Breakdown of binding mechanisms in amblyopia

I. Kovács, U. Polat, A. M. Norcia

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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 Kovács 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 φ is varied across cards, where φ = noise-spacing / contour-spacing. Binding efficiency is defined by the minimal value of φ yielding contour segregation. The following four conditions are employed: (a) complete contours (1.1 > φ > 0.65), (b) 10 to 50% of the GPs are randomly removed, (c) 1 to 5λ random positional jitter of the GPs, where λ 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 (φmin > 1.1) as compared to their performance with the fellow normal eye (φmin = 0.7). 2. Normal control subjects readily perceive all contours in conditions (a) to (d) (φmin < 0.65). Conclusions. Contour segregation is poorly served by amblyopio eyes when only long-range correlation between elements defines the target (φ ≤ 1). According to result 2., the poor performance of amblyopes cannot be explained by uudersampling 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.

Original languageEnglish
Pages (from-to)S670
JournalInvestigative Ophthalmology and Visual Science
Issue number3
StatePublished - 15 Feb 1996
Externally publishedYes


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