The microgenetic development of the Ponzo and Zöllner illusions

It is argued that in order to most directly investigate perceptual processes and thereby to evaluate competing theories, one must observe the (microgenetic) development of the percept. In different experiments, variations of the Ponzo and Zöllner illusions were tachistoscopically presented, followed, after a variable ISI, by a disrupting pattern. The interaction responsible for an illusion of magnitude in the Ponzo and an illusory displacement in the ZSllner occur only after 150 msec of processing time (SOA), Prior to the illusion’s onset, the parts of the figure are clearly and accurately perceived, indicating that the parts of the figure are first processed independently, followed by the interaction of those parts. It is suggested how the application of information processing techniques to traditional perceptual material may, in future experiments, yield a positive theoretical statement about perceptual processes.