Distinct yet complementary roles of temporal and spectral predictions in auditory detection

Predictive processing enables the brain to anticipate both when and what sensory events will occur. Although temporal and spectral predictions are both known to facilitate perception, their functional contributions and interaction remain poorly understood, particularly in uncertain listening conditions where predictions must be inferred from implicit statistical regularities rather than explicit cues or rhythms. Here, we orthogonalized temporal and spectral predictability in a non-rhythmic auditory detection task and used a signal-detection framework to dissociate perceptual and decisional processes in humans of either sex. Temporal predictions primarily increased response readiness: predictable target timing led to faster responses and more hits but also more false alarms, reflecting a liberal shift in response bias. Spectral predictions, in contrast, selectively enhanced perceptual sensitivity without a comparable speeding of responses. Crucially, despite their distinct behavioral effects, temporal and spectral predictions interacted synergistically, such that perceptual sensitivity was greatest when both sound timing and frequency were predictable, consistent with a spectrotemporal filter mechanism. Furthermore, temporal and spectral variability were encoded differently: performance adapted strongly to the distribution of foreperiod durations but remained largely stable across the spectral distribution, suggesting that the brain exploits temporal and spectral statistics in distinct ways when forming predictions under uncertainty. Together, these findings demonstrate that temporal and spectral predictions make complementary contributions to auditory decision-making, interact synergistically to improve perceptual sensitivity, and rely on distinct encoding strategies for temporal and spectral variability.