Depth inversion with a 3D structure influences brightness perception

Whether or not depth perception influences brightness and/or lightness
perception has been repeatedly discussed, and some studies have emphasized
its importance. In addition, a small number of studies have empirically
tested and shown the effect of depth inversion, such as seen in the Mach
card illusion, on perceived lightness, and they interpreted such results
in terms of lightness constancy. However, how perceived brightness changes
contingent on depth inversion remains unexplained. Therefore, this study
used the matching method to examine changes in brightness perception when
depth inversion is observed. We created and used a three-dimensional (3D)
concave object, composed of three sides made of card stock, which could be
perceived as having two different shapes in 3D; it could be perceived as a
horizontal concave object, corresponding to its actual physical structure,
and as a convex standing object, similar in shape to a building.
Participants observed this object as both a concave object and as a convex
object, and judged the brightness of its surfaces during each observation.
Our results show that the perception of the brightness of the object’s
surfaces clearly changed depending on the perception of depth. When the
object was seen as convex, one part of the surface was perceived as darker
than when the object was seen as concave, but the other part of the
surface remained unchanged. Here we discuss the relationship between depth
perception and brightness perception in terms of perceptual organization.