Voluntary attention modulates the brightness of overlapping transparent surfaces.

A new class of brightness illusions is introduced that cannot be entirely accounted for by bottom-up models of neuronal processing. In these new illusions, brightness can be modulated by the location of voluntary attention in the absence of eye movements. These effects may arise from top-down or mid-level mechanisms that determine how 3D surfaces and transparent layers are constructed, which in turn influence perceived brightness. Attention is not the only factor that influences perceived brightness in overlapping transparent surfaces. For example, grouping procedures may favor the minimal number of transparent layers necessary to account for the geometry of the stimulus, causing surfaces on a common layer to change brightness together. Attentional modulation of brightness places constraints on possible future models of filling-in, transparent surface formation, brightness perception, and attentional processing.