Tuesday, July 14, 2015

3. Notes on the relevance of neurophysiology to self-knowledge

In ‘Self-knowledge as an imperative with comments by David Parker’’ (on my website) I write: ‘When we become aware of the profound discrepancy between our physical brain and the world of our consciousness, we realize that there must be another entity, different from the brain, which transforms the data processed in the brain into the world of our consciousness. The process of this transformation is entirely subconscious. Our conscious activities are focussed on and absorbed by the task of perceiving the world, as constituted by our subconscious activities, as the real world outside us in which we live.’

David remarks: I don’t follow the debates about consciousness and the nervous system that closely. Much of what neuroscientists add to this seems very trivial. Philosophy of mind is interesting but again I haven’t studied this in any depth. But is the assumption that consciousness is an emergent property of the integrated activity of neurons in various brain regions (integrated from different senses, motivational, emotional aspects, memory, current planning strategies) to be simply dismissed? And if so, why?

I find ‘the assumption that consciousness is an emergent property of the integrated activity of neurons in various brain regions’ meaningless. I don’t mean that the words strung together have no meaning. Trying to imagine the ‘emerging’ consciousness, I cannot help thinking of the Genie emerging from the lamp in Disney’s video of Aladdin, which I watched the other day with my daughter. But, on second thought, the Genie is not a property of the thing from which he emerges. Would the ring that Gandalf throws into fire in the Fellowship of the Ring, on which, after its being pulled out of fire, the infamous inscription begins to emerge, give us an example of an emergent property? – The words ‘emergent property’ lose for me their meaning when I think of consciousness in connection with neurons and their activities.
Wikipedia succinctly describes neurons as follows: ‘A typical neuron consists of a cell body (soma), dendrites, and an axon. Dendrites are thin structures that arise from the cell body, often extending for hundreds of micrometres and branching multiple times, giving rise to a complex "dendritic tree". An axon is a special cellular extension that arises from the cell body at a site called the axon hillock and travels for a distance, as far as 1 meter in humans or even more in other species. The cell body of a neuron frequently gives rise to multiple dendrites, but never to more than one axon, although the axon may branch hundreds of times before it terminates. At the majority of synapses, signals are sent from the axon of one neuron to a dendrite of another. There are, however, many exceptions to these rules: neurons that lack dendrites, neurons that have no axon, synapses that connect an axon to another axon or a dendrite to another dendrite, etc.’
Wikipedia characterizes the functional properties of neurons as follows: ‘All neurons are electrically excitable, maintaining voltage gradients across their membranes by means of metabolically driven ion pumps, which combine with ion channels embedded in the membrane to generate intracellular-versus-extracellular concentration differences of ions such as sodium, potassium, chloride, and calcium. Changes in the cross-membrane voltage can alter the function of voltage-dependent ion channels. If the voltage changes by a large enough amount, an all-or-none electrochemical pulse called an action potential is generated, which travels rapidly along the cell's axon, and activates synaptic connections with other cells when it arrives.’
Wikipedia succinctly describes neural networks as follows: ‘A neural network is a series of interconnected neurons whose activation defines a recognizable linear pathway. The interface through which neurons interact with their neighbours usually consists of several axon terminals connected via synapses to dendrites on other neurons.’

Let me now confront these properties of neurons and neural networks with what I am presently conscious of.  In front of me is a key-board. The keys are black, on the keys are white letters; the primitive ‘sorting’ of these features begins on retina by cones, sensitive to different wavelengths of the electromagnetic waves scattered by the key-board. I see the square shapes of the keys, different shapes of the white imprints on the keys, which I see as different letters, numbers, punctuation marks – all this involves a lot of neural networks in the visual centre, for ‘receptors in the eye convey information about only a miniscule part of the retinal image, in effect a single pixel; but after a few levels have been passed, in the visual cortex, we find units that are able to respond to a specific type of stimulus, such as a moving edge, over wide areas of visual field’, as Carpenter and Reddi put it in their Neurophysiology (p.10). While being aware of all this, I am typing, which involves networks of motor neurons. As I type, my sense of touch and hearing is involved … How can I possibly view the key-board in front of me and all that is involved in my typing this text on it as ‘an emergent property of the integrated activity of neurons in various brain regions’?

It may be objected: I can take a picture of the scene I am involved in or video it, and the artificial neural networks in the camera immediately generate a picture or a video of it on its screen. Why can’t the neural networks do the same?

To this objection I reply: The ‘neural networks’ in the camera electronically pick up the image from the camera’s pick up device, digitally process it and reproduce it on the screen of the camera. But the image the camera thus generates exists on its screen only for a human eye, not for the screen; it is not generated as a picture anywhere in the artificial neural networks involved in the digital processing of the picture. But I see the key-board, I am not only aware of my typing the text on it, I constantly monitor it on the computer screen, I am thinking about it as I am producing the text; all this is intimately connected with the activities of neural networks that are involved in all this, but these conscious activities are not their emergent property.

No comments:

Post a Comment