at four months infants still prefer infant-directed speech to adult-directed speech. whereas 1-month-olds only exhibit this preference if the full speech signal is played to them, 4-month-old infants prefer infant-directed speech even when just the pitch contours are played. this shows that between 1 and 4 months of age, infants improve in tracking the suprasegmental information in the speech directed at them. by 4 months, finally, infants have learned which features they have to pay attention to at the suprasegmental level.