Efficacy of induction and difficulty level in durability of posthypnotic suggestions

We examined whether participants instructed to reenter a hypnotic state as part of the posthypnotic suggestion (PHS) show less decay in responding ove r an 8-week period than participants who do not receive such instructions. We also attempted to replicate Trussell, Kurtz, and Strube's (1996) finding on impact of difficulty level. of suggestion on response curve. Fifty-nine highly susceptible participants were selected by the Stanford Hypnotic Sus ceptibility Scale: Form C (SHSS:C) and were assigned to one of four groups (two levels of Difficulty [easy-hard] x two levels of Condition [hypnotic P HS, non-hypnotic PHS]). Participants were tested for PHS at 1, 3, 6, and 8 weeks. A 2 x 2 x 4 (Difficulty x Condition x Time) factorial ANOVA was cond ucted, with Time as a repeated-measure. The outcome variable at each time w as either pass or fail for relevant suggestion. None of the effects contain ing Condition as a term were significant indicating there is no advantage t o using Berrigan, Kurtz, Stabile, and Strube's (1991) atypical induction te chnique to influence the durability of PHS. We found a significant Time eff ect but failed to replicate Trussell et al.'s findings for Difficulty level . The differing results found in these three recent studies (Berrigan et al ., Trussell et al., and the current study) suggest the effects for durabili ty of PHS may be quite fragile in spite of rigorous experimental controls u sed in all three studies.