Altered states phenomena induced by visual flicker light stimulation

Abstract

Flicker light stimulation can induce short-term alterations in consciousness including hallucinatory color perception and geometric patterns. In the study at hand, the subjective experiences during 3 Hz and 10 Hz stroboscopic light stimulation of the closed eyes were assessed. In a within-subjects design (N = 24), we applied the Positive and Negative Affect Schedule (mood state), time perception ratings, the Altered State of Consciousness Rating Scale, and the Phenomenology of Consciousness Inventory. Furthermore, we tested for effects of personality traits (NEO Five-Factor Inventory-2 and Tellegen Absorption Scale) on subjective experiences. Such systematic quantification improves replicability, facilitates comparisons between pharmacological and non-pharmacological techniques to induce altered states of consciousness, and is the prerequisite to study their underlying neuronal mechanisms. The resulting data showed that flicker light stimulation-induced states were characterized by vivid visual hallucinations of simple types, with effects strongest in the 10 Hz condition. Additionally, participants' personality trait of Absorption scores highly correlated with the experienced alterations in consciousness. Our data demonstrate that flicker light stimulation is capable of inducing visual effects with an intensity rated to be similar in strength to effects induced by psychedelic substances and thereby support the investigation of potentially shared underlying neuronal mechanisms.

Fig 1. Study design and experimental procedure.

The initial assessment included an EEG-based screening for photosensitive epilepsy as well as a psychometric assessment with a personal data inventory, the NEO-FFI-2 personality trait questionnaire [22], the Edinburgh Handedness Inventory [21], and the Tellegen Absorption Scale [19]. The first experimental session [Constant Light Session], in which participants were exposed to constant light for 20 min was conducted immediately after the initial assessment. The subsequent two experimental sessions involved 20 min of exposure to flicker light with frequencies of either 3 Hz or 10 Hz (randomized order). During the light exposure, participants were asked to estimate the time elapsed since the beginning of the exposure either after 12, 14, or 16 min (randomized order over all three sessions within every participant). All sessions consisted of an assessment of mood changes (pre to post) with the Positive and Negative Affect Schedule [23] and divergent thinking with the Alternative Uses Task [24]. Additionally, participants retrospectively rated the subjective effects of the light exposure on the Altered States of Consciousness (ASC) Rating Scale [5D-ASC] [25] and the Phenomenology of Consciousness Inventory [26] and were also asked to describe their experiences in open reports. Experimental sessions [Flicker Session 1 and 2] were conducted with at least four days in between.

Fig 2. Psychometric assessment of Flicker Light Stimulation (FLS) effects.

(A) Retrospective ratings of FLS effects with the Altered States of Consciousness (ASC) Rating Scale [25] analyzed according to the five-dimensional ASC Rating Scale (5D-ASC) scheme and to the 11 subscales of the ASC Rating Scale (11-ASC). (B) Retrospective ratings of FLS effects on the major and minor dimensions of the Phenomenology of Consciousness Inventory [26]. Colors correspond to the 3 Hz (light yellow) and 10 Hz (bright yellow) flicker frequency conditions. Boxplots represent the first to third quartiles as boxes; the horizontal lines within the boxes visualize the median, the yellow points indicate the mean; bars represent 1.5 times the interquartile range of the data with points representing scores outside of that range. None of the differences between the dimension scores of 3 Hz and 10 Hz conditions were significant after Bonferroni-correction of the α-threshold for multiple comparisons.

Fig 3. Correlations between personality trait absorption and subjective experiences during Flicker Light Stimulation (FLS).

To test the hypothesis that the personality trait of Absorption affects the overall experience of an altered state of consciousness (ASC), we tested for respective correlations in the data. Correlations of participants’ trait of Absorption scores, as assessed with the Tellegen Absorption Scale (TAS) [19], with the G-ASC scores (global mean scores of three 5D-ASC dimensions, reflecting the etiology-independent core of ASCs) are depicted for the 3 Hz and 10 Hz condition. Significant correlations are indicated as *p < .025, **p < .005, and ***p < .0005 (α-threshold Bonferroni-corrected for two comparisons).

Fig 4. Comparison of ratings of different Altered States of Consciousness (ASCs) experiences induced by pharmacological and non-pharmacological means.

All ratings were obtained using the Altered States of Consciousness Rating Scale [25], and results reported according to the 11 factors scheme (11-ASC), constituting subscales of the 5D-ASC dimensions Oceanic Boundlessness (green), Dread of Ego Dissolution (orange), and Visionary Restructuralization (grey). Next to the ratings of 3 Hz and 10 Hz flicker light stimulation from the present study, data from 25 min of exposure to multimodal Ganzfeld stimulation [15] is provided, as well as ratings after the application of 100 μg LSD [57], 125 mg MDMA [59], and the effects of psilocybin at a dose of 300 μg/kg according to a meta-analysis on psilocybin dose-response relationships [5]. Rating scores were taken from the Altered States Database [4].