Dorsal-ventral integration in object recognition.

The idea of two parallel hierarchical pathways in vision has fueled a great deal of research and enhanced our understanding of visual processing in the brain. However, after 25 years, it has become clear that the earlier distinctions in terms of neuroanatomy and functional dissociation are less pure than originally considered. Dorsal visual areas may exhibit object-selective responses and many 3-D cues of shape, particularly structure-from-motion, appear to be computed exclusively by dorsal areas. These findings imply a more important role for dorsal visual areas in object recognition than previously considered and also place restrictions on the nature of ventral object representations. These representations will need to include information about the objects in 3-D, making them more viewpoint-invariant. They will also need to be invariant to the 3-D cue used to describe them. Through the discussion of relevant findings in psychophysics, single-unit electrophysiology, neuroanatomy and functional imaging, I suggest that these qualities are indeed present in ventral stream representations. Thus dorsal visual areas that extract 3-D structure of shapes from certain cues, can relate these representations to cue-invariant and view-invariant representations in the ventral stream.