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Jeff C. Rabin, Brandi Stewart, Veronica Wong, Jonathan Boster, Madison Ruelle, Thien Tran, John Gooch, Steve Wright; Binocular Enhancement of Color Contrast Sensitivity. Invest. Ophthalmol. Vis. Sci. 2012;53(14):6398.
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Object recognition, task performance, patient welfare and safety are enhanced when viewing the world with two eyes vs. one. Binocular enhancement of contrast sensitivity (CS) is certainly well-established for luminance contrast, but less is known about color-defined stimuli. Our purpose was to determine if binocular enhancement of color CS is comparable to the 40% improvement reported for luminance CS (Campbell FW, Green DG. Monocular vs. binocular visual acuity. Nature 1965; 208:191-2).
Color CS was measured with the computer-based cone contrast test (CCT) which presents a series of colored letters on a grey background visible only to red (L), green (M), or blue sensitive (S) cones. Cone contrast is varied from trial-to-trial based on a response-driven staircase algorithm to determine L, M and S CS thresholds. Monocular and binocular L, M, and S cone CS were measured in 20 color vision normal (CVN) and 10 color vision deficient (CVD) subjects confirmed to be CVN or CVD on a battery of screening tests (Ishihara, Dvorine, HRR).
Binocular CS exceeded monocular CS in both CVN (F=14.7, p<0.001) and CVD subjects (F=8.1, P<0.01). In CVN binocular exceeded monocular CS by 31% for L cone CS, 34% for M cone CS, and 48% for S cone CS; mean binocular enhancement = 38%. CVD subjects showed mean enhancement of 39% for the cone CS corresponding to their CVD (protan or deutan), 36% for the unaffected L or M cone CS, and 33% enhancement for S cone CS.
Enhancement of color CS with two eyes vs. one is comparable to the well-known improvement in luminance CS indicating that binocular cortical processing plays an essential role in detection of low contrast chromatic imagery. Our results exemplify the importance of binocular viewing for color based tasks and enhance our ability to predict real-world performance of color normal and color deficient individuals. The equivalence of CCT color CS values and luminance CS (Pelli-Robson test) suggests that common, parvocellular-projecting neurons capable of "double-duty" luminance and color processing are initially responsible for both luminance and color thresholds.
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