4. visual perception - disorders (2)

The two types of disorders discussed of visual perception are Hemispatial neglect and blindsight.
Neglect is a spatial mechanism and commonly a result of stroke and is associated with damage to the right parietal lobe. It is also caused from damage to the frontal cortex.
Those with damage to the left side can recover in as little as a few hours, however, damage to the right side can lead to long term neglect and there are no established treatments for neglect.
Object neglect is very rare and occurs when patients can see both parts of their surroundings but only have the ability to copy the image of what is presented on their right hand side.
Many experiments have been conducted to investigate this specific type of disorder. Many of the common ones used were the copying and painting task, reporting items in a room task and the cancellation task.
The cancellation task involved patients who were asked to cross out every line they see. (see left)

The video above demonstrates the concequences of visual difficulty caused by a stroke leading to neglect.
Gordon Holmes was a British Psychologist who found whilst studying bilateral lesions of parietal cortex following gun shot injuries, damage to the parietal cortex (which is involved in spatial representation) leads to visual disorientation.
Extinction is when patients are aware of objects in both areas of field but when there is visual information on both sides of the field, the patient will only see what is on the right hand side.
Neglect is modulated depending on a number of factors. If more stimuli compete in the visual field, the patient becomes distracted. The severity of neglect depends on the number of competing stimuli.
Kaplan et al constructed the group study task which suggested that neglect is not a lack of awareness of one half of space, it is a directional bias modulated by competing stimuli. patients with right parietal lesions also have impaired detection on their supposedly good right side.


Many neglect patients revisit locations on the right failing to keep track of where they have looked before.
Studies also suggest that neglect patients show deficits on non spatial tasks and it has also been found that spatial deficits interact with non spatial deficits. Research indicates that damage to the intraparietal sulcus affects memory.