The first study that we examine in this chapter confronts this challenge head on. One way of trying to model how we store and use linguistic knowledge is to build a machine that is capable of some form of linguistic understanding. The early days of artificial intelligence(AI) saw a number of attempts to write computer programs that could engage in some very elementary forms of conversational exchanges, but none of these programs was capable of anything that really resembled linguistic understanding.
The aim of programs such as ELIZA (written by Joseph Weizenbaum in 1966) was to simulate human conversation. The basic idea behind ELIZA (which, depending upon who one asks, was either based upon or intended to parody typical conversational exchanges between psychotherapists and their patients), was to create the illusion of conversation by rephrasing statements as questions and by programming the computer to give certain fixed responses where this is not possible. A sample“conversation” is given inBox 2.1.
Although ELIZA is said to have fooled a number of people into thinking that it was a human (including the unknowing participant in the conversation recorded in the box) nobody has ever suggested that it displays anything like a genuine understanding of language. For one thing, ELIZA does not in any sense analyze the syntactic structure or the meaning of the sentences that it encounters. It is simply programmed to respond to certain cues by making one of a small set of responses. Nor could ELIZA use the conver- sations in which it engaged to report on or navigate its environment. So-called chatterbot programs such as ELIZA are interesting for many reasons, but not as serious models of how we understand and use language.
Exercise 2.1 Explain in your own words what you think we can learn from programs such as ELIZA. Is it important that a person might be fooled by ELIZA into thinking that we were communicating with another human being?
Terry Winograd’s program SHRDLU, initially presented in his 1970 doctoral disserta- tion at MIT, was one of the first attempts to write a program that was not just trying to simulate conversation, but that was capable of using language to report on its environ- ment, to plan actions, and to reason about the implications of what is being said to it.
One of the distinctive features of SHRDLU is that it is programmed to deal with a very limited micro-world (as opposed to being a general-purpose language program, which is what ELIZA and other chatterbot programs are, in their very limited ways). The SHRDLU micro-world is very simple. It consists simply of a number of colored blocks, colored pyramids, and a box, all located on a tabletop, as illustrated inFigure 2.1. (The micro- world is a virtual micro-world, it should be emphasized. Everything takes place on a computer screen.)
SHRDLU is capable of various actions in the micro-world, which it can carry out through a (virtual) robot arm. It can pick up the blocks and pyramids, move them around, and put them in the box. Corresponding to the simplicity of the micro-world, SHRDLU’s language is relatively simple. It only has the tools to talk about what is going on in the micro-world.
There are three principal reasons why SHRDLU was very important in the develop- ment of cognitive science. The first is that it gave a powerful illustration of how abstract rules and principles such as those in the sort of grammar that we might find in theoret- ical linguistics could be practically implemented. If we assume that a speaker’s under- standing of language is best understood as a body of knowledge, then SHRDLU provided a model of how that knowledge could be represented by a cognitive system and how it could be integrated with other, more general, forms of knowledge about the environment.
B O X 2 . 1 A conversation with ELIZA (ELIZA’s responses are in upper case)
Men are all alike IN WHAT WAY?
They are always bugging us about something or other CAN YOU THINK OF A SPECIFIC EXAMPLE?
Well, my boyfriend made me come here YOUR BOYFRIEND MADE YOU COME HERE He says I’m depressed much of the time
I’M SORRY TO HEAR THAT YOU ARE DEPRESSED It’s true. I am unhappy
DO YOU THINK COMING HERE WILL HELP YOU NOT TO BE UNHAPPY? I need some help. That much seems certain
WHAT WOULD IT MEAN TO YOU IF YOU GOT SOME HELP? Perhaps I could learn to get along with my mother
TELL ME MORE ABOUT YOUR FAMILY (From Boden 1977: 106–7)
The second reason for highlighting SHRDLU is that it illustrated the general approach of trying to understand and model cognitive systems by breaking them down into distinct components, each of which carries out a specific information-processing task. One of the many interesting things about SHRDLU is that these distinct components are not completely self-contained. The separate processing systems collaborate in solving information-processing problems. There is cross-talk between them, because the pro- grams for each processing system allow it to consult other processing systems at particu- lar moments in the computation.
A final significant feature of the SHRDLU program is that it is based on the fundamen- tal assumption that understanding language is an algorithmic process. In Winograd’s own words,“All language use can be thought of as a way of activating procedures within the hearer” (1973: 104). As we will see, each component system is essentially made up of a vast number of procedures that work algorithmically to solve very specific problems. The system as a whole works because of how these procedures are linked up and embedded within each other.