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‘Extra-pharmacological’ factors that can determine psychedelic drug effects (Carhart-Harris and Nutt, 2017). “Trait factors may be biological [e.g., receptor polymorphisms (Ott, 2007)] or psychological in nature [e.g., personality (MacLean et al., 2011) or suggestibility (Carhart-Harris et al., 2015)]. The pre-state refers to such things as anticipatory anxiety, expectations and assumptions (which account for so-called ‘placebo’ and ‘nocebo’ effects), and readiness to surrender resistances and ‘let go’ to the drug effects (e.g., see Russ and Elliott, 2017). In the context of psychedelic research, the pre-state is traditionally referred to as the ‘set’ (Hartogsohn, 2016). State refers to the acute subjective and biological quality of the drug experience and may be measured via subjective rating scales or brain imaging (see Roseman et al., 2017). Dose relates to the drug dosage—which may be a critical determinant of state (Griffiths et al., 2011; Nour et al., 2016)—as well as long-term outcomes (see Roseman et al., 2017). Environment relates to the various environmental influences. In the context of psychedelic research this is traditionally referred to as ‘setting’ (Hartogsohn, 2016). We recognize that the environment can be influential at all stages of the process of change associated with drug action. The long-term outcomes may include such things as symptoms of a specific psychiatric condition such as depression—measured using a standard rating scale (Carhart-Harris et al., 2016a) as well as relatively pathology-independent factors such as personality (MacLean et al., 2011) and outlook” (Carhart-Harris and Nutt, 2017, p. 1097).

‘Extra-pharmacological’ factors that can determine psychedelic drug effects (Carhart-Harris and Nutt, 2017). “Trait factors may be biological [e.g., receptor polymorphisms (Ott, 2007)] or psychological in nature [e.g., personality (MacLean et al., 2011) or suggestibility (Carhart-Harris et al., 2015)]. The pre-state refers to such things as anticipatory anxiety, expectations and assumptions (which account for so-called ‘placebo’ and ‘nocebo’ effects), and readiness to surrender resistances and ‘let go’ to the drug effects (e.g., see Russ and Elliott, 2017). In the context of psychedelic research, the pre-state is traditionally referred to as the ‘set’ (Hartogsohn, 2016). State refers to the acute subjective and biological quality of the drug experience and may be measured via subjective rating scales or brain imaging (see Roseman et al., 2017). Dose relates to the drug dosage—which may be a critical determinant of state (Griffiths et al., 2011; Nour et al., 2016)—as well as long-term outcomes (see Roseman et al., 2017). Environment relates to the various environmental influences. In the context of psychedelic research this is traditionally referred to as ‘setting’ (Hartogsohn, 2016). We recognize that the environment can be influential at all stages of the process of change associated with drug action. The long-term outcomes may include such things as symptoms of a specific psychiatric condition such as depression—measured using a standard rating scale (Carhart-Harris et al., 2016a) as well as relatively pathology-independent factors such as personality (MacLean et al., 2011) and outlook” (Carhart-Harris and Nutt, 2017, p. 1097).

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How do psychedelic drugs produce their characteristic range of acute effects in perception, emotion, cognition, and sense of self? How do these effects relate to the clinical efficacy of psychedelic-assisted therapies? Efforts to understand psychedelic phenomena date back more than a century in Western science. In this article I review theories of...

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... Psilocybin appears to impact only select visual processes, while others are left intact [e.g., impairing global but not local motion detection; Carter et al. (2004); Kometer, Cahn, Andel, Carter, & Vollenweider (2011); Carbonaro et al. (2018); Aday et al. (2021)]. The phenomenology of psilocybin's visual effects can include alterations in the appearance of textures, the shapes/sizes of objects, motion, and colors-the visual field can take on a kind of fluidity, exhibiting animated dynamics described as pulsing, glowing, breathing, shifting, and dancing (Swanson, 2018). Given this visual phenomenology, it is plausible that center-surround interactions are in some way impacted by psilocybin, as surround suppression plays a critical role in certain visual processes (Angelucci et al., 2017;Nurminen & Angelucci, 2014), including visual saliency and pop-out (Knierim & van Essen, 1992), perception of object boundaries (Nothdurft, Gallant, & Van Essen, 2000), perceptual constancies (Allman, Miezin, & McGuinness, 1985), figure-ground segmentation (Lamme, 1995;Supèr, Romeo, & Keil, 2010), contour integration (Field, Hayes, & Hess, 1993;Hess & Field, 1999;Kapadia, Ito, Gilbert, & Westheimer, 1995;Polat, Mizobe, Pettet, Kasamatsu, & Norcia, 1998), and motion detection (Jones, Grieve, Wang, & Sillito, 2001). ...
... Despite its therapeutic promise, psilocybin's subjective effects have paradoxically (Osmond & Smythies, 1952) been characterized as "a schizophrenialike psychosis" (Vollenweider et al., 1998, p. 3897). This claim has remained controversial for nearly a century (Swanson, 2018) and has been called into question by recent studies (Leptourgos et al., 2020). Multiple investigations have found weakened visual surround suppression in people with schizophrenia compared with healthy controls (Dakin, Carlin, & Hemsley, 2005;Linares et al., 2020;Pokorny, Lano, Schallmo, Olman, & Sponheim, 2019;Schallmo, Sponheim, & Olman, 2015;Serrano-Pedraza et al., 2014;Tadin et al., 2006;Tibber et al., 2013;Yang et al., 2012;Yoon et al., 2009). ...
... Psilocybin's visual effects have previously been cited as points of similarity with early stages of acute psychosis (Vollenweider et al., 1998, p. 3897). Our results appear to be at odds with this and other long-held assumptions that psychedelic drug effects "mimic" psychosis in schizophrenia; assumptions that have been used to justify the "model psychoses" theories that began in the late 1800s and to classify the drugs as psychotomimetic (Swanson, 2018). In line with conclusions from recent comparisons (Leptourgos et al., 2020), our findings suggest caution is warranted when comparing psilocybin's visual phenomenology to that of schizophrenic psychosis. ...
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... These drugs are termed classic psychedelics and produce similar subjective effects yet vary widely depending on the dose. For example, at a low dose, psychedelics have been shown to evoke subtle intensification in sensory perception or at high doses, they may completely dissolve all sense of time, space and self (Swanson 2018). Aside from dosage, set and setting may account for this diversity of subjective effects (e.g. the mood of the individual and the environment in which the drug is taken). ...
Chapter
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... An increasingly common way to account for ordinary visual perception is to appeal to predictive processing (Clark, 2013(Clark, , 2016Friston, 2005Friston, , 2009Friston, , 2010Hohwy, 2012Hohwy, , 2013. Advocates of the Predictive Processing (PP) framework have recently suggested that this framework can be extended to account for psychedelic experiences caused by classical hallucinogens such as LSD, psilocybin, and mescaline (Carhart-Harris & Friston, 2019;Pink-Hashkes, 2017;Swanson, 2018). This chapter presents findings indicating that psilocybininduced visual distortions and impaired executive functioning originate in temporary disruptions of attentional mechanisms; it is then argued on the basis of these findings that the PP framework is unable to support a unified account of psychedelic experiences. ...
... In recent years, advocates of PP accounts of cognitive and neural processing have argued that the PP framework can offer a unified account of the psychedelic effects of classic hallucinogens, such as LSD, psilocybin, and mescaline (Carhart-Harris & Friston, 2019;Pink-Hashkes et al., 2017;Swanson, 2018). We are highly sceptical of this claim, and address one of the specific PP proposals below. ...
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A recent wave of research in psychiatry and neuroscience has re-examined the properties of ‘classic’ psychedelic substances—also known as serotonergic hallucinogens—such as psilocybin, lysergic acid diethylamide (LSD), and N,N-dimethyltryptamine (DMT). Evidence to date suggests that psychedelics can be given safely in controlled conditions, at moderate to high doses, and may have potential as therapeutic agents in the treatment of various addictive and mood disorders. The main mechanism of action appears to be the induction of a dramatically altered state of consciousness, but the details of how psychedelic-assisted psychotherapy works are hotly debated, as are the relations between psychedelic experiences themselves and the neural changes induced by the drugs. The chapters collected in this volume address the fascinating philosophical questions raised by the renewed psychiatric use of psychedelics. The topics of these chapters cluster around three main themes, in terms of which the volume is organized. Chapters in Section One, ‘Self and Mind’, ask: what can we learn about the self and the mind from psychedelic science? Chapters in Section Two, ‘Science and Psychiatry’, address methodological, theoretical, and clinical questions concerning how psychedelics can best be studied scientifically and used therapeutically, and how they might work to relieve psychiatric suffering. Finally, chapters in Section Three, ‘Ethics and Spirituality’, address broader questions about the interpretation of psychedelic experience, its ethical implications, and its possible role(s) in the broader culture.
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... Early psychedelic experiments were also conducted on unwilling participants at times, namely BIPOC who were incarcerated, and people who were hospitalized for mental health reasons, with some researchers irresponsibly administering extremely high doses of LSD to participants in inappropriate set and settings (Dore et al., 2019;La Torre et al., 2023;Strauss et al., 2022). Additionally, it was during this time that psychedelics were modeled as 'psychotomimetic', or drugs that mimicked psychotic symptoms in users, which in turn led to the idea that individuals with histories of psychosis may experience symptomatic exacerbation as a result of psychedelic drug administration (Swanson, 2018). Campaigns and propaganda from the War on Drugs however may have held the most significance in preventing the scientific pursuit of exploring psychedelic therapy for individuals with psychotic disorders by promoting the notion that drugs such as LSD are dangerous and cause people to go "insane" (Carhart-Harris & Goodwin, 2017;Dyck, 2008;Friesen, 2022). ...
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... Individual experiences often reflect personal history and symbolism [26,36,40]. The intensity and nature of these psychological effects vary widely based on factors like dosage, setting, and support [41]. ...
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... Este género, perteneciente a la familia Hymenogastraceae, ha cobrado una relevancia sustancial en el estudio de los hongos alucinógenos, siendo un enfoque fundamental para dilucidar la naturaleza y la evolución de la consciencia humana (Rodriguez Arce y Winkelman, 2021). Estos hongos, a lo largo de la historia, han ocupado un lugar destacado en las tradiciones chamánicas debido a su capacidad para provocar profundos cambios en los estados de consciencia (Swanson, 2018). El estudio específico de especies dentro del género Psilocybe ha permitido adentrarse en los mecanismos bioquímicos y psicológicos detrás de las alteraciones en la consciencia humana (Bradshaw et al., 2024). ...
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... This could be because having others around simply confers a sense of safety or ability to partially opt out of the experience should it become too challenging. This is consistent with the fact that controlled settings are important components in producing subjective effects (Carhart-Harris et al., 2018), and the importance of support, guidance, and stability (Swanson, 2018). ...
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Psychedelic experiences can be highly impactful for people's lives, thought to be underpinned by internal and external factors known as "set" and "setting". However, there is limited understanding of how aspects of set and setting differ in discrete parts of psychedelic experiences, from before, during, and after consumption. We leveraged reflexive thematic analysis to generate themes of psychedelic experiences before, during, and after naturalistic psychedelic experiences. Using a combined inductive-deductive approach under an experientialist realist framework, we constructed themes present at each of these timepoints. Generated themes were theoretically underpinned by the set and setting framework, which informed the deductive aspect of theme generation. Generated themes prior to experience were 1) subjective knowledge and perception of psychedelics, 2) intention and efforts to mentally prepare, and 3) experiential aids. Created themes during the experience were 1) sensory and cognitive distortions, 2) mindset and affective quality, and 3) environmental stability and support. Experiential impact emerged as the unitary theme following the experience. We outline the importance of these findings for development and reification of integrative practice and harm reduction frameworks. 3
... The filtration theory of cognition popularized by Aldous Huxley (1954) in The Doors of Perception and Heaven and Hell (after Henri Bergson and C. D. Broad; see Webb, 2023) states that the human brain filters out tremendous amounts of data to avoid an information overload that would be evolutionarily maladaptive (for contemporary accounts, see Kelly et al., 2007;Kripal, 2019); think, for example, of the tiny sliver (.0,0035%) of the electromagnetic spectrum visible to the human eye (Sliney, 2016). Interestingly, contemporary neuroscience has established that entheogens such as LSD inhibit the thalamus's gating function while increasing connectivity from cortex to thalamus, thereby allowing a greater inflow of sensory data than is ordinarily available (e.g., Bedford et al., 2023;Preller et al., 2019;Swanson, 2018). 17 Based on these findings, I hypothesize that most spiritual states/visions may emerge from the interaction between the reduction of brain filtering mechanisms that is arguably also facilitated by sustained contemplative or spiritual practice, on the one hand, and a constructive, top-down Ferrer "empowered imagination" (Hollenback, 1996; see also Wolfson, 1994) shaped by a plethora of contextual, conceptual, and doctrinal variables (e.g., Katz, 2004;Klein, 1986) on the other. ...
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This paper provides an assessment and clarification of the metaphysical status of the participatory approach to transpersonal and spiritual phenomena (Ferrer, 2002, 2017a). To that end, I first respond to several criticisms of the approach issued by scholars in recent years; for instance, that it hides a perennialist metaphysics (e.g., Abramson, 2015) or that it is metaphysically vague (e.g., Taylor, 2021). After reviewing these critical discussions, I describe the open and minimalist nature of the participatory metaphysics, arguing that such features cultivate a fertile soil for transpersonal scholarship, human flourishing, and interreligious relations. Applying a biomimetic approach, I argue that spiritual pluralism can be better understood—and more positively appreciated—when seen as an expression of life’s diversification. In this spirit, I suggest that rhizomatic, treelike images are helpful to visualize not only religious traditions’ differences and similarities, but also the problems of neo-perennialist and essentialist accounts of spirituality. I conclude with a vindication of the eminently pragmatist, edifying, and transformative nature of the participatory approach.