New Light on How the Brain Handles Brightness

June 23, 2004

New Light on How the Brain Handles Brightness

June 23, 2004

La Jolla, CA – Studies by a Salk Institute research team on 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.

The study, by professor Terry Sejnowski and colleagues and published in the April 15 issue of Nature, shows that timing as well as the intensity of a light determine how we judge a light’s brightness. Scientists knew that brightness depends on such factors as scene context, shadows and three-dimensional perspectives, but these spatial arrangements did not explain fully how brightness is perceived.

The team found that the timing intervals between brief and long bright light flashes could create an optical illusion. Volunteers were asked to fixate their vision at a point on a computer screen. Then, two lights were flashed; one short, the other long, and the volunteers were asked which one was brighter. When the short light flashed at the beginning of the long-duration light it appeared to the volunteers to be dimmer, but when it flashed at the end of the long light the short light was reported as brighter.

The illusion showed that timing is as important as spatial influences in allowing the brain to measure brightness, which raises new questions on how nerve cell networks encode visual signals to mediate our perception of brightness. The scientists concluded that the illusion arose from nerve cell activity in the cerebral cortex, specifically in the area of the brain that handles higher visual functions.

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

索尔克生物研究所（Salk Institute for Biological Studies）位于加利福尼亚州拉霍亚，是一个独立的非营利组织，致力于生命科学的基础发现、改善人类健康和条件，以及培养未来几代研究人员。乔纳斯·索尔克医学博士于1960年创立了该研究所，获得了圣地亚哥市政府赠送的土地以及“March of Dimes Birth Defects Foundation”（足迹慈善母婴健康基金会）的财政支持。.