The low and high frequency auditory steady state responses mature at different rates

The age-related changes in the fast rate (70-110 Hz) auditory steady state response elicited by multiple-frequency tones (MSSR) that were amplitude-modulated (AM) are reported here. The MSSR was recorded in a sample of 64 well babies distributed into three age groups: 0-29 days (n = 25); 1-6 months (n = 26); 7-12 months (n = 13). Four simultaneously presented AM tones (0.5, 1, 2 and 4 kHz) were delivered monaurally through TDH 49 earphones, at different intensities (between 90 and 30 dB SPL). Clear developmental changes were found between birth and 12 months of age in response threshold, amplitude and detectability. Statistical analysis revealed that these changes occurred at different rates for low- and high- frequency responses. Nonetheless adult-like hearing thresholds were estimated reasonably well in most newborns and well babies, for all frequencies tested. Therefore the MSSR technique could be useful for objective frequency-specific audiometry beginning at birth.