( When a human looks at a number letter ...)In the mind's eye: How the brain makes a whole out of parts

When a human looks at a number, letter or other shape, neurons in various areas of the brain's visual center respond to different components of that shape, almost instantaneously fitting them together like a puzzle to create an image that the individual then "sees" and understands, researchers at The Johns Hopkins University report.

A team from the university's Zanvyl Krieger Mind/Brain Institute describes the complex but speedy process in detail in a recent issue of the journal Neuron.

The question of how the brain sees, recognizes and understands objects is one of the most intriguing in neuroscience, associate professor and paper co-author Charles E. Connor said.

"This may not even seem like a scientific question to some people, because seeing is so automatic and we are so good at it ?far better than the best computer vision systems yet devised," Connor said. "That is because a large part of the human brain is devoted to interpreting objects in our world, so that we have the necessary information for interacting with our environment.

"Vision doesn't happen in the eye," Connor said. "It happens at multiple processing stages in the brain. We study how objects are signaled or encoded by large populations of neurons at higher-level stages in the object-processing part of the brain."

The report, based on recordings of nerve cells in the visual cortex of macaque monkeys, reveals that neurons in the higher-level visual cortex at first respond to a visual stimulus "somewhat indiscriminately," signaling all the individual features within a shape to which they are sensitive. For instance, a particular neuron may respond to objects with either a concave fragment at the top or a convex fragment at the bottom. At this point, the neural signals are ambiguous; the brain doesn't know whether the concavity, the convexity or both are present.

Milliseconds later, however, neurons begin to react exclusively to combinations of shape fr
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Source:Johns Hopkins University

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