The primary functions of the occipital lobe include certain aspects of visual processing. Information received by the eyes is sent on to the primary visual cortex in the occipital lobe, which is further processed by two levels of the visual association cortex. Damage to the primary visual cortex may result in blindness, while damage to the visual association cortex may cause visual agnosia.
The cerebral cortex is divided into four lobes: the frontal lobe, the temporal lobe, the parietal lobe, and the occipital lobe. As the brain is separated into two hemispheres, the right and left, it contains two of each lobe, each having a different function in the brain. The frontal lobe is involved in movement and planning, while the temporal lobe is involved in auditory processing. The primary function of the parietal lobe is body perception, or somatosensation, while the occipital lobe, located towards the back of the cerebral cortex, is involved with vision.
Visual processing is achieved by the primary visual cortex via the optic nerves connected to the eyes, which send information to the thalamus; this information is then sent on to the primary visual cortex. When information is received by the primary sensory cortex, it is sent on to regions located adjacent to it, called the sensory association cortex. One of the main functions of the occipital lobe is to send information from the primary visual cortex to the visual association cortex. The visual association cortex is located in more than one lobe, meaning that the other lobes, besides the functions of the occipital lobe, are also involved in vision. These areas analyze the visual information received by the primary visual cortex and store visual memories.
There are two levels of the visual association cortex. The first level, located around the primary visual cortex, receives information about movement of objects and color,as well as receives information about perception of shapes. The second level, located in the middle of the parietal lobe, is responsible for perception of movement and location. This level is also located in the lower part of the temporal lobe, which is responsible for information about three-dimensional form.
Damage to the functions of the occipital lobe cause different visual impairments. If the primary visual cortex is damaged completely, it will result in blindness because the primary visual cortex has a visual field mapped on its surface. Damage, therefore, results in a dysfunction in this mapped area. Lesions to the visual association cortex do not result in blindness; instead, a patient may have trouble recognizing objects, a deficit called visual agnosia. For example, a patient may be able to pick up a clock and recognize the object through touch; however, if shown a picture of a clock, will only be able to describe elements of the picture, such as the round surface of a clock face.