Mind Machines: A Controlled Study on the Effects of Electromagnetic and Optic-Acoustic Stimulation on General Well-Being, Electrodermal Activity, and Exceptional Psychological Experiences

Mind Machines: A Controlled Study on the Effects of Electromagnetic and Optic-Acoustic Stimulation on General Well-Being, Electrodermal Activity, and Exceptional Psychological Experiences

Harald Walach

Mind machines are said to induce relaxation and an altered state of consciousness. The influence of optical–acoustic (OAS) and electrical stimulation (ES) mind machines on general well-being, electrodermal activity, and altered states of consciousness was investigated and compared with pure rest and a placebo. Thirty participants underwent 4 conditions in random sequence: rest, placebo stimulation, OAS, and ES. Statistical evaluations before and after the experimental stimulations showed differences in general well-being and electrodermal activity measures but no between-conditions effect. ES and OAS produced significantly more visionary experiences and fear of ego dissolution than rest and placebo. Differences in mystical experiences were found between ES and OAS. Mind machines do not have a specific effect on general well-being and physiological relaxation, although they may produce unusual psychological experiences; people with psychiatric illnesses should not use such devices.

Index Terms: altered states of consciousness, mind machines, placebo, relaxation, sensory deprivation

Mind machines are becoming increasingly popular for inducing altered states of consciousness and relaxation by means of purported direct or indirect stimulation of the brain. They are said to trigger alpha activity by subliminal electric currents applied to the head or to induce relaxed states by low-level sensory stimulation from flickering light and slowly altering sounds. Both modes of stimulation are varied and novel enough to maintain attention. At the same time, they are monotonous and circular, producing a relaxation effect, presumably similar to different types of attention-focusing meditation, such as Zen or mantra meditation.[1]

Manufacturers and vendors rarely define the exact meaning of the altered states of consciousness and relaxation allegedly produced by mind machines, but relaxation in this context can generically be taken to indicate an integrated response of the parasympathetic system. This consists of reduced adrenergic activation and cortical arousal and, as a consequence, a general state of well-being produced by stimuli that either are in the alpha range of the EEG or facilitate this mode of brain activity. This specific brain state is said to produce even deeper relaxation and altered states of consciousness that are allegedly experiences of oneness with the universe and an enlarged sense of self.

Among the commercially available devices, the most common give optical and acoustical stimulations, using goggles with optical diodes and headphones that send acoustic impulses (optical-acoustic stimulation–OAS). Other types of mind machines use electrical stimulation (ES), sending a minimal electric current of low frequency to the head through electrodes that are usually placed on the ears. The frequencies normally used range from 0.5 to 30 hertz (Hz), and the current is about 100 [micro] A. For this research, we studied OAS and ES.

In spite of their increasing use, the effects of mind machines have not been well studied. Madden and Kirsch[2] reported a controlled, randomized, blind study. While participants played a computer hit-and-run game, the 39 individuals in the experiment were exposed to either an extremely weak, biphasic electric field of 200 [micro] A and 0.5 Hz or to the same electrodes without power supply. The experimental group was significantly more effective in learning the appropriate movements (p = .01).

Another study used electrostimulation to enhance performance and well-being in fencers.[3] The fencers (n = 24) underwent their usual training of 30 minutes twice a week over a period of 6 weeks. They used either a Brainman (Alexander Technik, Heidelberg) stimulator (7.83 Hz, current below sensory threshold) or a disconnected stimulator. The experimental group showed significant increases in all parameters (subjective well-being, performance) compared with the control group. The statistics of this study seem wrong to us because the authors used a chi-square analysis for intra-individually controlled and, hence, dependent data. A chi-square analysis is known to overestimate effects in dependent data.[4]

Linke[5] studied the effects of OAS stimulation with 12 Hz lowered to 4 Hz, then raised again to 12 Hz with 60 participants divided into two groups. One group was subjected to OAS for 30 minutes on 3 subsequent days, and the other group was resting. No differences were reported in the measures used (intelligence, general well-being, anxiety, vigilance), although spontaneous reports were suggestive of effects that did not appear in the data.

The studies are equivocal and the results are not clear. The point at issue is whether between-group designs are valid to study highly subjective responses. Intra-individual controls are called for so that it is possible to control for individual-specific responses and to separate them from stimulus-specific responses.

In Brauchli’s study,[6] OAS stimulation was compared with relaxing music in an intra-individually controlled design: 16 participants received OAS stimulation and, after 1 week, listened to relaxing music. Physiological parameters (muscle activity, electrodermal activity, heart rate, and EEG), salivary immunoglobulin A (IgA) and cortisol, and subjective changes (adjective list) were measured. Changes similar in direction and magnitude were found for both experimental conditions from pretreatment to posttreat-merit. The author concluded that OAS mind machines had a relaxing effect. Although this study used a broad spectrum of measures, it is difficult to draw valid conclusions from it. The sequence of the trials was not randomized and sequence effects could have masked treatment effects. In addition, no attempt was made to control for the strong placebo effect of machines of complex and impressive make-up[7-9] and of situations suggestive of changes.[10]

We therefore designed a placebo-controlled, within-group study to test the effects of different stimulation conditions. We asked whether two different types of mind machines–ES and OAS–would produce effects on subjective well-being, subjective exceptional experiences, or electrodermal activity different from pure rest and a placebo condition.



We recruited volunteer participants through advertisements in the local press and by word of mouth. They participated in the experiment out of curiosity; no payment or any other explicit or implicit obligation or benefit was offered, although they were told that they have a chance to use the latest machines and programs freely when the last experimental session was finished. All gave written consent to being included in the experiment.

Thirty-six individuals (22 women, 14 men) answered the advertisements and came to the first session; 30 of these (18 women, 12 men) finished all four experimental conditions. Data are reported for those 30 participants, most of whom were university students.


Each person was subjected to four 25-minute conditions on 4 different days; each condition was separated by at least I day for washout. The conditions were rest (baseline), placebo stimulation (PS), ES, and OAS. Every participant started with the rest condition. The three experimental conditions were then randomly permuted for each individual to exclude sequential effects within these conditions. We thought this preferable to a completely counterbalanced design because we wanted the setting to be as natural as possible, although counterbalancing surely would have been optimal.

People coming to an experiment would probably expect an introductory phase first. They would begin to form hypotheses about the nature of treatments in case of complete randomization of sequences, thus guessing at possible placebos. With the kind of sequencing we used, participants might reasonably suspect that rest was an introduction that would be compared with three different sets of mind machines. Thus, we opted for an enhancement of the likelihood of a placebo effect over the counterbalancing of sequential effects from rest to the other treatment conditions. We gave the test to each person at the same time of day ([+ or -] 15 minutes for organizational reasons) so that circadian phases would be the same.

The placebo condition was an ES apparatus identical to that used for ES but inactivated by the manufacturer; it was coded before the start of the experiment, with the code unknown to the experimenter. Therefore, the comparison of ES with PS was double blind. The electric current we used was below the sensitivity threshold for most people. We measured the parameters before and after rest as well as after each experimental session, except for measuring the presence of exceptional psychological experiences.


For descriptive purposes, we administered the most widely used German personality inventory (FPI-R),[11] which has recently been gauged in a representative sample; the German version of the locus of control scale (IPC)[12]; and an ad hoc questionnaire gathering demographic data, information about experiences with meditation, relaxation, psychotherapy, fear of electrical equipment, and motivation.

In addition, we used a questionnaire assessing exceptional psychological experiences and altered states of consciousness (APZ-Fragebogen zur Erfassung abnormer psychischer Zustande[13]) to capture the alleged alteration of subjective experience by the mind machine. We opted for this instrument, which was originally developed in German, because it is notoriously difficult to assess altered states of consciousness reliably and translations are usually fraught with semantic and cultural problems. This inventory is specifically designed to measure exceptional psychological experiences that might occur in certain types of psychosis or as transient phenomena in studies of hallucinogenic drugs or induced by consciousness-altering activities, such as mantra meditation, sleep or sensory deprivation, and hypnosis. The test had been systematically constructed from existing item pools in the literature. The items can be summed to yield one general dimension of exceptional experiences and three subdimensions: mystical experience and oceanic diffusion, fear of ego dissolution, and altered visual experience.

“Mystical experience and oceanic diffusion” denotes experiences of oneness with the world and others (eg, “I experienced the wonder, the joy, and the peacefulness of the world”). “Fear of ego dissolution” means experiences of loss of personal identity, depersonalization, and derealization (eg, “The border between self and environment seemed to blur”). “Altered visual experience” indicates expressly visual sensations and hallucinations, such as pleasurable, vivid, and real visual imagery and abstract visual experiences of patterns (eg, “I saw colors in total darkness or with my eyes closed”). The scales have proved sufficiently consistent (Cronbach’s alpha between .76 and .87). There are no population norms, but the instrument has proved sensitive to change under weak sensory deprivation conditions[14] with hallucinogenics,[15] with other drugs, and with alcohol.[16]

We also used the three subscales of this questionnaire as postmeasurements of experiences of altered states of consciousness after each session. In addition, before and after each session, we used a well-known and widely used German adjective list for assessing general well-being (EWL-Eigenschaftsworterliste).[17] This is a list especially constructed for assessing minor changes in subjective general well-being. Self-assessed responses to 161 adjectives can be combined into 6 dimensions: activity, disactivation, extroversion/introversion, general well-being, emotional tenseness, and anxiety.

We measured electrodermal activity (EDA) as skin resistance with silver ear electrodes (supplied by Brainman) applied to both ears. Each measurement was repeated with the polarity of the electrodes swapped electronically by a circuit that simulates a physical swapping of the electrodes without the necessity of replacing them. As soon as the first measurement was stable, we read the meter (HI-TEC DT 210) and swapped the electrodes. We took the second measurement when the second meter reading was stable again, which usually took a few seconds. The two meter readings of skin resistance, which usually were different when the electrodes were swapped, were then summed as a measure of general EDA. We used the ears as sites of measurement because the manufacturer suggested that this was how the most valid results of measuring mind machine effects could be obtained.

Procedure and Devices

We carried out the experiment in Freiburg, Germany, in the commercial rooms of a local provider where people buy the machines or rent them for recreational use on the premises. We asked participants to remove any jewelry or metal. Before they started the baseline condition, we informed the participants about the experiment and its purpose and gave them an opportunity to ask questions. They could also inspect the site, without, of course, receiving information about the full design of the study.

After becoming comfortable with the setting, the participants filled out the questionnaires and we took EDA measurements, after which the rest period started. During the rest period, as well as during the three following experimental conditions, the experimenter left the room after completing the last measurement, leaving the participants to themselves.

After 25 minutes, the experimenter quietly reentered the room, finished the stimulation, measured EDA, and administered the questionnaires again. There was space for a maximum of three participants to be stimulated simultaneously. The mind machines were supplied by the manufacturers. Brainman, the ES device, emits a biphasic squared impulse of the order of 0-450 [micro]A at a frequency of 6.4-34.1 Hz. In this study, we used 7.83 Hz at a power of 100 [micro]A, which is below the sensitivity threshold of most people. It is also said to be the frequency band that best triggers brain entrainment because it is the frequency between EEG alpha and theta bands. It is widely used as a standard frequency for mind machines.

The experimenter used the same ear electrodes that were used for resistance measurements to apply electric current. The electrodes remained fixed and were either connected to the resistance meter or to the ES/PS device. The electrode gel and wiring, which came with the apparatus, was used according to the manufacturer’s instructions.

The PS device was optically identical to the ES device, but the emission component was deactivated by the manufacturer so that it emitted no current. Thus, it was not possible to judge from appearances whether the mind machine was functioning as an ES device or was disconnected as a PS device. The participants and the experimenter did not know which machine was deactivated, but both machines were numbered.

The OAS machine, Mind Explorer (Brain Tech, Heidelberg), has goggles with two white and two red optical display diodes and headphones. The diodes and headphones emit impulses of different frequencies that result in different optical and acoustical sensations, depending on the program used. The intensity (ie, brightness and volume) can be adjusted by the participant, the frequency is set by predefined programs that transmit changing patterns of impulses. The program used in this study was Number 1, Relaxation. It starts with impulses of a 35 Hz frequency, then comes down to 7.83 Hz within the first 4 minutes, where it stays for 20 minutes. In the last 4 minutes it returns to its original frequency.

We used the two types of mind machines for this experiment. They are common commercial devices, can be purchased, and are therefore representative, according to advertisements and the manufacturer’s statements. Because we were interested in the real life effects of the mind machines tested, we did not select a shielded psychophysiological laboratory, but did our experiment in the back lounge of the biggest local mind machine shop, which is also used commercially for mind machine relaxation.

Statistical Analysis

We used SPSS for Windows 6.0 for statistical analysis, with a 4 x 2 repeated measurements analysis of variance (ANOVA) calculated with the four treatment conditions and the prescores and postscores as two within-participants factors for each variable, except for the APZ scores. Contrasts were formulated for the following differences: baseline v placebo stimulation, placebo v both experimental conditions, and ES v OAS. For the before and after measurement factor, we used repeated contrasts. The APZ posttreatment scores were analyzed as repeated measurements analysis of covariance (ANCOVA), with the baseline score as covariate, using BMDP, Version 7, 2V,[18] and the same contrasts as above.



The personality inventory data (FPI-R) showed that the 30 people attracted by the experiment who completed all four experimental conditions were roughly within the norms of four to six standard nine scores. The inventory has recently been gauged on a representative sample of the German population. The deviations from the mean in our sample indicate rather favorable deviations for our purposes, like higher social orientation and fewer problems with health or health-related thoughts, and being very open minded.

Those in the sample were comparatively young (M = 28.3 years, range = 21-52 years, with two thirds of the participants younger than the age of 30). The scores for the three scales of the IPC (internal control, powerful others, chance) were within the normal range, with the volunteer sample feeling less controlled by others and by chance and having average internal control, compared with a reference population of students.

Two thirds of the sample had had experience with some form of meditation (n = 20), relaxation (n = 19), and psychotherapy (n = 19). Many where motivated by curiosity (n = 21) and did not believe that electrical equipment was dangerous (n = 18; maybe dangerous = 11; definitely dangerous = 1). Only two participants had previous experience with OAS. The APZ scores showed that the sample had only a minor propensity for experiencing unusual psychological phenomena.

On the whole, the sample can be characterized as psychologically well-organized, unconventional, with a lower level of external control, and with experience in the field of relaxation and meditation techniques. The people in the sample were not accustomed to and had not used mind-machine stimulation.

Change Induced by Mind Machines

Statistical analysis revealed no differences between the treatment conditions in any of the adjective list dimensions. There is a strong before and after effect in general activity, F(1, 29) = 27.15, p [is less than] .0001; disactivation, F(1, 29) = 14.11, p = .001; and emotional tension, F(1, 29) = 11.41, p = .002, which is not present in extroversion/introversion, general well-being, and anxiety. No treatment main factors were significant, indicating that there was no difference between treatments. Interactions were negligible, with only slight tendencies. For details, see Table 1.

TABLE 1 Means and Standard Deviations Before and After Application of Four Stimulus Conditions in Study of Mind Machine Effects

Control Placebo Electric

Measure Pre Post Pre Post Pre Post

Adjective list


M 11.1 8.1 13.3 8.9 11.7 7.5

SD 5.7 6.2 6.8 6.5 6.8 6.6


M 5.7 7.4 3.3 6.4 4.3 7.1

SD 6.5 7.5 4.8 7.1 5.5 6.7



M 5.7 5.2 5.2 5.4 5.3 5.4

SD 1.5 1.6 2.1 2.7 2.0 1.9



M 11.0 11.3 11.6 11.5 11.5 9.7

SD 7.1 7.5 6.7 7.6 7.7 7.8

Emotional tension

M 4.8 3.4 3.3 3.3 4.5 3.3

SD 6.4 5.7 4.7 5.3 5.3 4.5


M 5.8 6.1 4.2 4.9 5.1 5.4

SD 5.8 5.8 5.6 5.8 5.8 4.3



M 573.9 294.9 531.1 248.4 531.3 188.3

SD 324.4 173.9 318.7 142.0 283.9 109.0

Altered states of

consciousness Fear

of ego dissolution

M 5.0 2.3 — 1.7 — 3.1

SD 5.0 2.6 2.1 3.6



M 3.8 2.8 — 3.1 — 3.1

SD 2.5 2.2 3.7 3.2



M 2.8 0.9 — 1.2 — 2.4

SD 1.9 1.2 1.6 2.7


Measure Pre Post

Adjective list


M 13.4 7.9

SD 6.4 6.1


M 2.8 6.7

SD 4.0 6.8



M 5.1 5.0

SD 2.2 2.5



M 11.3 10.9

SD 7.4 6.5

Emotional tension

M 5.0 1.9

SD 6.9 2.7


M 4.5 5.1

SD 6.0 4.9



M 447.9 152.3

SD 288.5 84.3

Altered states of

consciousness Fear

of ego dissolution

M — 3.4

SD 3.8



M — 4.6

SD 3.8



M — 4.0

SD 3.1

A strong effect in the change of electrodermal activity could also be seen in the before and after factor, F(1, 29) = 134.89, p [is less than] .0001, and a smaller but significant effect in the treatment main factor, F(3, 87) = 3.32, p = .024, which is mainly attributable to a difference in control v placebo stimulation (p = .02).

The data of the APZ questionnaire (exceptional psychological experiences) revealed effects in the repeated measurements ANCOVA with baseline scores as covariates. Fear of ego dissolution showed a significant tendency of differences in the main factor between conditions, F(3, 87) = 2.78, p = .05 (Huynh-Feldt corrected). This was the result of significantly more experiences of ego dissolution while under ES and optical OAS stimulation together, as opposed to placebo, F(1, 29) = 7.76, p = .009. The other contrasts showed no differences.

Mystical experiences and oceanic diffusion also showed a significant change in the main factor, F(3, 87) = 3.28, p = .03; Huynh-Feldt corrected, resulting from more experiences with OAS than with ES, F(1, 29) = 4.17, p = .05. Again, the other contrasts revealed no differences. Respondents also had significantly more altered visual experiences during the experiment, F(3, 87) = 12.05, p = .0001 (Huynh-Feldt corrected). This difference was seen mainly between the placebo condition and the two experimental conditions, F(1, 29) = 51.55, p [is less than] .0001, and in a tendency also between ES and OAS, F(1, 29) = 3.32, p = .078, with OAS producing more such experiences.


To our knowledge, this is the first intra-individually controlled study of the effects of mind machines that employs a placebo control. The sample was certainly not representative of the general population, but mind machines are also not used by the general population. Because we had no preconceived ideas about the average mind machine user, we thought advertising and word of mouth would be the most valid way of arriving at a meaningfully selected sample. The data of the personality inventory FPI supported this idea: the sample ranged in the normal spectrum and appeared to be on the more unconventional, extroverted, socially oriented side, with fewer health problems than average.

Our respondents came primarily from the campus community, and their locus of control was more internally situated than most people’s. This we took to indicate that the participants were not prone to overrely on impressive machinery but were curious to know what would happen to them. Most of them were used to being introspective, reporting their impressions, focusing inward, and paying attention to their experiences.

In situations with small and variable effects, control of intra-individual variance is of paramount importance. We attempted to achieve this by subjecting every person to every experimental condition, with random permutation of the experimental conditions except for the rest condition. We deliberately started with a rest control for all participants to make the subsequent applications of the three different experimental conditions more plausible, thus minimizing the chance that participants would guess at a possible placebo device among them. In our design, it was plausible for participants to recognize that, after a phase of warm-up rest, the three different mind machines would follow, enhancing credibility of the placebo control.

We kept the time of day the same throughout the four conditions and provided at least 1 day for washout between each condition. Error variance and individual differences should therefore have been controlled. Blinding was applied where possible: the placebo stimulation was not discernible by outward appearance from the working ES, although some very sensitive persons might have sensed the 100 [micro] A current.

The attrition rate was low. We used an adjective list known to be sensitive to change, electrodermal activity, and a questionnaire especially designed to assess the presence of exceptional psychological experiences phenomenologically. This questionnaire had been used previously in comparable studies on inducing altered states of consciousness. It has proved sensitive and useful for the assessment of experiences under sensory deprivation and drug stimulation with hallucinogenic drugs, which are both known to produce different types of altered experiences (eg, hallucinations, visual impressions, altered time, self- and person perception).

Against this background it is interesting to note the results of this study. Although there were no differential treatment effects, as reflected by the adjective list or electrodermal activity, there were strong effects for the before and after factor, indicated by highly significant p values for change in activity, disactivation, and emotional tension, as well as for change in electrodermal activity. All of the treatment conditions lowered activity levels and emotional tension and increased general disactivation, which is an indicator of the effect of the 25-minute rest. Well-being, anxiety, and the dimensions of extroversion/introversion were not affected.

We found no noticeable differential effects between the conditions. Therefore, the effects of mind machines on self-reported general activation and emotional tension, as measured by an adjective list, were unspecific effects related to rest and not to the electric devices.

Emotional tension seemed to be reduced more by active treatment, compared with placebo. But considering the multiplicity of tests in this multiple univariate approach, this effect was far from convincing. The statistical tendencies indicating that the placebo condition was more effective than pure rest in reducing activity also vanished when corrected for multiple testing.

Electrodermal activity was expressed as the sum of two different values that measured changes in activity. We found no difference between any of the conditions. However, there was a definite decrease in activation, measured by the sum of the two different EDA scores, which was quite similar for all conditions, with the small exception that the difference was more marked between control and placebo. This was congruent with the self-report data.

Our findings were different with the APZ data regarding exceptional psychological experiences. The sample was not pathological. Therefore, no simple statistical reason (eg, natural regression) can be offered for the differences we found in all three APZ dimensions. Participants had more experiences of ego dissolution and more unusual visual experiences during the experimental stimulation, compared with placebo stimulation. They also experienced more mystical experiences of oceanic diffusion and more unusual visual experiences while under OAS than ES. The latter difference is rather trivial because OAS is designed to induce visual experiences.

The strong effect of more mystical experiences of oceanic diffusion with OAS, with no other apparent differences, indicated that OAS operates distinctly by inducing such experiences of diffusion. We found no difference between rest and placebo stimulation in any of the three APZ variables, an indication that the experiences were not just the result of expectation or fear of the equipment.

At any rate, the active stimulation introduces stimuli that are novel and seem to alter the state of consciousness toward more fluid ego boundaries. In that respect, OAS is more effective than ES. Whether this effect is clinically beneficial or not is difficult to judge from our data and can only be determined by long-term observation. But we can warn that psychiatrically ill persons with boundary problems should not use mind machines. Such people are likely to experience fear of ego dissolution and loss of self that healthy people might find to be an interesting and new experience.

The APZ questionnaire on exceptional psychological experiences showed clear and interpretable differences between experimental conditions, but the adjective list and EDA did not (although they exhibited clear overall changes from prestimulation to poststimulation). Consequently, the negative differential finding for our adjective list and EDA data are unlikely to be the result of a lack of sensitivity in measurement or low statistical power. Intercorrelations among the different measures were erratic; there was no apparent, consistent trend in the data. That is, the adjective list and APZ measures seem to be of a different nature. Although the adjective list data assessed statelike emotions and well-being, which were not altered, the APZ captures exceptional experiences. In other words, people might experience strange things and still feel all right without being greatly bothered.

In conclusion, we cannot support the claim that mind machines introduce a specific state of relaxation different from rest or from that effected by sham stimulation, as measured by a validated adjective list. However, the mind machines provided more experiences that are different from everyday life, more exceptional visual images, and more fear of ego dissolution than either placebo or rest. These are clear-cut effects of active stimulation.


The authors wish to thank various anonymous referees for helpful comments and Marcus Majumdar for improving the style.


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Drs Walach and Kaseberg are with the Department of Psychology at the University of Freiburg, Germany.

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