Newborns' orientation toward sound: possible implications for cortical development.

The precedence effect is an auditory illusion produced by presenting the same signal through 2 loudspeakers, with 1 leading the other by several milliseconds. Adults perceive a sound localized exclusively on the leading side and directionally equivalent to a single source sound. Because the precedence effect is thought to involve cortical functions, newborns were expected not to respond with directional head turning toward these sounds. Newborns were presented with a tape-recorded rattle sound produced in 3 ways: through a single loudspeaker located right or left, through both loudspeakers with 1 onset leading the other by 7 msec, and control stimuli in which both loudspeakers sounded simultaneously, resulting in an apparent center location of the sound. Newborns turned toward the single source sound, but neither to precedence effect stimuli nor control stimuli. These results were related to maturation of the auditory cortex.