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Unconscious processing in an abnormal and normal brain

Let’s take some examples of influence of unconsciousness and start from neurological disorders. The first disorder is a blindsight syndrome, of which patients think to be blind although their eyes are physically unharmed. Their “blindness” is in their brains, because of a lesion in the areas responsible for processing visual information. Due to this lesion the visual information coming from the eyes never reaches the conscious mind, although the information still exists in the brain. If the patient is asked to tell what they have been presented, they answer that they can’t see it and therefore do not know. But when they are asked to make a guess, they often answer correctly.

The second example disorder is so-called split-brain, in which the individual’s corpus callosum, the part of the brain that delivers information from one hemisphere to another, has been cut and therefore the person is not aware of visual stimuli if the picture has been presented only to the other eye. However, they are still able to correctly select the presented item with their hands from a group of different items. So, although patients are not aware that they have been presented anything at all, much less what they should have seen, they are still able to correctly pick the given item without knowing why.

The third interesting disorder, although extremely rare, is an alien hand syndrome, which causes limb movements without the patient’s awareness or will. The person can feel normal sensation in the hand but has lost the control of it. Sometimes the patient is not aware of what the hand is doing until it is brought to his or her attention, or until the hand does something that draws the patient’s attention to it. Less intrusive symptoms include involuntary grasping, touching the face or tearing at clothing, while more extreme include involuntarily stuffing food in the mouth, preventing the other hand from completing simple tasks and picking up objects and using them.

The above mentioned disorders demonstrate that there is information in our brains that we are not aware of. And the principle is the same in “normal brains”. You have probably noticed it when you hear your own name spoken in a conversation across the room that you thought you were not listening to. Your ears recorded the conversation, but because your conscious attention was focused on other tasks, you were not processing that information. At least not until the unconscious mind picked up something it decided should be passed to the conscious level for further analysis. Your name.

Thus, although the conscious level does not process that much information, the information may still be in the brain. One study investigated if people are able to process unattended information, even high-level functions that are traditionally associated with consciousness. Therefore researchers asked test subjects to concentrate on visible images while they were presented other images outside their awareness including or excluding unrelated objects. As a result, the researchers found that processing of visual imagery does not require visual awareness, but unrelated objects in images were found unconsciously. Similarly, the researchers found that the brain recognized and semantically processes words before people become aware of them. If that was surprising, consider this: yet another group of scientists noticed that people succeeded at solving subtraction and addition equations unconsciously without knowing they had been presented these arithmetic stimuli in the first place and another study even found brain activation in the areas responsible for semantic processing during presentation of sentences with ambiguous words while persons were deeply sedated.

So it already seems quite clear that information may exist at an unconscious level without distributing the information to the conscious mind. For example, you are partly blind, and yet you don’t have a clue about it, right? Every single eye has a spot without the light detecting cells required for seeing. Basically, it means that we all should have a blind spot, a small area in our field of vision without any visual information. Yet we can’t detect it. Again, the reason lies with the unconscious mind which interpolates the blind spot in one eye based on information from the other eye. Thus, we can be totally unaware of this existing handicap. Don't take my word for it, try it yourself (see below).

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