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Attention, Imagery and Memory: A Neuromagnetic Investigation

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Annual technical rept. 1 Mar 1988-28 Feb 1989

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This report describes a number of experiments related to the effects of mental imagery and other high-level cognitive tasks on the spontaneous activity of the brain. The basic procedure involves narrowly bandpassing the magnetoencephalogram MEG, computing the average response to a stimulus or event within that bandpass, and computing the variance around the average. The variance at any point in time subsequent to the stimulus is a measure of mean square field power. Power in the alpha band 8-12 Hz was found to show a prominent change in level subsequent to presentation of form. Simply watching the form results in a dip in alpha power, but when subjects attempt to determine if the form had been seen previously, the duration of the reduction in alpha power increases significantly, and is correlated with reaction time RT. The distribution of alpha across the occipital and pairetal areas shows remarkable individual differences in both symmetry and magnitude. The changes in this distribution during the course of performing a search of visual memory suggests that the effects are localized to visual cortex. In another experiment subjects either tried and form an image of an object represented by a visually presented word, or to find a rhyming word. The latter task did not produce a change in activity of visual cortex, while the same words produced a profound change in activity cortex during imaging. Acoustically presented words were also found to produce changes in MEG activity arising in the visual areas when they were used as cues to forming a mental image.

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  • Psychology
  • Anatomy and Physiology

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