From orientations to objects: Configural processing in the ventral stream.

The ventral or form vision hierarchy comprises a sequence of cortical areas in which successively more complex visual attributes are extracted, beginning with contour orientations in V1 and culminating in face and object representations at the highest levels. In addition, ventral areas exhibit increasing receptive field diameter by a factor of approximately three from area to area, and conversely neuron density decreases. We argue here that this is consistent with configural combination of adjacent orientations to form curves or angles, followed by combination of these to form descriptions of object shapes. Substantial data from psychophysics, functional magnetic resonance imaging (fMRI), and neurophysiology support this organization, and computational models consistent with it have also been proposed. We further argue that a key to the role of the ventral stream is dimensionality reduction in object representations.