Keeping watch: The paintings that will look at you

Those who have ever felt the eyes of a portrait following them as they move around a room might want to avoid the National Gallery this autumn. Because there they'll probably be proved right.

Those who have ever felt the eyes of a portrait following them as they move around a room might want to avoid the National Gallery this autumn. Because there they'll probably be proved right.

The gallery, in central London, is to conduct the world's largest "eye-tracking" experiment, to examine the way people look at paintings, as part of a major new exhibition which opens in October.

Working with researchers from the Applied Vision Research Unit from the University of Derby, the gallery is to install equipment which reveals how a viewer's eye travels around a painting as they stand in front of it, and shows how the same picture will be seen differently by different people.

The results of the live experiment will be shown as patterns on a screen - and will reveal whether the Old Masters, who used perspective to try to control the gaze of their viewer in a way that has been followed by artists for generations since, were actually correct. Elsewhere in the gallery, a hidden camera behind an unmarked painting will broadcast a live relay of the painting's view of its audience onto a screen in another room, providing another view of how people look at paintings.

"Visitors won't know what painting the camera is behind," said Razeetha Ram, a gallery spokeswoman. "The image will be shown in another room. But we'll be able to come to conclusions about how the eye moves around the painting. Leonardo da Vinci employed perspective to make the viewer look at a picture in a particular way. This way we'll be able to see if he was right, so it will be fascinating." The technology in the exhibition has been used only on a small scale, and never in a public gallery. Organisers hope for thousands of visitors during the three-month run, to provide valuable scientific data for the university and the gallery.

The experiments will form part of the Telling Time exhibition, examining the relationship between time and painting. The exhibition will show how artists have struggled to depict the passing of time or movement in still images.

The British satirist Hogarth, for example, used a sequence of images to show the progression of a story in his Before and After, a device that can be traced from the earliest surviving manuscripts to the modern comic strip.

In Giovanni di Paolo's Saint John The Baptist retiring to the Desert, a chain of events over time is contained in a single image, but in Rembrandt's Belshazzar's Feast the artist tries to encapsulate an entire tale in an instant of terror. Rembrandt's painting shows, for example, cups spilling their contents.

The study will also look at how painters attempted to show movement. The exhibition will feature what is believed to be the earliest surviving example of a blurred wheel, the seventeenth century Woman Spinning by Rembrandt's pupil, Nicolaes Maes.

The final part of the exhibition will also examine the effects of time on the paintings themselves, which can cause colours to alter, or for once-invisible changes to reveal themselves where the underpaint has started to show.

* The Telling Time exhibition will run from 18 October to 14 January 2001.