EEG Evoked Potential, Hypnotic Anosmia, and Transient Olfactory Stimulation in High and Low Susceptible Subjects
The Stanford Hypnotic Susceptibility Scale Form C (SHSS:C) was administered to 93 University of Canterbury (New Zealand) students. High susceptibility Ss (N=4) consisted of those who scored above 10 on the SHSS:C. Low susceptibility Ss (N=5) consisted of those who scored 0 or 1 on the SHSS:C. Ss were seated in an olfactorium and exposed to a waking condition and a hypnotic induction condition which included an eye catalepsy test and a suggestion for anosmia to all odors. Low susceptibility subjects were instructed to simulate hypnotic response so that the experienced hypnotist remained blind with respect to S’s susceptibility status. A strong odor (6.615 mg/L eugenol), weak odor (4.525 mg/L of eugenol) or no odor (air puff only) was administered to each subject in random sequence (lsec. duration each) by PDP 11/10 computer using a continuous flow bypass olfactometer. Throughout the experiment Ss breathed only by nose. Respiration was measured by a bellows transducer amplified and recorded on a Lafayette datagraph. Respiration data was sampled at 10Hz by the PDP 11/10 computer which used inhaling as a pre-condition for stimulus presentation. EEG data from left and right hemispheres (temporal and occipital sites) were amplified via a San-Ei electroencephalograph. Statistical analysis of the P300 (300msec latency) positive wave demonstrated amplitude increases for weak and strong odors for high hypnotizable Ss in hypnosis but not for these Ss in the waking condition. No such amplitude increases were found for the low hypnotizable simulator subjects in waking or hypnosis exposure conditions.
This investigation was concerned with the generic problem of objectifying alterations in the subjective experience which constitutes hypnotic responsiveness. Orne (1979) noted that the most satisfying proof of the reality of hypnosis is to demonstrate abilities of the hypnotized individual that are present only in that state. If it can be demonstrated that the hypnotized S can do things that the waking individual cannot, there is little need to worry about the reality of the phenomena.
Orne (1979) also presented evidence that the search for characteristics of hypnosis that are “intrinsic” is exceedingly difficult. Experimental demand characteristics (Orne, 1959), e.g. cues in the procedure which might influence S’s performance, might be unwittingly communicated before or during the hypnotic procedure by the hypnotist. Orne (1971) developed the use of simulating subjects as a quasi-control group. The procedure aids recognition of aspects of an S’s response, if any, that were due to hypnosis, as opposed to those that were the result of S’s prior knowledge, expectations and experimental demand characteristics.
Hilgard (1979b) noted that while deep hypnosis may be accepted as a genuine change in state, we need more research to specify exactly how the state should be characterized. The search for specific EEG patterns characteristic of hypnosis has not been successful (Beck and Barolin, 1965; Tebecis et al., 1975; Ulett et al., 1972). However, recent preliminary investigations, focussed on EEG evoked potentials, have suggested that this more precise form of EEG methodology may be helpful in defining the hypnotic state for highly hyp-notizable subjects (Deehan and Robertson, 1980; Javanovic, 1979; Mészáros et al., 1980; Zakrzewski and Szelenberger, 1981). Most notable was the finding of increased amplitudes of the late components of visual evoked potentials (N-250&P300) in hypnosis when contrasted with a waking condition.
EEG evoked potentials have also been recorded in response to olfactory stimulation (Barabasz and Gregson, 1979). Men who wintered over in Antarctica showed significant increases in hypnotizability (Barabasz, 1980). These Ss also demonstrated increased olfactory evoked potential amplitudes in the late components for suggested odors following winter over isolation (Barabasz and Gregson, 1979). Unfortunately, evoked potential scoring was crude and experimental constraints precluded clear differentiation between waking and hypnosis conditions or comparisons with control subjects.
The investigations noted above suggest that hypnosis might be uniquely characterized by amplitude increases in the late components of EEG evoked potentials. To date, however, no investigation of this type has provided adequate controls for situational variables or experimental demand characteristics which could account for these early findings. The purpose of this investigation was to determine whether or not olfactory evoked potential late component amplitude responses can be modified by hypnotically induced anosmia, while controlling for important experimental factors not considered in previous investigations.
KeywordsP300 Amplitude Strong Odor Olfactory Stimulation Odor Condition Susceptible Subject
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