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Electrophysiological Alterations During Hypnosis for Ego-Enhancement: A Preliminary Investigation

American Journal of Clinical Hypnosis,  Apr 2004  by Stevens, Larry,  Brady, Brian,  Goon, Angela,  Adams, Deanna,  Et al

<< Page 1  Continued from page 5.  Previous | Next

Design and Analysis

Because of non-random assignment to hypnotizability conditions, the present study represents a quasi-experimental, double-blind, 4 (hypnotizability levels) ? 7 (baseline and hypnosis stages) mixed design with repeated measures on the later factor and with 4 dependent variables (delta, theta, alpha, and beta power). The betweengroups configuration was as follows: Eow Hypnotizables: N = 15; Moderate Hypnotizables: N= 15; High Hypnotizables: N = 23; Very High Hypnotizables: N = 7. Main and interaction effects were examined using separate ANOVAs for each dependent variable. Because the frequency distribution of EEGs is often negatively skewed with high kurtosis, a natural log transformation of EEG power was used in all data analyses (Crawfordetal., 1996; Sterman, Mann, Kaiser, & Suyenobu, 1994). Where violations of the sphericity assumption for the variance-covariance matrix occurred, Huynh-Feldt corrections to degrees of freedom were utilized in reporting significance. Also, as this was an investigational study and predictions were made a priori regarding significant increments in theta and beta power across stages of hypnosis, separate planned analyses were conducted for each bandwidth using the Least Significant Difference test and alpha was set at . 10.

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Results

Participant Characteristics

The 60 participants were a mean age of 22.95 years (SD = 5.40); 41 were females. They were rather evenly distributed across five academic classes, with 13 freshman, 12 sophomores, 4 juniors, 14 seniors, and 15 graduate students. Forty-three reported no prior experience with hypnosis, 25 reported experience with meditation, 22 had had formal relaxation training, only 9 had had an EEG before the present study, 13 had experienced some previous head injury, 16 had been unconscious at some time in their lives, 17 were currently taking medications including birth control pills, 20 used drugs recreationally, 35 reported using alcohol, and 12 smoked tobacco. Of the 60 participants, 7 stated a preference for left handedness. Each of these categorical demographic variables was subjected to Pearson Chi-Squared analyses for differences among the four hypnotizability groups; none of these analyses were statistically significant (p > .004, Bonferroni corrected for number of separate comparisons), suggesting an even distribution of demographic characteristics across the four hypnotizability conditions. Age was correlated with each of the dependent variables and was found to be not significantly correlated with any measure (p > .001, Bonferroni corrected for multiple correlations).

Age, TAS, CIS, and SHSS:C scores were compared across each of the four hypnotizability groups. With the exception of age, all overall F values were statistically significant. Table I presents means, standard deviations, and F and p values for each of the groups for each of these measures as well as gender counts for each group and [chi]^sup 2^ analysis results.

EEG Analyses

Theta EEG Analyses. Analysis of theta EEG power changes across conditions revealed a main effect for stages (F (5.19, 51)=9.58, p

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