Further elaborations upon possible materialistic explanations of consciousness with a look at the emergence of qualia. (This posting is intended as a continuation of my previous posting.)

Controversial issues concerning consciousness may be understood as constituted by the debate between dualistic and monistic world views. The dualistic notion of separate mental and physical realms suffers greatly from the difficulty of explaining their interaction. The complete separation of a mental realm also precludes any physical explanation of mental phenomena. The monistic assertion of an entirely idealistic existence is difficult to absolutely refute since our awareness is ever constrained within a subjective and ideal reality but we sensibly assume that this results from a shared objective world. My previous posting adhered strongly to a monistic, materialistic paradigm and attempted to outline functionalism as an approach which may provide an adequate explanation of the emergence of consciousness. Suffering, as I do, from a severe case of confirmation bias, this posting further elaborates on the possibility of a materialistic explanation through exploration of the subjective side of the explanatory gap in the form of qualia. The acceptance of a materialistic standpoint does not eliminate controversy but, instead, situates it amongst various current psychological explanations. Due to respect for the wealth of experience and research offered, I hesitate to assert the superiority of any one particular stance from amongst these theories, preferring to simply outline plausible alternatives. The functionalist approach was one such alternative. This posting centres on John Taylor’s (2001) theory of relational consciousness and how it addresses the existence of qualia.

Qualia may be introduced by revisiting the zombie of my in-class presentation. She was like you in every way, every atom arranged in just the same manner, all past experience exactly the same. The question asked was ‘is it possible that she has no subjective awareness? Is she a zombie?‘ If, for you, it is possible, then you aren’t a materialist concerning theories of mind, since the material of your zombie replica doesn’t give rise to the subjective awareness that I presume, no, am sure, that you possess. If you believe that, given the exact same material components and organisation as yourself, your zombie would continue to experience almost the same awareness as you do (only from about three feet to one side!) then you accept the materialistic view that consciousness results from purely physical processes. The proposed similarity of experience also points to its dependence on similar relational organisation of the physical constituents of consciousness.

The subjective awareness which we (may) have granted our zombies is often discussed in terms of qualia; ‘the introspectively accessible, phenomenal aspects of our daily lives’ (http://plato.stanford.edu/entries/qualia, as cited in Dennett 2006)

Despite the difficulties of the singular form of ‘a quale’ (how to delimit a single aspect of experience?), qualia are a useful tool in the discussion of consciousness even if only providing a shorthand for ‘aspects of subjective experience’. To further detail the concept of qualia it may be interesting and informative to restate the philosophical argument of Mary the colour scientist.

Although she knows all there is to know about the neural mechanisms of colour vision, Mary has never directly experienced colour (due to a perverse captivity arrangement, or perhaps a physical defect in her eyes). When, at last, she is released, or undergoes surgery, she encounters the full colour experience of a banana; how does she respond? Does she show surprise at the new experience or does she, through her extensive knowledge of colour vision, already have a fair idea of what it would be like to see a banana? Dennett (2006) argues that failure to imagine the possibility of knowing ALL there is to know about colour vision obscures the question and leads us to suppose that she would be surprised. He has been described as an eliminativist and, indeed denies the existence of qualia (p.79, Dennett, 2006). The intuitive response seems to be that she would be surprised by her new experience. Knowing is distinguishable from experiencing in the sense that we may theoretically know something without ever having done it. The experience of seeing a banana in full Technicolor is new for a Mary who possessed only the normal knowledge of the ‘recipe’ for colour vision but perhaps not new for a Mary who truly embodied the entire field of knowledge related to seeing in colour. To elucidate further; if we knew ALL the intricacies of sensual awareness, interactive, motivational and experiential possibilities of being a bat, might we not be able to anticipate what it was like? That we have limited knowledge of these things may be the only limitation of our imaginative capability.

The two thought experiments of zombiehood and Mary, the colour scientist, are intended to emphasise the subjective, introspectively accessible nature of experience and the distinction this has from objective knowledge. The difficulty then ensues as to how we may bridge the ‘explanatory gap’ between the physical observations of the behaviour of the body (at all levels) and the subjective experience which is a feature of consciousness; how to give a physical account of qualia.

Functionalism progressed theories of mind through largely ignoring details of the mechanism of activity and concentrating on the combinations of the abilities of various modules and how they may globally function to produce purposeful activity. Homuncular functionalism as outlined in the previous posting recognised that some emergent properties of the modules may depend upon the qualities of their constituent components. In the case of the functioning mind, the components are (almost) ultimately the neural physiology, neurons and neural nets. To this end, and with the advancements in brain imaging and neuroanatomy, the physical underpinnings of local brain activity may usefully contribute to the understanding of more global brain functions such as consciousness. The teleological functionalism, briefly touched upon in my last post, would attempt to answer WHY we should have any qualia rather than none. Here we are only concerned with HOW qualia may arise. What follows is a possible materialistic account of phenomenal consciousness in terms of a brief outline of Taylor’s relational model.

John Taylor has incorporated much compelling evidentiary psychological research into his theory of relational consciousness (Taylor, 2001). He argues that consciousness develops along with the organism and may be the result of the comparison of a current state with previously experienced states; consisting of the difference between them rather than being identified with one state or the other.

Taylor identifies at least three broad types of consciousness which may be experienced on a daily basis. Due to the relational nature of consciousness, these naturally involve different types of memory; perceptual, non-declarative and declarative; including semantic and episodic. He suggests that passive or phenomenal consciousness results from mainly semantic and perceptual memory systems. Self consciousness is mostly concerned with episodic memory. Active or intentional consciousness again involves semantic memory, and hence elements of passive consciousness, as well as an inhibition of episodic memory (unless in an active problem solving capacity). The results of brain lesions are cited by Taylor as indicating that these different forms of consciousness arise independently from different brain regions. Passive or phenomenal consciousness is mainly centred in posterior regions after processing in the appropriate primary audio, visual or somatosensory cortices. Both active and self conscious processes rely on regions of the frontal lobes, with episodic memories located in posterior areas.

In consideration of the visual illusions offered in-class (and readily available on the web); active awareness that the stimuli is stationary (or the same length/size) along with the retained perception that it is moving (or shorter/smaller) highlights the independence of these forms of consciousness.

Taylor suggests that phenomenal consciousness may be present in a wide variety of species, active (intentional) consciousness may be somewhat more limited and self consciousness limited to some higher primates (including ourselves of course).

A physical explanation of the most basic, phenomenal aspect of consciousness will suffice to bridge the ‘explanatory gap’ and to that extent we again turn our attention to qualia. Taylor sidesteps the philosophical difficulties of the actual existence of qualia in the brain. Instead he uses the concept of qualia as adequately encapsulating some of the qualities of the ‘raw feel’ of experience; that is the indescribable, indivisible and transparent ‘just so’-ness of passive awareness. He asserts that this includes perceptual awareness and memories. These are formed from pre-processed stimuli. Consideration of the stage at which they emerge as awareness rather than unconscious processing is the crucial question of materialist accounts of consciousness.

Taylor develops an argument that consciousness arises from self reinforcing (as well as locally inhibiting) ‘activity loops’ in groups of neurons in regions of working memory buffers. He terms these ‘bubbles’ with regards to their development and duration. Activity may be sustained for up to two seconds in the posterior working memory sites and up to thirty seconds in the frontal lobe active working memory sites. ‘Pre-processing neural nets’ support various ‘working memory nets’ in these sites which gives rise to consciousness in a ‘winner take all’ manner rather than in an additive, global manner. As evidence for this view he offers the phenomena of our alternating viewpoint of ambiguous visual stimuli. When looking at the duck-rabbit picture or the Necker cube for instance, we can only perceive one of the possible interpretations at a time and we tend to jump from one to the other with no intermediate representations. Taylor demonstrates that we show ongoing neural activity relating to each representation but only one at a time gains access to our conscious awareness (much akin to Dennett’s, 2006 ‘fame in the brain’ model).

The temporal and continuous aspects of phenomenal awareness also supports Taylor’s model of consciousness arising as a result of competition between pre-processing neural nets. Awareness results from neural activity in a buffer working memory which can sustain activity at a given level for a short period of time. As the activity of any given working memory net wanes there are further pre-processing nets competing for dominance. This can then explain both the temporal and the continuous nature of qualia.

Taylor uses Libet’s experiments of 1964 and 1987 to demonstrate that conscious awareness depends upon a minimum level of stimulation as well as requiring a certain amount of time to emerge and that ongoing awareness requires ongoing stimulation. (Libet produced tactile awareness by electrically stimulating the cortex during brain surgery on Parkinson’s disease patients). This supports the competitive model of consciousness insofar as it is those ‘successful’ neural nets which make it to the buffer working memory; this takes time (allowing irrelevant or transient stimulation to fall out of the competition). The existence of a threshold stimulation level also suggests that competition due to enhanced activity of some elements and inhibition of others gives rise to conscious awareness of a stimulation. Below a certain level the stimulation fails to attain any level of awareness as it is subsumed by other, more vigorous neural activity.

The explanation of emergence of passive awareness through competitive neural activity within regions of buffer working memory, as briefly described above, gives rise to predicted aspects of consciousness which are similar to the qualities ascribed to qualia by Metzinger (1995);

The temporal presence of qualia are said to possess qualities of persistence, latency and seamlessness. These properties are exhibited by the ‘bubbles’ in that they have duration, constantly developing and waning as other ‘bubbles’ seamlessly take their place. Qualia are further described as complete, intrinsic and ineffable. These qualities are produced in Taylor’s model due to the ‘bubbles’ representing the final stage of processing (thus complete and integrated) with no feedback to earlier processing and thus no awareness of attaining these conscious states, only a sense of immediate presentation. The sense of uniqueness ascribed to qualia is also modelled here by the ‘winner takes all’ nature of attaining awareness; only one ‘bubble’ at a time contributes to subjective experience.

This posting represents an attempt to ‘flesh out’ otherwise overly philosophical assertions of materialistic explanations of consciousness. Functional explanations attempt to describe emergence from a global and interactive perspective. Taylor offers detailed neuro-anatomical descriptions of processes which accord well with experimental observations of conscious phenomena. He demonstrates the possibility of arriving at a detailed biological description of how consciousness emerges. This supports the materialistic approach to consciousness. Physical explanations of consciousness are seen to be possible, albeit complex and extensive. We should not expect otherwise; simple explanations would indicate a phenomena that was far more widespread and ordinary than this wonderful awareness which illuminates our entire existence. Why we are conscious still remains a mystery, it doubtless confers some adaptive advantage but the prevalence of suicide, depression and ideological warfare suggests that that advantage may not be as great as we might wish. Perhaps consciousness is simply an epiphenomena from previous selection or perhaps an indubitable reason for conscious awareness may yet be realised.

References

Dennett, D.C. (2006). Sweet Dreams: Philosophical obstacles to a science of consciousness. MIT Press

Taylor, J.G. (2001). The race for consciousness. MIT Press

Libet, B., Alberts, w.w., Wright, E.W. Jr., Delattre, D.L., Levin, G. and Feinstein, B. (1964). Production of threshold levels of conscious sensation by electrical stimulation of human somato-sensory cortex. J. Neurophysiol 27, 546-578

Libet, B. (1987). Consciousness: Conscious, subjective experience. In Encyclopaedia of Neuroscience I, Adelman, G. (ed). Boston: Birkhauser.

Metzinger, T. (1995). The problem of consciousness. In Conscious Experience, Metzinger, T. (ed). Paderborn: Shoeningh: pp 3-40

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~ by lisajoyce on April 19, 2010.

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