inadequate for relative disparity judgements in our experimental conditions.