Infants' Sensitivity to Vowel and Tonal Contrasts

Recently, evidence has been accumulating which indicates that infants from 1 to 5 months of age can discriminate speech or speechlike contrasts. It has been shown, for example, that infants can discriminate between synthetic samples of the voiced and voiceless stop consonants [b] and [p] (Eimas, Siqueland, Jusczyk, & Vigorito, 1971; Trehub & Rabinovitch, 1972), natural speech versions of [b] and [p] as well as [d] and [t] (Trehub & Rabinovitch, 1972), and synthesized samples of [b] and [g] (Moffkt, 1971; Morse, 1972). In all of these studies the stimuli were consonant contrasts in the initial position which were embedded in a common vocalic environment. Vowel discrimination which, for adults, is cued by the frequency relation among formants, has not received comparable attention. Brackbill (1962) reported a Russian study by Koltsova, who used classical conditioning techniques and failed to demonstrate discrimination throughout infancy when vowels were the discriminative stimuli. In fact, differentiation was accomplished only when the stimuli were consonants within the infant's vocal repertoire. Since consonant articulation involves more muscular movement