title: Contrast and phase combination in binocular vision.
abstract: BACKGROUND
  How the visual system combines information from the two eyes to form a unitary binocular representation of the external world is a fundamental question in vision science that has been the focus of many psychophysical and physiological investigations. Ding & Sperling (2006) measured perceived phase of the cyclopean image, and developed a binocular combination model in which each eye exerts gain control on the other eye's signal and over the other eye's gain control. Critically, the relative phase of the monocular sine-waves plays a central role.
  
  
  RESULTS
  We used the Ding-Sperling paradigm but measured both the perceived contrast and phase of cyclopean images in three hundred and eighty combinations of base contrast, interocular contrast ratio, eye origin of the probe, and interocular phase difference. We found that the perceived contrast of the cyclopean image was independent of the relative phase of the two monocular gratings, although the perceived phase depended on the relative phase and contrast ratio of the monocular images. We developed a new multi-pathway contrast-gain control model (MCM) that elaborates the Ding-Sperling binocular combination model in two ways: (1) phase and contrast of the cyclopean images are computed in separate pathways, although with shared cross-eye contrast-gain control; and (2) phase-independent local energy from the two monocular images are used in binocular contrast combination. With three free parameters, the model yielded an excellent account of data from all the experimental conditions.
  
  
  CONCLUSIONS
  Binocular phase combination depends on the relative phase and contrast ratio of the monocular images but binocular contrast combination is phase-invariant. Our findings suggest the involvement of at least two separate pathways in binocular combination.
authors.affiliation: Laboratory of Brain Processes (LOBES), Department of Psychology, Neuroscience Graduate Program, University of Southern California, Los Angeles, California, United States of America.
authors.forename: Chang-Bing
authors.initials: CB
authors.lastname: Huang
authors.forename: Jiawei
authors.initials: J
authors.lastname: Zhou
authors.forename: Yifeng
authors.initials: Y
authors.lastname: Zhou
authors.forename: Zhong-Lin
authors.initials: ZL
authors.lastname: Lu
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003287:Contrast Media / Q000494:pharmacology; D015350:Contrast Sensitivity; D006801:Humans; D008875:Middle Aged; D015233:Models, Statistical; D015588:Observer Variation; D015357:Vision Disparity; D015348:Vision, Binocular / Q000502:physiology*; D015349:Vision, Monocular / Q000502:physiology; D014785:Vision, Ocular
chemical_list: D003287:Contrast Media