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Wenxun Li, Todd E. Hudson, Leonard Matin; Is the midline dependence of Binocular Depth Contrast based on the retinal midline or the head-and-body midline?. Journal of Vision 2011;11(11):330. doi: 10.1167/11.11.330.
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We recently reported that induction of perceived inclination (visual pitch), the well-known Binocular Depth Contrast phenomenon (BDC) of Werner (1938) and Ogle (1950) does not cross the median plane but is restricted to the side of the visual field containing a unilateral inducer (Hudson, Li, & Matin, PNAS, 2008). The present experiments investigated whether the median-plane restriction relates to the midline of the retina or the midline of the head-and-body. METHOD: The experiments involved 12 conditions in which each employed a unilateral inducer and a unilateral test target along with a small foveal fixation target in otherwise total darkness. The inducer and test target were either on the same or opposite sides of the retinal midline while simultaneously being on either the same or opposite sides of the head-and-body midline. All combinations were examined (same retina/same head-and-body; same retina/opposite head-and-body; opposite retina/same head-and-body; opposite retina/opposite head-and-body). The inducer (70°-long) and test target (33°-long) were single pitched-from-vertical straight lines separated by either 16.7° or 33.3° and either 8.3°, 25°, or 41.6° from each midline (all combinations of retinal and head-and-body eccentricities). Inducer pitch ranged over +25° (topforward/topbackward). Visually perceived erect (VPE) settings of the test line to appear erect in the frontoparallel plane were measured psychophysically. RESULTS: Although both midlines contribute to BDC, the retinal midline plays a major role and the head-and-body midline plays a minor role: Thus, the slope of the VPE-vs-pitch function was 0.38 for the same retina/same head-and-body condition and 0.28 for the same retina/opposite head-and-body condition, but was only 0.07 for the opposite retina/opposite head-and-body condition and 0.17 for the opposite retina/same head-and-body condition. A weighted average of the two midlines inserted into the 2-channel/3-stage neuromathematical model that accounts for the earlier results also accounts for the present results.
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