Development of the voicing contrast: perception of stop consonants.

Perceptual development of the voicing contrast was investigated in two-year-old children, six-year-old children, and adults. Subjects were required to identify prevocalic stop consonants from synthetic speech stimuli--bees/peas, bear/pear, dime/time, and goat/coat. The stimuli differed with respect to the acoustic cue, voice onset time (VOT). Identification functions for labial, apical, and velar stops were plotted for each subject. Measurements of 50% crossover, lower and upper limits of the phoneme boundary, and phoneme boundary width were obtained from the identification functions. Significant age-dependent differences in perception of the voicing contrast were observed. The results were interpreted as indicating that the magnitude of VOT difference required for distinguishing between prevocalic stop cognates decreases as a function of the age of the listeners.