Binaural beat induced Theta EEG activity and hypnotic susceptibility: Contradictory results and technical considerations

American Journal of Clinical Hypnosis,  Apr 2003  by Stevens, Larry,  Haga, Zach,  Queen, Brandy,  Brady, Brian,  Et al

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Instrument

The Stanford Hypnotic Susceptibility Scale: Form C (SHSS:C) was employed as the measure of hypnotic susceptibility in this study (Weitzenhoffer & Hilgard, 1962). The SHSS:C has been recognized as "the gold standard" of hypnotic susceptibility testing (Kurtz & Strube, 1996) against which all other measures are compared. The SHSS:C has a very satisfactory Kuder-Richardson total scale reliability of .85, with validity correlations of .72 with the SHSS:A and .68, .60, and .57 with the HGSHS:A (Kurtz & Strube, 1996; Perry, Nadon, & Button, 1992).

Apparatus

EEG Recording

The NRS-2D (Lexicor Medical Technology, Inc., Boulder, Colorado) Electroencephalograph (EEG) was used to measure participants' 4.0-8.0 Hz theta activity during training. The NRS-2D records EEG data from 2 channels at a sampling rate of 128 Hz across 2-second epochs at a frequency resolution of 0.5 Hz. Low pass and high pass filters are set at 32 Hz and 0.5 Hz respectively, with notch filtering factory definable at 60 Hz. A built-in impedance meter allows convenient measurement of electrode impedances, with valid results obtained for impedances as high as 20K ohms; for the present study, electrode impedances were held at lOK ohms or less. An artifact inhibit feature stops all recording when the artifact (e.g., eye movement or other muscle signals) exceeds the selected artifact inhibit amplitude threshold. The NRS-2D was supported by a 486DX2 PC operating with BIOLEX (BLX) neurotherapy EEG acquisition software, comprising an array of tools including an audiovisual display system, graphing and reporting features, Fast Fourier Transformation, and spectral analysis of complex wave forms, as well as conventional EEG recordings. For the EEG data analysis, Fast Fourier Transformation (FFT) was performed and a power spectrum was calculated for each 2second epoch and integrated across baseline and treatment components.

Auditory Binaural Beat Stimulation

Since the aim of this study was to increase the duration of the binaural beat exposure provided in the previous study, the original 20-minute tapes utilized in the Brady and Stevens (2000) study were sequentially duplicated in order to produce a 40-- minute experimental and control tape and compact disk. The original binaural beat tapes were produced for our research purposes by the Monroe Institute (Atwater, 1996). Both a control tape/CD and an experimental tape/CD were used. The experimental tape/ CD was produced with a complex theta brainwave binaural beat pattern imbedded in carrier tones and pink sound. In order to encourage listener vigilance, carrier tones were changed periodically according to the following sequence: 0-3 minutes, C-Major-7th (292 Hz, 330 Hz, 392 Hz, 466 Hz); 3-6 minutes, C-Major (292 Hz, 330 Hz, 392 Hz, 523 Hz); 6-10 minutes, G-Major (196 Hz, 247 Hz, 294 Hz, 392 Hz); 10-15 minutes, D-Minor (294 Hz, 349 Hz, 440 Hz); 15-20 minutes, C-Major (292 Hz, 330 Hz, 392 Hz, 523 Hz). The theta effect for the experimental tape was generated by continuously varying a 7 Hz left-right frequency difference by plus or minus 1.5 Hz over a period of 4 seconds; the theta stimulus thus cycled from 5.5 Hz to 8.5 Hz and back to 5.5 Hz over a period of 4 seconds. The control tape/CD was produced with pink sound and the same tones as the experimental tape/CD but without binaural beats, so that the control and experimental tapes/CD's were perceptually indistinguishable. An auditory spectrum analysis of the waveforms on the duplicated tapes and CD's conducted after the study was completed revealed a binaural beat effect on the theta training media within the theta range. Both participants and experimenters were blind as to presentation of control or experimental media. During all sessions, participants wore stereophonic headphones providing either the control or the experimental recording. Signal volume was adjusted by each participant to a comfortable sound level and maintained at that level throughout stimulus presentation.