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Comment
. 2022 Mar 2;22(4):16.
doi: 10.1167/jov.22.4.16.

Are mirror-symmetric objects of special importance for 3D shape perception? A reply to Sawada and Pizlo (2022)

Alexander A Petrov  1   2 , Ying Yu  1   3 , James T Todd  1   4
Affiliations
Comment

Are mirror-symmetric objects of special importance for 3D shape perception? A reply to Sawada and Pizlo (2022)

Alexander A Petrov et al. J Vis. .

Abstract

Yu, Todd, and Petrov (2021) and Yu, Petrov, and Todd (2021) investigated failures of shape constancy that occur when objects are viewed stereoscopically at different distances. Although this result has been reported previously with simple objects such as pyramids or cylinders, we examined more complex objects with bilateral symmetry to test the claim by Li, Sawada, Shi, Kwon, and Pizlo (2011) that the perception of those objects is veridical. Sawada and Pizlo (2022) offer several criticisms of our experiments, but they seem to suggest that the concept of shape is defined by what is computable by their model. If stimuli are used that cannot be discriminated by their model, they are dismissed as degenerate, and tasks that cannot be performed by their model are assumed to be based on something other than shape. This allows them to disregard empirical evidence that is inconsistent with their model. We argue, in contrast, that all reliable aspects of shape perception are deserving of explanation. We also argue that there are many different attributes of shape and many different sources of information about shape that may be relevant in different contexts. It is unlikely that all of them can be explained by a single model.

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Figures

Figure 1.
Figure 1.
Stereograms of a pyramid (top) and a cylinder (bottom) at a fronto-parallel orientation. The model by Pizlo and colleagues is unable to estimate the shapes of these objects because they do not satisfy its underlying assumptions. They therefore label them as “degenerate.” However, human observers with functioning stereo vision can identify these objects quite easily.
Figure 2.
Figure 2.
Images of abstract sculptures and natural rock formations that do not satisfy the underlying assumptions of Pizlo and colleague's model. Almost all observers report that these images provide compelling perceptions of 3D shape.
See this image and copyright information in PMC

Comment on

References

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    1. Li, Y., Pizlo, Z., & Steinman, R. M. (2009). A computational model that recovers the 3D shape of an object from a single 2D retinal representation. Vision Research, 49(9), 979–991, 10.1016/j.visres.2008.05.013. - DOI - PubMed
    1. Li, Y., Sawada, T., Shi, Y., Kwon, T., & Pizlo, Z. (2011). A Bayesian model of binocular perception of 3D mirror symmetric polyhedra. Journal of Vision, 11(4):11, 1–20, 10.1167/11.4.11. - DOI - PubMed
    1. Pizlo, Z., & de Barros, J. A. (2021). The concept of symmetry and the theory of perception. Frontiers in Computational Neuroscience, 15, 681162, 10.3389/fncom.2021.681162. - DOI - PMC - PubMed
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