Brain selects among sights and sounds.

The gleaning of useful information from the jumble of sensory input the environment provides is a major task of animals' nervous systems. This focusing of attention seems to begin as information first enters the nervous system (SN: 11/9/85, p. 295) and continue at various levels in the brain. Scientists are analyzing the information-screening process for auditory and visual input, as well as for pain.

The screening of auditory information is called the "cocktail party effect"-- in a noisy room you can screen out all conversations except the one in which you are participating. Josef M. Miller of the University of Michigan in Ann Arbor reports that experiments on trained monkeys demonstrate that cells in the lower brain stem influence whether the animal pays attention to a specific stimulus. This influence is not at the first nerve cell connection, or synapse, as in the pain experiments. But it is considered to occur early in processing--the third synapse in a path of six or seven synapsis.

Researchers examining vision also find brain centers that control what they call "the flashlight of attention." David Lee Robinson of the National Eye Institute in Bethesda, Md., reports that cells in the brain area called the pulvinar thalamic nucleus respond more strongly when an animal has been trained to pay attention to the visual stimulus than when it is not paying attention. "Previously, we had no idea what this part of the thalamus did with vision," Robinson says.

In the cortex, generally considered the highest processing area of the brain, specific regions recently have been implicated in information screening. For example, Joaquin M. Fuster, of the University of California at Los Angeles has identified cells in the monkey prefrontal cortex that respond to color, but only when the color is relevant to the task the money is performing. When there is a delay between the viewing of the color and the opportunity to choose a similarly colored disk to earn a reward, some of the cells continue responding until the choice has been made. These cells in effect retain information for a short time to allow the animal to perform a desired behavior.