The gratings in the two eyes, as illustrated in
Figure 1, were defined as:
where
L0 is the background luminance,
C0 is the base contrast in the nondominant eye,
f is the spatial frequency of the gratings,
δ is the interocular contrast ratio, and
θ is the interocular phase difference. In our test,
L0 = 46.2 cd/m
2 (on the screen);
C0 = 100%;
f = 1 cycle/°;
δ = [0, 0.1, 0.2, 0.4, 0.8, 1.0] in different trails and
θ = 45°. Surrounding the gratings, a high-contrast frame (width, 0.11°; length, 6°) with four white diagonal lines (width, 0.11°; length, 2.83°) was always presented during the test to help observers maintain fusion.