Evidence against a specialized mechanism for transparent surface perception

Yi Xiong Zhou, Robert Shapley

Research output: Contribution to journalArticle

Abstract

Purpose. We identify transparent surfaces easily in natural scenes. Does that mean the human visual system is sensitive to the physical invariants that are specific for transparent surfaces, such as the luminance cues in the figure? Methods. Eight subjects participated in 3-alternative forced choice experiments. They reported whether either the left or right square was perceived as a surface in front of the other, or if neither was seen in front. αRRLL are the contrasts of the edge sections of the two squares. The stimuli used satisfied αLβL>0 and αRβR>0 (Metelli's first rule). Results. 1) Transparent surface segmentation depended on contrast not absolute luminance. 2) A large contrast step along a contour, e.g. |αR|≫|βR| indicates that the right square is occluded by a surface (left square) in front. Subjects were sensitive to this cue. 3) When the contrast step was not large, e.g. |αR| ≈ |βR|, subjects were not sensitive to sign of the contrast step, i.e. whether |αR|>|βR| or |αR|< βR. This caused them to perceive a surface that was not consistent with physics, e.g. perceiving the left square as a surface in front when |αR, < |βR|. Conclusion. Our results suggest that the visual system may not have a specialized mechanism for the perception of transparency based on physical cues; the most sensitive cue (large contrast step along a contour) is likely to be detected by a mechanism that responds to T-junctions. Transparency stimuli can be used to study general mechanisms of surface segmentation. (Figure Presented).

Original languageEnglish (US)
JournalInvestigative Ophthalmology and Visual Science
Volume37
Issue number3
StatePublished - Feb 15 1996

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  • Ophthalmology

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Evidence against a specialized mechanism for transparent surface perception. / Zhou, Yi Xiong; Shapley, Robert.

In: Investigative Ophthalmology and Visual Science, Vol. 37, No. 3, 15.02.1996.

Research output: Contribution to journalArticle

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abstract = "Purpose. We identify transparent surfaces easily in natural scenes. Does that mean the human visual system is sensitive to the physical invariants that are specific for transparent surfaces, such as the luminance cues in the figure? Methods. Eight subjects participated in 3-alternative forced choice experiments. They reported whether either the left or right square was perceived as a surface in front of the other, or if neither was seen in front. αR,βR,αL,βL are the contrasts of the edge sections of the two squares. The stimuli used satisfied αLβL>0 and αRβR>0 (Metelli's first rule). Results. 1) Transparent surface segmentation depended on contrast not absolute luminance. 2) A large contrast step along a contour, e.g. |αR|≫|βR| indicates that the right square is occluded by a surface (left square) in front. Subjects were sensitive to this cue. 3) When the contrast step was not large, e.g. |αR| ≈ |βR|, subjects were not sensitive to sign of the contrast step, i.e. whether |αR|>|βR| or |αR|< βR. This caused them to perceive a surface that was not consistent with physics, e.g. perceiving the left square as a surface in front when |αR, < |βR|. Conclusion. Our results suggest that the visual system may not have a specialized mechanism for the perception of transparency based on physical cues; the most sensitive cue (large contrast step along a contour) is likely to be detected by a mechanism that responds to T-junctions. Transparency stimuli can be used to study general mechanisms of surface segmentation. (Figure Presented).",
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