Collinearity improves alignment in amblyopia as well as in normal vision

In normal vision, three contrast patches containing black and white bars are aligned more precisely when the bars are collinear across the patches [Popple, A., Polat, U., & Bonneh, Y. (2001). Collinear effects on 3-Gabor alignment as a function of spacing, orientation and detectability. Spatial Vision, 14(2), 139-150]. Normally, offsets between the bars in successive patches make the configuration appear tilted, but this effect is reduced in amblyopia [Popple, A. V., & Levi, D. M. (2000). Amblyopes see true alignment where normal observers see illusory tilt. Proceedings of the National Academy of Science of the United States of America, 97(21), 11667-11672]. Our aim was to examine whether collinear bars nonetheless improve the precision of alignment in amblyopia. In a sample of 13 amblyopes, we found that collinear bars did indeed improve the precision of alignment in amblyopia, although both alignment bias and thresholds were higher in the amblyopic eyes for both collinear and non-collinear bars.