Perky effect
the tendency for an imagined stimulus to interfere with seeing an actual target stimulus when the imagined form is close to that of the target. In one study, for example, a participant was positioned in front of a blank screen and asked to imagine a leaf, while simultaneously, without the participant’s knowledge, a blurry picture of a leaf was projected onto the screen, gradually becoming brighter; the intensity of the picture was well above the threshold for detection before the participant reported seeing it. [described in 1910 by Cheves West Perky (1874–1940), U.S. psychologist]