Chapter 11: The Occipital Lobes

- More is known about the occipital lobes than any other region of the cortex
- Even though vision is the exclusive function of the occipital lobes, other parts of the cortex have visual functions that are closely associated with occipital areas
    - More cortex is devoted to visual function than any other activity (in primates)
- Anatomy 
    - Form the posterior pole of the cerebral hemispheres- under the occipital bone
    - Distinguished from parietal lobe by the parietal-occipital sulcus
    - Calcarine fissure divides the upper and lower halves of the visual world 
- Subdivisions
    - Can identify at least 6 different optical regions (V1, V2, V3, V3A, V4, and V5)
        - Area V5 is also called MT
        - Area V3 is sometimes subdivided into dorsal (dV3) and ventral (vV3 or VP)
            - Upper and lower fields may have different functions
- Information assembled in V1 and V2 areas before sending out to other areas
    - Like mailboxes
- 3 parallel pathways from V1 and V2 that are concerned with different attributes of vision

    - Information from V1 goes to V4- color area
    - V1-> V2 -> V5- motion detection
    - Input to V3- shape of objects in motion
- Damage to V3, V4, & V5 produce specific deficits in vision
    - Damage to V4- only see shades of gray
        - Cannot recall colors from before injury
        - Loss of color cognition
    - Damage to V5- inability to perceive objects in motion
    - V1 lesions- people act blind even though visual input can get to higher areas
        - Say they see nothing, but they can act on visual information
- Multiple visual regions in the parietal, temporal, & frontal lobes
    - Vision for action- function of the parietal visual areas
        - Reaching out hand to pick up a cup, etc.
    - Action for vision
        - Make more eye scans directed to the left visual field of a person's face
            - May be important in the way we process faces because not found in the scanning of other stimuli
    - Visual recognition- recognizing faces, putting a meaning to letters and symbols
    - Visual space- visual information comes from specific locations in space
        - Probably some form of spatial processing in both the parietal and temporal regions
    - Visual attention- we cannot process all the visual information around us at one time.
- Disorders of visual pathways
    - Destruction of the retina or optic nerve of one eye produces monocular blindness
        - Loss of sight in that eye
    - Lesion of the medial region of the optic chiasm- produces bitemporal hemianopia
    - Lesion of the lateral chiasm resul
ts in a loss of vision of one nasal field- nasal hemianopia
    - Complete cuts of the optic tract, LGN, or area V1 result in homonymous hemianopia
        - Blindness of one entire visual field
        - If lesion is partial, then quadrantic anopia occurs- destruction of one portion of a visual field
    - Small lesions of the occipital lobe- produce scotomas
        - Small blind spots in the visual field


Image: http://www.lea-test.fi/en/vistests/pathways/images/pathway3.jpg

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