Abstract
Phase information is a fundamental aspect of visual stimuli. However, the nature of the binocular combination of stimuli defined by modulations in contrast, so-called second-order stimuli, is presently not clear. To address this issue, we measured binocular combination for first- (luminance modulated) and second-order (contrast modulated) stimuli using a binocular phase combination paradigm in seven normal adults. We found that the binocular perceived phase of second-order gratings depends on the interocular signal ratio as has been previously shown for their first order counterparts; the interocular signal ratios when the two eyes were balanced was close to 1 in both first- and second-order phase combinations. However, second-order combination is more linear than previously found for first-order combination. Furthermore, binocular combination of second-order stimuli was similar regardless of whether the carriers in the two eyes were correlated, anti-correlated, or uncorrelated. This suggests that, in normal adults, the binocular phase combination of second-order stimuli occurs after the monocular extracting of the second-order modulations. The sensory balance associated with this second-order combination can be obtained from binocular phase combination measurements.
Highlights
One of the key aspects of primate vision is its binocularity
While there have been numerous studies investigating the nature of the binocular combination of features such as luminance [1,2,3], contrast [4,5,6,7,8,9,10,11], color [12,13,14,15] disparity [16,17,18,19,20], and binocular rivalry [21,22,23,24,25], little is known about the binocular combination of phase information between the two eyes
If the visual input in one eye is more dominant than that of the other eye, the binocular perceived phase will be shifted in the direction of the phase of the grating in the dominant eye; if each eye contributes to binocular combination, the binocular perceived phase will be at 0u
Summary
One of the key aspects of primate vision is its binocularity. Even though the visual inputs to the two eyes may not be identical, binocular visual perception is always single. Ding & Sperling introduced the dichoptic phase combination paradigm to study how the two eyes’ inputs combine [27] In their paradigm, two horizontal sine-wave gratings with same spatial frequency and size, but equal and opposite phaseshifts (relative to the centre of the screen) were dichoptically presented to the two eyes; the perceived phase of the binocular percept was measured for a range of interocular contrast differences. They kept the contrast in one eye fixed and varied proportionally the contrast in the other eye in normal adults, and found that the perceived phase of the binocularly combined grating was related to the interocular contrast ratio in a non-linear way and that the two eyes were balanced when the contrast in two eyes were the same They proposed a gain-control model to account for the binocular perceived phase vs interocular contrast ratio function, in which the visual inputs in two eyes first go through an interocular gaincontrol stage and linearly combine to provide a binocularly fused percept. This gain-control model has been successfully used in predicting the binocular perceived phase for people who have sensory imbalance, e.g., amblyopes [28,29,30,31,32] or normal adults under abnormal viewing conditions, e.g. when the two eyes have different luminances [32]
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