Evaluation of Frontocentral and Temporal Auditory Evoked Potentials in Children with Auditory Processing Disorder

Abstract

Early identification of auditory processing disorder (APD) is critical to mitigate its negative impact on academic performance. However, substantial variability in cortical auditory responses among children with APD has limited the identification of a consistent neurophysiological biomarker. This variability may be partially stem from methodological limitations including use of non-ecologically valid listening conditions and stimuli with limited temporal variation. Background noise and speech stimuli with distinct temporal dynamics, such as short and long voice onset time (VOT) may provide a more sensitive framework for evaluating auditory processing impairments. More importantly, no previous study has investigated the T-complex in APD. The T-complex, which matures earlier than Frontocentral responses (P1, N1, P2, N2), may represent a promising candidate for early identification of APD. Furthermore, even in typical populations, T-complex has not been examined in response to VOT contrasts in the presence of noise. The present thesis therefore evaluated both frontocentral and T-complex responses in quiet and noisy conditions, using various stimuli in normal-hearing adults and typically developing (TD) children, followed by children with APD. The aim was to characterize typical patterns of both frontocentral and T-complex in noisy conditions and determine how these responses are altered in APD. In adults, noise induced enhancements of responses to speech, possibly reflecting the increased engagement of top-down processing during speech perception in noise. The rightward lateralization was also observed in noise, suggesting adaptive cortical mechanism to maintenance auditory processing efficiency. Although TD children showed prolonged latency and suppressed amplitude of AEPs, there was no noise-induced enhancement and rightward lateralization patterns. Such finding presumably can indicate developmental maturation of auditory cortical adaptation. Despite of developmental differences in speech-in-noise processing, both adults and TD demonstrated a rightward lateralization of VOT representation indexed by the T-complex, suggesting that hemispheric asymmetry for temporal processing is established in childhood. Children with APD exhibited significant difference in AEPs between APD and TD groups, highlighting the impairments of auditory processing in children with APD at cortical levels. Also, there was not a strong pattern of lateralization of temporal processing in APD group. Given the early maturation of T-complex and consistent lateralized processing of temporal features across development, these findings support its potential as a stable biomarker of temporal auditory processing and a promising candidate for the early identification and intervention of APD.