Visually impaired people will soon have much less difficulty in following television programmes thanks to an audio commentary that fills in the gaps between dialogue.

Known as Audiotel, the technique has been developed by the University of Manchester's age research centre in collaboration with the Independent Television Commission, the BBC, the Royal National Institute for the Blind and a clutch of firms, including Motorola.

It was on show last week as part of a Royal Society/Royal Academy of Engineering exhibition highlighting the contributions of science and engineering to health and wealth creation.

The system uses a skilled describer who prepares the commentary on a PC work station which acts as a word processor, videotape controller and editor.

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The commentary is aligned with the programme timecode and at transmission time, the descriptions are automatically slotted into the teletext system for nationwide broadcast. A special receiver in the viewer's home decodes the description and presents it with the main programme audio either via speakers or through headsets.

The commentary describes to the viewer actions, scenery, facial expressions and body language during programmes. Trials last year showed it helped comprehension and enjoyment among blind and partially sighted viewers.

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Manchester researchers' contribution focused on making the technology accessible to visually impaired people, particularly the elderly. Pat Rabbitt, director of the age research centre, said this meant acknowledging their slowness of response and the danger of information overload.

Professor Rabbitt said that audio commentary has also found favour with elderly people not visually impaired: "This is true with some of the more sloppy drama or thriller productions where they use complicated flashbacks and flashforwards to cover up for an essentially banal plot."