Behavioral threshold for tones in 6- and 10-month-old infants

Behavioral thresholds for 500, 2000, and 8000 Hz tone bursts were determined for 6- and 10-month-old human infants using a transformed up-down tracking procedure in a conditioned head turn paradigm. In experiment 1, stimuli were presented in free field and tracking was initiated at an intensity well above threshold. For 10-month-old infants, threshold estimates were approximately 15 dB above adult values at all three frequencies. Six-month-old thresholds were slightly higher and relatively flat across frequencies. In experiment 2, stimuli were presented via earphone, tracking was initiated below threshold, and supra threshold probe trials were introduced to assess the infants' motivation to respond. With these changes in procedure, 6-month-olds showed the adult U-shaped sensitivity function. [Work supported by NINCDS.]