Effects of psilocybin on feelings of awe
The descriptives for feelings of awe in the different experimental conditions are presented in Table 2. In line with our preregistered H1awe, we observed a main effect of Video, F(2, 58) = 94.144, p < 0.001, η2 = 0.765, indicating that our experimental manipulation was successful and that awe videos induced stronger feelings of awe than positive and control videos (see Fig. 2). Also H2awe was confirmed: we found a main effect of Condition, F(1, 29) = 8.309, p = 0.007, η2 = 0.223, reflecting that participants felt more awe in the microdosing compared to the placebo condition (see Fig. 2).
In line with our H3awe, we found a marginally interaction between Condition and Session: F(1, 29) = 4.934, p = 0.034, η2 = 0.145, which was further qualified by a three-way interaction between Condition, Session, and Video, F(2, 58) = 3.308, p = 0.044, η2 = 0.102. However, this effect did not survive correction for multiple comparisons.
To test our H4awe we included block order as an additional between-subjects factor in our statistical design. Indeed, in line with our expectations we found an interaction between Block Order, Condition, and Video, F(2, 56) = 3.950, p = 0.025, η2 = 0.004. As can be seen in Fig. 2, this interaction reflected that participants felt more awe in the psilocybin condition to positive and neutral videos, but only in the first block, but not during the second block of the experiment. We also found a significant interaction between Block Order, Condition, and Session, F(1, 28) = 10.502, p = 0.003, η2 = 0.010. This interaction reflected that feelings of awe were only affected by psilocybin in the first session of the first block, whereas in the other experimental sessions, there was no effect of psilocybin microdosing on awe (see Fig. 2).
To test H5awe we included absorption as a covariate in the analysis. In line with our predictions, we found a main effect of Absorption, F(1, 28) = 18.36, p < 0.001, η2 = 0.396, reflecting that high absorption participants overall reported stronger feelings of awe. However, in contrast to our second prediction, absorption did not interact with Condition (F(1,28) = 0.92, p = 0.346, η2 = 0.002).
Effects of psilocybin on body size estimation
The descriptives for body size estimation in the different experimental conditions are presented in Table 3. The same confirmatory hypotheses as conducted for the awe ratings were conducted for the body-perception measures. In contrast to our H1awe we did not find that awe videos resulted in smaller body size estimates (F(2,58) = 0.118, p = 0.889). We also found no evidence for H2awe: psilocybin microdosing did not decrease body size estimates (F(1, 29) = 0.766, p = 0.389). We found partial evidence for H3awe: the interaction between Condition and Session was significant, F(1,29) = 11.382, p = 0.002, η2 = 0.022; this interaction reflected that participants tended to overestimate the size of their body in the psilocybin microdosing condition in the second compared to the first block, although the post-hoc tests were not significant (see Fig. 2). In line with H4awe we found a significant interaction between Video, Condition, and Block Order, F(2,56) = 4.805, p = 0.012, η2 = 0.010. In contrast to our predictions however, this interaction reflected that participants tended to overestimate the size of their body in the psilocybin compared to the placebo condition to neutral videos in the first block, but not in the second block (see Fig. 2). Including absorption as covariate, as specified in H5awe did not show the expected main effect (F(1,28) = 2.190, p = 0.150) and moderation effect of absorption on body size perception (F(2,56) = 0.030, p = 0.970).
Effects of psilocybin on positive aesthetic experiences
The descriptives for positive aesthetic experiences in the different experimental conditions are presented in Table 4. In contrast to H1art, psilocybin microdosing did not affect positive aesthetic experiences (F(1,27) = 2.542, p = 0.122). In contrast to H2art we also did not observe an interaction between Condition and Session (F(1,27) = 3.467, p = 0.074), nor between Condition and Block Order (F(1, 26) = 0.15, p = 0.702). Including Absorption as a covariate in the analysis revealed the hypothesized (H3art) main effect of Absorption, F(1, 26) = 7.651, p = 0.010: high absorption participants experienced more positive emotions to artworks. However, in contrast to the other sub-hypothesis of H3art, Absorption did not interact with our psilocybin manipulation (F(1,26) = 0.063, p = 0.804). We found a main effect of painter, F(3, 81) = 15.011, p < 0.001, η2 = 0.357, indicating that participants felt strongest positive aesthetic feelings in response to paintings by Kandinsky and least strong feelings in response to works by de Kooning (see Fig. 3). No other significant effects were observed.
Effects of psilocybin on negative aesthetic experiences
The descriptives for negative aesthetic experiences in the different experimental conditions are presented in Table 5. In contrast to H1art no main effect of Condition was found, F(1,27) = 2.337, p = 0.138. H2art could also not be confirmed: the interaction between Condition and Session was not significant, F(1,27) = 0.016, p = 0.899, and neither was the interaction between Condition and Block Order, F(1,26) = 3.662, p = 0.067. Finally, in line with H3art we found a main effect of Absorption, F(1,26) = 7.915, p = 0.009, reflecting that high absorption participants also experienced more negative aesthetic emotions in response to artworks.
Following each block participants were asked to guess whether they had been assigned to the microdosing or the placebo condition in the preceding weeks. They could respond by indicating “yes,” “no,” or “maybe” in response to the question “In the past few weeks, do you think you were taking an active microdose?.” A Chi2 analysis of the contingency table indicated that participants were breaking blind, both following the first block, Chi2(2) = 10.90, p = 0.004 (i.e., 20 out of 30 correctly guessed their condition), and following the second block, Chi2(2) = 13.93, p < 0.001 (23 out of 30 correctly guessed their condition; see Table 6).
Effect of expectations
In order to investigate to what extent participants’ prior expectations could affect the effects we observed of psilocybin microdosing on feelings of awe, we included expectations as measured prior to blocks 1 and 2 as an additional covariate in the analysis. We thus conducted a similar repeated measures ANOVA as described above, with a Condition (psilocybin vs. placebo) ∗ Session (Session1 vs. Session2) ∗ Video (awe, positive, neutral) design, with “expectations” as an additional covariate.
When prior expectations in block 1 were included as covariate, the main effect of Condition was no longer significant (F = 0.086, p = 0.772). A main effect of expectations, F(1,28) = 4.80, p = 0.037, η2 = 0.146, indicated that participants with stronger expectations experienced more profound feelings of awe. The same pattern emerged when including expectations prior to the second block as covariate, also rendering the effect of Condition mute (F = 0.266, p = 0.610), while the main effect of expectations was significant, F(1,28) = 9.210, p = 0.005, η2 = 0.248.
In a post-hoc analysis we decided to provide a more in-depth analysis of the expectations that people reported. Participants’ expectations prior to each block are represented in Fig. 3. As can be seen, the expectations were comparable prior to both blocks; only the expectation to experience more thrill was lower following the first block, t(29) = 3.22, p = 0.003. The strongest expectations regarding microdosing were to experience increased flow and creativity, while participants had lower expectations regarding the effects on fear, sleep, and addiction.