Recent theoretical work emphasizes the role of expectation in neural processing, shifting the focus from feed-forward cortical hierarchies to models that include extensive feedback (e.g., predictive coding). Empirical support for expectation-related feedback is compelling but restricted to adult humans and nonhuman animals. Given the considerable differences in neural organization, connectivity, and efficiency between infant and adult brains, it is a crucial yet open question whether expectation-related feedback is an inherent property of the cortex (i.e., operational early in development) or whether expectation-related feedback develops with extensive experience and neural maturation. To determine whether infants' expectations about future sensory input modulate their sensory cortices without the confounds of stimulus novelty or repetition suppression, we used a cross-modal (audiovisual) omission paradigm and used functional near-infrared spectroscopy (fNIRS) to record hemodynamic responses in the infant cortex. We show that the occipital cortex of 6-month-old infants exhibits the signature of expectation-based feedback. Crucially, we found that this region does not respond to auditory stimuli if they are not predictive of a visual event. Overall, these findings suggest that the young infant's brain is already capable of some rudimentary form of expectation-based feedback.O ver the past two decades, theoretical focus has shifted from predominantly feed-forward hierarchies of cortical function, where sensory cortex propagates information to higher level analyzers on the way to decision and motor control areas, to models in which feedback connections to lower-level cortical regions allow extensive top-down functional modulation based on expectation (1). An influential model for incorporating feedback is predictive coding, which compares expectations or predictions to input at each level of the processing hierarchy (2-4). There is extensive and compelling evidence for expectation-based modulation even at the earliest levels of sensory processing in both humans (5-7) and nonhuman animals (8). Because complex, naturalistic sensory input is characterized by temporal, spatial, and contextual regularities, the ability to modulate early sensory function as a result of expectations is believed to support adaptive perceptual abilities (4).Empirical evidence for expectation-based feedback, however, is restricted to adult humans and nonhuman animals. With their extensive experience, adults already have developed sophisticated internal models of the environment and have a highly interconnected brain and efficient neural processing. Comparatively, human infants are born with a demonstratively immature behavioral repertoire, have underdeveloped sensorimotor and cognitive capacities, and lack sophisticated internal models of the environment. These internal models undergo substantial postnatal development even in the early sensory cortex. For example, spontaneous activity of primary visual cortex (V1) in ferrets converges with e...

Implicit statistical learning (ISL) is exclusive to neither a particular sensory modality nor a single domain of processing. Even so, differences in perceptual processing may substantially affect learning across modalities. In three experiments, statistically equivalent auditory and visual familiarizations were presented under different timing conditions that either facilitated or disrupted temporal processing (fast or slow presentation rates). We find an interaction of rate and modality of presentation: At fast rates, auditory ISL was superior to visual. However, at slow presentation rates, the opposite pattern of results was found: Visual ISL was superior to auditory. Thus, we find that changes to presentation rate differentially affect ISL across sensory modalities. Additional experiments confirmed that this modality-specific effect was not due to cross-modal interference or attentional manipulations. These findings suggest that ISL is rooted in modality-specific, perceptually based processes.