Titchener's ⊥ in context 1--delimited, discrete monomotif patterns, line arrangements, and branching patterns

Three experiments tested the effects of the presence of nontarget ⊥s on Titchener's (1901) ⊥-illusion. Experiment 1 used patterns of four separate ⊥s, Experiment 2 used branching patterns in which four ⊥s were stuck together, and Experiment 3 used patterns of four triangles or four beehive forms for which the ⊥ could be seen as a skeleton. Three independent samples of 12 observers each had to haptically indicate the lengths of target lines and verbally judge the relative lengths of the two lines of target ⊥s. The illusion to judge or indicate the ⊥’s undivided line as longer than its divided line survived throughout except for the branching patterns: here, haptic indications did not differ between the two types of lines. Specific features of these patterns and of the ⊥ itself may be responsible for these effects.