Unlike the brightness dial on a monitor, which boosts image and static equally, the brain has a signal amplifier for superior object recognition, says a study in the April 22 edition of the Proceedings of the National Academy of Sciences.

The study focused on covert attention, the ability to identify objects without moving the eyes or turning the head.

“Most people believe that it’s the covert attention that drives the overt attention. It’s very critical,” said Bosco Tjan, associate professor of psychology at USC College and co-author on a team led by Zhong-Lin Lu, professor of psychology and biomedical engineering at the College.

A basketball player making a no-look pass or an airplane pilot monitoring a gauge off to the side both rely on covert attention. Advertisers and the military, among others, are interested in improving covert attention.

It has long been known that heightened covert attention increases awareness across the field of vision, much like the brightness control on a screen.

The researchers found that the brain also has a unique ability to increase the “gain” during object recognition, effectively dampening static while homing in on an object.

“The real dispute in the field is whether attention is only raising the response baseline or also raising the sensitivity,” Lu said. “Our finding that covert attention does both resolved a lot of disputes in this area of vision.”

Functional imaging trials on human subjects at the Dornsife Cognitive Neuroscience Imaging Center also showed that covert attention increases the oxygen flow to all parts of the visual system at once, suggesting that the phenomenon may have deep evolutionary roots.

The PNAS study is the first to paint a coherent picture of how covert attention influences neuronal responses and improves brain oxygen flow and human performance, Lu said.

“Attention is a very basic component of vision,” Tjan added. “One could even argue that without attention you can’t see.”

The greatest improvements in gain occurred for gray objects against a white background, somewhere between 1 and 30 percent contrast.

Previous studies had ignored that range, the researchers said.

“The real contribution of this paper is actually the measurement of the entire function over the full contrast range,” Lu explained.

The researchers concluded that heightened covert attention can turn two “knobs” in the brain: one for general response level, one for signal amplification.

It is one of the many ways that the brain’s visual system outperforms computers and televisions.

The other members of the research team were USC postdoctoral researcher Xiangrui Li, USC graduate student Wilson Chu and cognitive sciences professor Barbara Dosher from the University of California, Irvine. Research funding came from the National Science Foundation and the National Institutes of Health.

The project was one of many to take advantage of the powerful magnetic resonance imaging equipment at the Dornsife Center. Researchers at the Brain and Creativity Institute have been using the facility for several studies.

Lu and the institute’s Antoine Bechara co-authored a recent study in Neuroimage on envisioning emotional events that might happen in the future. Lu and psychologist Franklin Manis of the College co-authored a different Neuroimage study on reading.