July 23, 2003 Researchers at the University of California, San Diego (UCSD) School of Medicine have provided new evidence that resolves a long-standing scientific controversy regarding human visual attention and the ability to divide that attention between more than one stimulus within a broad visual field.
Published in the July 17, 2003 issue of the journal Nature, the study measured brain electrical activity in response to lighted symbols shown on a computer monitor. The researchers found that people are able to pay attention to multiple, peripheral stimuli, while staring at a central point on the screen.
Although previous studies had indicated that the "spotlight of attention," as it's called, can be enlarged, but can't be split, the new findings indicate a greater flexibility in the human attentional system.
According to senior author Steven Hillyard, Ph.D., UCSD professor of neurosciences, the findings have applications for people who handle high information loads, such as air traffic controllers, or even for drivers on busy highways.
"These experiments demonstrate that, when necessary, people can effectively direct their attention to widely separated objects or events at the same time," Hillyard added.
In addition, because the study shows that normal individuals can pay attention to multiple locations at once, it provides new directions for research on attention-deficit conditions such as autism, schizophrenia, and attention deficit hyperactivity disorder (ADHD).
To determine a normal individual's response to multiple stimuli, the researchers studied the reactions of 15 volunteers who were hooked up to brain-wave recording electrodes. The participants were told to fix their gaze upon a central symbol, while additional lighted symbols continuously flickering at varying rates – two to the right and two to the left of the central object. The flickering symbols activated electrical waves in the visual parts of the brain that oscillated at the same rate that the stimulus was flickering in the environment. This allowed the researchers to get brain responses to many stimuli simultaneously because each stimulus was flickering at a different rate and therefore produced a different brain signature.
On separate tests, the volunteers were asked to pay attention to either the two left field positions (1 and 2), the two right field positions (3 and 4), or to two separated positions (1 and 3 or 2 and 4).
The researchers found that the spotlight of attention can be divided to facilitate processing of stimuli in spatially separated locations over periods of several seconds. They considered this to be a highly efficient mechanism for distributing attention optimally to dispersed stimuli in the visual surroundings.
The first author of the study was M.M. Mueller, Ph.D. of the Institut fur Allgemeine Psychologie, Universitat Leipzig, Germany, who began his studies of attention while a visiting scholar in Hillyard's lab. Additional authors were P. Malinowski, School of Psychology, Liverpool John Moores University, United Kingdom, and T. Gruber, Institut fur Allgemeine Psychologie.
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