We’ve discussed here previously the enigma of what grief is for; but almost equally puzzling is the function of laughter. Apparently laughter is not unique to human beings, although in chimps and other animals the physical symptoms of hilarity do not necessarily resemble the human ones very closely. Without going overboard on evolutionary explanation, it does seem that such a noteworthy piece of behaviour must have some survival value, but it’s not easy to see what a series of involuntary and convulsive vocalisations, possibly accompanied by watering eyes and general incapacitation, is doing for us. Shared laughter undoubtedly helps build social solidarity and good feeling, but surely a bit of a hug would be fine for that purpose – what’s with the cachinnation?
Igor M. Suslov has a paper out, building on earlier thoughts, which presents an attempt to explain humour and its function. He thinks it would be feasible for a computer to appreciate jokes in the same way as human beings; but the implication of his theory seems to be that a sophisticated computer – certainly one designed to do the kind of thinking humans do – would actually have to laugh.
Suslov’s theory draws on the idea (not a new one) that humour arises from the sudden perception of incongruity and the resulting rapid shift of interpretation. When cognitive processes attain a certain level of sophistication, the brain is faced with many circumstances where there are competing interpretations of its sensory input. Is that a bear over there, or just a bush? The brain has to plump for one reading – it can’t delay presenting a view to consciousness until further observations have resolved the ambiguity for obvious practical reasons – and it constructs its expectations about the future flow of events on that basis: but it has the capacity to retain one or two competing interpretations in the background just in case. In fact, according to Suslov, it holds a number of branching future possibilities in mind at any one time.
The brain’s choice of scenario can only be based on an assessment of probability, so it is inevitably wrong on occasion - hey, it’s not a bear, after all! In principle, the brain could wait for the currently assumed scenario to drain away naturally when it reached its current end: but the disadvantages of realising one’s error slowly are obvious. Theoretically another alternative would be to delete all recollection of the original mistake: but the best approach seems to be to tolerate the fact that our beliefs about the bush conflict with what we remember believing. The sudden deletion of the original interpretation is the source of the humorous effect.
Suslov has drawn on the views of Spencer, which had it that actual physical laughter was caused by the discharge of nervous energy from mental process into the muscles. This theory, once popular, suffered the defect that there really is no such thing as ‘nervous energy’ which behaves in this pseudo-hydraulic style; but Suslov thinks it can be at least partially resurrected if we think of the process as excess energy arising from the clearance of large sections of a neural network (when a scenario is deleted). He recognises that this is still not really an accurate biological description of the way neurons work, but he evidently still thinks there’s an underlying truth in it.
One further point is necessary to the plausibility of the theory, namely that humour can be driven out by other factors. We may laugh when we realise the ‘bear’ is really a bush, but not when we make the reverse discovery. This is because the ‘nervous energy’, if we can continue to use that term, is directed into other emotions, and hence goes on to power shaking with fear rather than laughter. Suslov goes on to explain a number of other features of humour in terms of his theory with a fair degree of success.
An interesting consequence if all this were true, it seems to me, is that a network-based simulation of human consciousness would also necessarily be subject to sudden discharges. It seems to me this could go two ways. Either the successful engineers are going to notice this curious and possibly damaging property of their networks, or at some stage they are going to encounter problems (the frame problem?) which can in the end only be solved by building in a special rapid-delete facility with a special provision for the tolerance of inconsistency. Use of this facility would amount to the machine laughing.
Would it, though? There would be no need, from an engineering point of view, to build in any sound effects or ‘heave with laughter’ motors. Would the machine enjoy laughing, and seek out reasons to laugh? There seems no reason to think so, and it is a definite weakness of the theory that it doesn’t really explain why humour is anything other than a neutral-to-unpleasant kind of involuntary shudder. Suslov more or less dismisses the pleasurable element in humour: it’s more or less a matter of chance, he suggests, just as sneezing happens to be pleasant without that being the point of it. It’s true that humans are good at taking pleasure in things that don’t seem fun at first sight; making the capsaicin which is designed to deter animals from eating peppers into the very thing that makes them taste good, for example. But it’s hard to accept that funny things are only pleasant by chance; it seems an essential feature of humour is being left on one side.
It’s also possible to doubt whether all humour is a matter of conflicting interpretations. It’s true that jokes typically work by suddenly presenting a reinterpretation of what has gone before. Suslov claims that tickling works in a similar way – our expectations about where the sensation is coming from next are constantly falsified. Are we also prepared to say that the sight of someone slipping on a banana skin is funny because it upsets our expectations? That might be part of it: but if conflicting interpretations are the essence of humour, optically ambiguous figures like the Necker cube should be amusing and binocular rivalry ought to be hilarious.
There are of course plenty of technical issues too, apart from the inherent doubtfulness of whether the metaphor of ‘nervous energy’ can really be given a definite neurological meaning.
One aspect of Suslov’s ideas ought to be testable. It’s a requirement of the theory that the discarded interpretation is deleted, otherwise there is no surplus ‘nervous energy’. But why shouldn’t it simply recede to the status of alternative hypothesis? That seems a more natural outcome. If that were what happened, we should be ready to change our minds back as quickly as we changed them the first time: if Suslov is right and the discarded reading is actually deleted, we should find it difficult to switch back to the ‘bear’ hypothesis once we’ve displaced it with the ‘bush’ reading. That ought to show up in a greater amount of time needed for the second change of mind. I doubt whether experiments would find that this extra delay actually occurs.