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Shannon Moore, Glen L McCormack; Motion Sharpening of Looming Vertical Bars. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):2928.
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© ARVO (1962-2015); The Authors (2016-present)
Our lab previously showed, at ARVO '14, that nonfixated blurred vertical bars moving in stereoscopic depth appear sharper than when stationary. This sharpening exceeded that of conjugate lateral motion having the same retinal image velocities. The purpose of this study was to determine whether nonfixated blurred vertical bars appearing to loom within a monocular optical flow field would also be sharpened more than bars appearing to move laterally.
15 normally binocular young adults monocularly viewed four 30 minarc-wide vertical bars drawn on a monitor 40cm from the eyes. All bars appeared simultaneously for 0.5 sec about a 5 minarc white fixation spot. Two of the bars (above or below fixation) loomed toward (or away) from the subject with horizontal velocities of 1.75, 3.5, or 7∆/sec, while the other two bars were static. The edges of the bars were blurred by cosine luminance profiles, which were fixed at 25 minarc for the moving bars and adjusted by an adaptive staircase procedure for the static bars to match the blur of the moving bars. Looming bars underwent horizontal separation, vertical size change, and vertical position change commensurate with looming. In the horizontal motion control condition the two moving bars laterally separated from each other, without vertical size or position change. In the vertical motion control condition the moving bars grew and moved vertically in a manner commensurate with looming, but without a horizontal position change.
A mixed ANOVA evaluated the effects of motion type (looming, horizontal, or vertical), subject, and velocity (1.75, 3.5, or 7) on sharpening. Motion sharpening increased significantly with velocity (f=156, p≈0.0), and differed significantly between subjects (f=4.56, p≈0), like we found previously. At the highest velocity, the looming bar edges were subjectively sharpened by 13% of their base blur of 25 minarc. Motion sharpening differed between motion types (f=20.7, p≈0), but this difference was mostly between the vertical condition and the other two conditions. Sharpening during looming was only 3% greater than during lateral motion (insignificant).
While motion sharpening was clearly evident in the looming and lateral motion conditions, the trivial difference between them argues that the appearance of motion in depth by way of looming does not add to motion sharpening.
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