Failures of stereoscopic shape constancy over changes of viewing distance and size for bilaterally symmetric polyhedra

Abstract

Two shape matching experiments examined the effects of viewing distance and object size on observers’ judgments of 3D metric shape under binocular viewing. Unlike previous studies on this topic, the stimuli were specifically designed to satisfy the minimal conditions for computing veridical shape from symmetry. Concretely, the stimuli were complex, mirror-symmetric polyhedra whose symmetry planes were oriented at an angle of 45 o relative to the line of sight in a shape-matching task. Although it is mathematically possible to accurately compute the 3D shapes of these stimuli using relatively simple algorithms, the results indicated that human observers are unable to do so. Indeed, the apparent shapes of the objects were systematically expanded or compressed in depth as a function of viewing distance, in exactly the same way as has been reported for simpler stimuli that do not satisfy the minimal conditions for an accurate computational analysis. For objects presented at near distances, we also obtained statistically significant effects of object size on observers’ shape judgments.

Hill on perceptual relativity and perceptual error

“…Johnston found that to be deemed perfectly cylindrical, a shape had to be physically compressed when it was nearby the observer (53.5 cm), almost perfectly cylindrical at medium distances (107 cm), and elongated when it was further away (215 cm) (see Figure 2). Johnston took these results to suggest that a shape's length in depth is perceptually overestimated at near distances, approximately accurate at medium distances, and underestimated at far distances (see also Yu et al, 2021).…”

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

“…Our recent experiments ( Yu, Petrov, & Todd, 2021 ; Yu, Todd, & Petrov, 2021 ) were designed to examine if the use of more complex stimuli at different orientations would have any effect on the systematic distortions of apparent shape caused by changes in viewing distance that have been reported in previous investigations. According to Pizlo and de Barros (2021) : “When an object is mirror-symmetrical, shape constancy is perfect, or nearly so” (p. 14).…”

“…“Our model cannot tell the difference between the three shapes in Figure 11 in ( Yu et al, 2021 ) or between the two shapes in Figure 5 in ( Yu et al, 2021 ), unless we add binocular depth perception to our shape model. Note that the reader will have a hard time making out this difference as well ” (p. 2).…”

Testing a formal theory of perception is not easy: Comments on Yu, Todd & Petrov (2021) and Yu, Petrov & Todd (2021)

“… Yu, Todd, and Petrov (2021 , Journal of Vision) and their follow-up study ( Yu, Petrov, & Todd, 2021 , i-Perception) aimed at evaluating the role of three-dimensional (3D) symmetry in binocular shape perception by comparing their experimental data to predictions they derived from our computational models. We point out in this note that their predictions were incorrect, so their studies can neither reject nor support our models of 3D shape perception.…”

“…In this note, we are commenting on the article by Yu, Todd and Petrov (2021 ) published in Journal of Vision and a follow-up article by Yu, Petrov and Todd (2021) , published in i-Perception . We will refer to these articles as Yu1 and Yu2, respectively.…”