Discrete episodes of conscious access revealed by the psychological refractory period

When does conscious access occur relative to sensory stimulation? Although perceptual experience is often assumed to track the continuous presence of sensory input, recent neurophysiological findings challenge this assumption by showing that prefrontal activity does not scale with stimulus duration. Interpreting these findings has been difficult because prior studies did not directly probe the temporal profile of conscious access itself. Here, we address this gap using the psychological refractory period (PRP) effect as a report-free, time-resolved marker of central-stage processing associated with conscious access. Across two dual-task experiments, we measured delays in auditory responses induced by visual stimuli of varying duration and task relevance, with auditory probes time-locked to stimulus onset and offset. Visual stimulus onset reliably induced a PRP effect, even for task-irrelevant stimuli that did not elicit overt responses, indicating transient conscious access independent of stimulus duration. Task relevance prolonged this access, whereas stimulus disappearance elicited a markedly weaker and less consistent PRP effect, contingent on stimulus duration. Participants showed limited introspective awareness of these delays. Reanalysis of intracranial EEG data revealed that prefrontal decoding dynamics mirrored the behavioral modulation of the PRP. Together, these findings show that conscious access is transient and context-dependent, rather than a continuous reflection of sensory input, establishing the PRP as a precise, report-free chronometric tool for studying the timing of conscious access.