Expectation triggers a change-like EEG response without acoustic change

Predictive processing theories posit that the auditory system continuously generates expectations and updates internal models when incoming evidence violates those expectations. Whether such updating can be expressed as a temporally precise, change-like neural response at a context-defined moment during continuous stimulation--without any physical change--has remained unclear. Using a transitional click-train paradigm in human EEG, we show that listeners reliably detect subtle midpoint transitions when click timing is fixed, whereas temporal uncertainty markedly weakens this sensory-driven detection. Strikingly, even in a physically unchanged stimulus, variable click timing elicits a robust response time-locked to the nominal midpoint. This endogenous change-like signal is stimulus-statistics dependent--absent in the fixed-timing no-change control--temporally confined to the early post-change window, and strongly state dependent, being amplified during active change detection relative to passive listening. Moreover, within identical no-change trials, the response tracks subjective change reports. Together, these findings show that temporal uncertainty and task engagement jointly gate predictive updating in continuous auditory streams, providing a compact assay to dissociate sensory-driven change responses from context- and state-dependent predictive signals.