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Occipital Lobe Pathologies

Cortical blindness The occipital cortex is topographically mapped to the visual field, and lesions here lead to corresponding cortical blindness in the contralateral area of the visual field.

Blindsight Some cortically blind people may respond to visual stimuli. This phenomenon is known as blindsight and has been extensively studied by British psychologist Lawrence Weiskrantz (1926—), who conducted studies in the early 1970s after German neuroscientist Ernst Poppel (1940-) had observed the phenomenon. Some blindsighters can negotiate complex environments without relying on touch or sound. Some can catch thrown balls. Thus, blindsighters retain nonconscious yet vision-related capacities for understanding where objects are in space. We all have such capacities, but they are masked by conscious visual perception. Any fast enough visually dependent action, such as returning a fast ball in baseball or a highspeed tennis serve, makes the need for blindsight-related capacities clear, as there is no time for a conscious reaction.[1]

Visual agnosia: not knowing what is seen Occipital lobe damage may lead to impaired ability to visually recognize familiar objects. In some cases, a person may have difficulty in recognizing all objects. In other cases, the agnosia may be limited to faces (prosopagnosia) or written text (alexia). As we will see, damage to the temporal lobe may lead to visual agnosia as well.

Occipital lobe summary

The occipital lobe is a starting point for visual processing with a topographic map of the visual field. As one follows the forward-moving dorsal and ventral streams of processing, one finds structures for identifying and locating things in space. Lesions in them can give rise to many conditions with phenomenological effects.

  • [1] Further reading on blindsight: Holt (2003).
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