Detecting violations of temporal regularities in waking and sleeping two-month-old infants

► Two-month-old infants were tested with an auditory event-related potential paradigm. ► A repeating sound was occasionally exchanged for a different sound, i.e. a deviant. ► Mismatch responses were elicited not only by spectral but also by temporal deviants. ► Temporal deviants were affected by state of alertness mostly on negative-going waves. ► Spectral deviants were affected by state of alertness mostly on positive-going waves.