Visual extinction

Visual extinction is a neurological disorder which occurs following damage to the parietal lobe of the brain. It is similar to, but distinct from, hemispatial neglect. Visual extinction has the characteristic symptom of difficulty to perceive contralesional stimuli when presented simultaneously with an ipsilesional stimulus, but the ability to correctly identify them when not presented simultaneously. Under simultaneous presentation, the contralesional stimulus is apparently ignored by the patient, or extinguished. This deficiency may lead to difficulty on behalf of the patient with processing the stimuli’s 3D position. Visual extinction is a neurological disorder which occurs following damage to the parietal lobe of the brain. It is similar to, but distinct from, hemispatial neglect. Visual extinction has the characteristic symptom of difficulty to perceive contralesional stimuli when presented simultaneously with an ipsilesional stimulus, but the ability to correctly identify them when not presented simultaneously. Under simultaneous presentation, the contralesional stimulus is apparently ignored by the patient, or extinguished. This deficiency may lead to difficulty on behalf of the patient with processing the stimuli’s 3D position. Visual Extinction is the result of unilateral cerebral damage and has always been poorly understood. Researchers have been studying visual extinction in great depth since the 1990s. It has since been commonly associated with damage to the right hemisphere of the brain. Studies have suggested that visual extinction may be a result of sensory imbalance. This imbalance is due to weak or delayed afferent inputs in the hemisphere affected by the extinction. Research done by Pavlovskaya, Sagi, Soroker and Ring show that visual extinction is dependent on simple stimuli properties. These properties are thought to reflect connectivity constraints during the early steps of visual processing. Visual extinction arises from damage to the parietal lobe of the brain. This damage most frequently arises following a stroke or other infarction in that area – however, any traumatic event sufficient to cause widespread tissue damage in the area may cause sufficient harm. Although both sides of the brain are vulnerable to such damage, it is more unusual for extinction to occur when the left hemisphere is damaged than the right. When presented with simultaneous stimuli, the patient will ignore the contralesional stimuli, and only report the ipsilesional. Their ability to report the stimuli correctly when presented singly indicates that this is not a problem with vision per se. This bias against contralesional stimuli is evident even when patients are presented with two signals within the ipsilesional visual field, whose processing remains intact following the damage, since it is done in the opposite brain hemisphere. This implies that extinction can be somewhat controlled by biasing the point of visual fixation contralesionally, such that all relevant stimuli are contained within the functioning side of the visual field, findings supported in experiment Fatigue and habituation effects have previously been connected to visual extinction; experiments such as those done by Vuilleumier and Rafal eliminate the connection of these effects with visual extinction. Historically, it was believed that the parietal damage weakened afferent neuron input to the visual cortex, and so the extinction event was caused by the signals originating in the contralesional field being lost during transmission. However, this does not account for the ability of extinction patients being able to correctly identify contralesional stimuli in isolation. A more current theory is called the 'race theory.'