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The visual cortex is the part of the cerebral
cortex that is responsible for processing visual stimuli. It
is located at the back of the brain in the occipital lobe. It is highly specialized for processing information about static and moving objects and is
excellent in pattern recognition. Anatomically, the visual
cortex occupies the entire occipital lobe, the inferior temporal
lobe (IT), posterior parts of the patietal lobe, and a few small regions in the frontal lobe.
The visual cortex occupies about one third of the surface of the cerebral cortex in humans. It is divided into approximately thirty interconnected visual areas. The first
cortical visual area, the one that receives information directly from the Lateral Geniculate Nucleus, is the Primary Visual Cortex, or V1.
V1 transmits information to two primary pathways, called the ventral
stream and the dorsal
stream.
The ventral stream begins with V1, goes through Visual area V2, then
through Visual area V4, and to the inferior temporal
lobe. The ventral stream, sometimes called the "What Pathway", is associated with form recognition and
object representation. It is also associated with storage of long-term
memory.
The dorsal stream begins with V1, goes through Visual area V2, then
to Visual area V3, Visual area MT (also known as V5) and
to the inferior parietal lobule. The dorsal stream, sometimes called the "Where Pathway" or the "How Pathway", is associated with
motion, representation of object locations, and control of the eyes and arms, especially when visual information is used to guide
saccades or reaching.
Neurons in the visual cortex fire action potentials when visual
stimuli appear within their receptive field. A receptive field is a small region within the entire visual field. Any given neuron only
responds to a subset of stimuli within its receptive field. This property is called tuning. In the earlier visual areas, neurons
have simpler tuning. For example, a neuron in V1 may fire to any vertical stimulus in its receptive field. In the higher visual
areas, neurons have complex tuning. For example, in the inferior temporal cortex (IT), a neuron may only fire when a certain face
appears in its receptive field.
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