Phenomenological and physiological correlates of altered states of consciousness induced by rhythmic auditory stimulation

Rhythmic auditory stimulation has long been used across cultures to induce altered states of consciousness (ASC), yet its phenomenological and physiological correlates remain incompletely characterized under controlled laboratory conditions. Here, we investigated whether drumming-derived rhythmic auditory stimulation reliably induces ASC and how stimulus structure and individual expertise shape their expression. Forty-six adults, including trained musicians and non-musicians, were exposed in randomized order to three 15-minute conditions: a looped rhythm depicting a regular two-beats pattern, a live-performance-derived rhythm containing natural micro-variations, and a silent near-dark control condition approximating sensory restriction. Subjective experience was assessed through a questionnaire and a structured evaluation of hallucinatory-like perceptual phenomena, while ocular indices of attention and arousal (eye blink rate and pupil diameter) were continuously recorded via eye tracking.Both rhythmic auditory stimulation conditions robustly increased global ASC relative to the control condition, with no reliable difference between regular and micro-variable rhythms in overall ASC intensity. However, micro-variable stimulation was associated with greater structural complexity of visual imagery-like experiences. Subgroup analyses indicated that non-musicians showed broader ASC modulation across psychometric dimensions, whereas musicians exhibited more selective effects, primarily related to perceptual restructuring. Ocular measures revealed pronounced temporal dynamics and condition-sensitive modulation, consistent with evolving attentional and arousal states during prolonged rhythmic exposure.These findings demonstrate that rhythmic auditory stimulation constitutes a reliable, non-pharmacological route to ASC beyond the effects of sensory restriction alone, and that global intensity, qualitative structure, and physiological dynamics of altered experience can dissociate as a function of stimulus properties and listener expertise.