Detecting disorder in spatial vision

In normal foveal vision, visual space is accurately mapped from retina to c ortex. However, the normal periphery, and the central field of strabismic a mblyopes have elevated position discrimination thresholds, which have often been ascribed to increased 'intrinsic' spatial disorder. In the present st udy we evaluated the sensitivity of the human visual system (both normal an d amblyopic) to spatial disorder, and asked whether there is increased intr insic' topographical disorder in the amblyopic visual system. Specifically, we measured thresholds for detecting disorder (two-dimensional Gaussian po sition perturbations) either in a horizontal string of N equally spaced sam ples (Gabor patches), or in a ring of equally spaced samples over a wide ra nge of feature separations. We also estimated both the 'equivalent intrinsi c spatial disorder' and sampling efficiency using an equivalent noise appro ach. Our results suggest that both thresholds for detecting disorder, and e quivalent intrinsic disorder depend strongly on separation, and are modestl y increased in strabismic amblyopes. Strabismic amblyopes also show markedl y reduced sampling efficiency. However, neither amblyopic nor peripheral vi sion performs like ideal or human observers with added separation-independe nt positional noise. Rather, the strong separation dependence suggests that the 'equivalent intrinsic disorder' may not reflect topographic disorder a t all, but rather may reflect an abnormality in the amblyopes' Weber relati onship. (C) 2000 Elsevier Science Ltd. All rights reserved.