What is Artificial Intelligence?

By Jack Copeland

© Copyright B.J. Copeland, May 2000

Micro-World AI

The real world is full of distracting and obscuring detail: generally science progresses by focussing on artificially simple models of reality (in physics, frictionless planes and perfectly rigid bodies, for example). In 1970 Marvin Minsky and Seymour Papert, of the MIT AI Laboratory, proposed that AI research should likewise focus on developing programs capable of intelligent behaviour in artificially simple situations known as micro-worlds. Much research has focussed on the so-called blocks world, which consists of coloured blocks of various shapes and sizes arrayed on a flat surface.

An early success of the micro-world approach was SHRDLU, written by Terry Winograd of MIT (details of the program were published in 1972). SHRDLU controlled a robot arm that operated above a flat surface strewn with play blocks (both the arm and the blocks were virtual). SHRDLU would respond to commands typed in natural English, such as "Will you please stack up both of the red blocks and either a green cube or a pyramid". The program would plan out a sequence of actions and in the virtual world the robot arm would arrange the blocks appropriately. SHRDLU could correctly answer questions about its world of blocks, for example "Can a pyramid be supported by a pyramid?" (SHRDLU attempts to stack up two pyramids and fails) and "Is there anything which is bigger than every pyramid but is not as wide as the thing that supports it?" (to which SHRDLU answered "Yes, the blue block"). SHRDLU could also answer questions about its own actions:

Had you touched any pyramid before you put one on the green block?
YES, THE GREEN ONE.
When did you pick it up?
WHILE I WAS STACKING UP A RED CUBE, A LARGE GREEN CUBE, AND A LARGE RED BLOCK.
Why?
TO GET RID OF IT.
Why did you do that?
TO CLEAN OFF THE RED CUBE.
Why did you clear off that cube?
TO PUT IT ON A LARGE GREEN CUBE.
Why did you do that?
TO STACK UP A RED CUBE, A LARGE GREEN CUBE, AND A LARGE RED BLOCK.
Why did you do that?
BECAUSE YOU ASKED ME TO.

Although SHRDLU was initially hailed as a major breakthrough, Winograd soon announced that the program was in fact a dead end. The techniques pioneered in the program proved unsuitable for application in wider, more interesting worlds. Moreover, the appearance that Shrdlu gives of understanding the blocks micro-world, and English statements concerning it, is in fact an illusion. Shrdlu has no idea what a red block is.

Another product of the micro-world approach was Shakey, a mobile robot developed at the Stanford Research Institute by Bertram Raphael, Nils Nilsson and their group, during the period 1968-1972. (Shakey can now be viewed at the Boston Computing Museum.) The robot occupied a specially built micro-world consisting of walls, doorways, and a few simply-shaped wooden blocks. Each wall had a carefully painted baseboard to enable the robot to "see" where the wall met the floor (a simplification of reality that is typical of the micro-world approach). Shakey had about a dozen basic abilities, such as TURN, PUSH and CLIMB-RAMP. These could be combined in various ways by the robot's planning programs. Shakey's primary sensor was a black-and-white television camera. Other sensors included a "bump bar", and odometry that enabled the robot to calculate its position by "dead reckoning". A demonstration video showed Shakey obeying an instruction to move a certain block from one room to another by locating a ramp, pushing the ramp to the platform on which the block happened to be located, trundling up the ramp, toppling the block onto the floor, descending the ramp, and manoeuvring the block to the required room, this sequence of actions having been devised entirely by the robot's planning program without human intervention. Critics emphasise the highly simplified nature of Shakey's environment and point out that, despite these simplifications, Shakey operated excruciatingly slowly--the sequence of actions in the demonstration video in fact took days to complete. The reasons for Shakey's inability to operate on the same time-scale as a human being are examined later in this article.

FREDDY, a stationary robot with a TV "eye" mounted on a steerable platform, and a pincer "hand", was constructed at Edinburgh University under the direction of Donald Michie. FREDDY was able to recognise a small repertoire of objects, including a hammer, a cup and a ball, with about 95% accuracy; recognising a single object would take several minutes of computing time. The robot could be "taught" to assemble simple objects, such as a toy car, from a kit of parts. Envisaged applications included production-line assembly work and automatic parcel handling. FREDDY was conceived in 1966 but work was interrupted in 1973, owing to a change in the British Government's funding policy in the wake of a disparaging report on AI (and especially robotics) by the Cambridge mathematician Sir James Lighthill. Work on FREDDY resumed in 1982 with U.S. funding.

Roger Schank and his group at Yale applied a form of the micro-world approach to language processing. Their program SAM (1975) could answer questions about simple stories concerning stereotypical situations, such as dining in a restaurant and travelling on the subway. The program could infer information that was implicit in the story. For example, when asked "What did John order?", SAM replies "John ordered lasagne", even though the story states only that John went to a restaurant and ate lasagne. FRUMP, another program by Schank's group (1977), produced summaries in three languages of wire-service news reports. Impressive though SAM and FRUMP are, it is important to bear in mind that these programs are disembodied and have no real idea what lasagne and eating are. As critics point out, understanding a story requires more than an ability to produce strings of symbols in response to other strings of symbols.

The greatest success of the micro-world approach is a type of programs known as an expert system.

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