Dr. Livingstone, a leading expert on visual perception, said that she first noticed something different about Rembrandt's eyes several years ago when she was gazing at several of his self-portraits at the Louvre. The eyes were just slightly asymmetrical.

Sometimes the right eye was out of register and sometimes the left eye, she said. It was unclear if the effect was random or systematic.

To find out, Dr. Livingstone and her a colleague, Bevil R. Conway, examined high-resolution images of self-portraits, both oil paintings and etchings, that are generally acknowledged to be genuine Rembrandts. Most of the works, made over a period of four decades, show one eye gazing directly at the viewer and the other eye deviating to the side. Rembrandt's portraits of others generally show the eyes properly aligned, Dr. Livingston said.

The researchers looked for the pattern in 24 oils and 12 etchings in which both eyes could be seen clearly, and confirmed the walleye effect in 35 of those 36 works. In 23 of the 24 paintings, the eye on the right side of the painting tends to look straight ahead and the other eye deviates outward. In the 12 etchings, the asymmetry is reversed because the artist scratches lines onto the plate to produce a reverse image, she said.

Walter Liedtke, the curator of European painting and specialist in Dutch and Flemish art at the Metropolitan Museum of Art, who has also focused on visual perception, said the findings seemed plausible. "But I worry a little in the case of self-portraits that Rembrandt may have been looking in a mirror to make them," he said. "The easel would be to one side and a mirror to the other, with one eye more or less perpendicular to the mirror. As to the other eye, it's hard to say. He'd be moving back and forth."