Split-brain and the Unnecessity of Consciousness for “Conscious” Behaviour

In this article we will discuss the observations done in some experiments with split-brain patients. Specifically we will consider two kinds of neurological experiments and their impact on our understanding of consciousness. The first experiment you can see here:

People who have had their corpus callosum cut are said to have a split-brain. The corpus callosum is the part of the brain which allows the two hemispheres of the brain, the left and the right, to communicate; to send signals to each other. Thus, when the corpus callosum is cut, the two hemispheres cannot communicate – meaning that the left does not “know” what the right does and vice versa. Typically, the corpus callosum is cut to treat severe epilepsy and most research about lateralization of the brain has been done on so-called split-brain patients.

Tests done on such patients have revealed very interesting things, particularly when it comes to consciousness. In most people, the left-hemisphere controls speaking. Furthermore, the left hemisphere controls the physical right part of the body (right arm, right eye etc.) and vice versa.

  • Experiment 1: The patient is told to fix their eyes on a dot on a screen. Then words or objects will be shown on the left or right of the dot. After a word or object is shown, the patient is asked to repeat the word or name the object. 

When an object or word is shown to the right of the dot, so that the information goes to the left hemisphere, the patient can easily name or repeat what is shown. When the word or object is shown to the left of the dot so that the right hemisphere receives the information, the patient says he/she did not see anything. They are not consciously aware that they saw anything because whatever the consciousness is, the information from the left eye is not given to it. However, and here comes the interesting part, when the patient is asked to close his eyes and draw with his left hand, he draws without exception what was shown. When asked why he drawed whatever it was, he cannot answer why – he does not consciously know.

It seems that what is going on is that the right hemisphere knows what was shown, but this is not communicated to the verbal, conscious hemisphere. When asked to draw it, his consciousness does not know what to draw – there is nothing to draw because he did not see anything. However, the right hemisphere is obviously also capable of hearing and understanding this question, and will therefore, using the left hand that it controls, draw what it saw.

Thus, we see that consciousness is not necessary to perceive and answer questions, or interpret input. In the video the test subject is shown the word “pan” and draws a pan, meaning that the unconsciousness is capable of relating abstract concepts to physical objects.

There is also a variation of this test, where the subject is presented two separate visual cues at the same time, one in each visual field. Upon being asked to pick out a word from a list matching what he saw using his left hand, the subject would correctly choose the word most related to what his left eye saw. However, when asked why this particular word was chosen, the subject would try to connect it to what the right eye saw – even if the connection is less direct than to what the right eye saw.

  • Experiment 2: In an experiment similar to the one above, lightbulbs were fixed in a horizontal line on a plate and the test subject was told to focus on the middle of the plate. Then the lights would be turned on and off in different patterns.

When asked if he saw any light being turned on, the test subject would always answer correctly for the lights on the right side, but say that he saw no lights on the left side – even when they were lit. This is what he consciously observed. When asked to point at the lights as they turned on, the test subject would point at both the lights to the right and to the left, using his right and left arm respectively. His consciousness did not perceive the lights on the left, but the part of the brain, that controls the left arm, both understood the command to point and perceived the lights, and, thus, performed the correct action: pointing.

This is sometimes called “alien hand syndrome”; the action of the hand is clearly deliberate and purposeful – an outside observer would immediately recognize it as conscious behaviour – but the person himself cannot control it or explain why he did it.

Inconclusive conclusions and some speculation

Exactly what consciousness is and its role in everything is a mystery even today, but at least it is clear that complicated information processing and behaviour can be performed without consciousness as we commonly think of it, lending weight to the claim that consciousness is “overrated”. It is not necessarily the controlling organ as we think of it.951147-futurama

The first experiment also illustrates that our reasoning often works, not to decide our actions, but to explain them. The real reason why the left hand chose a particular word was unknown to the left hemisphere, yet the test subject tried to find an explanation. Only when the action performed by the left side of the body was sufficiently foreign to the consciousness did the subject admit ignorance. This is something I think most people without split-brains also experience. When we do something that, when we stop to think about the action, we cannot really make sense of, we just say that we do not know why we did it; we felt like it, etc. However, even if we are able to give a sensible explanation, it may not be the correct explanation. It often seems that we do not consciously think of any reason before being challenged to do so – which often happens after the action is performed. Since the consciousness does not necessarily have any part in deciding the action, it may be that it really does not know and can only speculate.

Indeed, if I allow myself to speculate – and I must specify that what I say now is pure speculation – it seems, speculation, in the sense of explaining and justifying, is an important role for consciousness.

Consciousness is important for communicating with other human beings. The test subjects performed all the right actions, movements and so on in the above experiments; it was their ability to communicate what they were doing to others that was harmed the most by the lack of conscious awareness.

I think it can safely be claimed, that humanity as a species is dependent on being able to comprehensibly communicate thoughts, ideas and experiences with each other to a much greater extent than any other species. It may then be that the primary role of consciousness is not to think through and decide our actions – or even thoughts – but to collect a comprehensive image of things for the sake of communication. And if the goal is social communication – which has an important purpose in itself for society and humans – it may well be that the consciousness is not meant for, and has no need of, really understand what actually goes on in the brain and the actual motivations for our behaviour.

In fact, as we have pointed out in several articles, if we are to coolly analyze our experience, we only experience thoughts coming to our consciousness (see e.g. Human Cognition 101 and 102). Thinking of consciously performing a thought process as in a sense just “observing” an otherwise unconscious process in the brain matches our experience equally well as the idea of “consciously performing”. And for the sake of communication, observation is all one needs – it only requires that one can give an account of the thought process. One does not need to take any part in or have any control over a conversation in order to be able to give an account of it. The consciousness behaves like a spokesperson.


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