Infant cortical tracking of speech shows emerging spatial release from masking in the first year of life

Natural listening environments are filled with competing sounds. One mechanism that helps overcome this challenge is spatial release from masking (SRM), whereby spatial separation between a target signal and interfering sounds improves perception of the target. SRM has been observed in a wide range of species including songbirds, crocodilians, ferrets, and human adults, suggesting an evolutionarily conserved strategy for listening in noise. However, an important question remains: Is an infant’s developing brain able to tap into the same mechanism to cope with the noisy world? To address this question, we recorded electroencephalography (EEG) from 7- and 11-month-old infants (N = 53; 25 female) and adults (N = 20; 12 female) as they listened to natural speech in quiet, collocated noise, and spatially segregated noise. Our results revealed that both infants and adults showed robust cortical tracking of speech across quiet and noisy listening conditions. For adults, spatial separation between the target speaker and distracting talkers led to enhanced cortical tracking of the target speech, consistent with SRM. Infants also showed SRM, with stronger tracking in segregated than collocated noise, although the effect was confined to a fronto-central region rather than broadly distributed across the scalp as in adults. These findings provide the first neurophysiological evidence that, although immature, the developing brain can benefit from spatial cues in the first year of life. The results add new insight into how the infant brain solves a fundamental perceptual problem - identifying a relevant voice in noise - using an evolutionarily grounded mechanism. Significance statement Understanding how the human brain separates relevant speech from competing sounds is a central problem in auditory neuroscience, yet little is known about how this ability emerges early in life. By investigating cortical representation of natural speech in the developing brain, this work provides new insight into the early foundations of human auditory processing. Using electroencephalography in human infants, we show that the neural mechanisms supporting spatial release from masking emerges in infancy, prior to mature language comprehension and attentional control. These results help bridge established accounts of speech-in-noise perception in adults with their developmental origins, providing an objective neural basis for studying how infants navigate complex auditory environments.