A developmental look at an auditory illusion: the precedence effect.

Infants aged 2 and 6 months were tested with the precedence effect, an auditory phenomenon involving sound localization. Each infant was tested with two types of stimuli: sound from a single loudspeaker and precedence-effect sounds produced by the same sound put through two loudspeakers, with one output leading the other by 7 msec. Older infants localized precedence-effect stimuli as they did single-source stimuli, indicating that they perceived this phenomenon as expected. Two-month-olds turned their heads toward single-source sounds, but did not localize precedence-effect sounds, suggesting that that more difficult perceptual task had not been achieved at this age. In general, head-turning toward sound proved far more difficult to elicit in younger infants. A click train was ineffective, but a tape-recorded human voice elicited above-chance low-level turning. The developmental changes in auditory behavior are discussed in terms of the rapid growth of the auditory cortex.