The article below is pasted from New Scientist Nov. 24.
Did you hear the one about the computer with a sense of
humour?; A physicist has proposed a model explaining
how information processing in the brain leads to humour
- and it could herald computers able to tell jokes
Mark Buchanan
DID you hear the one about the computer with a sense of humour?
Didn't think so. Computers can do many things, but stand-up
comedy is not one of them. Yet the idea that computers can be
witty might not be all that far-fetched. Perhaps machines need
not be conscious to understand humour, and even to invent and
tell jokes.
Physicist Igor Suslov of the Kapitza Institute for Physical
Problems in Moscow, Russia, has designed a computer model which
he says explains the evolution of humour. Our ability to
experience humour, he suggests, ultimately depends on quirks in
how the brain handles information.
As a student, Suslov performed in the university theatre. "We
didn't have much time to write our plays," he recalls. "I began
to wonder if it might be possible to create jokes more or less
automatically." He didn't work out how back then, but he never
forgot the problem. Now he thinks he sees at least the broad
outline of how humour works and why it evolved in the first place.
Verbal jokes, Suslov suggests, work by drawing the mind into
error. It first settles on one meaning, and then has to correct
itself and see another. Take this joke, for example:
Father (reprovingly): "Do you know what happens to liars when they
die?"
Johnny: "Yes sir, they lie still."
The wit of the line comes from the way the brain pirouettes to
interpret "lie" in two different ways. This kind of error, Suslov
argues, is at the root of most humour, and stems from a
fundamental difficulty the brain faces when trying to interpret
incoming data. Whether it's words, sounds or visual images, the
brain has to link incoming information to patterns it knows from
experience. Much of this process takes place unconsciously. Only
when the brain settles on an interpretation for a chunk of data
does it send that interpretation into consciousness, where it
might prompt action.
As Suslov points out, however, to make rapid decisions, the brain
often has to settle quickly on an interpretation without enough
information to be sure it is the correct one. Yet it must also
remain ready to take advantage of further data streaming in,
which may lead to a better interpretation. Consequently, he says,
there's just no way a well-functioning brain can entirely avoid
making these errors of interpretation. "The nature of the
processing algorithm makes mistakes inevitable."
And that, he claims, also makes humour inevitable. He argues that
humour is the brain's way of dealing with such errors: a rapid
emotional response makes us aware of a mistake, and brings new
information into consciousness especially swiftly. "Its
biological function," says Suslov, "is to make brain operations
more efficient." We laugh as the brain squirms its way out of a
contradictory state.
Suslov hasn't yet made a computer that laughs, but he has proposed
a specific computational model, based on a neural network, that
would mimic the information processing he describes, and
necessarily be prone to the same recognition errors
(www.arxiv.org/abs/0711.2058 ). Ultimately, he suggests, there
may be no reason why we won't be able to program computers to
tell and understand jokes .
The idea is consistent with what we know about the brain, says
neuroscientist Peter Latham of University College London, but it
is not clear from Suslov's work why it should be humour that is
linked to the processing difficulty he describes. "There are lots
of positive emotions that might play the required role," he says.
And why, he wonders, if humour evolved to solve an internal
processing problem, does it involve an outward physical display,
such as laughter, that others can see?
That characteristic of the humour response, according to biologist
David Sloan Wilson of Binghamton University in New York, suggests
it probably evolved in connection with social interactions. Human
laughter, he points out, appears to be closely linked to similar
behaviour that has important social roles for our primate
relatives. During social play, such as tickling and chasing, many
primate species display a particular facial expression, a "play
face", and often produce a panting vocalisation that many
biologists see as akin to laughter.
There's also evidence that something very similar to humour and
laughter exists in non-primate species. Over the past decade, for
example, Jaak Panksepp of Washington State University in Pullman
and colleagues have shown that rats make frequent ultrasonic
noises similar to laughter during positive social interactions.
Researchers can even make rats laugh by tickling them on the nape
of the neck, an area to which rats themselves direct their
playful activities. Panksepp suggests that the rat's behaviour is
closely related to laughter in babies (Behavioural Brain Research
, vol 182, p 231).
Laughter, Wilson points out, is also famously contagious. "People
are roughly 30 times more likely to laugh in the presence of
others than when they are by themselves," he says.
All this evidence, Wilson suggests, makes a strong case that
humour evolved in association with social activity. This doesn't
mean that Suslov's idea is necessarily wrong, he says. "It could
be that humour evolved for one function, and was later co-opted
for another."
For example, the emotional response involved in humour might have
arisen first as an aid to social organisation and bond-forming
among our distant ancestors, and then later, when the brain
evolved higher cerebral functions, such as language processing,
evolution may have hijacked the pre-existing emotional pathway
linked to humour. If so, humour could sometimes play a role much
as Suslov suggests, with the outward sounds we make, such as
laughter, merely a by-product of earlier evolution.
Yet Suslov has some other problems to work out too. After all, we
don't always laugh when we misread a sentence, or misinterpret an
image.
"This is the first real theoretical model I've seen proposed for
humour," says psychologist Daniel Levine of the University of
Texas, Arlington. "It's laudable for that. What is lacking is an
explanation of what is or isn't humour-producing. It's not the
case that every phrase that tricks the mind into an error is
funny."
On the other hand, Suslov argues, the idea does explain quite a
lot about jokes, including why hackneyed jokes don't work, and
why the timing of a joke's delivery is so important. Both
situations fail to lure the brain into making the required
decision error, either because the brain recognises the joke, or
because it has enough time to correct the misinterpretation
before sending the correction into consciousness.
So perhaps a computer that can understand and tell at least simple
jokes may not be too far away. The humour we see in other
primates and rats may only be a beginning. "Some people still
regard laughter as a uniquely human trait," says Panksepp, "but
the joke's on them."Joke in a box Mark Buchanan
Computers already play chess and compose music. Igor Suslov of the
Kapitza Institute for Physical Problems in Moscow, Russia, thinks
one day they may also understand emotions. As a first step, he is
working towards a computer that can react to humour - at least to
simple jokes in which individual words switch their meanings as
the joke is understood.
A computational system capable of understanding such jokes, he
suggests, has to be able to recognise meanings. It also requires
a mechanism enabling a subsequent improved recognition to
supersede the first. To accomplish this, Suslov envisions a
neural network of artificial elements, similar to biological
neurons. A network capable of reacting to humour requires a
sensory system that gathers information from outside and sends it
to a memory system, which can recognise patterns. When it does,
this system would send its result to a third network,
representing the computer's "consciousness".
This network would then also link into a subnetwork of neurons
corresponding to the motor cortex. Improved recognition of an
incoming stimulus would trigger this cortex to kick off the
humour response, a mechanical reaction expunging the incorrect
interpretation and replacing it with the improved version - while
making some funny noises perhaps. Building such a system, Suslov
suggests, should be possible in a few years
(www.arxiv.org/abs/0711.2061 ).
"This is a brave attempt to make a computer model of humour," says
Leonid Perlovsky, an expert in artificial intelligence at Harvard
University. "It is interesting to see even a first step toward
understanding humour in a mathematical way."
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