Current Biology
June 1, 2005
Olivia Carter, David E. Presti, C. Callistemon et al.
262 citations
Tibetan Buddhist monks with extensive meditative training can voluntarily alter the normal fluctuations in conscious awareness that occur during perceptual rivalry tasks such as binocular rivalry and motion-induced blindness. In binocular rivalry, a one-point meditation that focuses attention on a single object led to extreme increases in the duration of perceptual dominance, with some monks reporting complete perceptual stability for up to five minutes. In contrast, compassion meditation had no observable effect on rivalry rate. During motion-induced blindness, monks reported longer disappearance durations than meditation-naive individuals, and one highly experienced monk could sustain the disappearance of a visual target for over 12 minutes. These results suggest that intense attentional focus, rather than meditation per se, can modulate the neural mechanisms underlying conscious visual perception.
Journal of Psychopharmacology
May 20, 2006
Marc Wittmann, Olivia Carter, Felix Hasler et al.
245 citations
Psilocybin impairs the ability to reproduce time intervals longer than 2.5 seconds, to synchronize movements to beats longer than 2 seconds, and slows preferred tapping rate. These objective timing deficits are accompanied by working-memory impairments and subjective changes including depersonalization and derealization. The findings indicate the serotonin system is selectively involved in processing durations longer than 2–3 seconds and in voluntary movement speed control. The disruption of longer intervals likely results from interactions with cognitive dimensions of temporal processing via 5-HT2A receptor stimulation.
Journal of Cognitive Neuroscience
October 1, 2005
Olivia Carter, David C. Burr, John D. Pettigrew et al.
236 citations
A hallucinogenic drug that activates serotonin receptors, psilocybin, impaired healthy volunteers' ability to track moving objects but did not affect their spatial working memory. Blocking the 5-HT2A receptor with ketanserin before psilocybin did not prevent this attentional deficit, pointing to the 5-HT1A receptor as the likely cause. The authors suggest the impairment may stem from a reduced ability to filter out distractions rather than a loss of attentional capacity. Eight participants completed both tasks under placebo, psilocybin, ketanserin, and the combination.
Perception
March 1, 2003
Olivia Carter, John D. Pettigrew
171 citations
Perceptual rivalry causes conscious experience to oscillate even when sensory input stays constant. The neural site of binocular rivalry, a well-known form, remains debated, with different cortical regions implicated. This work shows that the temporal pattern of disappearances and reappearances in motion-induced blindness (MIB) closely correlates with binocular rivalry patterns within the same individual, across wide inter-individual variation. The hallucinogen LSD increases rhythmicity in both phenomena identically. MIB also shares two hallmark properties of binocular rivalry: dominance periods approximate a gamma distribution, and increasing one perceptual phase's predominance reduces the opposing phase's time, consistent with Levelt's second proposition. The authors conclude MIB is a form of perceptual rivalry and that a common oscillator may time all such oscillations.
Neuroscience of Consciousness
January 1, 2018
Tim Bayne, Olivia Carter
153 citations
The popular and academic claim that the psychedelic state is a 'higher' state of consciousness is critically examined. The article distinguishes between conscious contents and global states, reviewing lab-based findings on psilocybin and LSD. While some aspects of consciousness are enhanced, many functional capacities are seriously compromised. The authors argue that because psychedelics affect different dimensions of consciousness in opposing ways, the unidimensional 'level-based' view of consciousness is unsupported; instead, a multidimensional conception is strongly supported. The analysis also considers implications for Global Workspace Theory and Integrated Information Theory.
Psychopharmacology
September 13, 2007
Olivia Carter, Felix Hasler, John D. Pettigrew et al.
150 citations
Binocular rivalry, where each eye sees a different image and perception alternates between them, was slowed by psilocybin (215 µg/kg) in ten healthy adults. Pretreatment with ketanserin (50 mg), a 5-HT2A receptor blocker, prevented most of psilocybin's hallucinogenic symptoms but did not reverse the slowing of rivalry switching or the drug's negative-type symptoms such as reduced arousal and vigilance. These findings link slower binocular rivalry switching to subjective levels of arousal and attention, and suggest that psilocybin's effect on rivalry is not mediated by the 5-HT2A receptor.
Neuropsychopharmacology
January 26, 2005
Olivia Carter, John D. Pettigrew, Felix Hasler et al.
122 citations
Binocular rivalry, where each eye sees a different image and perception alternates between them, is influenced by psilocybin. In 12 healthy volunteers, both low (115 µg/kg) and high (250 µg/kg) doses of psilocybin significantly reduced the rate and rhythmicity of perceptual alternations 90 minutes after administration, compared to placebo. Over time, switch rates increased, with some exceeding pretest levels at 360 minutes, though mean phase duration did not significantly differ from placebo. Drug-induced changes in rivalry phase durations corresponded to altered states of consciousness measured by the 5D-ASC scale. The findings implicate serotonergic pathways and support a brainstem oscillator's role in perceptual rivalry and psychosis symptoms.
Journal of Research in Personality
March 21, 2017
Anna Antinori, Olivia Carter, Luke D. Smillie
112 citations
People high in openness to experience tend to have more flexible and inclusive cognition, and this extends to basic visual perception. In two studies using binocular rivalry—where the brain alternates between competing perceptual images—openness was positively associated with longer durations of mixed percept, a state where neither image is fully suppressed. Study 1 ruled out response bias as an explanation. Study 2 found that a positive mood induction increased mixed percept duration, especially for open individuals. The results indicate that openness is linked to differences in low-level visual perceptual experience, possibly driven by common neural processes.
Biological Psychiatry
December 4, 2010
Michael Kometer, B. Rael Cahn, David Andel et al.
101 citations
The hallucinogenic compound psilocybin, which activates 5-HT2A/1A serotonin receptors, alters how the brain processes visual information. In a placebo-controlled experiment with 17 healthy volunteers, psilocybin dose-dependently reduced the N170 brain response, especially when viewing incomplete object figures, while slightly enhancing the P1 component over occipital areas. The reduction in N170-related brain activity in the right extrastriate and posterior parietal regions correlated with the intensity of visual hallucinations. These findings point to a central role of 5-HT2A/1A receptors in visual processing and suggest that a diminished N170 response may be a key mechanism underlying visual hallucinations.
Science
January 25, 2018
Olivia Carter, Jakob Hohwy, Jeroen J. A. van Boxtel et al.
86 citations
A commentary argues that Dehaene et al.'s review on consciousness and machines asks and answers the wrong questions, implying that their conclusions about not being on the verge of creating conscious machines may be premature or misdirected.
Neuroreport
August 1, 2004
Olivia Carter, John D. Pettigrew, David C. Burr et al.
83 citations
The hallucinogenic drug psilocybin, which activates serotonin receptors, selectively impairs the ability to perceive coherent motion in random dot patterns, a task that relies on high-level global motion detectors, while leaving contrast sensitivity for drifting gratings, mediated by low-level detectors, unaffected. This pattern of visual processing deficits mirrors those seen in schizophrenia, suggesting psilocybin may serve as a pharmacological model for studying psychosis and the neural basis of visual perception.
Australian & New Zealand Journal of Psychiatry
March 21, 2021
Daniel Perkins, Jerome Sarris, Susan L. Rossell et al.
53 citations
Psychedelic substances such as psilocybin, ayahuasca, LSD, and MDMA are gaining renewed medical interest due to the need for new psychiatric treatments and promising study results. This viewpoint reflects on the Royal Australian and New Zealand College of Psychiatrists' Clinical Memorandum on Psychedelics and notes regulatory developments, including applications for down-scheduling and access approvals. The authors argue that rigorous research is needed to assess benefits, safety, and therapeutic mechanisms. They summarize recent findings on mechanisms of action and the psychedelic-assisted psychotherapy model, suggesting medicinal psychedelics could become a new class of psychiatric treatments when used under medical supervision with psychotherapeutic support. However, sufficiently powered trials and safety protocols are required before clinical use, and untrained practitioner access could be harmful.
Neuropsychopharmacology
April 23, 2024
Julia Colcott, Olivia Carter, Sally Meikle et al.
37 citations
A comprehensive systematic review and meta-analysis of 13 studies found that MDMA-assisted psychotherapy (MDMA-AP) is associated with increased odds of side effects compared to control conditions. In Phase 2 trials, MDMA-AP roughly doubled the odds of any side effect during medication sessions and in the following week. In Phase 3 trials, the odds of any adverse event during treatment were about 3.5 times higher with MDMA-AP than with placebo-assisted psychotherapy. Most side effects were transient and mild or moderate. However, the evidence had very low to moderate certainty, most trials had high risk of bias, and none adequately followed CONSORT Harms 2022 reporting guidelines, highlighting the need for further safety research.
The Journal of Comparative Neurology
May 3, 2020
Olivia Carter, Bruno van Swinderen, David A. Leopold et al.
29 citations
Multistable perception—where sensory ambiguity causes spontaneous alternations between two or more perceptual interpretations—occurs across many animal species. This review covers research on visual perceptual rivalry in insects, fish, reptiles, and primates, highlighting binocular rivalry and the Necker cube as examples. Common behavioral indicators of perceptual alternation appear across species. The comparative approach offers insights into how brains suppress conflicting sensory signals and generate shifts in perceptual dominance, suggesting that ambiguous sensation is a fundamental problem that has shaped brain evolution.
Schizophrenia Bulletin
December 7, 2020
Ilvana Dzafic, Kit Melissa Larsen, Hayley Darke et al.
26 citations
People with schizophrenia have reduced neural prediction-error signals (mismatch negativity in stable contexts, P300 in volatile contexts) that are specific to the schizophrenia spectrum, whereas altered brain connectivity—decreased intrinsic connectivity in the left primary auditory cortex and right inferior frontal gyrus (IFG), reduced bottom-up and increased top-down frontotemporal connectivity—occurs across all participants as psychotic experiences intensify. Impaired sensory learning behavior was linked to lower intrinsic connectivity in the IFG, which also decreased with greater severity of psychotic experiences. The findings suggest that distinct neural mechanisms underlie schizophrenia-specific deficits versus general psychosis-related connectivity changes.
Behavioral and Brain Sciences
January 1, 2016
Piers D. L. Howe, Olivia Carter
26 citations
Perception can be actively shaped by top-down processes such as prior knowledge and expectations, not merely influenced by them. Two clear examples—hallucinations and mental imagery—demonstrate this, and importantly, both avoid the six confounds that Firestone and Scholl previously argued undermined claims of top-down effects on perception. This suggests that top-down influences on perception are real and not artifacts of experimental design.
Frontiers in Psychology
July 8, 2020
Toby J. Woods, Jennifer Windt, Olivia Carter
25 citations
Expert texts on Shamatha, Transcendental, and Stillness Meditation describe silence/quietness as a key feature of contentless experiences—states where thoughts, perceptions, and mental images are absent. Using evidence synthesis, 135 expert texts were systematically selected and analyzed. Silence/quietness is closely linked to stillness, absence of concepts, mental activity/noise, thoughts, and disturbance. It may also reflect absence of non-auditory perceptions, mental images, and negative feelings, fitting a conception of complete calm. The texts do not clearly distinguish silence/quietness from other features like stillness. Connections between silence/quietness and other features vary in closeness, revealing fine distinctions and ambiguities that raise new research questions.
The International Journal of Neuropsychopharmacology
February 8, 2017
Alexander Bryson, Olivia Carter, Trevor R. Norman et al.
19 citations
Functional neurological disorders are common, have poor outcomes, and few treatments exist. Their cause is unknown, but leading theories suggest a disturbance in how the mind represents the body, with abnormal top-down cognitive influences on sensorimotor function despite intact neural pathways. Recent studies indicate that 5-HT2A agonists, such as psychedelics, alter brain activity in ways that disrupt hierarchical dynamics and modulate networks involved in self-processing. Converging evidence suggests these agents may hold unique therapeutic potential for these disorders. Given the personal and societal burden, the authors argue a clinical trial to test this hypothesis is warranted.
Australian & New Zealand Journal of Psychiatry
September 28, 2023
Sally Meikle, Olivia Carter, Gillinder Bedi
18 citations
No Summary
Phenomenology and the Cognitive Sciences
May 24, 2022
Toby J. Woods, Jennifer Windt, Olivia Carter
17 citations
Meditation experiences often described as contentless—such as those in Shamatha, Transcendental, and Stillness Meditation—are not truly devoid of mental content. A review of 135 expert texts from these three traditions identified 65 features reported or implied across the practices, with most shared among all three. However, Shamatha involves substantially greater attentional stability and vividness. Numerous forms of content, including wakefulness, naturalness, calm, bliss/joy, and freedom, are present in these experiences. The findings challenge the classical view that such states are an identical pure consciousness, leaving it an open question whether they should be classed as such.
Mindfulness
June 1, 2023
Toby J. Woods, Jennifer Windt, Lydia Brown et al.
15 citations
People who practice Shamatha, Thai Forest, or Stillness Meditation typically report a highly positive experience of stillness or silence with little awareness of thoughts and perceptions, but with a high degree of abstract content such as calm and mental relaxation. Across the three traditions, robust differences emerged in reports of bliss/joy, wakefulness, absorptiveness, and depth. The experiences are contentless only in the sense of lacking obvious mental content like thoughts, not in being devoid of all content, challenging the classical view that such states are identical across traditions.
Phenomenology and the Cognitive Sciences
June 2, 2022
Toby J. Woods, Jennifer Windt, Olivia Carter
13 citations
Contentless experience, or pure consciousness, is a state free of mental content like thoughts, perceptions, and imagery. Three meditation practices—Shamatha, Transcendental, and Stillness Meditation—are said to access this state, but the paths differ. A review of 135 expert texts reveals that Shamatha and Transcendental Meditation superficially require focusing on an object, while Stillness Meditation does not. However, a detailed analysis shows Shamatha is posturally closer to Stillness Meditation but differs in requiring greater attentional stability, vividness, focusing, less tolerance of mind-wandering, more monitoring, and deliberate control. Achieving contentless experience through Shamatha is slower, more difficult, and less frequent. These findings inform meditation taxonomies, consciousness research, neuroscience, clinical practice, and practitioners.
Psychology of Consciousness Theory Research and Practice
June 12, 2025
Etzel Cardeña, Aviva Berkovich‐ohana, Katja Valli et al.
11 citations
A multidisciplinary, international group used taxonomic principles and a modified Delphi method to create a taxonomy of altered states of consciousness based on central phenomenological features. They identified eight distinct states, some with subcategories: proto and transitional, delirium, minimal to no awareness, experiential detachment, enhanced physicality, altered identity, imaginary/fantasy/visionary, and unity/mystical. The authors hope this taxonomy will foster conceptual clarity and stimulate research across specializations, helping reveal what is common and different across triggers and antecedents of altered states, and encouraging phenomenological, psychological, cultural, and neuroscientific understanding.
Journal of Vision
March 17, 2010
Olivia Carter, David C. Burr, John D. Pettigrew et al.
6 citations
A hallucinogenic drug that activates serotonin receptors, psilocybin, impairs the ability to track multiple moving objects but does not affect spatial working memory, indicating a functional separation between these two cognitive processes. Blocking one type of serotonin receptor (5-HT2A) with ketanserin did not prevent this attentional deficit, pointing to the involvement of another receptor (5-HT1A) instead. The impairment may stem from difficulty ignoring distractions rather than a reduction in attentional capacity itself.
Acta Neuropsychiatrica
November 4, 2025
Chiranth Bhagavan, Alexander Bryson, Olivia Carter et al.
4 citations
Combining psychedelics with physiotherapy may offer a new treatment for motor functional neurological disorder (FND), a condition with no effective medications and often persistent disability. This protocol describes the first trial testing two psilocybin-assisted physiotherapy regimens in 24 people with refractory motor FND. Participants are randomly assigned to either 15 mg psilocybin with movement tasks during the drug's acute effects or 25 mg psilocybin alone. All receive two physiotherapy sessions before dosing and six after, with follow-ups at one and four weeks. The study assesses tolerability, feasibility, symptom severity, and brain imaging to inform a larger definitive trial.