Response Expectancy and Experimenter Bias as Factors Affecting Hypnotic Responsiveness

This study examined the effect of subjects' expectations regarding their hypnotizability, and the effect of experimenter bias, on subsequent levels of hypnotic responsiveness. Ninety undergraduate psychology students, none of whom had previously been hypnotized, participated in the study. Subjects were divided into four groups (two groups of 30 and two groups of 15), in a two by two design. The two experimental groups received a manipulation (subtle alterations of lighting conditions in the experimental room in order to confirm suggestions given under hypnosis) designed to increase their level of expectations regarding their hypnotic performance. Their actual hypnotic responsiveness was then measured using the Stanford Hypnotic Susceptibility Scale: Form C (SHSS:C). Subjects in the control groups received only the SHSS:C. For the two Aware groups, the experimenter was aware of the group membership of the subject, and therefore knew if the manipulation had been administered. In the two Unaware groups, the experimenter was blind to this variable. These last two conditions made it possible to detect any experimenter bias that may have affected hypnotizability scores. Results indicated that the expectation manipulation did in fact increase the subjects' level of expectation regarding their hypnotizability. However, since the expectation level of subjects in the Experimental groups after the manipulation had been administered was not statistically different than that of subjects in the Control groups, the effect of those expectations on hypnotizability scores is extremely difficult to determine. Experimenter awareness of group membership was shown to have no significant effect on hypnotizability scores.