10 adult Ss were given the task of adjusting the rotational rate of one disc so that a small target dot near its edge appeared to be moving at the same speed as the target dot on another rotating disc. Thresholds were about half those found in previous studies. An attempt was made to relate discrepancies in results to differences in methods of experimentation. (PsycINFO Database Record (c) 2006 APA, all rights reserved)