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Perceived depth predicts stereoacuity for wallpaper patterns| old_uid | 968 |
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| title | Perceived depth predicts stereoacuity for wallpaper patterns |
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| start_date | 2006/03/29 |
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| schedule | 11h |
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| online | no |
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| summary | If an observer converges steadily on a point in front of a repetitive pattern, such as wallpaper, the pattern will appear to shift forward in depth to the convergence plane — the famous Wallpaper Illusion. However, the illusory shift is usually not instantaneous, particularly if the pattern is fairly narrow. We have demonstrated that sinusoidal grating segments (6 deg wide) are initially matched in depth at the disparity of the segment edges, independent of the interocular phase of the grating. Like all repetitive patterns, the perceived depth of the segment will shift to the plane nearest fixation after 3–6 seconds of stable convergence.
It is well-known that stereoacuity thresholds, for thin bar targets, rise exponentially as the absolute disparity of the bars is increased. We measured stereoacuity for a briefly presented (200msec) grating segment (3cpd, 6 deg wide) as a function of its edge disparity. As the edge disparity is increased from 0 – 20 arcmin, i.e., one period of the carrier, the interocular phase disparity cycles from 0 through 360 deg (back to zero). If stereoacuity is limited by interocular phase, it should also cycle with the carrier phase. If, instead, stereoacuity depends on perceived depth, thresholds should rise with increasing edge disparity, in agreement with the initial stereo match. We found that the rise in grating thresholds as a function of edge disparity was virtually identical to the rise observed for bars. However, with prolonged stable convergence, a grating segment with an edge disparity of 20 arcmin will appear to shift in depth to the fixation plane. What happens to stereoacuity following the shift in perceived depth? Even through the physical stimulus has not changed, the threshold improves dramatically to the same low value associated with targets actually presented in the fixation plane. In short, stereoacuity is contingent on stereo matching. |
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| responsibles | Mamassian |
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