Two separate neural mechanisms of brightness induction.

A particular rate of quantal absorption by photoreceptors may result in a dim or an intense percept, depending on light stimulating other parts of the retina. The brightness of an object in a natural scene, therefore, depends on the amount of light reflected from the object in comparison to light from other parts of the scene. We show this phenomenon is mediated by two separate neural mechanisms at distinct levels of the visual system. The first mechanism depends on retinal image contrast between adjacent regions. The second mechanism depends on the binocularly fused "cyclopian" representation and is influenced by more remote, noncontiguous areas of the visual field.