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.

El Instituto Salk de Estudios Biológicos, ubicado en La Jolla, California, es una organización independiente sin fines de lucro dedicada a los descubrimientos fundamentales en las ciencias de la vida, la mejora de la salud y las condiciones de vida de las personas, y la formación de las futuras generaciones de investigadores. El Dr. Jonas Salk fundó el instituto en 1960 gracias a una donación de terrenos por parte de la ciudad de San Diego y al apoyo financiero de la Fundación March of Dimes para los Defectos Congénitos.