This type of visual neglect can sometimes occur after a stroke, unfortunately there is no established treatment for this disorder and therefore it is important that research continues to be carried out, in order for us to understand the underlying mechanisms. So far researchers have identified a few different areas of the brain that they believe to be involved in this disorder, damage to the parietal lobe and lesions to the inferior frontal lobe have both been found to be related. The good news about this disorder is that two thirds of people diagnosed with Hemispatial neglect do recover with time.
There are a number of tasks that are used to study people with this disorder. Firstly researchers can track eye movements, this shows exactly where the individual looks, when they are shown an image, patients with hemispatial neglect tend to only focus on the right side of an image.
Another task often used is a copying or painting task. This involves asking the individual to either copy an image that is displayed to them on a screen, or paint something, such as a self portrait. Below there are two examples of drawings done by people who have hemispatial neglect. This clock is a particularly good example of how this disorder works, nearly the whole of the left side of the clock is not visible to the patient showing they are lacking severely in visual perception on the left side of their visual field. The flower drawing below is another example of a patient with a very limited visual field.
Patients can also be assessed by means of a cancellation task.. Patients would be given a piece of paper with lines, like the image to the right and asked to put a line through all of the lines they could see, very often only the lines to the right of the centre would receive a cross.
There are three main defecits that people with hemispatial neglect can have, these factors can vary in quanity which help to explain why there can be such vast differences between individuals who suffer from the disorder
1. A reduced processing capacity
2. An impairement in keeping track of there eye movements and remembering where they have looked before.
3. Inability to sustain attention on a given task.
Blindsight- This is a phenomenom where people have been found to have blindness in a certain area of there visual field. Patients have no visual awareness of stimuli, however when they are asked to predict aspects of a certain stimuli such as location or movement of an object, they are able to predict correctly, at levels significantly above chance. This is different from residual blindness because patients with residual blindness only have light perception- this is the ability to tell light from dark and judge the direction of a light source, they can not make predictions of the movement of locations of objects within the visual field.
Blindsight suggests a seperation between conscious perception and fast motor reactions, Milner and Goodale offer an explanation for this in there'two visual brains' theory. They suggest that there are TWO vision systems one for visual perception (conscious awareness) )and one for visuomotor control (unconscious).
Visuomotor control happens in the Dorsal stream which provides automatic, unconscious vision for action, it processes spatial information and is responsible for abilities such as returning a football that is passed to us. It contains a map of the visual field and is also good at detectig and analysong movements. It is responsible for Online/unconscious decisions that are made in the here and now, it is the evolutionary 'older' cortical pathway and ends in the posterior parietal cortex.
However the Ventral Stream is in charge of the visual perception system and travels to the temporal lobe, it is involved in object identification and form representation.
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