Dichoptic Orientation Summation
33.449, Sunday, May 12, 8:30 am - 12:30 pm, Orchid Ballroom
Oren Yehezkel1,2, Uri Polat1, Dennis Levi2; 1Faculty of Medicine, Goldschleger Eye Research Inst, Sheba Medical Center, Tel Aviv University, Israel, 2School of Optometry and Helen Wills Neuroscience Institute, UC Berkeley, Berkeley, CA, USA
Although binocular integration of luminance, contrast and phase has been in the spotlight of the fundamental vision research over the past several decades, the manner in which different orientations in the two eyes are combined has not yet been resolved. Here we used dichoptic stimulation to measure the perceived orientation of a foveal Gabor target. The stimuli were presented with orientations of 80, 85, 90, 95 and 100 deg. in 12 dichoptic combinations with 10, 15 or 20 deg. orientation difference between the two eyes. In each combination, one eye was stimulated with a fixed high contrast (20%), and the fellow eye was presented with a contrast of 15, 10 or 5%, the threshold contrast for binocular detection (5%). The threshold for monocular contrast detection was 8%. Subjects were asked to rate the perceived orientation using 5 options (80, 85, 90, 95 and 100 deg.); 6th option was reserved for the "cant decide" response. Each combination was repeated in 100 trials. Binocular and monocular presentations with 20% contrast served as baseline orientation curve per subject with clear stimulation-driven responses. The results show that even stimulation below the monocular threshold of contrast detection combined with the supra-threshold stimulation of the fellow eye to significantly affect the resulting orientation perception. This effect was quantified as a shift in the perceived orientation, with the magnitude of the effect proportional to the contrast presented in the second eye. Moreover, a differential pattern of binocular summation was observed depending on the difference in the orientations presented to the two eyes. Our results suggest that 1) even subliminal input to one eye significantly modifies the overall orientation perception and that 2) the orientation difference between the two eyes determines the extent of binocular integration.