The paranoid program

by Paul Curzon, Queen Mary University of London

One of the greatest characters in Douglas Adams’ Hitchhiker’s Guide to the Galaxy, science fiction radio series, books and film was Marvin the Paranoid Android. Marvin wasn’t actually paranoid though. Rather, he was very, very depressed. This was because as he often noted he had ‘a brain the size of a planet’ but was constantly given trivial and uninteresting jobs to do. Marvin was fiction. One of the first real computer programs to be able to converse with humans, PARRY, did aim to behave in a paranoid way, however.

PARRY was in part inspired by the earlier ELIZA program. Both were early attempts to write what we would now call chatbots: programs that could have conversations with humans. This area of Natural Language Processing is now a major research area. Modern chatbot programs rely on machine learning to learn rules from real conversations that tell them what to say in different situations. Early programs relied on hand written rules by the programmer. ELIZA, written by Joseph Weizenbaum, was the most successful early program to do this and fooled people into thinking they were conversing with a human. One set of rules, called DOCTOR, that ELIZA could use, allowed it to behave like a therapist of the kind popular at the time who just echoed back things their patient said. Weizenbaum’s aim was not actually to fool people, as such, but to show how trivial human-computer conversation was, and that with a relatively simple approach where the program looked for trigger words and used them to choose pre-programmed responses could lead to realistic appearing conversation.

PARRY was more serious in its aim. It was written by, Kenneth Colby, in the early 1970s. He was a psychiatrist at Stanford. He was trying to simulate the behaviour of person suffering from paranoid schizophrenia. It involves symptoms including the person believing that others have hostile intentions towards them. Innocent things other people say are seen as being hostile even when there was no such intention.

PARRY was based on a simple model of how those with the condition were thought to behave. Writing programs that simulate something being studied is one of the ways computer science has added to the way we do science. If you fully understand a phenomena, and have embodied that understanding in a model that describes it, then you should be able to write a program that simulates that phenomena. Once you have written a program then you can test it against reality to see if it does behave the same way. If there are differences then this suggests the model and so your understanding is not yet fully accurate. The model needs improving to deal with the differences. PARRY was an attempt to do this in the area of psychiatry. Schizophrenia is not in itself well-defined: there is no objective test to diagnose it. Psychiatrists come to a conclusion about it just by observing patients, based on their experience. Could a program display convincing behaviours?

It was tested by doing a variation of the Turing Test: Alan Turing’s suggestion of a way to tell if a program could be considered intelligent or not. He suggested having humans and programs chat to a panel of judges via a computer interface. If the judges cannot accurately tell them apart then he suggested you should accept the programs as intelligent. With PARRY rather than testing whether the program was intelligent, the aim was to find out if it could be distinguished from real people with the condition. A series of psychiatrists were therefore allowed to chat with a series of runs of the program as well as with actual people diagnosed with paranoid schizophrenia. All conversations were through a computer. The psychiatrists were not told in advance which were which. Other psychiatrists were later allowed to read the transcripts of those conversations. All were asked to pick out the people and the programs. The result was they could only correctly tell which was a human and which was PARRY about half the time. As that was about as good as tossing a coin to decide it suggests the model of behaviour was convincing.

As ELIZA was simulating a mental health doctor and PARRY a patient someone had the idea of letting them talk to each other. ELIZA (as the DOCTOR) was given the chance to chat with PARRY several times. You can read one of the conversations between them here. Do they seem believably human? Personally, I think PARRY comes across more convincingly human-like, paranoid or not!


Activity for you to do…

If you can program, why not have a go at writing your own chatbot. If you can’t writing a simple chatbot is quite a good project to use to learn as long as you start simple with fixed conversations. As you make it more complex, it can, like ELIZA and PARRY, be based on looking for keywords in the things the other person types, together with template responses as well as some fixed starter questions, also used to change the subject. It is easier if you stick to a single area of interest (make it football mad, for example): “What’s your favourite team?” … “Liverpool” … “I like Liverpool because of Klopp, but I support Arsenal.” …”What do you think of Arsenal?” …

Alternatively, perhaps you could write a chatbot to bring Marvin to life, depressed about everything he is asked to do, if that is not too depressingly simple, should you have a brain the size of a planet.


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This blog is funded through EPSRC grant EP/W033615/1.

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