Stroboscopically induced visual hallucinations: historical, phenomenological, and neurobiological perspectives

Abstract

Exposure to rapid and bright stroboscopic light has long been reported to induce vivid visual hallucinations of colour and geometric formations. This phenomenon was first documented by Purkinje over 200 years ago. Since then, significant progress has been made in understanding the effects of stroboscopic light and the experiences it induces through multiple waves of interest from the scientific, therapeutic, and broader cultural communities. Despite these advances, fundamental questions remain unanswered, including comprehensive characterizations of its phenomenology, its precise physiological origins, under which conditions it may lead to altered states of consciousness phenomena, and potential clinical or therapeutic applications. This narrative review provides a historical summary of research into stroboscopic light stimulation (SLS) alongside its use in recreation and lay-therapeutic contexts. It also discusses the phenomenology of these experiences, current perspectives on the potential neural mechanisms of stroboscopically induced experiences, and provides an outlook for future research in this field.

Keywords: consciousness; contents of consciousness; hallucinations; perception; phenomenology.

Figure 1

Timeline of the history of SIVHs. Key scientific and cultural milestones are shown. (A) Purkinje’s drawings of his SIVHs, the first known documentation of the phenomena (Purkinje, 1819) (B) A rendering of the four Klüver form constants (1926), which are geometric forms posited to make up simple geometric VHs, consisting of checkerboards (top left), targets (top right), tunnels (bottom left), and spirals (bottom right). (C) An early EEG experiment involving SLS at the laboratory of William Grey Walter. Such experiments eventually led to the rediscovery of SIVHs and the first wave of research into the phenomena (Başar, 2012). Photograph by Desmond Tripp. (D) Kroger and Schneider’s Brainwave Synchronizer, an early stroboscope sold as a medical device. Photograph by Paul Czerniak. (E) Gysin’s Dreamachine, a hallucination-inducing stroboscope that can be constructed from household materials which he invented, and which is often credited with introducing SIVHs to culture at large (Gatewood, 1970; Gysin, 1994). Photograph from Plutochaun, Wikimedia Commons. (F) A schematic of the arrangement of the dark and light frames used by Conrad for his short experimental film “The Flicker” (1966), created to induce SIVH experiences in the audience using a variety of SLS frequencies synchronised to sound (Hubby, 2016). Image courtesy the Tony Conrad Estate and Greene Naftali, New York. (G) One of Gorges’ ‘Mind Gyms’, where members of the general public could use SLS goggles for their posited therapeutic benefits (Ressmeyer, 1987). Photograph by Floris Leeuwenberg. (H) fMRI data of neural activations during SIVHs gathered by Dr Dominic ffytche, showing a correlation between thalamocortical activity and SIVHs (ffytche, 2008). Reprinted from Cortex Volume 44, Issue 8, Dominic ffytche, The hodology of hallucinations, Page 1075, Copyright 2008, with permission from Elsevier (I) An early group strobe session with the Lucia N°03 strobe light. Image courtesy of Light Attendance GmbH. (J) Rule, Stoffregen, and Ermentrout’s models of SIVHs, which simulate the content of SIVHs using neural field equations (2011). Images by Ethan Grove. (K) Collective Act’s Dreamachine, an experience which used stroboscopic lighting combined with music to induce SIVHs for tens of thousands of people within a collective setting, with many attendees reporting experiences reminiscent of ASCs (Collective Act, 2020). Image courtesy of Collective Act.

Figure 2

Visual depictions of geometric SIVHs. (A) Purkinje’s early drawings of SIVHs induced by waving his hands in front of his closed eyes while observing a candle flame (Purkinje, 1819). This appears to be the first published drawing of SIVHs, and more than a century would pass before any new drawings of SIVHs would be published. (B) Participant drawings of SIVHs, adapted from Smythies (1959b). (C) Selected drawings of SIVHs from participants in Dreamachine, courtesy of Collective Act.

Figure 3

Four models of neural mechanisms and correlates of SIVHs. (A) Schematic of the Ermentrout and Cowan model of simple visual hallucinations (Ermentrout and Cowan 1979), later applied to SIVHs by Rule, Stoffregen, and Ermentrout (Rule et al., 2011). This model suggests that the visual cortex is predisposed to form spatially periodic patterns of neural activity (visualized in the four images labelled ‘cortex’ in panel A), which may give rise to percepts resembling Klüver form visual hallucinations of tunnels, targets, and spirals (see Fig. 1B). Images by Michael Rule and Ethan Grove. (B) Neural entrainment refers to the phase synchronization between periodic SLS and neural oscillations, which is most evident over visual areas of the brain. Top of Figure: Reprinted from Current Biology, Vol 29 Issue 28, Lakatos, Gross & Thut, A New Unifying Account of the Roles of Neuronal Entrainment, Page R891, Copyright 2019, with permission from Elsevier. (C) Recent fMRI studies show activity in higher order visual regions, as well as interactions between these regions and higher order thalamic nuclei (specifically the ventral anterior thalamic nucleus; VA), as the main correlates of SIVHs. (D) Predictive processing models suggest that phenomenal experiences result from comparisons between internally generated predictions (top-down) and sensory inputs (bottom-up). SIVHs may result from distorted approximate computation of Bayes’ theorem, due to rhythmic bottom-up input to the canonical microcircuits, potentially causing timing sensitive imbalances in cortical excitation and inhibition. In this context, individual differences in SIVHs may be explained by the variations in the influence of top-down signals, specifically in the weight or precision of priors.