Simple brain mechanisms explain arbitrary human visual... (asked to indicate which type of image th...)

Simple brain mechanisms explain arbitrary human visual decisions

Date:11/9/2008

asked to indicate which type of image they believed they had seen by either moving their eyes in a particular direction if they had seen a face or pointing their hand in the same direction if they had seen a building.

"This decision is not automatic," Corbetta says. "It requires both attention to the stimuli and control of the response."

Researchers took functional magnetic resonance imaging scans of subjects' brains as they performed the task. The scans were conducted at the Institute of Technology and Advanced Bio-imaging in Chieti as a collaboration between Corbetta; Gaspare Galati, Ph.D., associate professor of psychology at the University of Rome; and Gian Luca Romani, Ph.D., professor of physics at the University of Chieti. To help distinguish between the influx of sensory information and the decision to move the eye or hand, subjects had to wait for 10 seconds after seeing the image before indicating which type it was.

Scientists concentrated on regions of the brain that are responsible for planning actions (eye or hand movements) in the parietal lobe. Activity in these different regions would increase in correspondence with the type of stimulus a subject was being shown (face or building) and the type of response they were planning as a result (eye or hand movement). When the stimulus had less noise and subjects were more confident in their choice, brain activity levels in the appropriate area rose proportionally. In addition, these regions showed activity that related to the choice even when the stimulus was ambiguous.

"This suggests that these regions in the parietal lobe processed all the sensory, decision and motor signals necessary to make and act on the decision," Tosoni says. "In contrast, no area in the frontal lobe, thought to be involved in decision-making, significantly increased its activity at the time of decision."

The training period that preceded the scans could have involved the frontal lobes,
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Contact: Michael C. Purdy
purdym@wustl.edu
314-286-0122
Washington University School of Medicine
Source:Eurekalert

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