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Christopher Tyler, Lora Likova, Spero Nicholas; Slant stereomotion: A new kind of depth motion from modulation of interocular spatial frequency difference. Journal of Vision 2009;9(8):641. doi: 10.1167/9.8.641.
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When observers view vertical gratings drifting in the opposite directions in the two eyes, they report a percept of whole-field cyclic motion in depth that is attributable to either the local disparity change (LDC) or local interocular velocity difference (LIOVD) cues as the bars drift past each other. Tyler & Sutter (1979) showed that, at velocities where the stereomotion from LDC/LIOVD fails completely due to motion rivalry, introduction of an interocular spatial-frequency difference still supports disparity slant percepts. We modify this paradigm in two ways to show that whole-field depth motion is not supported by either the LDC or LIOVD cue under binocular orientation rivalry conditions and to reveal the existence of a new kind of depth motion from the rivalrous slant conditions.
Experiment 1. Vertical sinusoidal gratings in a circular 5° aperture were drifted in opposite horizontal directions in the two eyes to determine the optimal velocity for perceiving cyclic depth motion from LDC/LIOVD cues.
Experiment 2. Introducing an interocular orientation difference of ± 45° (and increasing spatial frequency by Ö2) provided a condition of continuous orientation rivalry. Although both the LDC and LIOVD cues remained the same along any one horizontal line, cyclic depth motion was no longer perceived, implying that the interocular orientation difference blocked the ability to process either cue to depth motion.
Experiment 3. Implementing temporal modulation of the interocular spatial-frequency difference, under the orientation rivalry conditions, generated strong percepts of slant stereomotion around a vertical axis despite the blocked ability to process LDC or LIOVD cues.
The results establish the existence of slant stereomotion and imply that the processing mechanism of this new kind of depth motion is separate from that for whole-field stereomotion based on either LDC or LIOVD cues.
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