Also known as Perky effect. Both eponyms refer to the American psychologist Cheves West Perky (1874-1940). They refer to the phenomenon of mistaking a sensory percept for a product of the imagination. The phenomenon was first reported by Perky in 1910, after she had subjected a group of trained introspectionists to a test in which they were requested to look at a blank screen and to imagine as vividly as possible an object such as a tomato or a banana. Without their knowledge, these objects were subsequently back-projected onto the screen. The introspectionists dismissed the images as products of their imagination. Because the images were actually perceived, but misinterpreted as imaginary in nature, the phenomenon does not count as a *negative hallucination.
References
Perky, C.W. (1910). An experimental study of imagination. American Journal of Psychology, 21, 422-452.
Segal, S.J., Glicksman, M. (1967). Relaxation and the Perky effect: The influence of body position on judgements of imagery. American Journal of Psychology, 80, 257-262.
Dictionary of Hallucinations. J.D. Blom. 2010.