Archive for December, 2011

Smelling soundIs trilled smell possible? Ed Cooke and Erik Myin raise the question in the JCS.  Why do we care? Well, for one thing smell has always tended to be the poor relation in discussions of conscious experience. The science of vision is so much better developed that seeing generally looks a more tractable area to attack, but arguably the discussion is somewhat lop-sided as a result; ‘seeing red’ isn’t necessarily a perfect epitome of all sensory experience, so a bit of clarification around smells might well be useful.

But the main point of asking the question is to test what Cooke and Myin call the independence thesis: the view that the experienced character of sensations includes a ‘something it is like’ over and above the gross physics of the business: that there’s an ultimate smelliness about smell that has nothing to do with the details of the sensory process. I would say there’s a range of possible positions here. Hardly anyone, I think would say that the physics of perception is irrelevant to how the experience seems. We know that that the wave structure of light and sound determines some of the characteristics of the experiences of vision and hearing, for example, and we know that smell is vaguer about location than vision because it depends on gases wafting around rather than sharply defined rays of light.  But beyond that the consensus breaks down. Some would say that these physical characteristics are just the basics and the real excitement lies in the ineffable qualities of experience. Purple is a thing in itself, not a blank sensory token which would do equally well for the smell of coffee, they might say.

Some would go further and accept that the qualities of experience are very largely determined by the physics of the medium and sensory apparatus, but that there’s a certain something beyond that which doesn’t reduce to the simple physics.  Rigorous materialists will be tempted to go further still and take the view that however complex and indefinable our experiences may seem, they are fully determined by the qualities of the processes that give rise to them: this of course, amounts to denying the existence of ineffable qualia. (My own view, for what it’s worth, lies an infinitesimal distance short of this extreme.)

Cooke and Myin’s approach is to look at the consequences of the independence thesis. If it’s true then we ought to be able to transfer the forms of one sensory modality to another without it losing its identity. So, in sound we can have a trill, a very rapid alternation of two notes; if independence is true, we ought to be able to have trilled smells.

Before tackling the thought experiment in more detail, Cooke and Myin provide a brisk review of some of the relevant science, including some odd and interesting facts. The smell of pressure-cooked pork liver is made up of 179 different compounds; airflow is indispensable to smell (having your nose full of smelly stuff or your receptors stimulated produces no sensation unless there’s airflow); and so sniffing is more important than you may have thought. It turns out that human beings are pretty well incapable of identifying single components of a smell when there are more than three – so much for perfume designers – and perception of smell is also very heavily conditioned by previous experience (if you’ve encountered smell b together with lemony smells in the past, you’ll tend to think smell b has lemony notes even when the lemon smells are objectively absent).  It looks as if we might each be working with a typical vocabulary of about 10,000 known smells, out of a theoretical 400,00 that the nose can distinguish: best estimates suggest that smell-space has a minimum of somewhere between 32 and 68 dimensions (as compared to human colour vision’s paltry 3).

Now we come to the thought-experiment itself.  It seems that Jesse Prinz has denied the possibility that a sound could become a smell merely by changing the structure of the experience (could the sound of a fire alarm ever become the smell of smoke?), so with fine daring, that is the first transition Cooke and Myin propose to anatomise in a thought-experiment.

Thought-experiments are always a little unsatisfactory because they don’t really force people to accept your conclusions in the way that a proper argument does. In this case, moreover, it seems to me there’s a particularly difficult trick to bring off because for the experiment to convince, Cooke and Myin want the transfer of properties to seem plausible; yet the more plausible it seems the more plausible independence seems too.  They want us to believe that they’re doing the best possible description of a transfer that could plausibly happen, in order to convince us that once we understand it it’s not plausible that it’s really a transfer at all.

However, I think they do a commendable job. First, sounds have to become less distinct in their onset and direction; they have to be more like generalised hums which float around appearing and dispersing slowly (no good for rapid warnings any more). The we have to imagine that we use our noses to detect sounds, that they only become perceptible when we breathe, and that sniffing or breathing deeply affects their intensity. We must imagine that it’s now a little more difficult to pick out single sounds when there are several at once: we might have to think about it for few moments and take some extra sniffs.

That’s not too bad, but there are bigger problems. We’ve noted that smell space appears to be huge; Cooke and Myin suggest we could enlarge sound space the same way by imagining that the differences in sound are like the differnces in timbre between musical instruments (though we have to suppose that we can readily distinguish the timbres of 10,000 or so different instruments). On the other hand, musical notes fit on an organised scale with perceptible relationships between different notes: smell doesn’t really have that, so we must drop it and assume that sounds are essentially monotonous. To round things off with behavioural factors, we should think of sound as no longer used for communication, but mainly for the evaluation of the acceptability of food, people and other biological entities; and we should imagine that sounds now have that characteristic of certain smells which allows them to evoke memories with particular potency.

If you’re still with the experiment, you’ll now have some intuitive idea of what it would be like if sounds had the structural and other characteristics of smells. But no, say Cooke and Myin: isn’t it apparent now that the sensations we’re talking about wouldn’t be sounds any more (in fact they would pretty much have become smells)? Isn’t it clear, in short, that in order to be trillable, smells would have to cease being smells? They go on to a further thought experiment in which smells become colours.

This is a valuable exercise, but as I say, thought experiments are not knock-down arguments, and I am willing to bet there wil in fact be plenty of people who are prepared to go along with Cooke and Myin’s transition but insist at the end that the sensations they’re imagining are still in some way sounds, or at least have a core soundiness which makes them different from echt smells. (You notice how I criticise the weakness of thought experiments and yet here I am doing something worse – a kind of third-person thought-experiment where I invite agreement that in certain odd circumstances other people would think in a certain way.)

Personally I think some of the most interesting territory revealed here is not so much at the ends of the transition as in the middle. The experiment raises the possibility of mixed modalities never before imagined, chimerical experiences with some of the characteristics of two or more different standard senses. Not just that, either, because we can invent new physical constraints and structures and develop possible sensory modalities which have nothing whatever in common with any real ones, if our imagination permits.

This gives Cooke and Myin some possible new ammunition. Do all these imaginary new modalities get their own essence, their own qualia? If we mix smell and hearing in different ways, do we have to suppose that there are distinct qualia of, er, smearing and hell?

For that matter, what if we took a subject (all right, victim) through the transition of sound to smell; and then separately gave him back sound? has he now got two distinct experiences of sound? Then if we move the new sound2 though the transition to smell, does he have two smells? And if we then give him back a separate sense of sound again? And so on.

I can’t help thinking it would be quite a Christmas present if we could have a sense with the spatial distinctness of vision, the structured harmonics of sound, and the immense dimensionality of smell. There would be some truly amazing symphonic odours to be painted.

Merry Christmas, all!