Neural Representation of Amplified Speech Sounds

In Brief Objective: To determine if (1) evoked potentials elicited by amplified speech sounds (/si/ and /∫i/) can be recorded reliably in individuals, (2) amplification alters neural response patterns, and (3) different amplified speech sounds evoke different neural patterns. Design: Cortical evoked potentials were recorded in sound field from seven normal-hearing young adults in response to naturally produced speech tokens /si/ and /∫i/ from the Nonsense Syllable Test. With the use of a repeated-measures design, subjects were tested and then retested within an 8-day period in both aided and unaided conditions. Results: (1) Speech-evoked cortical potentials can be recorded reliably in individuals in both aided and unaided conditions. (2) Hearing aids that provide a mild high-frequency gain only subtly enhance peak amplitudes relative to unaided cortical recordings. (3) If the consonant-vowel boundary is preserved by the hearing aid, it can also be detected neurally, resulting in different neural response patterns for /si/ and /∫i/. Conclusions: Speech-evoked cortical potentials can be recorded reliably in individuals during hearing aid use. A better understanding of how amplification (and device settings) affects neural response patterns is still needed. Cortical evoked potentials (P1-N1-P2/ ACC) were recorded in sound field from seven normal-hearing young adults in response to naturally-produced speech tokens /si/ and /i/ from the Nonsense Syllable Test (NST). Using a repeated measures design, participants were tested and then retested within an eight-day period in both aided and unaided conditions. Although our results show that speech evoked cortical potentials can be reliably recorded in individuals in both aided and unaided conditions, and that different speech sounds evoke unique waveform patterns; surprisingly, there was no significant effect of amplification. A mild high frequency gain hearing aid did not significantly alter peak latency and amplitudes as one would have expected. These results reinforce the importance of understanding how amplification (and device settings) affects the output of the stimulus, as well as the evoked neural response patterns. This point is important because our current understanding of evoked potentials might not generalize to situations where sound is first processed (and altered) by a hearing aid.