Yiya Chen¹ (), Zijiang He², Teng Leng Ooi¹; ¹The Ohio State University, ²University of Louisville

Coupled with binocular disparity, the background surface provides a reference frame for perceiving the absolute location of a target in midair in the intermediate distance range (2-25 m). However, other depth information, namely, relative height (angular declination/elevation), is also present in the natural environment. We examined how consistent and conflicting binocular disparity and relative height information affected observers’ ability to discriminate the absolute distances of two midair targets. Paired, dimly-lit targets (0.2 degree, 805 msec) in a dark room were presented from two target arrays located 4.5 m and 5.75 m from the observer. The first array had six vertically arranged targets at different relative heights (declined or elevated 0.66-0.90 m from an eye-level of 1.2 m) and the second array had one target. The relative binocular disparity between the two arrays was 10 arc min. The observers’ task was to report in a two-interval forced choice (2IFC) procedure whether the target in the first or second array was nearer. The main comparisons tested were (i) binocular versus monocular viewing and (ii) texture background versus dark (no-texture) conditions, respectively, to examine the interaction between binocular disparity and visible background surface. The texture background was a 2x4 parallel array of dimly-lit elements either on the floor or ceiling. The average results (n=9) reveal absolute depth discrimination was significantly better with binocular than monocular viewing (p<0.001). Performance was superior in the presence of texture background compared to the dark, but only with binocular viewing (p=0.003) and not monocular viewing (p=0.933). The influence of relative height increased as the observers’ binocular depth ability weakened (r2=0.8913, p<0.001); and with monocular viewing, it was stronger when the texture background was present (p=0.012). This indicates both binocular depth and relative height information contribute to locating a midair target. Notably, binocular disparity has a higher weighted contribution.

Acknowledgements: NIH R01EY033190