The role of background similarity in aftereffect transfer from second-order motion faces to first-order static cartoon faces. a–d, Psychometric functions from two naive subjects (VH, VKD) and two experimenters (HX, JW) under the following conditions: 0-cfd, no adaptation and test on the dot-added cartoon faces (solid red); mf-cfd, adaptation to the saddest motion face and test on the dot-added cartoon faces (dashed red); 0-cfl, no adaptation and test on the background-luminance-matched cartoon faces (solid blue); mf-cfl, adaptation to the saddest motion face and test on the background-luminance-matched cartoon faces (dashed blue); mf-cfd-dir, same as mf-cfd, but the subjects judged motion direction (up or down) above the midpoint of the mouth curves of the test cfd faces (solid green). e, Summary of all four subjects' data.