An adaptive up/down tracking procedure was used in combination with a visually reinforced head-turn response to examine infants' (6 to 18 months of age) auditory sensitivity for 500-, 2000-, and 8000-Hz tone bursts. Six-month-olds were significantly less sensitive to the 8000-Hz tone than to either lower frequency; older infants demonstrated approximately equal sensitivity for all three. (Author/RH)