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Goro Maehara, Benjamin Thompson, Behzad Mansouri, Robert Hess; The roles of contrast and luminance in amblyopic suppression. Journal of Vision 2009;9(8):1055. doi: 10.1167/9.8.1055.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: It is known that amblyopes perceive little mismatch in supra-threshold contrast between the amblyopic eye (AME) and the fellow fixing eye (FFE) under monocular viewing [Hess, R. F. & Bradley, A. (1980). Nature, 287, 463–464]. However, under binocular viewing the information from the amblyopic eye is suppressed. Here we examined whether this suppression involves predominantly luminance- or contrast-based information.
Methods: Two squares appeared within the top-left and bottom-right quadrants of one eye, while the other two appeared within the top-right and bottom-left quadrants of the other eye. In the luminance matching task, observers adjusted the luminance of the squares presented to one eye. In the contrast matching task, gratings were presented within all four squares. Observers adjusted the contrast of the gratings presented to one eye. Contrast detection thresholds were also measured for these stimuli under monocular and dichoptic viewing conditions.
Results and Discussion: Amblyopic observers showed interocular mismatches for the luminance matching task. Mean matching luminance was 35.8 cd/m2 for the AME and 24.7 for the FFE. That is, squares seen by the AME looked darker than squares seen by the FFE. On the other hand, in the contrast matching task, there was little mismatch between the two eyes for a wide range of luminance contrasts. This is consistent with previous findings under purely monocular viewing. Contrast detection thresholds for these stimuli were higher for the dichoptic presentations than for the monocular presentations, suggesting a stronger suppression of the AME under dichoptic viewing. Amblyopes reported that mean luminance was perceived to be darker by the AME compared with the FFE. This observation is in line with our results showing there is substantial mismatch in the luminance matching task, but not in the contrast matching task. We are currently studying the role of luminance-based processing in amblyopia.
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