External Qualities and perceptual computation
by Titus Rivas
It is sometimes claimed that the phenomenal qualities of perception might in theory exist not only in the subjective mind but in physical reality as well, or even that they would not really exist as properties of consciousness but exclusively as external properties of the material world. In this short essay I will show why these claims are baseless if we accept the existence of neurological computation of perceptual stimuli in our nervous system.
The irreducible phenomenal qualitative aspects of perception of for example vision and audition would, according to some theorists, also be real, objective and irreducible (non-quantitative) aspects of the physical objects perceived. They would not only be secondary qualities in the mind, but also occur in matter itself.
Most materialists and dualists endorse a theory of sensory perception which includes neurological computation of sensory stimuli. By computation I mean that the incoming stimuli are exclusively broken down to their quantitative, mathematical properties and that the subjective percept is somehow the phenomenal end-product (integrated by an immaterial self or only by the brain itself) of neurological 'calculations' applied to those quantitative properties.
If we accept that in sensory perception there is always computational processing of stimuli going on, we also have to accept that if there are really external non-quantitative qualities in the outside world, one never has any direct access to them in normal perception. This creates a serious problem for the theory of external qualities. Even if there were external non-quantitative qualities in the physical world, neurological perceptual computation must simply ignore them. This is because neurological computation can only work with quantitative aspects of patterns of stimuli which can be processed computationally. Any non-quantitative aspects that matter might have are simply outside the reach of sensory perception as sensory perception always works with the neurological computation of stimuli.
The justification of the assumption of external qualities
The normal empirical reason to assume that there are external qualities is based on our sensory perception. We would normally see or hear such supposed external material qualities. However, we have just concluded that normal sensory perception cannot be based on a direct perception of external qualities. Instead, it is always based on the exclusively quantitative computation of quantitative properties of matter. In other words, the qualia of (sensory) perceptual consciousness cannot in any way be based on the processing of any possible non-quantitative qualities in the physical world. Therefore, the so called empirical, normal reason to believe in external qualities is unfounded. If we still wished to believe in external qualities, we would have to believe in something for which we can by definition have no sensory evidence whatsoever. Moreover, the normal reason for which people believe in external qualities in the physical world is precisely their sensory perception of them. If there are external qualities in the physical world, we have absolutely no reason to believe that those hypothetical qualities correspond to the ones we find in our perceptual consciousness.
A way out of our conclusion might seem that we'd simply reject the neurological part of perception. Although neurology seems to be important for normal perception, we would choose to ignore its data. Of course, this is possible, but only if we reject all other empirical, scientific data concerning physical reality as well, as it is arbitrary (and therefore irrational) to limit our rejection to neurological data. There is only one reasonable way to do so, namely ontological idealism. However, ontological idealism is a theory which cannot be reconciled with a concept of external non-quantitative qualities either, because it rejects the existence of a non-subjective matter altogether.
I can still think of the following additional counter-arguments against my line of reasoning.
- A reductionistic theory of qualia sees qualia as nothing but a level of abstraction of purely quantitative cerebral processes. Thus, if the external qualities are broken down to quantitative patterns, we can still have an adequate perception of those external qualities, because there really is no difference between quantitative patterns and qualia. However, my analysis explicitly takes place within a non-reductive theory and rejects the concept of qualia as mere higher levels of abstraction of exclusively quantitative patterns. The possible existence of qualia or external qualities in any other sense is simply another, unrelated issue.
- Extra-sensory perception of the physical world is also reported to include qualia. This may be the most sophisticated counter-argument. Due to their remarkable results, empirical studies that indicate the operation of so called Extra-Sensory Perception (ESP), for example so called Ganzfeld-studies or Remote-Viewing Experiments, are more and more being taken seriously by main-stream scientists and philosophers. Such studies seem to show that there are subjective perceptions of the outside world which use neither the physical senses nor neurological computation and are characterised by the same kind of qualia as those of normal, sensory perception. However, we already know from normal perception that qualia are intrinsically part of this form of perception, rather than a part of the physical world itself. Therefore, if we see ESP as a form of perception, we can in principle expect it to possess qualitative dimensions that are identical or at least similar to those of normal perception, while such dimensions per se do not need to refer to any external qualities. In other words, ESP cannot possibly give us any compelling, conclusive reasons to believe in qualitative aspects of matter either.
Moreover, we already know that the qualities perceived in normal perception aren't real properties of the external world, but only of our own mind as a result of interaction with quantitative patterns of the physical world. Therefore, we would have to postulate an exact parallel of this process of the creation of qualitative patterns from quantitative patterns in the physical world if we would want to uphold external qualities in relation to possible Extra-Sensory Perception of those qualities. Just as qualia are not part of the physical brain but of the mind, postulated qualities would not exist in the same way as quantitative patterns of matter (as they are irreducible to such patterns), but instead emerge from them in a separate non-quantitative qualitative "physical" realm (see footnote). Even if this picture of matter were true, it is altogether different from the one the proponents of external qualities believe in on the basis of their normal perception.
The normal reason for postulating irreducible qualitative aspects of the physical world is based on our irreducible qualitative perception of that world. However, if we accept the role of neurological computation in normal perception, this normal reason should be rejected. Counter-arguments certainly cannot rehabilitate the normal reason for believing in external qualities. Besides, the only (possibly) tenable version of a theory about external qualities in the physical world or matter, i.e. emergence of a separate qualitative dimension within matter which might be perceived directly in ESP, is completely different from the straight-forward, "normal" version in which qualitative aspects of the material world would be quite unproblematically perceived in normal perception.
Moreover, postulating external qualities would not at all solve the qualia part of the mind-body problem. It would rather create an additional ontological problem, which cannot be reduced to the problem of subjective qualia, namely how postulated (non-subjective) qualitative properties of matter would relate to (and interact with) its quantitative properties. Summing up, as long as it is not strictly necessary to postulate external qualities there cannot be any good reason for doing so. The normal reason should be seen as disqualified.
Footnote: One might wish to claim that the postulated external qualities are not only irreducible to quantitative patterns in the physical world but even completely unrelated. However, if there were no relation between quantitative patterns and external qualities, it would be completely impossible that the subjective qualia of normal perception created on the basis of the information of the quantitative patterns computed by neurology are similar, let alone identical to the postulated external qualities. Therefore, if there are external qualities they simply must be intimately related to quantitative properties of matter.
This paper was published in 2006.
Acknowledgements: I wish to thank René van Delft and Arnold Ziegelaar (and the other members of their philosophy circle) for inspiring me to write this essay after a discussion of The Concept of Mind by Gilbert Ryle.
Another paper which inspired me was written by Peter Unger