Visual Extinction is a condition caused by damage to the parietal lobe, and is similar, although distinct from Visual Neglect.
It is characterised by the ability to see stimuli in the opposite visual field to the brain damage, but only when there is no competition from other stimuli in the visual field on the same side as the brain damage. If there are stimuli in both visual fields then only the one which is projected to the intact side of the brain will be seen.
It is diagnosed using confrontation testing:
– the experimenter wiggles their left/right fingers or both in the air while sitting opposite the patient
– patient can detect each finger when they are presented separately
– however, if both are presented then they can only detect the finger on the left (assuming the right parietal lobe is damaged)
The video below shows a variation of this technique:
However, there are some circumstances in which extinction can be reduced.
Riddoch (2003) presented patients with pairs of objects, which were correctly or incorrectly presented for action. For example, a corkscrew pointing towards the cork in a wine bottle (correct), or at the bottom of the bottle (incorrect).
The results showed that they were better at reporting both items when they were correctly presented for action. When one item was extinguished, they were more likely to report the active item, even if it is in the impaired visual field.
Therefore, which object they reported was influenced by the interaction between them.
This finding was important as it suggests that extinction occurs quite late, in higher-order visual areas and there is some unconscious processing of extinguished items.
Like Neglect, extinction can also occur in motor actions, not just vision.
For example, several case studies have shown that patients can use both arms equally well separately, but become much worse at using their bad arm when doing so at the same time as the good arm.
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