The effects of self-generated expectancy of stimulus content on the evoked to physically identical stimuli were studied in college students. The subject set up his own internal expectancy by choosing to see either a bright or dim flash. When a bright or dim flash was anticipated, the potentials evoked by a medium stimulus intensity resembled the responses elicited by an actual bright or dim flash, respectively. Significant differences in visual evoked potential amplitude were obtained between identical medium intensity stimuli depending on the stimulus intensity expected, despite the constant physical properties of the stimulus. The results suggest that a subject's expectancy of certain physical parameters of a stimulus are as important in determining the resultant visual evoked potential as the actual physical features of the stimulus. [ABSTRACT FROM AUTHOR]
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