On the role of figural organization in perceptual transparency.

Abstract

Metelli (1974) made an important contribution by identifying order and magnitude restrictions for a pattern of intensities and showing that when they are satisfied the perception of transparency readily occurs. These restrictions were derived from a physical model of transparency. We argue that the visual system does not use intensity information to compute indices of transmittance and reflectance analogous to what an optical engineer might do in describing a physical instance of transparency. Rather, a lightness pattern affects perceptual transparency, just as geometric properties do, through processes that impose an organization on sensory information rather than through processes that recover quantitative descriptions. In the absence of depth cues, such as stereopsis and motion parallax, the perception of transparency occurs when the lightness relations in a pattern favor the perception of a continuous boundary across x-junctions. We present evidence for two kinds of violations of the order and magnitude restrictions: simple and strong. Transparency judgments, although reduced in number, still occur for simple violations of the order and the magnitude restrictions. Transparency judgments occur relatively infrequently for strong violations. A physical model of transparency fails to capture the difference between simple and strong violations of the order and magnitude restrictions. We discuss (1) the basis for differentiating between simple and strong violations of the order and magnitude restrictions, (2) the effect simple and strong violations have on the perception of transparency, and (3) the occurrence of transparency with and without color constancy (i.e., the color seen through the transparent surface looks or fails to look the same as the color seen directly).