How We Scan: Point to Point to Point

The mind's eye scans like a spotlight

You're meeting a friend in a crowded cafeteria. Do your eyes scan the room like a roving spotlight, moving from face to face, or do you take in the whole scene, hoping that your friend's face will pop out at you? And what, for that matter, determines how fast you can scan the room?

Researchers at MIT's Picower Institute for Learning and Memory say you are more likely to scan the room, jumping from face to face as you search for your friend. In addition, the timing of these jumps appears to be determined by waves of activity in the brain that act as a clock. The study, which appears in the Aug. 13 issue of the journal Neuron, sheds new light on a long-standing debate among neuroscientists over how the visual system picks out an object of interest in a complex scene.

In the study, monkeys were given the task of searching for one particular tilted, colored bar among a field of bars on a computer screen. By monitoring the activity of neurons in three of the animals' brain regions, researchers found that the monkeys spontaneously shifted their attention in a sequence, like a moving spotlight that jumped from location to location.

What's more, the study showed that brain waves act as a kind of built-in clock that provides a framework for shifting attention from one location to the next. The work could have implications for understanding or treating attention deficit disorder or even potentially speeding up the rate of cognition in the brain.

"For many years, neuroscientists have been debating competing theories on whether humans and animals spontaneously search elements of a visual scene in a serial or parallel manner," said lead author Earl K. Miller, the Picower Professor of Neuroscience. "Ours is the first study based on direct evidence of neurophysiological activity."

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