"It turned out that that changes in viewing direction had remarkably little effect on the observers' perceptions," Todd said.
The only difference they found is that, when viewed from an angle, the torso looked "squashed" in other words, it looked thinner to viewers. But the far points and near points, and the overall relief of the depicted object, remained proportionally the same.
The key is that the near points and far points of the picture remained the same no matter the angle the picture was viewed from, Todd said.
"When observing real surfaces in the natural environment the visual information that specifies near and far points varies when we change viewing direction," he said.
"When we observe a picture on the wall, on the other hand, the visual information that defines near and far points is unaffected by viewing direction. Still, we interpret this perceptually as if it were a real object. That is why the eyes appear to follow you as you change your viewing direction."
Todd said people may be surprised by this phenomenon because of the unique perceptual aspects of viewing a picture. We perceive the object depicted in a painting as a surface in 3-dimensional space, but we also perceive that the painting itself is a 2-dimensional surface that is hanging on the wall.
"When we look at a picture, you have these two perceptions simultaneously, but it is difficult to make sense of that conceptually. That's why this issue has fascinated people for hundreds of years."
In fact, many researchers have continued to follow the theories of La Gournerie, a French researcher who proposed a mathematical analysis in 1859 of why eyes in a painting seem to follow viewers.
"One of the contributions of our study is that we showed that while La Gournerie had the basic idea right, his mathematical description was wrong," Todd said. "We were able to use new methodologies to give
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Contact: James Todd
Todd.44@osu.edu
614-292-8661
Ohio State University
20-Sep-2004