Conscious visual representations built from multiple binding processes: evidence from neuropsychology.
I review neuropsychological evidence, from patients with selective brain lesions, indicating that there can be several kinds of binding in vision. Damage to early processes within the ventral visual stream impairs the binding of contours into shapes. This impairment can leave unaffected a more elementary operation of binding form elements into contours. Thus the process of binding elements into a contour is distinct from the process of binding contours into more wholistic shapes. In other patients with damage to the parietal lobe, there can be poor binding of shape to surface information in objects. This problem in turn can co-exist with a relatively intact process of binding of contours into shapes. These findings suggest that there are multiple stages of binding in vision, including binding to derive shape descriptions (in the ventral visual stream) and binding shape and surface detail together (involving interactions between the ventral and dorsal streams). I also discuss evidence for transient binding based on common onsets of stimuli. I conclude that the unity of consciousness is derived from several separable neural processes of binding.