Some Thoughts on P-Zombies and the Gap Explanatory Argument

Dedicated to Anna Traußnig...for the several hours of intellectual orgasms, as she likes to call it

Parts of this article have been inspired by the writings of Robert Kirk, William Seager and Daniel Dennett

A philosophical zombie (or p-zombie as it is often called), is a curious creature that is central to the basic idea of the explanatory gap. It is a hypothetical being that is indistinguishable from you and I, or any normal human being for that matter, except for one fundamental detail. Such a zombie, for example, cries in pain (when you kick it), but it feels no pain. In other words it lacks any conscious experience. But, given their definition, this singular fact will have no bearing on the physical processes that the zombie will undergo in it's own world. Put another way, a zombie's behaviour should be indistinguishable from the behaviour and physical state of a genuine human being. This first case is the well known "zombie duplicate" -There exists a philosophical zombie that is physically indistinguishable from me , assuming of course that I can be granted consciousness. Let's stick with that for the moment. We shall come back to this point later.

Now I could argue that a perfectly physical duplicate of me should live in a perfectly duplicate realm of reality. It could also be argued that the only possible world that could have a perfectly physical duplicate of me is one which is perfectly duplicated , which might be the very same possible world. Are zombies nomologically or even physically possible? To state that they are nomologically possible would be to state that in some world that shares all physical and natural laws of this world, there exists a "human being" who lacks consciousness. But wait, what happens if certain natural and physical laws do not bear any causal relation? If all natural laws are physical laws or at least dictate physical laws and if, consciousness is causally related to physical states (and there is some evidence for that), then there cannot exist any world with the same physical and natural laws as ours and yet have a zombie. It's not possible. On the other hand, if physical laws were dissociated from natural laws, then zombies could exist by breaking natural laws but not the physical ones. Remember, we have access only to physical laws (which we assume, by default to be natural laws, although this may not necessarily be true). Going further, if mental states (such as consciousness) were non physical, it seems reasonable to claim that zombies are not only nomologically possible but even logically (or physically) possible. Of course, the question still remains whether such another distinct reality, separate from ours does exist (this in itself is another huge philosophical debate). Now if this were the case, one would have a tough time proving what consciousness really is (or is not). It raises another question. How are we to assume that a zombie that exists in another physical realm sharing the same physical laws as ours but not the natural laws does not have consciousness? It may possess a different kind of consciousness that is drawn from the natural laws that govern it's world.

In 1999, Robert Kirk, presented an argument which attempted to demonstrate that philosophical zombies are logically impossible. He starts by assuming that a zombie suddenly acquires non-physical qualia. A weak definition of qualia would be the property that distinguishes us from zombies (consciousness if you will). Parts of his argument are as follows:

1. My zombie twin is unaffected by anything non-physical
   
2. So he remains unaffected when he acquires non-physical qualia
3. In order to become conscious following acquisition of this non-physical qualia, he must be affected by it in some way
4. But nothing non-physical affects him. So he doesn't become conscious.
5. To tell the difference between the subjective character of two different perceptual experiences, he must be sensitive to them or detect them in some way
6. In any case, nothing non-physical affects the zombie, so he cannot distinguish non-physical qualia from having no qualia
7. Friends of the zombie maintain that a "conscious" being is simply the zombie component with non-physical qualia. This position entails that "conscious" humans cannot tell the difference between tea and coffe, for example.
8. But we can tell the difference between tea and coffee.
9. Hence, we are nothing of the sort that friends of zombies maintain we are and hence zombies in their sense are not genuinely possible

Kirk's paper has been criticized but it presents an interesting case.

One final word on physicalism. In short, there are no kinds of things other than physical things (including consciousness). Daniel Dennett argues that even if consciousness were purely physical, our own conviction that we are not zombies, is simply a product on the external physical world. But, we could still be zombies who think we're conscious, who think we have qualia and who think we feel pain, in ways that are we could never discover. If such were the case, it wouldn't be careless to say that "consciousness" could never be defined or understood or even proved. 

I for one remain hopeful that science may one day provide a good theory on how consciousness works, but Anna and I both think that even if one ends up showing how it works, one would never be able to show what it really is.  

References

Kirk, R. (1999). The Inaugural Address: Why There Couldn't Be Zombies Aristotelian Society Supplementary Volume, 73 (1), 1-16 DOI: 10.1111/1467-8349.00046

Seager, W.E., Are Zombies Logically Possible?-And Why it Matters

http://www.scar.utoronto.ca/~

The Small Network Argument

Not long ago, the problem of consciousness was thought to be scientifically non-tractable. But with a lot more psychophysical and brain mapping data coming in from studies being done on normal subjects and people with brain disorders, the field has opened up. In the last decade, a variety of brain processes were proposed to account for consciousness and several more keep coming in but as of today, no concrete model exists. Typical examples include recurrent computation (Grossberg (1999) and Lamme (2006)), synchronized neural activity (Bachmann (1994), Engel et. al (1999)), winner takes all computation (Grossberg (1999)), closed loop action-perception processing (O'Regan and Noe (2001)). In the midst of the madness, comes a paper by Herzog et. al titled Consciousness and the Small Network Argument (Herzog, Esfeld and Gerstner (2007)). They propose that none of the current models can fully account for consciousness because of what they call the small network argument:

For each of the above models, there exists a very small neural network that fulfills the respective characteristics of the model but does not exhibit consciousness

1) Recurrent Computation (Lamme (2006))

Two mutually connected neurons make up a recurrent systems. Thus if recurrence is sufficient for consciousness, a network of two neurons must create consciousness (to which not may of us may accede).

2) Winner Takes All Computation (Grossberg (1999))

The basic operation of a winner-takes-all (WTA) circuit is to suppress the activity of all neurons except the one having the largest input. Minimal models require only three neurons fully connected to three presynaptic neurons, plus a neuron for vigilance, taking the tally to seven. Such a network can develop states allowing learning and memory. And so are we willing to grant consciousness to a network of seven neurons?

3) Synchronized Neural Activity (Bachmann (1994), Engel et. al (1999))

If synchronized firing in neurons is the main characteristic of consciousness, then a group of three inter connected neurons firing in synchrony is conscious

4) Closed-loop action perception processing (O'Regan and Noe (2001))

Herzog et. al give the example of a thermostat with a temperature sensor ('perception') controlling a heater ('action'). This could be formulated as a two neuron feed-forward network with a sensory neuron connected to an output neuron controlling the switch.

Thus they argue that if one does not want to attribute consciousness to such small networks, other components are needed. Additional characteristics are often imposed. Typical examples being attention, number of neurons and complexity of the network. Yet, none of these additional components necessarily solves the small network argument.

1) O'Regan and Noe (2001) combined their sensorimotor contingency approach with attention based processing. They state that perception occurs in a closed loop of action and information processing but consciousness emerges only when attention comes into play. The most common example of this being a person driving a car in an unconscious and automatic mode (unconsciously perceiving other cars on the road and taking correct measures), but conscious perception, e.g. of a traffic signal, arises only when attention comes into play. However, in this model, attention can be incorporated with just one single extra input arising from a second group containing a very small number of cells

2) It is often proposed that consciousness may emerge if the brain exceeds a certain number of neurons. In a model with a simple linear arrangement of neurons where each neuron is connected only to it left and right neighbors, there is no reason to believe why a network of 10^10 neurons is more capable of generating consciousness than a network of three neurons. hence size alone cannot account for this

3)Other approaches state that a certain level of complexity must be met before a network can yield consciousness. Herog et. al give the example of Tononi and Edelman (1998) who proposed to measure complexity by defining a functional cluster that was loosely connected to the rest of the network but still has a rich repertoire of internal states. But this complexity criterion can be met even by a small network. Herzog et al. propose a network of nine neurons, organized into clusters of three. Assume the following model of interaction. The state of each neuron is described by p bits. Therefore, each neuron has can take up 2^p possible states. Now in the first 100 msec, the three neurons agree on the first bit by a majority vote, in the next 50 msec, on the second bit and so on, until the last 200/(2^p) msec, when they decide on the last bit. Thus for any arbitrary p, three neurons will agree on p bits in 200 msec, showing a large level of complexity in a small cluster.

Hence, Herzog et. al argue that all the above mentioned components are important aspects to understand consciousness but they are only trivially necessary rather than sufficient. Finally, they argue that one way out of the small network argument is to assume that each network, however small, has a vanishingly small consciousness, but this form of "panpsychism" also has it's problems. What happens if two networks, each with it's own vanishingly small consciousness, are connected? Do the two consciousness merge, do they stay separate (as proposed in split brain patients) or are there new coalitions of neurons making up new consciousness?

Overall, the paper seems to have created a bit of a ripple in the community of neuroscientists working on consciousness. Taylor (2007) in "Commentary on 'the small network' argument" states

..paper of this issue (Herzog, Esfeld, & Gerstenr, 2007) has derived an interesting criterion for any neural model of consciousness, with the disturbing result that a whole raft of neural models of consciousness are deficient when looked at by this criterion. The criterion itself is that a neural model of consciousness is suspect if it can be shown to work using only a relatively small network of neurons (of the order of 10–100 or so) 

Reference

HERZOG, M., ESFELD, M., & GERSTNER, W. (2007). Consciousness & the small network argument Neural Networks, 20 (9), 1054-1056 DOI: 10.1016/j.neunet.2007.09.001