Neonatal frequency discrimination in 250-4000-Hz range: electrophysiological evidence.

Objective: The precision of sound frequency discrimination in newborn infants in the 250-4000-Hz frequency range was determined using the neonatal electrophysiological mismatch response (MMR), the infant equivalent of adult mismatch negativity (MMN).

Methods: The electroencephalogram (EEG) was recorded in 11 full-term sleeping newborn infants mostly in active sleep (67% of the time). Pure tones were presented through loudspeakers in an oddball paradigm with a 800-ms stimulus onset asynchrony (SOA). Each stimulus block contained a standard (p=0.76) of 250, 1000, or 4000Hz in frequency (in separate blocks) and deviants with a frequency change of either 5% or 20% of the standard (p=0.12 of each).

Results: A positive ERP deflection was found at 200-300ms from stimulus onset in response to the 20% deviation from the 250, 1000, and 4000Hz standard frequencies. The amplitude of the response in the 200-300ms time window was significantly larger for the 20% than 5% deviation.

Conclusions: We observed in newborn infants automatic frequency discrimination as reflected by a positive MMR. The newborns were able to discriminate frequency change of 20% in the 250-4000-Hz frequency range, whereas the discrimination of the 5% frequency change was not statistically confirmed.

Significance: The present data hence suggest that the neonatal frequency discrimination has lower resolution than that in adult and older children data.