Effects of noise and age on the infant brainstem response to speech.

OBJECTIVE: Background noise makes hearing speech difficult for people of all ages. This difficulty can be exacerbated by co-occurring developmental deficits that often emerge in childhood. Sentence-type speech-in-noise (SIN) tests are available clinically but cannot be administered to very young individuals. Our objective was to examine the use of an electrophysiological test of SIN, suitable for infants, to track developmental trajectories. METHODS: Speech-evoked brainstem potentials were recorded from 30 typically-developing infants in quiet and +10 dB SNR background noise. Infants were divided into two age groups (7-12 and 18-24 months) and examined across development. Spectral power of the frequency following response (FFR) was computed using a fast Fourier Transform. Cross-correlations between quiet and noise responses were computed to measure encoding resistance to noise. RESULTS: Older infants had more robust FFR encoding in noise and had higher quiet-noise correlations than their younger counterparts. No group differences were observed in the quiet condition. CONCLUSIONS: By two years of age, infants show less vulnerability to the disruptive effects of background noise, compared to infants under 12 months. SIGNIFICANCE: Speech-in-noise electrophysiology can be easily recorded across infancy and provides unique insights into developmental differences that tests conducted in quiet may miss.