Effect of Repetition Rate on Speech Evoked Auditory Brainstem Response in Younger and Middle Aged Individuals.

Speech evoked auditory brainstem responses depicts the neural encoding of speech at the level of brainstem. This study was designed to evaluate the neural encoding of speech at the brainstem in younger population and middle-aged population at three different repetition rates (6.9, 10.9 and 15.4). Speech evoked auditory brainstem response was recorded from 84 participants (young participants=42, middle aged participants=42) with normal hearing sensitivity. The latency of wave V and amplitude of the fundamental frequency, first formant frequency and second formant frequency was calculated. Results showed that the latency of wave V was prolonged for middle-aged individuals for all three-repetition rates compared to the younger participants. The results of the present study also revealed that there was no difference in encoding of fundamental frequency between middle aged and younger individuals at any of the repetition rates. However, increase in repetition rate did affect the encoding of the fundamental frequency in middle-aged individuals. The above results suggest a differential effect of repetition rate on wave V latency and encoding of fundamental frequency. Further, it was noticed that repetition rate did not affect the amplitude of first formant frequency or second formant frequency in middle aged participants compared to the younger participants.