Humans and mice fluctuate between external and internal modes of sensory processing

2Perception is known to cycle through periods of enhanced and reduced sensitivity to external information. Here, we asked whether such infra-slow fluctuations arise as a noise-related epiphenomenon of limited processing capacity or, alternatively, represent a structured mech{-}anism of perceptual inference. Using two large-scale datasets, we found that humans and mice waver between alternating intervals of externally- and internally-oriented modes of sensory analysis. During external mode, perception aligned more closely with the external sensory information, whereas internal mode was characterized by enhanced biases toward perceptual history. Computational modeling indicated that dynamic changes in mode are enabled by two interlinked factors: (i), the integration of subsequent inputs over time and, (ii), infra-slow anti-phase oscillations in the perceptual impact of external sensory information versus internal predictions that are provided by perceptual history. Simulated data suggested that between-mode fluctuations may benefit perception by generating unambiguous error signals that enable robust learning and metacognition in volatile environments. 3 One sentence summaryHumans and mice fluctuate between external and internal modes of sensory processing.