ARVO'96 I. Kovacs, U. Polat and A. M. Norcia. Breakdown of binding mechanisms in amblyopia. Invest. Opth. Vis. Sci., 37(3):670, 1996

Purpose. Amblyopia is a disorder of spatial vision that is due to abnormal binocular interaction during a developmental critical period. Recently, facilitatory spatial interactions have been shown to be abnormal in the amblyopic human visual cortex (Polat & Norcia, ARVO'95). Here we ask whether abnormal spatial interactions result in deficient binding mechanisms in amblyopic human observers. Methods. Based on a contour detection task developed by Kovacs and Julesz (PNAS, 1993), we have generated a battery of test cards that enable us to test a large number of patients and control subjects. Each card consists of a contour (closed chain of colinearly aligned Gabor patches, GPs) and noise (background of randomly oriented and positioned GPs). Subjects are asked to identify the location of the contour within each card. The value of phi is varied across cards, where phi = noise-spacing / contour-spacing. Binding efficiency is defined by the minimal value of phi yielding contour segregation. The following four conditions are employed: (a) complete contours (1.1 >phi> 0.65), (b) 10 to 50% of the GPs are randomly removed, (c) 1 to 5 lambda random positional jitter of the GPs, where lambda is the wavelegth of the GPs, (d) combined removal and jitter of the GPs. Results. 1. Amblyopic subjects perform poorly in condition (a) with the amblyopic eye (phi_min>1.1) as compared to their performance with the fellow normal eye (phi_min=0.7). 2. Normal control subjects readily perceive all contours in conditions (a) to (d) (phi_min<0.65). Conclusions. Contour segregation is poorly served by amblyopic eyes when only long-range correlation between elements defines the target. According to result 2., the poor performance of amblyopes cannot be explained by undersampling and/or filter-jitter. We suggest that the observed binding deficit is due to abnormal long-range intracortical connections. The card format is suitable for use with young children.