The term "visual form agnosia" describes a disorder characterized by problems recognizing objects, poor copying,and distinguishing between simple geometric shapes despite normal intellectual abilities. Visual agnosia has been interpreted as a disorder of the magnocellular visual system, caused by an inability to separate figure from ground by sampling information from extended regions of space and to integrate it with fine-grain local information.
The parvocellular and magnocellular pathways are thought to be largely independent visual processing streams, which process different aspects of visual information. The magnocellular pathway is thought to process information about the location and movement of objects, while the parvocellular pathway is thought to process information that is useful for recognition and identification of objects.
In strabismic amblyopia, the cells in the parvocellular pathway may be more involved, whereas the magnocellular pathway may be relatively spared.
Evaluation of the Functions of the Parvocellular and Manocellular Pathways in Strabismic Amplyopia.
Journal of Pediatric Ophthalmology and Strbusmus (July / August 2002)