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Bart Farell, Yu-Chin Chai; Relative depth from pattern disparities and from component disparities. Journal of Vision 2007;7(9):821. doi: https://doi.org/10.1167/7.9.821.
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Two simultaneously presented stimuli might appear at the same depth even though their disparities are very different. This happens when the two stimuli have very different orientations (Farell, J. Neurosci. 2006). Even for two-dimensional patterns that have no perceptually dominant orientation, the relative orientation of the patterns' Fourier components can affect the perceived stereo depth separation between the patterns (Chai & Farell, VSS2006). Thus component disparities carry relative depth signals.
Is the perceived depth of two-dimensional patterns determined only by independent component disparities? To answer this question, we examined perceived depth matches between a sinusoidal grating and a plaid made of two superimposed sinusoids. We varied the orientation of the grating relative to the orientation of the plaid's components and we varied the orientation of the grating relative to the disparity direction of the plaid as a whole.
The plaid was confined to an annular envelope and the grating probe was presented as a Gabor patch in the center of the annulus. The disparity of the plaid was fixed while the disparity of the grating varied across trials while the observer judged the grating as ‘near’ or ‘far’ relative to the plaid. We then determined the relative-depth PSE. If the grating had the same orientation as a plaid component, our observers perceived a depth match when the grating and the component had the same disparity. There was no independent effect of the plaid's disparity magnitude or its disparity direction on the depth match. However, if the grating differed in orientation from both plaid components, our observers perceived a match when the grating and the plaid had the same disparity magnitude and disparity direction. This result shows that two-dimensional pattern disparities are functionally distinct from component disparities and that both disparities support relative depth percepts.
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