The hypothesis tested was that the rate of alternation in binocular rivalry is a function of the "strength" of the alternating figures. Five subjects using a Renshaw Stereo-Disparator responded to alternations by pressing a telegraph key. Four stereograms representing two levels of figure-ground contrast and two degrees of contour completeness were observed. The range of rates for all subjects was from 4 to 45 cycles per minute. The fields which included the strong figures alternated at a significantly greater rate than the weak fields. (PsycINFO Database Record (c) 2006 APA, all rights reserved)