Effect of noise on T-complex responses: an evoked-related potential study

Cortical auditory evoked potentials (CAEPs), including the frontocentral (P1-N1-P2) and temporal (T-complex) components, have distinct neural generators. The T-complex appears to mature earlier and remains relatively stable with age. This stability may suggest that the T-complex may better reflect auditory processing in real-life listening conditions compared to frontocentral responses. One critical aspect of real-world listening is the presence of background noise; however, no previous study has examined its impact on the T-complex. The present study investigated the effects of background noise on both T-complex and frontocentral responses in adults during a passive paradigm, using /da/ and a 1-kHz tone pip presented in white and babble noise. In noise compared to quiet, the latency of all components was generally prolonged, and CAEP amplitudes were reduced. However, N1 and Ta amplitudes were enhanced in non-speech noise, and Tb amplitude was enhanced in babble noise. This enhancement pattern was observed only with speech stimuli. Larger CAEP amplitudes in noise may reflect top-down adaptive mechanisms that support speech understanding in adverse conditions. Notably, the larger Tb response to speech in babble noise suggests that the T-complex may index greater adaptation to real-life listening environments compared to frontocentral responses. The differences in CAEPs evoked by noise masked stimuli may highlight the various contributions of different auditory cortical structures to listening in noise. The T-complex also showed rightward lateralization in noise, consistent with findings from the primary auditory cortex.