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Laser measurements reveal biological basis of distance perception

Using a laser range-finder, neurobiologists have scanned real-life scenes to gather millions of distance measurements to surfaces in each scene -- analyzing the mass of data to explain a series of long-known but little-understood quirks in how people judge distances.

The measurements reveal, for example, that the tendency of people to estimate the distance of isolated objects as being six to 12 feet away arises because that is the average distance of actual objects and surfaces in the visual scenes people encounter.

Thus, said the Duke University Medical Center neurobiologists, the findings support their theory that the visual system has evolved to make the best statistical guess about distances and other features of visual scenes, based on past experience.

The researchers, Zhiyong Yang and Dale Purves, published their findings in the June 2003 issue of "Nature Neuroscience" (online version posted May 18, 2003). Their research was supported by the National Institutes of Health and the Geller Endowment. Yang is a postdoctoral fellow and Purves is the George B. Geller Professor for Research in Neurobiology.

"All the characteristics of the visual world that we take for granted -- for example the diminution of size with distance -- are a result of perception," said Purves. "So, a question for centuries has been, 'What is the biological reason we see space in the peculiar way that we do?'"

In their past research on the perception of the geometry, color, brightness and motion, Purves and his colleagues have accumulated evidence that visual processing is not the result of logical calculations about the image that falls on the retina of the eye as such. Rather, they have shown that vision is a fundamentally empirical phenomenon, in which the connections between nerve cells in the visual system evolved as a result of the success of organisms that correctly interpreted the inherently ambiguous visual world. Such ambiguity arises because the photons
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Contact: Dennis Meredith
dennis.meredith@duke.edu
919-681-8054
Duke University
20-May-2003


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