The 5D-ASC scale was used in both studies to assess the overall peak alterations of consciousness. The 5D-ASC scale measures altered states of consciousness and contains 94 items (visual analog scales). The instrument consists of five subscales/dimensions (Dittrich 1998 (link)) and 11 lower-order scales (Studerus et al. 2010 (link)). The 5D-ASC dimension “Oceanic Boundlessness” (27 items) measures derealization and depersonalization associated with positive emotional states, ranging from heightened mood to euphoric exaltation. The corresponding lower-order scales include “experience of unity,” “spiritual experience,” “blissful state,” and “insightfulness.” The dimension “Anxious Ego Dissolution” (21 items) summarizes ego disintegration and loss of self-control phenomena associated with anxiety. The corresponding lower-order scales include “disembodiment,” “impaired control of cognition,” and “anxiety.” The dimension “Visionary Restructuralization” (18 items) consists of the lower-order scales “complex imagery,” “elementary imagery,” “audio-visual synesthesia,” and “changed meaning of percepts.” Two additional dimensions describe “Auditory Alterations” (15 items) and “Reduction of Vigilance” (12 items). The scale is well-validated and widely used to characterize the subjective effects of various psychedelic drugs (Carhart-Harris et al. 2016b (link); Hasler et al. 2004 (link); Hysek et al. 2011 (link); Schmid et al. 2015 (link); Vollenweider et al. 2007 (link); Vollenweider and Kometer 2010 (link)). In addition to the subscale analyses, we also analyzed the effects on ego dissolution item 71 (the boundaries between myself and my surroundings seemed to blur) because the concept of ego dissolution was often used in recent imaging studies (Tagliazucchi et al. 2016 (link)). The 5D-ASC scale was administered 24 h after drug administration, and the participants were asked to retrospectively rate the drug effects. 5D-ASC ratings were also performed at 3 and 10 h in study 1.
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