Notes

VENTRAL STREAM

Comprises the what, object recognition pathway (or P pathway).
Cone photoreceptors are responsible for color detection and excite parvocellular ganglion cells of the what pathway.
Within this stream, components of objects are integrated to allow for cohesive object identification.

Comprises the where spatial localization (or M pathway).
Rod photoreceptors are responsible for motion detection and excite magnocellular ganglion cells of the where pathway.
Within this stream, numerous visuospatial processing centers exist.

Responsible for the cortical initiation of many different classes of eye movements.

Lies along the calcarine sulcus of the medial face of the occipital lobe at the tip of the lateral occipital pole.

Called V1 because visual cortical stimuli first collect in this area and called striate cortex because of the heavy myelination of its fourth cytoarchitectural layer, which produces a white stripe called the stria of Gennari.
V1 processes the most basic visual properties (eg, line orientation, motion direction, luminance, orientation, and color).
Encodes the visual field from the opposite half of the world - right V1 encodes the left visual field and left V1 encodes the right visual field.
The cortical representation of central, or macular, vision lies in the posterior calcarine sulcus and occupies a large cortical area relative to its small retinal expanse, whereas representation of the peripheral retina lies in the anterior calcarine sulcus and encompasses a small cortical area relative to its broad retinal expanse.
The upper bank of the calcarine sulcus encodes the lower half of the visual field and the lower bank encodes the upper half of the visual field.

Secondary visual cortex is V2 and corresponds to Brodmann area 18.
Tertiary visual cortex is V3 and corresponds to Brodmann area 19.
On the medial face of the cerebral hemisphere, V2 lies above and below V1, and V3 lies above and below V2.
On the lateral surface of the hemisphere, V2 comprises a small strip of the posterior occipital lobe, just anterior to V1; V3 lies in front of V2.
The secondary and tertiary visual cortices process simple visual properties akin to those processed in V1.
V2 also processes illusory boundaries - contours that cannot actually be visualized but that are implied by the context of a larger scene.

Lies on the medial and lateral surfaces of the cerebral hemisphere, in the ventral-occipital lobe, inferior to V3.
One important aspect of color processing found within area V4 is that of color constancy, which is the property of color vision wherein regardless of the illumination cast on an object, the object maintains its perceived color.
- Clinical corollary: ventral occipito-temporal injury causes a color processing deficit, called achromatopsia, which results in the visual world appearing drained of color.
- Injury to area V4, alone, may or may not be sufficient to cause achromatopsia.

Lies in the lateral aspect of the hemisphere, anterior to V4.
Responds disproportionately strongly for object recognition.
Displays perceptual constancy, meaning an object can be recognized equally well regardless of such properties as object viewpoint, size, or illumination; it also displays form-cue invariance, meaning, for example, that an object is equally identifiable whether it is viewed in the form of a drawing or a photograph.