Occipital Lobe

The Occipital Lobes are most posterior, at the back of the head.

Functions:

Vision.

Observed Problems:

Defects in vision (Visual Field Cuts).
Difficulty with locating objects in environment.
Difficulty with identifying colors (Color Agnosia).
Production of hallucinations
Visual illusions - inaccurately seeing objects.
Word blindness - inability to recognize words.
Difficulty in recognizing drawn objects.
Inability to recognize the movement of an object (Movement Agnosia).
Difficulties with reading and writing.

The occipital lobes are the center of our visual perception system. They are not particularly vulnerable to injury because of their location at the back of the brain, although any significant trauma to the brain could produce subtle changes to our visual-perceptual system, such as visual field defects and scotomas.
The Peristriate region of the occipital lobe is involved in visuospatial processing, discrimination of movement and color discrimination (Westmoreland et al., 1994).
Damage to one side of the occipital lobe causes homonymous loss of vision with exactly the same "field cut" in both eyes.
Disorders of the occipital lobe can cause visual hallucinations and illusions. Visual hallucinations (visual images with no external stimuli) can be caused by lesions to the occipital region or temporal lobe seizures. Visual illusions (distorted perceptions) can take the form of objects appearing larger or smaller than they actually are, objects lacking color or objects having abnormal coloring.
Lesions in the parietal-temporal-occipital association area can cause word blindness with writing impairments (alexia and agraphia) (Kandel, Schwartz & Jessell, 1991).

The occipital lobe is the main target for axons from the thalamic nuclei that receive input from the visual pathways. Damages to the occipital lobe causes blindness or what is called cortical blindness. A person with cortical blindness has normal eyes, normal pupillary reflexes and some eye movements, but no pattern of perception and no awareness of visual information. Kolb & Wishaw (1990) have identified eight principle symptoms of temporal lobe damage:
1) disturbance of auditory sensation and perception,
2) disturbance of selective attention of auditory and visual input,
3) disorders of visual perception,
4) impaired organization and categorization of verbal material,
5) disturbance of language comprehension,
6) impaired long-term memory,
7) altered personality and affective behavior,
8) altered sexual behavior.
Selective attention to visual or auditory input is common with damage to the temporal lobes (Milner, 1968). Left side lesions result in decreased recall of verbal and visual content, including speech perception. Right side lesions result in decreased recognition of tonal sequences and many musical abilities. Right side lesions can also effect recognition of visual content (e.g. recall of faces). The temporal lobes are involved in the primary organization of sensory input (Read, 1981). Individuals with temporal lobes lesions have difficulty placing words or pictures into categories.
Language can be effected by temporal lobe damage. Left temporal lesions disturb recognition of words. Right temporal damage can cause a loss of inhibition of talking.
The temporal lobes are highly associated with memory skills. Left temporal lesions result in impaired memory for verbal material. Right side lesions result in recall of non-verbal material, such as music and drawings.
Seizures of the temporal lobe can have dramatic effects on an individual's personality. Temporal lobe epilepsy can cause perseverative speech, paranoia and aggressive rages (Blumer and Benson, 1975). Severe damage to the temporal lobes can also alter sexual behavior (e.g. increase in activity) (Blumer and Walker, 1975).