Exemplar effect in Mueller-Lyer decrement.

Coren and Girgus in 1972 had each of their subjects inspect one of four Mueller-Lyer variants with the two segments set equal. In six interspersed Average Error test trials with the initial setting at zero illusion, the variants showed similar decremental rates. In 1962 Day had observed decrement when the test trials began with the segments equal; Eysenck and Slater in 1958 found no decrement when the test trials started with the segments clearly dissimilar. Present subjects addressed figures having either equal or unequal segments, and, over six trials, with and without inspection periods, came to approach the presented figures as exemplars.