Public Release: 

The brain's flashy tale

Salk Institute

How we perceive the brightness of light may reveal how the brain is wired to handle the wide ranges of light stimulation we encounter every minute. A Salk Institute study, published in the April 15 issue of Nature, shows that timing - as well as the intensity of a light and that background it is on-- determines how we judge a light's brightness.

Professor Terrence Sejnowski and his colleagues found that the timing of short and long bright light flashes could create optical illusions: when the short light came on at the beginning of the long light it appeared to be dimmer, but when it came on at the end of the long light the short light was brighter.

"This study reveals a new way in which the cerebral cortex handles light and suggests that the brain is processing light in the cortex through two parallel streams of nerve cells," Sejnowski says.

"One of the streams adapts its perceptual signaling to the brain in response to changes in light, and the other that does not waver from its initial assessment of a light's brightness."

The work is part of Sejnowski's continuing quest to unravel the complex networks of nerve cells created to handle perception, thought, language, consciousness and the other functions in the brain that make us uniquely human.


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