The Poggendorff and its variants do arouse the same perceptual process

The first two of five experiments reported show that the complete Poggendorff and three of its variants all produce the same illusory effect and that, for all four patterns, that effect is increased as the angle of interception of the obliques decreases and as the separation of the parallels increases. The third experiment shows that the differences in the magnitude of illusion produced by the variants is most probably due to the components retained in a particular variant and not to the simple reduction in the total amount of illusion pattern retained, which also correlates with magnitude of illusion. The final two experiments show that equal or greater positive transfer to the complete pattern is obtained from the variants as from the complete pattern after equal amounts of practice. The conclusion is reached that the complete pattern and the variants arouse the same single perceptual process. The data do not permit identification of that process.