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Now You See It …

Now you still do, even when lines are too small to register

THURSDAY, May 31 (HealthScout) -- Your mind may not tell you all that you see, claims new research.

Scientists at the University of Minnesota and the University of California at San Diego tested people's vision by projecting incredibly fine lines directly onto their retinas. They found the brain registered the lines -- 65 within the width of a pinky finger -- even when people saw them only as a blur.

The results show that not everything in the visual cortex, the part of the brain that processes visual information, becomes conscious knowledge, says says study co-author Sheng He, assistant professor of psychology at the University of Minnesota. The study was reported last week in Nature.

"This particular study tells us that even in the brain, the visual cortex in particular, neurons can still resolve very fine details that are not perceived. Neurons are capable of defining much further detail than previously thought," says He.

Even more intriguing is the evidence of a visual unconscious, says He.

"When we talk about consciousness, it's a very mysterious concept" and this work bolsters the idea that people see things they don't know they see, He says.

The study involved two people, a common practice when examining a very basic, uniform function in humans, He says.

Researchers projected either horizontal or vertical lines directly onto the subjects' retinas with a special type of laser that bypasses the cornea.

Then the researchers relied on a longstanding theory that says when humans are shown vertical or horizontal lines for several seconds, then shown a second grid, they are better able to perceive the second grid if it is perpendicular to the first. The theory says that different neurons perceive different line patterns, and when someone is shown the same pattern twice, the neurons are tired and don't work well.

Using that concept, the researchers made the patterns of lines so fine the first time that they were beyond the subjects' usual abilities to identify them. When the subjects were shown a larger, but identical second grid, they still could not discern the pattern. But when the second grid was made perpendicular to the first grid, the subjects could tell which way the lines were going.

The results show that neurons did see the first grid, though it was too small for the subjects to recognize, says He.

Visual perception expert Peter Lennie, professor of neural science at New York University in Manhattan, says the study is "a careful and elegant analysis of how visual information is used in the cortex to shape visual perception, while not itself being accessible to consciousness. We know from direct observations of neural activity that neurons at early stages in the brain respond to information that neurons at later stages do not, but until now this has not been shown in perceptual studies on humans."

Although the findings don't point to any immediate new treatments for eye diseases or degenerative conditions, He says, "In general, the more you know about a visual system, the more you can treat problems and diseases of the visual system."

The study was funded by the National Institutes of Health and the Alfred P. Sloan Foundation.

What To Do

Vision Science offers links to research on human and animal vision.

You can also click here to find more information about perception.

And these illusions come courtesy of The Joy of Visual Perception.

Read these HealthDay stories for more on vision.

SOURCES: Interviews with Sheng He, assistant professor, psychology, University of Minnesota, Minneapolis; Peter Lennie, professor, neural science, New York University, New York City; May 24, 2001, Nature
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