Discrimination of voice onset time by human infants: new findings and implications for the effects of early experience.

Discrimination of voice onset time (VOT) by 6--12-month-old infants was examined in 2 experiments. An operant head-turning technique assessed discrimination along a synthetic VOT continuum ranging from -70 msec to +70 msec. Infants from an English-speaking environment provided reliable within-subject evidence for discrimination of VOT contrasts located at both the plus and minus regions of the VOT continuum. These results provide strong evidence that infants from an English-speaking environment are capable of discriminating VOT contrasts that are not phonemic in English. Threshold delta VOT values indicated that the infants were more sensitive to VOT differences in the plus region of the VOT continuum than in the minus region. Threshold delta VOT values from English-speaking adults indicated greater sensitivity at every location along the VOT continuum. In addition, the adults showed heightened sensitivity to VOT differences near the voiced-voiceless boundary in the plus region of the VOT continuum, a finding that was not evident in the infants' data.