Developmental changes in auditory temporal perception.

Infants, preschoolers, and adults were tested to determine the shortest time interval at which they would respond to the precedence effect--an auditory phenomenon produced by presenting the same sound through 2 loudspeakers with the input to 1 loudspeaker delayed relative to the other. The delayed sound is not localized at its source until time delays between onsets are lengthened beyond a critical limit, or threshold. Thresholds for the precedence effect were defined as the delay interval below which listeners respond only to the leading loudspeaker and above which they respond to both loudspeakers. Threshold estimates were determined for adults and preschoolers with an ascending and descending series, followed by a method of constant stimuli series. Infants were trained to respond to the delayed sound using a visually reinforced headturning procedure. For clicks, preschoolers' and adults' thresholds were around 12 msec, while 6-month-olds stopped responding to the delayed sound around 25 msec. A similar developmental difference in threshold was expressed between preschoolers and adults for a more complex sound, with younger subjects hearing the precedence effect over a longer time delay.