This is a continuously updated document. We will keep adding information and resources. If you notice any mistakes, please send an e-mail to Timo Torsten Schmidt: timo.t.schmidt at fu-berlin.de
Multiple questionnaires have been developed to quantify the phenomenology of ASCs. Here, we provide an overview on available psychometric tools, their conceptual background and construction, and validation. Some questionnaires were designed to cover a broad range of different experiences (e.g. the Altered States of Consciousness Rating scale), others are designed to assess specific ASC phenomena (e.g. the Watts Connectedness Scale), and others were designed to assess the phenomena induced by a specific consciousness modifying technique (CMT). Based on their scope and on and prevalence in previous research, we aim to provide aid to decide which questionnaire can be best for a specific study. We discuss the tools in approximate order of prevalence/popularity. Table 1 gives an overview of the questionnaires in this collection, including some of their basic properties and key references. The most recent (and recommended version) is marked in bold. We included where currently new versions are under development.
| Questionnaire | Version | # items | # scales | response format |
|---|---|---|---|---|
| Altered States of Consciousness Rating Scale | APZ OAV 5D-ASC 11-ASC 11-ASC(AXP) |
72 66 94 42 22 |
3 (FA) 3(FA) 5(FA) 11(FA) 11 |
Yes/No VUS VUS VUS VUS |
| Phenomenology of Consciousness Inventory | PCI | 53 | 12+14(FA) | 7-point |
| Addiction Research Center Inventory | ARCI long-form ARCI short-form |
550 49 |
38 5 |
Yes/No Yes/No |
| Hallucinogenic Rating Scale | HRS | 126 | 6(FA) | 5-point |
| Mystical Experience Questionnaire | MEQ MEQ30 MEQ-4 SOCQ PEQ |
130 30 4 100 89 |
8+9 4(FA) 4 7 8 |
5-point 5-point 5-point 6-point 6,7,8-point |
| Psychometric States Inventory | PSI | 48 | 6(FA) | 4-point |
| Ego-Dissolution Inventory | EDI | 16 | 2(FA) | VUS |
| Abramson Questionnaire | AQ | |||
| Linton & Lang Questionnaire | LLQ | |||
| Near-Death Experience Scale | NDE | |||
| The Mysticism Scale | M-Scale | |||
| Personal Experience Questionnaire | PEQ | |||
| Assessment Schedule for Altered States of Consciousness | ASACS | |||
| Challenging Experience Questionnaire | CEQ | |||
| Watts Connectedness Scale | ||||
| Afterglow Inventory | AGI |
Table 1 Overview of the most commong questionnaires and their versions that ase used to assess ASC phenomena in current research
Please also find a slide deck of the workshop The Empirical Study of Altered States of Consciousness (2024) given at the ASSC conference by Dr. Timo Torsten Schmidt, Larry Fort and Cyril Costines on ResearchGate. This workshop includes a conceptual overview and additional suggestions and information for empirical research.
The currently used version(s) of the Altered States of Consciousness Rating Scale (ASC-R) (Dittrich et al., 2006, 2010) originated from two former versions and was originally developed in German. The ASC-R has become the most frequently used psychometric tools in the assessment of ASC phenomena. The development of the scale followed the assumption that ASCs have a common core that is independent of the particular induction method (ethiology-independent dimensions of altered states). Therefore, in contrast to other instruments, the ASC-R is supposed to investigate characteristics of ASCs that are invariant across various methods to induce ASCs, including both pharmacological (e.g., psilocybin, ketamine, DMT, MDMA) and non-pharmacological induction methods (e.g., sensory deprivation, hypnosis, autogenic training). However, it is noticeable in the item selection, that the original authors had a research focus on the effects of psychedelics. Over the course of more than 30 years, the questionnaire underwent several refinements. Due to a lack of systematic curation, there is currently different versions in use and confusion about how to analyze them and present results. To support future research we summarize the history of the questionnaire with its different versions and point to unfortunate ambiguities in how data is currently reported.
The name APZ is based on the original German name: Abnorme Psychische Zustände (abnormal mental states). An initial item collection was based on several self-assessment questionnaires on ASCs, and psychiatric rating scales, which resulted in a 158-item questionnaire version. In a series of experiments, which included data from variable induction methods, as well as factor and cluster analyses, the item pool was reduced to 72. These items comprise three common dimensions of ASC experiences: Oceanic Boundlessness (OBN), which measuring positive symptoms of dissolution of boundaries between self and surroundings; Dread of Ego Dissolution (DED) measuring negative symptoms of dissolution of boundaries between self and surroundings, and Visionary Reconstruction (VRS) measuring perceptual changes and imagination (Dittrich, 1985).
The name OAV uses the first letters of the German names of the three main dimensions of the APZ (Ozeanische Selbstentgrenzung (OSE = OBN); Angstvolle Ich-Auflösung (AIA = DED) und Visuelle Restrukturalisierung (VRS)). For the OAV version, the questionnaire was revised in terms of conceptualization, wording, and form in the scope of an unpublished master thesis (Bodmer, 1989). The most important modification was the replacement of the former dichotomous response format by visual analog scales to allow the assessment of the intensity of effects (Bodmer et al., 1994).
The common core dimensions OBN, DED and VRS were complemented by two additional empirically derived scales: Auditory Alterations (AUA) and Vigilance Reduction (VIR). These scales assess changes in auditory perception such as hallucinations and drowsiness or clouding of consciousness, respectively. As opposed to the former three, these additional dimensions are considered rather specific to certain induction methods (Dittrich et al., 2006, 2010), and their validation is not as good as the one of the main three dimensions (See below). The 5D-ASC version with 96-items that comprise 5 dimensions has become a standard tool for the assessment of effects of psychedelics (including clinical studies), and also a Handbook for the analysis is available (in German). For the analysis Mean scores of the items that belong to the corresponding dimension are calculated and expressed as percentage of maximum score (for convenience the original print version uses corresponding visual analog scales of 10cm length). Note: In some older publications one can find a sum score, instead of a mean percentage score, which causes problems for comparability as the dimensions contain different amounts of items. In the Altered States Database, such data has been converted (typically after confirmation from the authors of the accurate number of items). It is advised to report data, as percentage of maximum score.
Several methodological shortcomings of the 5D-ASC construction motivated a reanalysis which revealed a new analysis scheme for a subset of 42 items of the ASC-R (Studerus et al., 2010). This analysis was based on only the 66 items belonging to the three main dimensions of the 5D-ASC (the original OAV dimensions). Re-examination of the factorial structure was based on psilocybin and ketamine data and revealed that an 11-factorial model is suitable to fit the data and increases scale homogeneity (Studerus et al., 2010). Corresponding scales were named as: (1) Experience of Unity, (2) Spiritual Experience, (3) Blissful State, (4) Insightfulness, (5) Disembodiment, (6) Impaired Control and Cognition, (7) Anxiety, (8) Complex Imagery, (9) Elementary Imagery, (10) Audio-Visual Synesthesia, and (11) Changed Meaning of Percepts. These eleven factors can be regarded as basic/elementary subscales of the three original scales, which describe rather high-order concepts.
Within the Altered Xperience Project Citizen Science project (Schmidt et al. 2023) a 22-item version was applied. Items were selected based on the ‘items validation’ according to Studerus et al. This short version has not been validated, but the collected data is available on OSF and is open to be used for a validation (Go for it if you have time and let the authors know). To the best of our knowledge a team in the Netherlands is currently working on the validation of a even shorter version.
Note 1: Please note that the 11-factorial analysis scheme presented by Studerus et al. (2010) revealed 11 factors (!) and not 11 dimensions. Unfortunately, the original publication of the analysis scheme did not contain a suggestion for a new name, and multiple authors (including ourselves) started to name it “11D-ASC”. However, this is appears not appropriate and instead we suggest now to speak about the ASC-R to refer to the full questionnaire with 96-items, which can be analyzed according to the 5D-ASC or the 11-ASC analysis scheme. Note 2: Please note that the 11 factors of the 11-ASC can be assigned to the three main dimensions of the 5D-ASC. Unfortunately, some publications contain a wrong assignment of the 11 scales where the Disembodiment factor is assigned to DED (e.g. Vollenweider & Kometer 2010). However, the items that comprise the Disembodiment factor are taken from OBN and should be assigned correspondingly (Compare how they are displayed e.g. in Hirschfeld & Schmidt 2021 or Hirschfeld et al. 2023). Note 3: It should be noted that the three main dimensions of the 5D-ASC are calculated from the original set of 66 items. If only a 42-item version was applied, it is not possible to calculate the scores for OBN, DED or VUS. It is neither valid to take the mean score of the scales (mean of means), nor is it valid to take the mean score of all items belonging to the corresponding dimensions. Note 4: It is not clear to us what the situation with regards to Copyrights of the 5D-ASC is. The original publication states that the copyrights are with “PSIN PLUS Publicationes, 2006”. However, it appears that the corresponding publisher is highly limited in the responsiveness with regards to placing orders or issuing bills for license fees. Potentially the publisher does not exist anymore (We cannot find any traces online - If somebody has more information on this – please let us know and we are happy to make this information available here).
In terms of quality criteria, the German 5D-ASC and its former versions were repeatedly assessed as reliable and valid instruments. The validation of the APZ revealed good results regarding internal consistency, test-retest reliability as well as convergent and discriminant validity (Dittrich, 1985; Dittrich et al., 1985). Assessments of internal consistency estimated by Hoyt (0.89 to 0.95) and test-retest correlation (0.75<r<0.82) suggest the OAV’s reliability (Bodmer, 1989). Internal consistency (estimated by Hoyt) was also good for the 5D-ASC’s additional scales: 0.88 (AUA) and 0.88 (VIR) (Dittrich et al., 2006, 2010). The proposed 11-factorial structure was assessed in a pooled data analysis of several experimental studies, which were however limited to pharmacological induction methods of ASCs. This evaluation indicates high reliability for all scales with a mean Cronbach’s alpha of 0.83. Correlation with the EWL-60-S (short form of the Adjective Word List) and the STAI-S (state version of the State-Trait-Anxiety Inventory) suggest convergent and discriminant validity of this scale (Studerus et al., 2010). Together with alternative reliability assessments, these results demonstrate its suitability as a reliable and valid psychometric tool for the assessment of subjective experiences occurring during ASCs. Originally developed in German, the Altered State of Consciousness Rating Scale was translated into English and several other languages (Studerus et al., 2012). Recent application in neuroimaging studies demonstrates its wide acceptance and significance for the scientific study of ASCs (e.g., (Carhart-Harris et al., 2016a)). However, this questionnaire is, except for its earlier version APZ, is to the best of our knowledge not validated in other languages than German. A adaption for the assessment of effects of Floating-REST has been reported and termed Experienced Deviation from the Normal State questionnaire (EDN) (Kjellgren et al., 2001). A current trend in the field is to develop short and ultra-short version of questionnaires to take less time in the assessment. A 22-item version was used in the Altered eXperience Project (Schmidt et al. 2023), and we have heard about current attempts to validate a 11-item version (personal communication - We will post updates as soon as we have more information).
The Phenomenology of Consciousness Inventory (PCI) (Pekala, 1982, 1991) was developed in the context of an interdisciplinary approach that is described as empirical-phenomenological (Pekala, 1991). Most notably influenced by C. T. Tart’s (1975) conception of ASCs, it is hypothesized that different states are characterized by distinct structures and patterns of subjective experiences (Pekala, 1991). The subjective experience of a certain state can be characterized based on phenomenologically well-defined dimensions which can be quantified in terms of their intensity. The resulting pattern is assumed to be typical of a specific induction method and can be observed consistently whenever this method is applied. The PCI is a self-report questionnaire that is completed in retrospect, after acute ASC effects have subsided. Originating from three previous versions, the Phenomenology of Consciousness Questionnaire (PCQ), the (Abbreviated) Dimensions of Consciousness Questionnaire ((A)DCQ), and the Pre-PCI, the most recent version of the PCI is available in two different versions. Form 1 and Form 2 contain the same number of items, which are, however, arranged in a different order. The items of the PCI are presented as two opposing statements located on the two poles of a 7-point Likert scale. The statements address 12 major dimensions, five being further subdivided into more specific sub-dimensions: (1) Altered State of Awareness, (2) Altered Experience (Altered Body Image, Altered Time Sense, Altered Perception, Altered Meaning), (3) Volitional Control, (4) Self-awareness, (5) Rationality, (6) Internal Dialogue, (7) Positive Affect (Joy, Sexual Excitement, Love), (8) Negative Affect (Anger, Sadness, Fear), (9) Imagery (Amount, Vividness), (10) Attention (Direction, Absorption), (11) Memory and (12) Arousal. Corresponding scales were constructed on the basis of several cluster and factor analyses.
Several studies were conducted in order to evaluate the PCI’s quality in terms of validity and reliability. Assessments of the English PCI under different stimulus conditions (Pekala, 1991) demonstrate good overall internal consistency with an average Cronbach’s alpha ranging from of 0.75 to 0.83 for major dimensions. Evidence for the PCI’s good validity is given by the comparison with the Dimensions of Attention Questionnaire (DAQ) (0.69< r <0.78) (Pekala, 1991) and the prediction of hypnotic susceptibility as measured with the Harvard Group Scale of Hypnotic Susceptibility (HGSHS) on the basis of the PCI’s major dimensions; e.g. significant correlation (r=0.64, p<0.05) of predicted and actual HGSHS scores using the regression coefficients from a previous study (Pekala, 1995). In the scope of a diploma thesis Rux (2002) evaluated the German version of the PCI. The reliability assessment yielded a medium internal consistency for all scales with alpha coefficients being lowest for Love (0.37) and highest for Altered State of Internal Dialogue (0.86) and an average alpha of 0.69. The original version of the PCI was translated from English into German by Ott and subsequently authorized by Pekala (Rux, 2002). An Excel sheet, available from the questionnaire’s author upon request, allows for an automatic computation of item and factor scores. In summary, this broad questionnaire allows for a quite fine-grained assessment due to its 12 major and 14 minor scales. However, it should be considered that the PCI was designed with a focus on hypnosis and has primarily been applied in studies investigating effects of hypnosis, meditation, and related induction methods like shamanic-journeying or stress management techniques. Its administration in pharmacological studies is rather rare.
The ARCI has been developed by Haertzen et al. (1963) in the attempt to measure a broad range of physical, emotive, and cognitive effects of different drugs and subjective experiences related to personality and psychiatric disorders (Haertzen et al., 1963; Haertzen and Hickey, 1987). Items were derived from responses of opiate addicts made in a sentence completion task during baseline, and various drug states and supplemented with items from personality inventories (Haertzen et al., 1963; Haertzen, 1974). A pool of 3300 statements was reduced to a set of 550 true-false items (ARCI long-form) and assigned to five categories: (1) general information, (2) interest and drives, (3) sensation and perception, (4) bodily symptoms and processes, and (5) feelings and attitudes (Haertzen, 1974). Items are mainly phrased in present tense in order to refer to an acute state (Haertzen et al., 1963). Thirty additional items, repeating prior statements in the same or logically opposite form, were included to test for cooperation or carelessness (Haertzen and Hickey, 1987). To diagnostically differentiate between states, Haertzen and colleagues developed multiple scales to dissociate specific drug intoxications as well as psychiatric conditions (Hill et al., 1963a, 1963b; Haertzen, 1974). A final 38-scales scoring system for the 550-item long form of the ARCI was established (Haertzen, 1974). Amon those various empirical scales were derived with a focus on state-specific effects (Haertzen, 1974). As the ARCI was not necessarily intended to be applied in its entirety, many studies used only some scales relevant to their specific hypotheses (e.g. (Jasinski et al., 1971)). The most established short form developed by Martin et al. (1971) consists of 49 items that are clustered into five group variability scales: the Benzedrine scale (BG), the Lysergic Acid Diethylamide scale (LSD), the Morphine-Benzedrine and (MBG), and the Pentobarbital-Chlorpromazine-Alcohol scale (PCAG) of the ARCI long form supplemented with the empirically derived 11-item Amphetamine scale (A). Among the plurality of short forms is this the most commonly used questionnaire in current studies (e.g.(Griffiths et al., 2006; Schmid et al., 2015)).
Reliability assessments in five sample populations (criminals, addicts, alcoholics, mentally ill patients, normal population) yielded Kuder-Richardson KR-20 scores for each of the 38 scales (Haertzen, 1970). As the internal consistency demonstrated a large range from 0.06 (Marijuana scale in normal population) to 0.97 (Reactivity in alcoholic sample), the utility of some scales appears rather questionable. In addition, test-retest reliability was assessed (Haertzen, 1970). Several further studies evaluated the psychometric properties of the short form in different languages (Lamas et al., 1994; Arasteh et al., 1999; Riba et al., 2001). Acceptable reliability coefficients are particularly obtained for the Spanish version. Both long and short form have been translated and validated from English into multiple languages: long form: German, French, Spanish, Swedish (Haertzen, 1974); short form: Spanish (Lamas et al., 1994; Arasteh et al., 1999), French (Warot et al., 1997). Through its availability in different languages, the ARCI was a common instrument to measure drug effects both in clinical settings and experimental research, e.g. including studies on ayahuasca (Riba et al., 2001). As the long form is very time-demanding, the short form (Martin et al., 1971) is more feasible. In particular, its Spanish translation (Lamas et al., 1994) found wide-spread application and has been assessed in terms of psychometric features. However, a recent exploratory factor analysis performed on data from 158 ayahuasca practitioners suggests a three-factor (Euphoria, Activation, Sedation) structure comprising only 18 of the 49 items (Bouso et al., 2016). Another limitation is the application of a dichotomous response format. The use of categorical responses instead of individual intensity ratings precludes any correlational analysis, which is, however, often required in experimental research to establish direct relations between the subjective experience and physiologic measures.
Originally developed to quantify acute effects of synthetic dimethyltryptamine (DMT) (Strassman et al., 1994), the HRS has become a frequently used instrument in the assessment of hallucinogen induced ASCs (DMT/ayahuasca: (Riba et al., 2004); psilocybin: (Griffiths et al., 2006); ketamine: (Bowdle et al., 1998); salvinorin A: (MacLean et al., 2011)). The initial construction of this questionnaire was based on systematic interviews with 19 experienced hallucinogen users, describing the effects of smoked DMT freebase. Effects specifically induced by DMT as well as characteristic effects of hallucinogenic substances in general were supposed to be covered by the resulting collection of items (Strassman et al., 1994). The HRS measures six conceptually distinct dimensions of ASCs which were a priori defined and referred to as “clinical clusters”: (1) Somaesthesia: interoceptive, visceral, and cutaneous/tactile effects, (2) Affect: emotional/affective responses, (3) Perception: visual, auditory, gustatory, and olfactory experiences, (4) Cognition: alterations in thought processes or content, (5) Volition: a change in capacity to willfully interact with oneself, the environment, or certain aspects of the experience, and (6) Intensity: the overall strength and the course of the experience (Strassman et al., 1994). Revision and refinement of early versions finally resulted in the HRS 3.06 as the most recent version (available from the questionnaire’s author upon request), containing 100 statements, most of which are rated on a 5-point scale.
Application of a Spanish version of the HRS, assessing the effects of ayahuasca immediately after the ASC experiences, and its comparison with the ARCI short-form, confirmed the HRS’s sensitivity to prolonged alterations in consciousness caused by oral rather than intravenous DMT administration (Riba et al., 2001). Further studies explored and demonstrated its suitability for quantifying the effects of other psychoactive substances like psilocybin (Gouzoulis-Mayfrank et al., 1999; Griffiths et al., 2006), ketamine (Bowdle et al., 1998), MDE and methamphetamine (Gouzoulis-Mayfrank et al., 1999), MDMA (Tancer and Johanson, 2007), and salvinorin A (Johnson et al., 2011). Reliability assessments indicate a good internal consistency of the Affect, Somaesthesia, Cognition, and Perception scale and a comparison with the ARCI LSD scale revealed a moderate correlation with the Perception scale (r=0.28, p<0.05), and the Somaesthesia scale (r=0.33, p<0.05), respectively, suggesting acceptable convergent validity (Riba et al., 2001). The initial assignment of items to six “clinical clusters” has repeatedly been challenged. An initial principle component analysis (Strassman et al., 1994) did not reflect the a priori assignment. Riba et al. (2001) proposed a solution where 71 items are assigned to six factors and data by Bouso et al. (2016) suggests a substantially different distribution of 59 items in six factors. The HRS has been translated from English into Spanish, Portuguese, Italian, German, and Russian (Strassman, 1994) thereby demonstrating its wide acceptance. Though not validated in all languages, the HRS appears to be a suitable psychometric tool that covers a wide range of cognitive, affective, and perceptual phenomena occurring with pharmacologically-induced ASCs and allows with its additional categorical items for a distinct mapping of the direction of phenomenological changes. While factorial analysis of its structure propose substantial modifications (Riba et al., 2001; Bouso et al., 2016), it has to be emphasized that the huge variety of drugs’ effects assessed by the HRS is only comparable to the ARCI and the 5D-ASC. However, application with non-pharmacological induction methods has not been reported yet. Therefore, and due to its development in the context of effects typical of DMT, the HRS can currently be recommended only for supplementary use in studies investigating ASCs induced by hallucinogens and related substances. To date, it constitutes one of the best sources to compare the effects of psychoactive substances, however, does not contribute to comparisons to non-pharmacologically induced ASCs. Its suitability to map such states remains an open question for future studies.
Ethnographic studies suggest that hallucinogenic substances have been used in many cultures as part of religious rites in order to facilitate the experience of spiritual or mystical states. The Mystical Experience Questionnaire (MEQ) was first used in the famous ‘Good Friday Experiment’ (Pahnke, 1963, 1966), where it was intended to assess differences regarding aspects of mystical experience between a psilocybin and a control group. Since then, the MEQ has been frequently applied as an instrument for the quantitative assessment of pharmacologically induced mystical experience, in particular by psychedelics. Items of the initial version were chosen based on literature about mysticism including first-person accounts as well as theoretical work, most notably by William James (1902) and W. T. Stace (1960). The first version of the questionnaire consists of two parts. The first part (post-drug questionnaire) comprises 130 items and is completed within one week after the mystical experience (Pahnke, 1963, 1966). Answers are given on a 5-point Likert scale. Items are assigned to eight scales describing the following dimensions of mystical experiences: (1) Internal and External Unity, (2) Transcendence of Time and Space, (3) Deeply Felt Positive Mood, (4) Sense of Sacredness, (5) Objectivity and Reality, (6) Paradoxicality, (7) Alleged Ineffability, and (8) Transciency. Pahnke (1969) defined experiencing a mystical episode as having a total score of more than 60% of the maximum on each scale. The second part (follow-up questionnaire) contains 100 items, including a condensed version of the first questionnaire as well as additional items measuring positive and negative long-term effects. It is filled out approximately six months after the mystical episode.
The initial questionnaire has been further developed by Pahnke (1969), Richards (1975), Griffiths et al. (2006; 2011), and MacLean et al. (2012). Most prominent is the SOCQ, a shortened version consisting of only 43 of the original items intermixed with distractors (Griffiths et al., 2006). The original eight dimensions are differently organized in this version. Paradoxicality and Ineffability form a single dimension and the dimensions Objectivity, Reality, and Transciency are replaced by a new dimension called Noetic Quality. Persisting Effects Questionnaire (PEQ) The SOCQ is followed by the Persisting Effects Questionnaire (PEQ) which assesses long-term changes. It uses 89 items in its first version (Griffiths et al., 2006) and 143 items in a second extended version (Griffiths et al., 2011), and is based on the original follow-up questionnaire by Pahnke.
The most recent version is the MEQ30 (MacLean et al., 2012), a condensed version of the MEQ with empirical scales. Using the SOCQ as a starting point, MacLean and colleagues conducted exploratory and confirmatory factor analyses on two large independent samples from online surveys. As a result, thirteen of the 43 items were excluded and an underlying factor structure was revealed with the following four dimensions: (1) Sacredness, (2) Positive Mood, (3) Transcendence of Time/Space, and (4) Ineffability. This factor structure was replicated analyzing pooled data from five experimental studies (Barrett et al., 2015), and is therefore recommended for future studies. An alternative two-factor structure (Mystical Ecstasy, Transdimensionality) was recently proposed but not further validated (Bouso et al., 2016).
Recently an ultra-short version of the MEQ was presented, with only one item per scale (REF).
The original MEQ has been used for several decades but its psychometric properties have never been assessed systematically. More than twenty years after the ‘Good Friday Experiment’, the participants were asked to complete the follow-up questionnaire again (Doblin, 1991). Results indicated that the average scores of the main dimensions had not changed drastically over time, thereby suggesting the MEQ’s reliability. Moreover, mean scores on all subscales were significantly higher in the experimental group compared to the control group, supporting the questionnaire’s discriminant validity. The MEQ30 was assessed regarding reliability and validity by MacLean et al., (2012) in a group of 1602 participants who had taken psilocybin at least once during their lifetime. Internal consistency estimated by Cronbach’s alpha was very good for the total questionnaire (0.96), as well as for the four subscales (0.80 to 0.95). Similar results were also obtained by Barrett et al. (2015). Convergent validity was assessed by correlating MEQ30 scores with the single-experience version of Hood’s Mysticism Scale. The total score of the MEQ30 correlated rather strongly with the overall score of the Mysticism Scale (r=0.81, p<0.001), whereas the subscales showed somewhat lower correlations (r=0.41 to 0.79, p<0.001) (MacLean et al., 2012). To support construct validity, self-claimed mystical experience was shown to be associated with significantly higher questionnaire scores (MacLean et al., 2012). Currently, the MEQ30 is the best established instruments to quantify mystical/spiritual/religious experiences. In particular, clinical studies on the therapeutic potential of psychedelics use the MEQ30 (Majic et al., 2015).
Originally developed to assess the acute so-called “psychotomimetic” effects of cannabis and ketamine administration in healthy volunteers (Mason et al., 2008), the Psychotomimetic States Inventory (PSI) has also been applied to investigate the effects induced by short-term sensory deprivation among individuals prone to experience hallucinations and those without such a predisposition, as well as in experiments with hallucinogens (Mason and Brady, 2009; Daniel et al., 2014; Daniel and Mason, 2015; Carhart-Harris et al., 2016b). The PSI comprises 48 items, drawn from an item pool that was derived from on a variety of psychometric instruments for the assessment of phenomena related to psychosis and hallucination-proneness. A first item selection was based on multiple pilot studies, surveying student volunteers as well as recreational drug users (Mason et al., 2008). Subsequent factor analyses yielded the final set of items, addressing six empirically-derived dimensions of psychosis-like experiences as induced by diverse psychoactive substances and sensory deprivation: (1) Anhedonia, (2) Cognitive Disorganization, (3) Mania, (4) Delusional Thinking, (5) Perceptual Distortion, (6) Paranoia.
Full-scale test-retest reliability and Cronbach’s alpha coefficients for the PSI indicate good stability (0.84) and internal consistency (0.86 to 0.94 across conditions), respectively (Mason et al., 2008). While test-retest correlations for the different subscales range between 0.60 (Anhedonia) and 0.83 (Delusory Thinking) indicating acceptable stability, alpha coefficients for Mania (0.05) and Cognitive Disorganization (0.89) display a wider range of internal consistency. However, most estimates for the remaining scales suggest good internal consistency. Though not formally evaluated in terms of validity, significant correlations (Kendall’s tau: 0.54< tau <0.70, p<0.001 across conditions) between the PSI and the state of the Appraisals of Anomalous Experience Interview (AANEX), both measuring psychotic-like experiences, support the assumption of adequate convergent validity (Daniel et al., 2014). Being applied both in natural and laboratory environments (Mason et al., 2008) and assessing pharmacologically (Mason et al., 2008; Mason and Brady, 2009; Carhart-Harris et al., 2016b) as well as non-pharmacologically (Mason and Brady, 2009; Daniel et al., 2014; Daniel and Mason, 2015) induced changes in perception, cognition and emotion, the PSI appears to be a useful psychometric tool to investigate psychosis-like characteristics of ASCs. By focusing on rather aversive effects of the ASC experience, this questionnaire covers important aspects that are insufficiently addressed by other instruments. Insofar, the PSI points out conceptual shortcomings of previous tools and provides valuable suggestions for the assessment of ASCs. Its own limitation is, in turn, the omission of pleasant aspects. The subjective experience of ASCs – particularly, if induced by psychedelic substances – appears, however, to be characterized by either of these two opposite dimensions (Bodmer et al., 1994).
The phenomenon of ‘ego-dissolution’ is a substantial aspect of ASCs induced by psychedelic substances (Lebedev et al., 2015; Tagliazucchi et al., 2016) and ‘mystical experiences’ following religious rites (MacLean et al., 2012) or sensory deprivation in flotation tanks (Kjellgren et al., 2009). ‘Ego-dissolution’ is defined as derealization and depersonalization, which can be experienced as positive and negative. As a removal of boundaries between self and surroundings and feeling of all-embracing unity, ‘ego-dissolution’ is discussed in the context of psychosis (Scharfetter, 1981) as well as psychotherapy (Majic et al., 2015). The Ego-Dissolution Inventory (EDI) was only recently designed with the aim of providing a valid and reliable tool for the accurate, unidimensional assessment of this phenomenon (Nour et al., 2016). This self-report questionnaire comprises sixteen items covering both ‘ego-dissolution’ and its counterpart ‘ego-inflation’, the experience of enhanced self-consciousness. Each item is rated on a visual analog scale, corresponding to the response format of the 5D-ASC, and the two orthogonal scales were confirmed through factor analysis (Nour et al., 2016).
Evaluation of its psychometric properties (Nour et al., 2016) confirmed that the EDI differentiates between stimulus conditions (psychedelic substance vs. cocaine vs. alcohol), suggesting discriminant validity. Moreover, the positive correlation (Spearman’s rho=0.735, p<0.001) with the Mystical scale of the MEQ30 supports its convergent validity. As a first estimate of reliability, the internal consistency was assessed by Cronbach’s alpha (0.93). The EDI appears to be a psychometrically sound instrument. However, it covers only one specific aspect of the ASC experience and is, therefore, not suitable for studies investigating the common core of ASCs. As ‘ego-dissolution’ seems to be a phenomenon central to ASCs induced by different induction methods, the EDI might well contribute to comparability between studies that focus on this specific aspect. The quantification of ‘ego-dissolution’ and identification of its neural substrates is an important endeavor, particularly with respect to its psychotherapeutic potential. Moreover, as the response formats correspond, the EDI can be applied as a supplement to the 5D-ASC. Recently a German translation and validation has been published REF
The Abramson Questionnaire (AQ) was constructed in order to quantify the effects of lysergic acid diethylamide (LSD; (Jarvik et al., 1955)). It is mostly interesting for historical reasons, as it might not meet current psychometric standards and has not been used in recent years. The questionnaire is based on literature research into the effects typically reported after LSD intake. Abramson and colleagues (1955a) used it in a series of experiments in the late 1950s, also measuring the effects of drugs other than LSD (Jarvik et al., 1955). The questionnaire has a one-dimensional structure, measuring only the overall strength of the ASC experience. Its items are conceptually-defined and not confirmed through further data analysis. A later version excluded some items that did not distinguish between experimental and control subjects (Abramson et al., 1955b). Items are rated on a 6-point Likert scale, with the options +1 to +5 for positive symptoms, as well as an option ‘No’ for lack of symptoms. However, ratings are only treated as dichotomous Yes- or No-answers in the data analysis. The total score is therefore obtained by adding all positive responses, with the highest possible score being 47. The items include questions such as: “Do you have difficulty focusing your vision?”, and “Do you feel as if in a dream?”
The psychometric properties of the AQ have not been measured and evaluated in a systematic way. The validity of the questionnaire was somewhat confirmed through comparison between three groups (Abramson et al., 1955a): one experimental group receiving a medium dose of LSD (25-75 µg), one experimental group receiving a high dose (100-225 µg), and a control group receiving a placebo. The correlation coefficient between the rank positions of answers in both experimental groups (r=0.83) was markedly higher than between either of them and the placebo group(r=0.36, r=0.46). Even though this may be seen as supporting the discriminant validity of the questionnaire, it is not according to prove by today’s standards. Further testing would be required to validate this instrument. Interestingly, some subjects also showed high scores after taking a placebo (Abramson et al., 1955a). This might be due to suggestibility, especially, if considering that experimental and control subjects were jointly tested in a group setting. But it might also point to validity-related issues of the questionnaire itself. Even though the questionnaire does not fulfill current standards concerning quality criteria, it should be regarded as an early attempt at measuring qualitative aspects of ASCs. As such, it has historical relevance and influenced the development of later questionnaires. Researchers specifically interested in the assessment of ASCs induced by LSD might even consider applying it in addition to other instruments, or using it as a basis of a new questionnaire.
The Linton & Langs Questionnaire (LLQ) (Linton and Langs, 1962a) fits into the trend of the late 1950s of clinical and observational studies investigating the broad range of subjective phenomena during LSD experience. The questionnaire is based on literature research into changes in subjective experience typically reported after LSD administration. The development as well as the evaluation of the results was embedded in the framework of ‘Psychoanalytic Theory’. Whereas previous research tools like the AQ (Abramson et al., 1955a) focused primarily on the subjective somatic and perceptual experience, the LLQ was designed in order to measure a variety of perceptual, cognitive, affective, and somatic effects of LSD. A first collection of items relevant to affect, cognitive functioning, self and body image was used in a pilot study among research colleagues and subsequently adjusted on the basis of their experiences (Linton and Langs, 1962a). The questionnaire is comprised of 74 items and has a 17-dimensional structure including twelve major scales, four of which are further subdivided: (1) Difficulty in Thinking, (2) Disturbance of Time Sense, (3) Feeling Inhibited, Slowed Down, (4) Feeling of Loss of Control, (5) Ego-environment Relationship, (A) Closer to Environment, (B) Contact Loss, (C) Ego Change, Alienation, (6) Distortions of Visual Perception, (7) Feeling Less Inhibited, Opened Up, (8) Meaning Changes, (A) New Meaning Acquired, (B) Old Meaning Lost, (9) Feeling of Increased Functioning, (10) Suspiciousness, (11) Bodily Effects, (A) Body Image Change, (B) Somatic Symptoms, (12) Affect Changes, (A) Positive Affect, (B) Negative Affect. The scales were defined a priori and the assignment of items was performed based on their estimated relevance to the scales’ functional definition. Responses are given on a 3-point scale, ‘0’ indicated a negative answer, ‘0.5’ a partially positive and ‘1’ a positive answer. In an initial placebo controlled study, LSD was administered to a group of male professional actors. The questionnaire was administered seven times to also monitor the temporal course of the various drug effects (Linton and Langs, 1962a, 1962b): (1) pre-test day, (2) half an hour after drug administration, (3) two hours after drug administration, (4) five hours after drug administration, (5) eight hours after drug administration, (6) post-test day, (7) retrospective. The total questionnaire score, as well as the score for each scale separately, is computed by simply summing all responses. The LSD effects revealed five different temporal patterns with somatic effects being the earliest and distortion of visual perception having the latest onset. Based on factor analysis, four empirical scales were derived (Linton and Langs, 1964). These scales are termed A, B, C, D and comprise a heterogeneous collection of items. While the scale A contains items addressing impaired control of attention, loss of inhibition, elation, and the subjective feeling of the capacity to perceive new meanings, B includes items referring to the loss of contact to the environment, impaired sense of identity, feelings of having lost control over several function, and paranoid ideation. Items of scale C describe alterations in the body image, somatic symptoms as well as inhibitory mental and physical effects. Finally, scale D covers the dimensions of anxiety, fear of losing self-control, and somatic effects (Linton and Langs, 1964).
For the LLQ no state-of-the-art reliability and validity measures are available and the questionnaire was not further developed. In addition to the assessment of LSD effects (Linton and Langs, 1962a; Johnson, 1969), the LLQ was also used to compare these effects with symptoms of schizophrenia (Langs and Barr, 1968) and to investigate the effects induced by other hallucinogenic substances like tryptamine derivatives (Faillace et al., 1967). However, its application in recent research is quite limited. Particularly the absence of psychometric evaluation discards the LLQ as an adequate tool for cross-study comparisons.
According to Greyson (1983) near-death-experiences (NDE) are a critical marvel to examine, however no acknowledged criterion was established to quantify this phenomenon. Many studies in the past tried to find standard criteria to measure NDE but failed to construct reliable and valid instruments (Greyson, 1983). Greyson (1983) discusses an index known as the Weighted Core Experience Index (WCEI), which is based on 10 items to measure NDE, but does not conform to reliability or validity criteria. Moreover, the work of Noyes and colleagues is discussed (Greyson, 1983) who developed three clinically relevant factors, obtained from a sample of accident victims and from psychiatric patients. These factors are known as (1) depersonalization, (2) mental clouding, and (3) manifestation of mystical consciousness. The limitation that Noyes’ work rather assesses subjective responses to life threatening danger instead of NDE motivated the development of a new questionnaire. Greyson (1983) developed the NDE scale to differentiate organic brain syndromes from out-of-body experiences and NDEs. An initial collection of 80 items was divided into different clusters for (1) Affective States, (2) Thought Content, (3) Thought Processes, (4) Perceptual Content, (5) Perceptual Processing, (6) Bodily Sensation and (7) Miscellaneous. A preliminary 33-item questionnaire was developed including items from the WCEI and Noyes’ three factors. Statistical analysis off the data obtained from subjects with prior NDE reduced the questionnaire to sixteen items, which were assigned to one of four clusters: (1) Cognitive Component, (2) Affective Component, (3) Paranormal Component, or (4) Transcendental Component (Greyson, 1983). Items are rated on a 3-point scale (present, ambiguous/atypical, absent) and cluster as well as total score are computed as the sum of the items scores (Greyson, 1983).
The NDE full scale Cronbach alpha reliability was reported to be 0.88, while the split-half reliability was 0.92. In addition, test-retest reliability was approximated as 0.92 for the entire NDE scale, thus supporting internal consistency and stability, respectively. Greyson’s final 16-item questionnaire shows high correlations (r = 0.90) with Ring’s WCEI (Greyson, 1983).
The work of Hood (1975) can be seen as the starting point for the modern empirical study of mysticism based on the theoretical framework of W. T. Stace. Stace’s (1960) discussed characteristics for introvertive and extrovertive mysticism and describes characteristics of mystical experiences (Stace, 1960). While Stance had primarily focused on religious mystics, his analyses of mystical experiences have also been extended and applied in the context of states induced by pharmacological induction methods that were said to elicit mystical-type experiences. The Mysticism Scale (M-scale) was initially designed to measure lifetime occurrence of mystical experiences and not to quantify features of single mystical experiences. In a slightly revised version it has, however, also been applied for the assessment of single mystical experiences comparable to the Mystical Experiences Questionnaire (MEQ) (See (MacLean et al., 2012)). From an initial pool of 108 items, which were explicitly derived from Stace’s characteristics of mysticism, 32 items were selected. Items are rated on a 5-point scale (Hood, 1975). Always four items – two affirmative, two negating statements – are assigned to each of eight dimensions of mystical experiences: (1) Timelessness, (2) Ego-Loss, (3) Ineffability, (4) Inner subjectivity, (5) Unity – the experience of the world as a unified one, (6) Positive affect, (7) Sacredness, and (8) Noetic quality (Hood et al., 2001). Through factor analyses, three main empirical factors were identified that Hood relates to Stace’s common core thesis, formulated as “extrovertive and introvertive factors emerges separately” (Caird, 1988; Hood et al., 1993). The three factors, (1) Extrovertive Mysticism (2) Introvertive Mysticism, and (3) Religious Interpretation, were also confirmed in different cultural settings, and their relation to the original 8 scales is presented in Hood et al. (2001). According to this structure, scores on the M-Scale are computed for each of the three empirical factors as well as for the full scale and as a sum of item scores. As items in this version are rated on a 9-point scale, the score ranges from 32 to 288 (Hood et al., 2001). Hood also presented a modified version of the M-Scale (Hood, 1977) to assess a particular mystical experience (Further referred to as ‘single-experience M-Scale’). In this version, the verb tense is changed, e.g. ‘I have had an experience which I knew to be sacred’ to ‘I had an experience which I knew to be sacred’ (MacLean et al., 2012) When applied as single-experience M-Scale, Cronbach’s alpha reliability of the full scale (0.93) and individual factors (Extrovertive Mysticism = 0.88, Introvertive Mysticism = 0.84, and Interpretation = 0.86) were reported (MacLean et al., 2012). As the M-scale in its original form aims to quantify the occurrence of mystical experiences across a lifetime, it is not an instrument to assess acute states. Accordingly, it was mostly used in group studies to quantify the amount of such experiences, also in cross-cultural settings (Hood et al., 2001). The single-experience M-Scale could by contrast also be applied in work on the experimental induction of ASCs, however, data is rare (Griffiths et al., 2006; MacLean et al., 2012). In the empirical study of ASCs, the MEQ has found a broader application and the M-scale does not contribute much to comparability between studies.
The Personal Experience Questionnaire (PEQ) was designed by Ronald Shor to investigate the frequency and the intensity of ‘hypnotic-like’ experiences occurring in the ‘normal course of life’ (Shor, 1960). An initial long form of the PEQ consisted of 149 items (Shor et al., 1962) that was, however, reduced to 44 items for its latest version, also referred to as short form. The items address the appearance of particular experiences such as ‘thinking of nothing’ or, ‘staring into space’, to test for ASC phenomena such as absorption and dissociation. Besides the mere quantification of such events over a lifetime, it was also supposed to predict hypnotizability (Shor et al., 1962). The PEQ consists of 44 items describing ‘hypnotic-like’ experiences in everyday life. In a yes/no-response format, subjects are asked to report if they have ever had the requested experience. Only if the subject feels that a yes/no-response is inappropriate, additional information is supposed to be given in an open response format. Thereby, the questionnaire allows different ways to evaluate the data, e.g. Shor (1960) presented the frequency of natural occurrence.
Response consistency and internal consistency of the PEQ are reported to be high (0.90 to 0.96, p< 0.01, (Shor et al., 1966)). Based on data from London and colleagues (London et al., 1962), test-retest reliability was assessed over a 3-week interval resulting in a reliability coefficient of 0.94, p<0.01 (Shor et al., 1966). The PEQ did not find a major dissemination in the literature. It could however form a reference for the development of future studies aiming to establish the relationship between particular trait-personality scores (e.g. frequency of naturally occurring ASC phenomena) and the prediction of a response to a particular induction method for ASCs (e.g. hallucinogens or meditation).
The Assessment Schedule of Altered States of Consciousness (ASASC; original German: Erfassungssystem veränderter Bewusstseinszustände (EVB)) was developed in the context of a research project investigating the aftereffects of NDEs (van Quekelberghe et al., 1992). Whereas ASCs are sometimes described in relation to psychiatric disorders (See Epg Psychopahtology Inventory), van Quekelberghe and colleagues regard these phenomena as common everyday life experiences. As opposed to C. T. Tart’s definition of ASCs as “radically different” state (Tart, 1975), Ludwig’s broad definition as any “sufficient deviation in subjective experience” (Ludwig, 1966) was seen as accounting for this view and constitutes the theoretical basis of this questionnaire (van Quekelberghe et al., 1991). By providing a research tool that assesses recalled rather than currently experienced ASCs independent of stimulus and situation, it was intended to survey a wide range of different kinds of ASCs and related phenomena. Moreover, it was explicitly avoided to evaluate these experiences as pathological (van Quekelberghe et al., 1992). In contrast to questionnaires that assess the acute effects of a single experimentally induced ASC, the ASASC addresses frequency and intensity of induced and spontaneously occurring alterations of consciousness across a lifetime (van Quekelberghe et al., 1991). Although including a substantial amount of state-specific items, the ASASC primarily focuses on general dispositions, e.g. to imagination, absorption as well as the experience of parapsychological phenomena. Based on Ludwig’s theoretical framework, 14 a priori scales were defined: Personal data (F1) Demographic Data, (A2) Extraordinary Mental Processes, (P3) Parapsychology Experiences, (P4) Parapsychology Attitude, (E5) Esoterics, (M6) Positive Mystic Experiences, (M7) Negative Mystic Experiences, (I8) Imagination, (T9) Dreams, (D10) Dissociation, (H11) Hallucinations, (H12) Hypersensitiveness, (Z13) Changed Feeling of Time and Space, and (C14) Change. Factor analysis and subsequent adjustments finally led to a satisfactory grouping of items resulting in the 325-item ASASC (van Quekelberghe et al., 1992). A 128-item short form of the EVB is available (van Quekelberghe et al., 1992; Yeginer, 2000). An additional short form was developed by extension of the D10 and Z13 scale to provide a flexible, easily adaptable instrument (van Quekelberghe et al., 1991, 1992). Both the English version ASASC-D10 ERW and the German version EVB-D10 ERW include 60 items, which, however, are arranged in different order. The items are clustered in five a priori scales: (1) Suggestibility, (2) Trance, (3) Absorption, (4) Flow, (5) Dissociation (internal, external, body, person).
Initial evaluation of its psychometric features revealed good reliability with Cronbach’s alpha coefficients between 0.80 (E5) and 0.98 (M6). Guttman split-half coefficients ranged between 0.81 (E5, C14) and 0.96 (M6) (van Quekelberghe et al., 1991). The ASASC rather maps stable tendencies of imagination, absorption, and cognitive alterations and is, hence, suitable to assess the natural variability in the normal waking consciousness. However, its use for the assessment of experimentally induced ASCs is limited. Moreover, the reduced number of items in the 128-item short form, e.g. I8 comprises only 5 items, affects its reliability and thus the comparability to the 325-item version. Consequently, this questionnaire does not meet the requirements for a meta-analytical approach.
Literature review of both experimental and clinical reports indicates that the phenomenology of ASCs induced by the administration of classic hallucinogens potentially involves unpleasant experiences which might occur even in carefully prepared and supportive environments (Barrett et al., 2016). Based on three of the most frequently applied questionnaires – the HRS, the 5D-ASC, and the SOCQ – the Challenging Experience Questionnaire (CEQ) was designed to provide a tool for the comprehensive assessment of acute negative effects that will benefit research into their predictors and consequences (Barrett et al., 2016). The conceptual scope of the 26-item CEQ is informed by literature on psychological and physical distress following hallucinogen intake and covers a variety of adverse cognitive, affective, and somatic reactions which are clustered into seven distinct dimensions of challenging experiences: (1) Grief, (2) Fear, (3) Death, (4) Insanity, (5) Isolation, (6) Physical Distress, and (7) Paranoia (Barrett et al. 2017). Analyzing data from an online survey on negative experiences with psilocybin, corresponding scales for the first six dimension were derived by exploratory factor analysis, complemented by the Paranoia scale, and subsequently validated through confirmatory factor analysis (Barrett et al., 2016). Items are rated on a 6-point scale adopted from the SOCQ.
Since the CEQ was only recently developed, a systematic evaluation of its psychometric properties has not been conducted yet. However, confirmatory analyses performed on two separate samples revealed an acceptable model fit, suggesting internal validity of the CEQ model (Barrett et al., 2016). Reliability was assessed by Cronbach’s alpha, yielding good internal consistency estimates in the range of 0.65 (Paranoia) to 0.89 (Fear).
Similar to the PSI, the CEQ was designed as a single questionnaire focusing on acute negative effects. In contrast to the PSI, however, it covers a wide spectrum of aversive reactions that is not limited to effects typical of psychosis-like states. Moreover, the CEQ enables the fine-grained assessment of distinct dimensions and their relative intensity, thereby allowing for the generation of a multi-dimensional pattern description. Considering that the control of acute negative effects is desirable and that the subsequent integration of the experience is fundamental to therapeutic outcomes (Majic et al., 2015), the CEQ provides a valuable tool for further studies of adverse reactions to classic hallucinogens. To date, the CEQ was, however, only applied with psilocybin and not along with neuroimaging studies. Further research is, thus, required to demonstrate its sensitivity to other hallucinogens and suitability within neuroimaging studies. In advancing the vital understanding of underlying mechanisms that pinpoint stressful experiences, a translation of the CEQ, originally developed in English, into other languages will foster its application.
While it has become less common in the last decades to name a questionnaire according to a specific author, it appears that Rosalyn Watts wanted to have visibility for her last name. As this is uncommon we expect that many authors will choose to call the questionnaire simply “Connectedness Scale”. We will soon add a summary and assessment of this tool here.
This tool was developed to assess sub-acute effects, as they are commonly reported for 2-4 weeks after the use of psychedelics. The tool might become a new standard in clinical trials and might also find its application
The construction and validation was carried out in German and English, and both versions will be available upon publication soon. Until now the tool is available only upon request from Tomislav Majic (Charité Universitätsklinikum Berlin, Germany)
Besides the discussed above, please find some additional information and discussion of different Questionnaire tools in the following references:
In our research we found the following additional tools, which are worth to note. Some of them might be of historical interest and are not in use anymore, others are designed to assess very specific aspects of ASC experiences:
The information in this section were collected over multiple years and many people contributed in different ways. Within two study projects in 2017-18 within teaching activities in the MSc program Cognitive Science at the Institute for Cognitive Science at the University of Osnabrück inital information on questionnaires was collected. These study projects were led by Dr. Timo Torsten Schmidt together with Dr. Axel Kohler and Dr. Uwe Friese. After completion of these study projects, several students from different institutions contributed to the collection within internships, labrotations and similar research related activities. It was initially planned to publish an overview article and a corresponding manuscript was submitted to a journal. The editor of the journal advised to find a different format for publication and we agree that the accumulated collection of questionnaires (+corresponding background information) will be better accessible in a fully openly access format, which can regularily updated. We would like to thank and acknowledge the important contributions of the following people (some of them planned as authors on the intended research article): Katharina Dworatzyk, Ada Drochner, Michal Ljubljanac, Artur Czeszumski, Chiara Carrera, Aliona Cerednicenco, Aalia Nosheen, Philipp Kuhnke, Eelke de Vries, Hendrik Berkemeyer, Renato Garita Figueiredo, Nisha Jagannathan, J Jang, A Kesfhava, J Schott, O Vakhovska, MC Vargas Rivero, Ann Xavier (We hope that we did not forget anyone - otherwise please let us know). Further we would like to thank the following researchers for providing us with furhter information, discussion and feedback on this collection: Maja Maurer, Rick Strassman, Robin Carhart-Harris, Roland J Pekala, Eric Studerus, Frederick Barrett.
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