Five experiments were conducted to gather preliminary data on the magnitudes of the tilt illusion and aftereffect as a function of the relative lengths of single inducing and test lines. In general, the experiments suggested that the illusion and aftereffect are smaller when the inducing line is shorter than the test line but not when the inducing line is longer than the test line. Hence, the two effects do not appear to be line‐length specific. Although inducing line length seemed to affect the illusion and aftereffect to different extents, further evidence is required to substantiate this apparent differenc