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Yong Su, Ooi Teng Leng, Zijiang He; Binocular suppression in the monocular boundary contour display starts early (≤80 msec). Journal of Vision 2009;9(8):305. doi: 10.1167/9.8.305.
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© ARVO (1962-2015); The Authors (2016-present)
Boundary contour signal, elaborated at the surface representation level, affects binocular rivalry. We introduced an MBC-stimulus display where both eyes see the same vertical grating, but with a central circular area of one half-image's grating phase-shifted relative to the surrounding grating (Su et al, VSS 2008). The phase-shift creates a (monocular) boundary contour (MBC) defining the circular area as a vertical grating disc. With this display, the contrast threshold of a probe measured on the homogeneous grating is higher than that measured on the disc, indicating binocular suppression. This was surprising since the early feature (vertical grating) in each half-image is the same. Experiment-1 sought to confirm that the suppression of the MBC-stimulus is unaffected by binocular fusion at the early visual level. We changed the contrast of the MBC grating disc (2.2 cpd, 1.5 deg, 60cd/m2) from 0.9 to 1.7 log%, while keeping the contrast of the contralateral homogeneous grating at 1.5 log%, and measured the contrast thresholds of a monocular Gabor probe (FWHM: 0.43deg × 0.25deg) in each half-image. We found that while thresholds increased in the eye viewing the MBC disc as the contrast of the MBC disc increased, thresholds of the eye viewing the homogeneous grating were higher but did not change significantly. This indicates that the homogeneous grating was consistently suppressed and little affected by binocular fusion. Experiment-2 investigated the dynamic of the binocular suppression. We measured performance in detecting a suprathreshold Gabor probe presented on either half-image at various SOA (80–410 msec) between the MBC-stimulus onset and probe. We found suppression occurred as early as 80 msec after stimulus onset, and the magnitude of suppression (difference in percentage detection between the two eyes) is quite constant across SOA. This suggests that binocular suppression triggered by MBC is functional soon after stimulus onset.
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