Transparent layer constancy improves with increased naturalness of the scene.

The extent to which hue, saturation, and transmittance of thin light-transmitting layers are perceived as constant when the illumination changes (transparent layer constancy, TLC) has previously been investigated with simple stimuli in asymmetric matching tasks. In this task, a target filter is presented under one illumination and a second filter is matched under a second illumination. Although two different illuminations are applied in the stimulus generation, there is no guarantee that the stimulus will be interpreted appropriately by the visual system. In previous work, we found a higher degree of TLC when both illuminations were presented alternately than when they were presented simultaneously, which could be explained, for example, by an increased plausibility of an illumination change. In this work, we test whether TLC can also be increased in simultaneous presentation when the filter's belonging to a particular illumination context is made more likely by additional cues. To this end, we presented filters in differently lit areas of complex, naturalistically rendered 3D scenes containing different types of cues to the prevailing illumination, such as scene geometry, object shading, and cast shadows. We found higher degrees of TLC in such complex scenes than in colorimetrically similar simple 2D color mosaics, which is consistent with the results of similar studies in the area of color constancy. To test which of the illumination cues available in the scenes are actually used, the different types of cues were successively removed from the naturalistically rendered complex scene. A total of eight levels of scene complexity were examined. As expected, TLC decreased the more cues were removed. Object shading and illumination gradients due to shadow cast were both found to have a positive effect on TLC. A second filter had a small positive effect on TLC when added in strongly reduced scenes, but not in the complex scenes that already provide many cues about the illumination context of the filter.

The effect of scene articulation on transparent layer constancy.

In this article, we examine the influence of scene articulation on transparent layer constancy. We argue that the term articulation may be understood as an aspect of the more general concept naturalness of a stimulus that relates to the degree of enrichment compared with a minimal stimulus and to the extent to which a stimulus contains regularities that are typically found in natural scenes. We conducted two matching experiments, in which we used strongly reduced scenes and operationalized articulation by the number of background reflectances (numerosity). The results of the first experiment show that higher numerosity actually leads to an increase in transparent layer constancy when reflectances are randomly drawn from a fixed population. However, this advantage disappears if the spatial mean and the variation of the subset colors are controlled as in our second experiment. Furthermore, our results suggest that the mechanism underlying transparent layer constancy leads to a rather stable compromise between two matching criteria, namely, proximal identity and constant filter properties according to our perceptual model. For filters with an additive component, which appear more or less hazy, we observed improved recovered filter properties and correspondingly higher degrees of transparent layer constancy, suggesting an additional mechanism in this type of filter.

Transparent layer constancy is improved by motion, stereo disparity, highly regular background pattern, and successive presentation.

The visual system uses figural and colorimetric regularities in the retinal image to recognize optical filters and to discern the properties of the transparent overlay from properties of the background. Previous work suggests that the perceived color and transmittance of the transparent layer vary less under illumination changes than it would be expected from corresponding changes in the input. Here, we tested how the degree of this approximate transparent layer constancy (TLC) depends on factors that presumably facilitate the decomposition into a filter and a background layer. Using an asymmetric filter matching task, we found that motion, stereo disparity, and a highly regular background pattern each contribute to the vividness of the transparency impression and the degree of TLC. Combining these cues led to a cumulative increase in TLC, suggesting a "strong fusion" cue integration process. We also tested objects with invalid figural conditions for transparency (T-junctions). The tendency to perceive these objects as opaque and to establish a proximal match increased the more conspicuous the violation of this figural condition was. Furthermore, we investigated the gain in TLC due to alternating presentation. Alternating presentation enhanced TLC and color constancy to a comparable degree, and our results suggest that adaptation contributes to this effect.

Transparent layer constancy under changes in illumination color: Does task matter?

If the perceived transmittances of transparent objects are matched across illuminants, only incomplete constancy is found. This implies that physically identical objects may appear different. Nevertheless, it was reported in the literature that subjects could almost perfectly identify such objects across illuminants, even if a transparency impression was suppressed by violating geometric transparency conditions. A potential interpretation of these findings is that (a) identification and matching rely on different criteria and processes and that (b) identification is solely based on low-level color information. We here present evidence against these hypotheses. Our results show that the best match, that is, the transparent object under the test illuminant that appears most similar to the standard, is also the preferred object in the identification task. Furthermore, we found that the degree of constancy increases in both tasks, if figural cues support a transparency impression and the accompanying color scission. We discuss the relation between matching and identification suggested by these findings.