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Anna Ptukha, Pascal Mamassian; Interactions between horizontal and orientation disparities in stereopsis. Journal of Vision 2017;17(10):1056. doi: 10.1167/17.10.1056.
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© ARVO (1962-2015); The Authors (2016-present)
Stereoscopic vision is based on binocular disparities that correspond not only to spatial displacements between the images projected to the two retinas, but also other differences such as orientation disparities (Kato et al., 2016, Phil. Trans. R. Soc. B). We present here behavioral experiments to test this recent model. Observers viewed stereoscopically two types of stimuli presented in fovea: two parallel thin lines or the same lines connected with horizontal segments. The lines could be either oriented vertically or tilted by an angle up to 60 degrees. After a short (200 ms) presentation, observers reported which line appeared closer in depth. In a first experiment, the lines were presented only with horizontal disparities between the two eyes. In a second experiment, the lines were still parallel in each monocular image, but small orientation disparities were introduced between the two eyes. The difference between the two experiments created different percepts of parallelograms that were more or less slanted about the horizontal axis. In the first experiment, we found large shifts of the points of subjective equality in opposite directions for clockwise and counterclockwise tilts and worse sensitivity as tilt increased. The biases were even larger for closed contours. In the second experiment, we found that sensitivity was quite stable across different tilts. Our results suggest that observers have a preferred representation of a slanted plane that is closer to the one displayed in experiment 2. This preferred object appears to correspond to an object mostly slanted about a vertical axis, with little additional slant about the horizontal axis. The closed contour condition is presumably providing stronger evidence for a single plane in the visual scene. Our results are another example of interactions between orientation and horizontal disparities in the visual system (Farell, 2006, J. Neurosci.) that awaits to be tested physiologically.
Meeting abstract presented at VSS 2017
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