The Biology of Distance Perception

Study finds people make assumptions based on common experience

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THURSDAY, June 26, 2003 (HealthDayNews) -- In a study using laser measurement, Duke University Medical Center neurobiologists uncovered the biological basis of distance perception in humans.

The scientists used a laser range finder to scan real-life scenes and gather millions of distance measurements in each scene. They used that data to explain a number of long-known but little understood quirks in how people judge distance.

For example, the scientists concluded that people tend to estimate the distance of isolated objects as being six to 12 feet away because that's the average distance of actual objects and surfaces in the visual scenes encountered by people.

The Duke researchers say that supports their theory that the human visual system evolved to make the best statistical guess, based on past experience, about distances and other visual features.

Their findings appear in the June issue of Nature Neuroscience.

"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. So, a question for centuries has been 'What is the biological reason we see space in the peculiar way that we do?'" researcher Dr. Dale Purves says in a news release.

In previous research on perception of geometry, color, brightness and motion, Purves and his colleagues found evidence that visual processing isn't the result of logical calculations about the image information gathered by the eyes. Rather, it's mostly an empirical process driven by connections between nerve cells in the visual system that evolved as a result of the success of organisms that correctly interpreted the ambiguous visual world.

That visual ambiguity arises because photons striking the eyes' retinas don't carry any information about their origins. That means the visual system has to process information from the retina statistically to correctly interpret a visual world that can't be known directly.

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SOURCE: Duke University, news release, June 2003
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