Figure 1. Dichoptic stimuli in the binocular phase combination test.

Four dichoptic pairs were used in the test: First-order gratings, second-order gratings with correlated carriers (noise) in the two eyes, second-order gratings with anti-correlated carriers in the two eyes and second-order gratings with uncorrelated carriers in the two eyes. For each dichoptic pair, grating with fixed contrast (modulation) of 100% and phase-shift of 22.5° to one direction was inputted to the nondominant eye; grating with a proportional contrast with interocular contrast ratio of δ (δ = (0, 0.1, 0.2, 0.4, 0.8, 1)) and a reverse phase-shift by the same magnitude was inputted to the dominant eye. The phase of the binocularly combined cyclopean grating was then measured to access the two eyes contribution in binocular viewing. The perceived phase of the cyclopean grating was quantified by the half of the difference between the measured phase when the phase-shift was −22.5° in the dominant eye and +22.5° in the nondominant eye and the measured phase at the reversal configuration.