Figure 1.
Properties of natural scenes include material properties, such as surface reflectance and surface roughness, lighting properties such as shadows and shading, and occlusion-related features such as T junctions. Feedback to the primary visual cortex (V1) from subsequent stages that estimate surface material properties needs to be subtle enough that it does not disrupt the input to subsequent stages that estimate lighting properties, and vice versa. The same logic holds for all properties of natural scenes that are estimated by subsequent stages in the visual system. Thus, it is expected that under most circumstances, V1 responses will be dominated by feedforward signals and modestly influenced by feedback signals.