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Bart Farell, Julian Fernandez; Non-transitive Depth in Stereo Displays. Journal of Vision 2011;11(11):340. doi: 10.1167/11.11.340.
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© ARVO (1962-2015); The Authors (2016-present)
We have developed stimuli whose perceived relative depth is unrelated to horizontal disparity parameters. For these stimuli, knowing that the horizontal component of disparity is positive for one stimulus and negative for another is insufficient for predicting their perceived depth order (VR, 2009, p. 2209). The only non-standard feature of these stimuli–a grating and a plaid–is the oblique disparity direction of the plaid.
With these stimuli one can create non-transitive depth relations: Stimulus A is seen as farther than Stimulus B when they are presented together; Stimulus B is seen as farther than Stimulus C when they are presented together; but A is not seen as farther than C, but rather at the same depth or even nearer. Here we ask, What depths are seen when A, B, and C are all presented together?
In Experiment 1, observers attended to all three stimuli (one grating, two plaids) of A+B+C displays and selected both the nearest and the farthest stimuli. Grating disparity affected observers' judgments, making two plaids with equal horizontal disparities appear at different depths, a perceptual depth shearing that resolves the pairwise non-transitivity.
In Experiment 2, we examined the effect of an unattended stimulus on observers' depth judgments of the two task-relevant stimuli. With practice some but not all observers could use selective attention to modulate the perceived depth of some relevant stimulus pairs. However, observers were unable to eliminate the effect of an unattended grating. The grating again made plaids with equal horizontal disparities appear at unequal depths.
The results demonstrate a non-local disparity field affecting perceived stereo depth and subject to only limited attentional selectivity.
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