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Shanda Lauer, Jessica Holmin, Mark Nawrot; Implied motion does not generate an internal motion signal for the perception of depth from motion parallax. Journal of Vision 2016;16(12):283. doi: 10.1167/16.12.283.
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© ARVO (1962-2015); The Authors (2016-present)
Static images taken from an animation of continuous motion contain no real motion information; however these implied motion (IM) stimuli may activate the same brain regions as real motion. Real motion signals, and even motion-aftereffect, when combined with smooth pursuit, produce depth from motion parallax (MP). If IM generates the same neural motion signals as real motion, then IM may generate a percept of depth from MP. In the current study, IM stimuli were produced by placing an image of a human actor, in a running pose, above and below a fixation square. The pose above and below fixation faced opposite directions, generating IM in opposite directions. Observers were required to maintain fixation as the entire MP stimulus translated left or right at 3.1 deg/sec. To titrate IM with real motion, fixed amounts of motion (11 magnitudes: ± 0 – 0.54 deg/sec) were added to the figures. Observers indicated which of the two figures (top or bottom) appeared nearer in depth relative to fixation. The dynamic geometry of MP dictates that the actor translating in the same direction as fixation is perceived nearer. We determined whether IM, in the same or opposite direction as pursuit, influenced the depth phase judgment. In two control conditions, participants made depth phase judgments for MP stimuli that did not contain IM. A psychometric function (PF) for each condition was created by plotting the percentage of "top nearer" responses against each magnitude of real motion. If IM affected perceived depth from MP, the PF would be shifted horizontally away from zero. There was no shift in the PFs in any of the three conditions (F = 1.95, p = 0.16), indicating that perceived depth sign was not affected by IM. This result indicates that IM is not acting as a real motion signal for MP.
Meeting abstract presented at VSS 2016
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