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Different event-related potentials (ERPs) to pictures and words that describe the same object
By Blackwell Publishing Ltd.,
Aug 18, 2005 - 2:25:38 AM
A paper published in the recent issue of Psychophysiology describes differences in the brain's response (event-related potentials, or "ERPs") to pictures and words that describe the same object. In two studies, the authors evaluated how the brain reacts differently to a picture of an object or its name when people were looking for either the picture or the name in a visual display.
University students saw pictures of five simple objects and words corresponding to their names. Participants were instructed to keep a silent mental count of the appearance of a specific target. For instance, in the first study, they looked for the word "globe." Its appearance on screen created a noticeable brain response. "We found that the appearance of the word 'globe' elicited a large electrical response called the P300, a positive-going ERP that occurs about 300-500 ms after the presentation of a target, " author Todd Watson states. Although it was not a target, the picture of the globe elicited a similar (although less pronounced) electrical response. In a second study, the specified object was the picture of a globe. Again, the authors found that a picture of the globe elicited a large P300. However unlike the first experiment, the other version of the object -- the word "globe" -- failed to elicit a prominent electrical response. These intriguing results suggest that whereas a word may automatically activate a mental image of the same object (e.g., a globe), a picture does not necessarily activate its verbal name. In turn, these data suggest the possibility that processing images and words may involve distinct brain circuits that can, but do not always, "talk to" one another. These techniques could help us to understand how our brains respond differently to visual or verbal codes that describe the objects in the world around us, as well as how our brains evaluates similarity between different objects or concepts.
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