Interaction of optical parameters in the perception of transparency/translucency and their neural representation in the visual cortex

Transparency and translucency are important visual attributes that serve as cues for object recognition and discrimination. The interaction between light and objects involves complex processes encompassing multiple factors. In this study, we systematically manipulated parameters of light transmission, scattering, and reflection to investigate their effects on perceived transparency/translucency in human subjects. We found that the extinction coefficient, a parameter governing transmission, exerts the greatest influence on perceived transparency/translucency across objects of varying shape complexity. However, albedo, which indicates the amount of scattering, also significantly affects the perceived transparency/translucency of objects with relatively simple geometries. Additionally, surface roughness, a reflection parameter, strongly influenced perceived transparency/translucency. We then examined single-neuron activities in the inferior temporal cortex of the macaque monkey, where previous studies have identified gloss-selective neurons. We recorded neural responses using stimulus sets comprising the same parameters tested in our psychophysical experiments. Many neurons exhibited selectivity for parameters related to perceived transparency/translucency, including extinction coefficient, albedo, and surface roughness. Furthermore, population responses of neurons selective for these parameters showed interaction patterns consistent with those observed in our psychophysical experiments. This suggests that neurons selective for these parameters in this area are related to the perception of transparency/translucency.