We normally think of paying attention to an object as a way to perceive it better, but sustained attention actually worsens the perception of some visual stimuli, reports a study in the October 2006 issue of Nature Neuroscience.
Visual stimuli with more contrast between their lighter and darker areas are easier to see. Previous work has suggested that attention makes a visual stimulus easier to see by effectively increasing its contrast. However, contrast sensitivity decreases after prolonged periods of looking at high-contrast stimuli. Ling and Carrasco showed people black and white stripes, and had them report whether these stripes leaned to the left or the right; this task is harder to do when the contrast between the stripes is lower. The researchers found that when people paid attention to a particular set of stripes, they could initially do the task even with low-contrast stripes. However, after a prolonged period of attention, people needed higher-contrast stimuli to succeed at the same task. These results indicate that prolonged periods of attention to specific stimuli may eventually impair rather than improve perception.
Samuel Ling (New York University, NY, USA)
Abstract available online.
Nature Neuroscience press release.
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