A COMPARISON OF GANZFELD AND HYPNAGOGIC STATE IN TERMS OF ELECTROPHYSIOLOGICAL MEASURES AND SUBJECTIVE EXPERIENCE.
The aim of this exploratory study was to investigate electrophysiological correlates and subjective dimensions of experience of: (a) the hypnagogic state, at sleep onset, and (b) the ganzfeld state, induced by homogenization of perceptual field. Twelve female paid volunteers ranging in age from 22 to 39 participated in the study. Nineteen channels EEG, 2 channels horizontal EOG, and 1 channel EMG were recorded in 5 experimental conditions: (a) waking state at daytime, (b) ganzfeld, (c) waking state before sleep onset, (d) sleep stage 1, and (e) sleep stage 2. Following a predefined schedule, the participants were given an acoustic signal and asked for a verbal report of their momentary subjective experiences and ratings of the reported experiences on several ordinal self-rating scales. The reports were recorded and transcribed later. A total of 241 reports with simultaneous EEG recordings were collected.
Data preprocessing and analysis were divided into several phases. The first phase aimed at the characterization of the induced states in terms of spectral measures of the electrical brain activity (EEG). FFT analysis of 5 consecutive 2-s epochs of EEG activity immediately preceding the prompt proved that the average EEG spectrum in the ganzfeld is more similar to that of the relaxed waking state than to that of sleep on-set. Thus, the assumption of a hypnagogic basis of ganzfeld imagery is unsupported. The ganzfeld condition, compared to the relaxed waking state, shows a significant shift of the [alpha]-peak to higher frequencies, thus indicating higher activation. However, EEG indices of vigilance do not show any difference between the ganzfeld and waking states. Four factors, representing 35% of the subjective experiences, were obtained by a principal-component analysis. Factor I could be interpreted as the subjective dimension of vigilance. There was no difference between the ganzfeld and waking states in this factor; this result confirms the findings of the spectral analysis of EEG. Consistent and global correlations between [delta], [theta], and [alpha] frequency bands on one hand, and Factor I on the other hand, were found in all time segments.
It is concluded that, contrary to the common belief, the ganzfeld does not necessarily induce a true hypnagogic state and will surely not do so in most ganzfeld settings. Thus, ganzfeld imagery, although subjectively very similar to that at sleep onset, should not be labeled hypnagogic. Perhaps a broader category of "hypnagoid experience" should be considered, covering true hypnagogic imagery as well as subjectively similar imagery produced in other states.
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|Author:||WACKERMANN, JIRI; PUTZ, PETER; BUCHI, SIMONE; STRAUCH, INGE; LEHMANN, DIETRICH|
|Publication:||The Journal of Parapsychology|
|Date:||Sep 1, 2000|
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