Titchener's aSyen dissected

In three experiments, two independent samples of 12 observers each visually inspected modified versions of Titchener's aSyen from which the T-junctions had been deleted. For Experiment 1, the aSyenaEuro (TM) s two lines had been replaced by dashed lines not meeting in a common point; for Experiment 2, the aSyen had been reduced to five dots, representing the original lines' end- and midpoints; and for Experiment 3 (in which the second sample of observers served), the aSyen had been dissected into two separate lines, differently spaced from each other. Observers haptically indicated the lengths of the two orthogonal lines of the modified aSyens and verbally judged their relative lengths or the distances between the corresponding dots. The common perceptual illusions persisted in Experiments 1 and 2, but were markedly weakened in Experiment 3. Implications for a neurophysiological account of the illusions in terms of bottom-up, long-range interactions between orientation-sensitive mechanisms versus top-down activation of a figural schema are spelled out.