Dimensions of consciousness and the psychedelic state

Bayne and colleagues open by drawing a standard distinction in consciousness science between the 'contents of consciousness' (the particular things one is conscious of) and 'states of consciousness' (global conditions that shape which contents can appear and how they are used). They note that while contents are relatively well characterised, the notion of a conscious state is less settled and is often framed in terms of unidimensional "levels of consciousness"—a framing the authors question because it assumes all states can be placed on a single ordered scale. This paper sets out to examine how the psychedelic state, as induced by two serotonergic hallucinogens (psilocybin and LSD), bears on the prospect of treating conscious states as higher or lower relative to ordinary waking awareness. Focusing on subjective reports and psychophysical measures obtained in lab-based, peer-reviewed studies, Bayne and colleagues aim to determine whether psychedelic-induced changes support the idea of a single dimension of consciousness or instead favour a multidimensional conception. They organise the empirical literature into three domains—sensory/perceptual experience, cognitive function, and experiences relating to time, self and space—and use these to assess whether the psychedelic state can plausibly be described as "higher."

This article is a theoretical review constrained to laboratory-based empirical findings reported in peer-reviewed journals. Bayne and colleagues deliberately excluded neural and physiological data, concentrating instead on subjective questionnaires and psychophysical/behavioural measures that bear directly on what it is like to be in a given conscious state. For subjective effects the authors restricted their survey to studies employing the Altered States of Consciousness (ASC) rating scales (English or German OAV versions), citing the scale's validation and its broad use across psilocybin and LSD studies. They give particular weight to a clustering analysis of 327 individual psilocybin sessions that used the ASC instruments. Empirical results drawn from psychophysical paradigms include measures such as hue discrimination, pre-pulse inhibition (PPI), binocular rivalry, saccadic eye movements, temporal interval reproduction, and tasks probing memory, attention and speech production. The review is organised thematically rather than as a systematic review with explicit search dates or database lists; the extracted text does not report a formal search strategy, inclusion/exclusion criteria beyond the ASC restriction, or a quantitative meta-analytic method. Instead, the investigators synthesise consistent patterns across questionnaires and behavioural paradigms and group findings under three broad headings: sensory/perceptual experience, cognitive capacities, and experiences of unity (time, space, self).

Perceptual experience: Self-report data from ASC-based studies and the cluster analysis indicate strong increases in visual imagery under psychedelics, with two ASC factors—'Elementary Imagery' and 'Complex Imagery'—rating highly after psilocybin and LSD. Reports also indicate increased subjective salience or "changed meaning" of percepts and heightened colour vividness. However, objective psychophysical measures do not uniformly corroborate subjective claims of improved basic visual sensitivity. Laboratory tests found impairments in hue discrimination after psilocybin and LSD, and no evidence of increased sensitivity to contrast or brightness in at least one study. Bandwidth and perceptual gating: Multiple lines of behavioural evidence support an increase in the amount of sensory content reaching awareness. Psilocybin reduces pre-pulse inhibition (PPI), interpreted as lowered sensory gating. Binocular rivalry studies show longer periods of mixed percepts or incomplete suppression, and both psilocybin and LSD increase saccadic eye-movement frequency, which could raise sampling rate. An ASC item about everything "happening so fast" was more frequently endorsed after psilocybin. Together these findings point to increased perceptual intensity and permeability, even though basic sensory discriminations are sometimes impaired. Cognition: Across several domains, psychedelics are associated with impaired cognitive and behavioural control. The ASC clustering identifies an 'Impaired Control and Cognition' factor. Memory effects are mixed: some declarative tests and simple associative learning are spared, whereas tasks requiring mental control or manipulation (e.g. serial addition, reproducing passages, drawing) show deficits. Working-memory span measures (digit forwards/backwards) are often preserved, and spatial working-memory accuracy can be maintained despite slower reaction times. Attention and communication: Psychophysical studies report impairments in sustained, divided and covert orienting of attention under psilocybin, and early LSD reports document clear deficits in speech production including prolonged blocking of spontaneous speech in at least one subject. Creativity and abstract thought: Subjects commonly report novel insights and increased associative thinking; an ASC cluster labelled 'Insightfulness' captures these reports. Experimental work using semantic priming found increased indirect (remote) priming under psilocybin, interpreted as greater access to remote associations. However, multiple lines of evidence indicate impaired evaluative and abstract reasoning capacities—difficulty distinguishing important from unimportant details, a reduced ability to detect contradictions, impaired proverb comprehension, and 'flight of ideas' or tangential thought patterns. Thus, psychedelics appear to facilitate idea generation but to compromise the capacity to evaluate and integrate those ideas. Experiences of unity (time, space, self): Time perception is commonly distorted subjectively (reports of timelessness or "a touch of eternity"); objective interval reproduction and synchronization tasks show significant impairments for intervals longer than about 2–2.5 seconds. Self-related experience commonly features ego-dissolution, with ASC items indicating blurred boundaries between self and environment; lab studies have replicated ego-dissolution reports after psilocybin and LSD. By contrast, sensations of disembodiment—typical of dissociative anaesthetics—appear less prominent under psilocybin. At a basic perceptual level, psilocybin impairs integration and grouping mechanisms (e.g. detection of coherent motion, amodal completion), and synaesthesia-like cross-modal effects are reported. The authors note that whether these boundary changes count as improvements depends on contested metaphysical views, but they emphasise that boundary blurring is likely to undermine the organism's capacity for adaptive control.

Bayne and colleagues interpret the assembled evidence as weighing against a unidimensional 'levels of consciousness' account. They argue that the psychedelic state exhibits a complex pattern of dissociations—enhanced vividness, imagery and perceptual bandwidth on the one hand, and impaired attention, memory, communication and evaluative reasoning on the other—so it cannot be straightforwardly ranked as either higher or lower than ordinary waking awareness. The authors draw two main implications. First, proposals that psychedelics could be used to raise consciousness in patients with disorders of consciousness (DoC) are problematic, because psychedelic states do not uniformly restore the functional capacities that distinguish higher states from lower ones and may disrupt space, time and self representations crucial for behaviour. Second, prominent theories of consciousness must accommodate multidimensional state-structure. For Global Workspace Theory (GWT), the data challenge simplistic accounts that treat global availability as an all-or-none marker of consciousness; aspects of global availability may be preserved for some forms of control but not others. For Integrated Information Theory (IIT), the findings problematise the identification of a single scalar measure (phi) with the level of consciousness, given that conscious states dissociate across multiple functional axes. Positively, the authors suggest that psychedelic-induced patterns of association and dissociation provide valuable empirical constraints for developing a multidimensional state-space of consciousness. They pose empirical questions about why psychedelics enhance sensory vividness and bandwidth while impairing higher-level control and why they produce systematic unity effects across time, space and self. Methodologically, they recommend integrating subjective and behavioural measures with neural investigations to map these dimensions more precisely. Finally, Bayne and colleagues acknowledge limitations: their reliance on the ASC and similar measures provides a reliable but incomplete survey of psychedelic effects, and the available data do not permit a definitive determination of how many dimensions are required to characterise conscious states. They call for further empirical work to refine the dimensional structure of consciousness and to clarify what it would be like to occupy different conscious states.