Perceptual organization of speech sounds by infants

An operant head-turn procedure was used to test whether 6-month-old infants recognize the auditory similarity of speech sounds sharing a value on a phonetic-feature dimension. One group of infants was reinforced for head turns when a change occurred from a series of repeating background stimuli containing nasal consonants [( m, n, eta]) to repetitions from a category of syllables containing voiced stop consonants [( b, d, g]), or to a change from stops to nasals. The stimuli were naturally produced by both male and female talkers. The performance of infants in this "phonetic" group was compared to that of infants in a "nonphonetic" control group. Using the same procedures, these infants were reinforced for head turns to a group of phonetically unrelated speech sounds. Results indicated that the performance of infants in the group trained on phonetically related speech sounds was far superior to that of infants in the nonphonetic control group. These findings suggest that prelinguistic infants can perceptually organize speech sounds on the basis of auditory properties related to feature similarity.