Time flies like an arrow. A simple enough sentence, until Glasgow University professor Simon Garrod points out that it has at least 48 different meanings.

"Time" can be a noun or a verb, as in "to measure time", "flies" can be a verb, or a noun with at least two distinct meanings, insects or trouser zips, while "like" can be an adjective or a verb. And if there are fruit flies, why not time flies?

"When all these different possibilities are put together in even a simple sentence, it leads to an explosion of possible interpretations," he says. "However, when we read such a sentence, somehow we manage to get at the appropriate meaning."

Professor Garrod is deputy director of the Economic and Social Research Council's human communication research centre, based in Glasgow and Edinburgh Universities, which has been hosting an international conference, "Reading 2000", on scientific discoveries about how we read.

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The two traditional views are that reading depends on decoding the words, or that it is based on the degree to which the reader can predict what is coming next.

The centre has tried to establish how people read, using a sophisticated high resolution eye tracker, originally developed for NASA, which reflects infra-red light off various parts of the eye.

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The Glasgow team checked readers' eye movements when they interpreted sentences. It showed that reading is a combination of decoding and prediction, with readers establishing the words on the basis of what they see , but then establishing how to interpret them on the basis of the context.

"The initial analysis always prefers the simpler structure, irrespective of whether that's the one that's predicted," Professor Garrod says.