August 2023
Volume 23, Issue 9
Open Access
Vision Sciences Society Annual Meeting Abstract  |   August 2023
The disparity gradient limit has limited relevance to natural environments
Author Affiliations & Notes
  • Arleen Aksay
    York University
  • Laurie M. Wilcox
    York University
  • Footnotes
    Acknowledgements  Natural Sciences Research Council of Canada (NSERC); CF-REF program Vision Sciences to Applications (VISTA)
Journal of Vision August 2023, Vol.23, 5440. doi:
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      Arleen Aksay, Laurie M. Wilcox; The disparity gradient limit has limited relevance to natural environments. Journal of Vision 2023;23(9):5440.

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      © ARVO (1962-2015); The Authors (2016-present)

  • Supplements

Diplopia thresholds depend on disparity magnitude and the lateral separation of disparate elements. The disparity gradient limit is the ratio of these values; since Burt and Julesz (1980), a gradient limit of one has been commonly accepted as the limit for binocular fusion. This is true for isolated stimuli typically used in psychophysical studies. However, gradients greater than one are common in natural cluttered environments. Here we re-evaluate the relevance of the disparity gradient limit in more ecologically valid stimuli. We rendered realistic 3D branches viewed in a virtual reality headset. A low complexity condition comprised two isolated branches, presented on either side of a central reference branch. For high complexity, multiple overlapping branches were overlaid to create the equivalent of a ‘thicket’. The thicket comprised two identical but mirrored clusters of branches, centred on a reference branch. The two clusters were shifted in opposite directions in depth to vary the disparity range. Observers indicated the depth extent of the structure as a whole with a virtual ruler. We also measured diplopia thresholds for these stimuli. For the thickets, gradient limit violations are always present, so theoretically, diplopia should always be apparent. We found that diplopia was experienced at lower disparities in the thickets relative to the branches. However, there was a large range over which the thicket appeared fused. Further, there was a linear relationship between perceived and physical depth for the branches, but the functions obtained in the thicket condition exhibited a compressive non-linearity; following an inflection point, estimates plateaued. These data suggest that the disparity gradient limit has limited relevance to cluttered stimuli like those typically encountered in the natural environment. We propose that the resilience of fusion is achieved via coarse disparity mechanisms which have previously been shown to mediate depth percepts for diplopic targets.


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