These are some comments that were stimulated by Ned Block's article “On a Confusion about a Function of Consciousness”.

I have been heavily influenced by the work of Crick and Edelman that relates memory processes to consciousness.

I agree that forms of P-consciousness (P=perceptual=phenomenal=primary) are possible in the absence of some forms of the higher level episodic memory that we most often think about when we introspectively examine our mental processes. However, there are many forms of memory besides those that we are subjectively aware of.

It is important not to imagine that conscious episodic memories are all there is to memory. As a neurobiologist I use the general neurobiological meaning of “memory” which includes any adaptive modification of synaptic function in response to on-going brain activity. There is a hierarchy of brain mechanisms for memories and I suggest that the hierarchical progression from unconscious brain activity, to P-consciousness to A-consciousness (A="access" or "higher order") can be fruitfully examined in terms of recognition of the different memory mechanisms that are involved with each level of consciousness.

Crick’s Figure 1 of his recent article “Consciousness and Neuroscience”, Edelman’s Figure 3.4 of his book “The Remembered Present” and the first figure in Block's article “On a Confusion about a Function of Consciousness” are all similar in that they contain a hierarchy of input/output pathways through the brain. At the “low” end of this hierarchy are the various unconscious control systems of the brain, the activity of which need not enter into consciousness (the direct path from a “specialized module” to “response systems” in Block's figure). In the middle there is the “phenomenal consciousness” pathway. At the high end of the hierarchy is the “executive system” pathway. Both Block's diagram and Edelman’s include the temporal lobe “episodic” memory system (labeled Hippocampus in Edelman’s diagram). Crick has pointed out (in his book “The Astonishing Hypothesis”) the fact that short-term (millisecond time scales) synaptic memory mechanisms must be involved in allowing information to rise up the hierarchy from unconsciousness to P-consciousness to A-consciousness. Both Edelman and Crick include a cortical/thalamic feedback loop in their models of consciousness. It is explicit in Edelman’s model that nothing enters into perceptual consciousness independent of this feedback loop and the comparison between previously existing memories and on-going experience which it makes possible.

When I say, “....understanding the neuronal correlate of consciousness would be a sterile result in itself because what is really important to consciousness is meaning. A person can be conscious of sensory inputs, but if those experienced inputs have no meaning for a person, then no sensible behavior will result, you would have a zombie that has low-level awareness, but nothing more. It is hard to see the distinction between such a meaningless conscious existence and unconsciousness," what I am suggesting is that my guess is that there is very little functional difference between “pure P-consciousness” and unconsciousness. In humans, P-consciousness becomes most behaviorally important when its contents are available for promotion to A-consciousness. Although this is the situation in humans, Edelman’s theory nicely deals with P-consciousness without A-consciousness in non-human animals (Chapter 9 of “The Remembered Present”).

“On a Confusion about a Function of Consciousness” provides an heroic attempt to untangle P-consciousness from A-consciousness. I think that Crick started with an honest effort to attack the problem of “pure P-consciousness” but he has since realized that is a nearly sterile exercise. In a normal functioning human brain, P-consciousness is automatically linked to A-consciousness by filtering and selecting mechanisms that focus attention on a limited subset of sensory input. This filtering is partially by means of low-level feature detectors and unconscious processing (quick!) and partially by means of high-level conscious processes (slower, but more flexible). It is the involvement of various short-term and long-term memory systems that allow for flexibility of behavior under the control of conscious brain processes.

I share the view that, “......if we could isolate the low level meaningless sensory consciousness......I for one would be very interested”. Block has written well about the need to find ways to carefully distinguish between P-consciousness and A-consciousness. All I am suggesting is that we can try to use the various distinct memory systems that are present in the brain and involved with the different aspects of consciousness to provide us with empirical constraints on our understanding of consciousness.

It is a worthy simplifying research program to hypothesize that, “If the problem of low level sensory consciousness can be solved, we will be all the more prepared for meaning.” However, an alternative hypothesis is that we cannot really understand consciousness without first understanding the various memory mechanisms that make consciousness possible. I agree with Pat Churchland and imagine that what makes consciousness seem like such a hard problem is that we have tried to solve it without first confronting the basics of neurobiology such as learning and memory. Fortunately, the biological basis of memory is now being revealed. The task at hand is to integrate this new knowledge into our heuristic models of higher brain function.
  

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