Material theories of the Mind vs Descartes (1900s)
Material theories of the mind must be able to solve the problems raised by Descartes in 1641.
Problem 1 - Explaining qualia
Descartes showed that the existence of the external world can be doubted because we are only aware of qualia and indistinguishable qualia can exist even when there is no external object present. In order to solve this problem, British philosopher Michael Lockwood suggested that we should accept the disclosure view coupled with causal realism (Lockwood, pp.163-164).
Causal realism is the view that we can at least derive the existence of external objects from the phenomenal qualities they invoke. Irish philosopher George Berkeley had argued that causal realism will inevitably lead to scepticism about the external world and Lockwood uses the disclosure view to argue that these objections are not applicable to his theory.
The disclosure view is a kind of naive realism, this is an extreme version of common sense realism, which holds that there is a transparency between the external world and the phenomenal qualities we experience in consciousness. Lockwood agreed that this is false with respect to the external world but followed English philosopher Bertrand Russell in arguing that there is no reason to believe we cannot have a transparent grasp of the conscious states of our own brain (Russell, pp.320 and pp.383).
Lockwood described the disclosure view as being analogous to "a searchlight, sweeping around an inner landscape in part revealing qualities that were already part of the landscape" (Lockwood, pp.163) but this cannot be the complete story because awareness itself is "realised as a neural activity of some kind". This means that there is "no reason to suppose that the intrinsic character of the brain state is, in general, unaffected by our becoming aware of it" (Lockwood, pp.163-164). Lockwood argued that external objects must exist because we are not always conscious of what we perceive. If, for example, we focus on an object and then let our mind wander, qualia will drift in and out of our visual field without, at any time, ceasing to exist (Lockwood, pp.163).
Problem 2 - Where is my mind?
If material theories of the mind are able to show that both qualia and external objects exist, then they will still have to show where they exist within the mind. Lockwood argued that "it is not any neuronal firings per se that are registered in consciousness as phenomenal qualia, but something else that has an intimate causal connection with certain such firings" (Lockwood, pp.174). Identity theory states that qualia exist within the brain in an analogous way to how lightening exists in the same space as electrical discharge. The analogy breaks down however, because, as Austrian-British philosopher Ludwig Wittgenstein pointed out in 1958, we cannot determine the spatial location of mental events independently of the assumption that they must exist in the brain (Wittgenstein, pp.7-8). Lockwood claimed that this problem can easily be resolved if we accept that the mind exists in time. This is because Einstein's theory of special relativity shows that time and space are inseparable. This approach would not have been accepted by philosophers like Kant who argued that time is also a property of the mind.
The argument that there is no physical configuration to images was disputed in experiments conducted by American cognitive scientists Roger Shepard and Jacqueline Metzler in 1971. They gave people two pictures of the same three dimensional object from different angles and timed how long it took for each person to mentally rotate the first image to that of the second. The time was found to be in direct proportion to the difference in angle between the pictures. Objects that would have taken longer to physically rotate, took longer to mentally rotate.
Problem 3 - The unity of consciousness
Descartes also argued that the mind cannot exist as a physical substance because it is a unified whole. This argument was disputed in experiments conducted by American neurobiologists Roger Wolcott Sperry and Michael Gazzaniga in the 1970s (Sperry, 1966, pp.298-313). Sperry and Gazzaniga knew that the brain is composed of two hemispheres, each containing two lobes, these are connected by the corpus callosum which contains more than two hundred million nerve fibres (Tomasch, pp.119-35). In 1940, American neurosurgeon William Van Wagenen developed a form of surgery which splits the two hemispheres by severing this link (Van Wagenen and Yorke Herren, pp.740-759). This procedure is known as a corpus callosotomy and in extreme cases it can be performed to reduce epilepsy. People who have undergone a corpus callosotomy are sometimes referred to as split-brain patients. The fact that the brain can be divided led to the question of whether this was followed by a division in consciousness.
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Australian neurophysiologist John Eccles suggested that consciousness is only contained within the left hemisphere of the brain, but this was refuted by evidence of consciousness within people whose left hemisphere has been completely destroyed. Lockwood argued that consciousness exists across both hemispheres as "simultaneous overlapping phenomenal perspectives" (Lockwood, pp.89). If this is true then we would expect that after a corpus callosotomy, a patient's consciousness would either move to one hemisphere, or continue in two separate streams which cannot communicate. Sperry and Gazzaniga tried to determine which view was correct by providing the two hemispheres of split-brain patients with separate information for the left and right visual field. When asked what they can see with the right eye split-brain patients always know the correct answer, but they will always deny seeing anything with their left eye.
The right eye sends information to the left side of the brain and so it would appear that Eccles view is correct, consciousness only appears in the left hemisphere. This is an incorrect assumption however, because the speech centre for the brain is also associated with the left hemisphere. If the right hemisphere did register the information it would have no way to verbally communicate it. The right hemisphere is associated with pictorial information, it allows us to recognise patterns and faces, transforms our vision into three dimensions and is involved in musical recognition and ability. When split-brain patients were asked to draw what they saw the right hemisphere could express the information and Sperry concluded that "both the left and the right hemisphere may be conscious simultaneously in different, even in mutually conflicting, mental experiences that run along in parallel" (Sperry, 1974, pp.11).
Experiments on split-brain patients show that the two hemispheres almost always try to co-operate and it is impossible to get them to compete, even in simple games. There are a few examples of split-brain patients whose separate hemispheres have expressed contradictory behaviour, such as the man who simultaneously embraced his wife and pushed her away, the man who reached for a plate with one hand whilst the other removed it, or the woman whose left hand tried to strangle her. In all these cases however, there was far more intensive brain damage than just a split between hemispheres and Lockwood suggested that the part of the brain that initiates co-operation must also have been damaged.
If part of the brain exists to establish co-operation between two split hemispheres, then it would make sense to assume that it has a use even when the corpus callosum is intact. In 1973, American philosopher Roland Puccetti argued that there is a single mind present in both hemispheres even before the split (Puccetti, pp.339-355). This is illustrated with examples of divided attention, such as how we can talk and drive at the same time despite being too distracted to be consciously aware of what our hands and feet are doing. Lockwood described how the two minds are integrated in most tasks because they have "a lifetime's practice in mutual co-operation" (Lockwood, pp.81). Perhaps Puccetti's claim could be proven if we had an example of someone whose 'co-operation' system has been destroyed but who retains an intact corpus callosum, if Puccetti is correct then we would expect to see signs of a split consciousness.
In 1971, fellow American philosopher Thomas Nagel argued that there is no definite answer to how many minds we have (Nagel, 1971, pp. 396-413). In the case of split-brain patients, the hemispheres cannot communicate but they are not completely distinct either because there are properties that are experienced by both. Emotional phenomena, for example, are associated with the diencephalons. This is located below the hemispheres and so emotions are experienced equally by both minds.
Lockwood adopted English philosopher Derek Parfit's term 'co-conscious' to describe properties that are experienced by both hemispheres at the same time (Parfit, pp.250). Information that is not co-conscious cannot be communicated between the separate hemispheres of split-brain patients. It could be objected that there is still room for Descartes' sense of absolutes since a property is either fully co-conscious or it is not co-conscious at all but Lockwood dismissed this claim by arguing that there is no distinct point when a property stops being co-conscious. This is because the corpus callosum could be destroyed over a long period, one nerve fibre at a time and it is clearly ambiguous as to when certain aspects of the brain would cease to become fully co-conscious during this procedure.
Nagel suggested that there are other non-definite levels of consciousness, the boundary of our visual field, for example, does not appear to have a distinctive edge at the cut off point of conscious awareness. If this were the case we might expect to view the world as if we were looking through a pair of binoculars. Non distinctive boundaries also appear when we are focusing on one sensory experience or spatial region and are far less aware of what is happening in the background. One objection to the idea that there is a definite answer to how many minds we have is that it is difficult to conceive of what it would be like to be a split brain-patient. This problem is resolved by considering that consciousness is a subjective phenomenal experience and we cannot imagine a subjective phenomenal quality we have not experienced.
Problem 4 - Subjectivity
The final problem any material theory of the mind must overcome is caused by the fact that science is inherently objective and so cannot explain the subjective nature of consciousness. This may be an impossible challenge. In the 17th century, Hobbes had argued that there are some things our mind is just not capable of comprehending. In 1974, Nagel argued that we cannot image what it is like to be any creature that possesses a different type of brain to us. Nagel claimed that "if I try to imagine this, I am restricted to the resources of my own mind, and those resources are inadequate to the task" (Nagel, pp. 435-450). Nagel concluded that there are some things we can never truly comprehend, despite knowing that they are perfectly comprehendible in theory.
In 1989, English philosopher Colin McGinn suggested that the human mind is incapable of comprehending itself entirely. He stated that "just as a dog cannot be expected to solve the problems about space and time and the speed of light that it took a brain like Einstein's to solve, so maybe the human species cannot be expected to understand how the universe contains a mind and matter in combination" (McGinn, pp.182).
It is certainly true that we are limited by the capacity of our brains but we may not yet have to give up on explaining the subjective nature of consciousness. Quantum mechanics may require that our experiences are subjective.
References
Lockwood, M., 1992, 'Mind, Brain & the Quantum: The Compound "I"', Blackwell Publishers, Oxford
McGinn, C., 2003, 'The Making of a Philosopher: My Journey Through Twentieth-Century Philosophy', HarperCollins, New York
Nagel, T., 1971, 'Brain bisection and the unity of consciousness', Synthese, Vol.22
Nagel, T., 1974, 'What Is It Like to Be a Bat?', The Philosophical Review, Vol.83
Parfit, D., 1986, 'Reasons and Persons', Oxford University Press, Oxford
Puccetti, R., 1973, 'Brain bisection and personal identity', British Journal for the Philosophy of Science, Vol.24
Russell, B., 1927, 'The Analysis of Matter', Kegan Paul, London
Sperry, R.W., 1966, 'Brain bisections and mechanisms of conflict', Brain and Conscious Experience, Eccles, J. (ed), Springer, Berlin
Sperry, R.W., 1974, 'Lateral specialization in the surgically separated hemispheres', Third Neurosciences Study Program, Schmitt, F. and Worden, F. (eds.), MIT Press, Cambridge, pp. 5-19
Tomasch, J., 1954, 'Size, distribution, and number of fibres in the human corpus callosum', Journal Analytical Records, Vol.119
Van Wagenen, W.P. and Yorke Herren, R., 1940, 'Surgical Division of Commissural Pathways in the Corpus Callosum; Relation to spread of an epileptic attack', Archives of neurology and Psychiatry, Vol.44
Wittgenstein, L., 1965, 'The Blue and Brown Books', HarperCollins, New York