Visual Pathways: neuroscientists distinguish between two visual systems. The “What System” is located on the junction of the "occipital" and "temporal lobes," and is involved in object recognition. The “Where System” is located on the junction of the occipital and "parietal lobes," and is involved in location information. (Goldberg, 22)
Signals from the eyeballs are initially processed in the “primary visual cortex” at the back of the brain, and then diverge into two visual pathways: the “how pathway” in the parietal lobe of the brain, and the “what pathway,” linked to memories, in the temporal lobes. (SAM Oct/Nov07, 20) Messages from the retina of the eye get transmitted along the “optic nerve” before diverging into two parallel anatomical pathways, which we may call “old” and “new” pathways to indicate their evolutionary sequence. (Ramachandran, 73)
Blind Sight: (a case where) people have damaged the part of the brain that allows them to have conscious awareness of “vision.” (However), visual information (routes) to other (undamaged) parts of their brain and they are able to act in ways that show that this visual information is actually reaching those other parts, even though they have no conscious awareness of being able to see. (CampbellVA, 101)
New Pathway: one of the two pathways by which visual information enters the cortex. Allows sophisticated analysis and recognition of complex visual scenes and objects. (RamachandranTTB, 63) A neural highway that travels .... to a cluster of cells called the “lateral geniculate nucleus,” which is a relay station, en route to the primary visual cortex. From there, visual information is transmitted to (an) estimated thirty visual areas for further processing. This purportedly leads to conscious experience. (Ramachandran, 73) Required for identifying an item, even though it is incapable of locating it or orienting to it. The new pathway “projects” to the primary visual cortex in the back of the brain, where the features of the object are analyzed for color, orientation of edges, movement, and so on. Information from the new pathway splits into two pathways farther along the visual-processing course: the “how pathway” and the “what pathway.” (SAM Dec08/Jan09, 21)
How Pathway: pathway (that) goes to the regions in the parietal lobe dealing with depth and motion-allowing you to grab or dodge objects and to move around the world. (Ramachandran, 110) Answers the question) “How” do I use or interact with this object? (SAM Dec08/Jan09, 21) Concerned with space, motion, and depth. When an eye or limb needs to be moved to select one out of many targets, the (how pathway) processes (visual-spatial) cues necessary for reaching and guiding the eye, hand, or arm (that is, for action). (Koch, 129) Also referred to as the ‘dorsal pathway,’ ‘vision for action pathway,’ and ‘pathway 1.’
What Pathway: massive anatomical stream that originates in primary visual cortex, projects into “V4” and into the temporal cortex. From there, it sends “sensory neurons” into the “prefrontal cortex.” (Koch, 346) The majority of the thirty visual areas are located in this pathway. (Ramachandran, 77) This pathway goes to the regions in the temporal lobe dealing with shape, color, and object recognition. (Ramachandran, 110) Responsible for the analysis of form, contour, color, and for detecting and discriminating objects. (Koch, 129) Linked to memories in the temporal lobes. (SAM Oct/Nov07, 20) Also referred to as the ‘what system,’ the 'what circuit,' the ‘ventral pathway,’ and the ‘vision-for-perception pathway.’
Old Pathway: one of the two pathways by which visual information enters the (cerebral cortex). (RamachandranTTB, 62) Involved in location information. (Goldberg, 22) Starts in the retinas, relays through an ancient “midbrain” structure called the “superior colliculus,” and then projects, via the “pulvinar,” to the parietal lobes. Concerned with ‘spatial’ aspects of vision: where, but not what, an object is. Enables us to orient toward objects and track them with our eyes and heads. If you damage this pathway in a hamster, the animal develops a curious tunnel vision, seeing and recognizing only what is directly in front of its nose. (RamachandranTTB, 62) Also referred to as the 'where pathway,' 'where circuit, and 'where system.'
Other Visual Pathway References:
Dorsal Pathway: also referred to as “how pathway.”
How Circuit: also referred to as the "how pathway."
Ventral Pathway: also referred to as the “what pathway.”
Vision for Action Pathway: also referred to as the “how pathway.”
Vision for Perception Pathway: also referred to as the “what pathway.”
What Circuit: also referred to as the "what pathway."
What System: also referred to as the “what pathway.”
Where Circuit: also referred to as the "old pathway."
Where Pathway: also referred to as the “old pathway.”
Where System: also referred to as the “old pathway.”