Research Update: How Long Do Posthypnotic Suggestions Last?

I. Topic:

Consciousness--Hypnosis

II. Article Reference:

Barnier, A. J., & McConkey, K. M. (1998). Posthypnotic responding away from the hypnotic setting. Psychological Science, 9, 256-262.

III. Overview:

Posthypnotic suggestions provide instructions regarding behavior following hypnosis. Essentially, the person who was hypnotized engages in posthypnotic behavior unaware of the motivation for such behavior. Although a small body of research has examined the variables that appear to govern posthypnotic suggestions, much of it is marred by methodological limitations. One such limitation is that fact that posthypnotic behavior is often examined in the experimental setting and thus may be influenced by social and other contextual cues relevant to that setting. Barnier and McConkey's study was aimed at disentangling posthypnotic behavior from the experimental setting.

IV. General Method:

Two experiments using highly-hypnotizable subjects were conducted. In Experiment 1, subjects were given either a posthypnotic suggestion or a social request to mail the experimenter a prepaid postcard everyday. Some posthypnotic subjects were told how long to continue mailing the postcards, others were not. In Experiment 2, real hypnotized subjects, simulating nonhypnotized subjects, and nonhypnotized control subjects were given the same task as subjects in Experiment 1. (The control subjects were given a social request to mail the postcards.) As in Experiment 1, the posthypnotic suggestion was either limited or unlimited in its duration.

V. Conclusions and Implications:

In Experiment 1, subjects given the social request mailed more post cards (nearly 100%) to the experimenter than did subjects given either the limited (about 50%) or unlimited posthypnotic (also about 50%) suggestions. However, hypnotized subjects reported feeling a "compulsion" to mail in what postcards they did return while social request subjects reported sending in the postcards because of a "contractual obligation" they felt toward the experimenter. In Experiment 2, real hypnotized subjects returned more postcards (about 55 to 60%) in both the limited and unlimited conditions than did the simulating subjects. However, only the real hypnotized subjects in the unlimited condition sent in more postcards than control subjects. Of significance in these two studies is the finding that some, but not all, real hypnotized subjects continued to return postcards for up 4 months following being hypnotized. Moreover, the subjects given the limited posthypnotic suggestion continued to sent in postcards longer than subjects given the unlimited posthypnotic suggestion. Thus, the efficacy of posthypnotic suggestions seems due to its specificity.