Perceptual distortions in the neural representation of visual space

The visual mechanism by which human observers determine the separation betw een objects has long been of interest. This study examines the extent to wh ich separation in visual space can be misperceived in foveal and extrafovea l vision. Foveally, vertical separations were consistently overestimated re lative to horizontal separations, a result which is consistent with the wel l-documented horizontal-vertical illusion (HVI). Extrafoveally, much larger misrepresentations of visual space were perceived. In addition, separation s tangential to fixation were consistently perceived as being greater than separations in a radial direction. These marked misperceptions of visual sp ace which occur in extrafoveal vision take the form of a radial/tangential anisotropy combined with an overestimation of vertical distance. The result s have important implications for meridional anisotropies which have previo usly been documented in a number of visual performance tasks.