Attending to speech and discriminating among its features are essential precursors to infants learning to extract meaning from it. The objective of this application is to isolate the features of speech and other acoustic signals that reinforce neonates and to determine whether the features that are reinforcing change during the first six months of life. To reach this objective, auditory stimuli will be made contingent upon infants' suck duration and upon their rate of high- amplitude sucking. A second objective is to identify the features of auditory signals that are discriminated at birth and to determine whether the features that are discriminated change between birth and six months. To reach this objective, auditory stimuli will be used in a dishabituation procedure and as discriminative cues in chaining and multiple-schedule operant conditioning paradigms. Thus, for each goal we will employ converging operations across early infancy to assess the effects of segmental suprasegmental, simple and multidimensional acoustic manipulations. The data will clarify the development of attention to speech and its discrimination.