Figure 43: How the Brain Makes Sense of What It Sees - The Dorsal and Ventral Visual Pathways, and a 3 Tiered Approach to Vision

1) Ventral ("what") stream - this begins with the ‘P' retinal ganglion cells à parvocellular layers of the lateral geniculate nucleus (LGN, 3-6) à V1/striate cortex (in blue) à V4/V4a (fusiform and lingual gyri) à occipitotemporal regions. 2) Dorsal ("where") stream - this begins with the ‘M' retinal ganglion cells à magnocellular layers of the LGN (1, 2) à V1/striate cortex à V5/V5a à occipitoparietal regions. Balint syndrome consists of simultanagnosia, optic ataxia, and oculomotor apraxia, although one feature (e.g., simultanagnosia) can be appreciated in the absence of the others. *For objective identification (general visual agnosia) - in the left hemisphere, think "words" (pure alexia) and in the right hemisphere, think "faces and places" (prosopagnosia, topographagnosia). (The classification of cerebral visual dysfunction using a 3-tiered approach is courtesy of Dr. Jason Barton. The figure was developed with the input of Dr. Victoria Pelak.)