To obtain information regarding dependence of nonreinforcement (E-sub(0)) effects on other variables, E-sub(0)'s were presented with varying response-contingent frequencies. With 24 student Ss in each of 8 groups, mean choice frequencies and sequential statistics indicated (a) that S tends to perseverate on the response chosen on an E-sub(0) trial, and (b) that the effect of an E-sub(0) preceded by E-sub(1) in the reinforcement series is different from the effect of E-sub(0) preceded by E-sub(2). (PsycINFO Database Record (c) 2006 APA, all rights reserved)