Neural Coding of Phonemic Fricative Contrast With and Without Hearing Aid

Abstract

To determine whether auditory event-related potentials (ERPs) to a phonemic fricative contrast ("s" and "sh") show significant differences in listening conditions with or without a hearing aid and whether the aided condition significantly alters a listener's ERP responses to the fricative speech sounds. The raw EEG data were collected using a 64-channel system from 10 healthy adult subjects with normal hearing. The fricative stimuli were digitally edited versions of naturally produced syllables, /sa/ and /∫a/. The evoked responses were derived in unaided and aided conditions by using an alternating block design with a passive listening task. Peak latencies and amplitudes of the P1-N1-P2 components and the N1' and P2'' peaks of the acoustic change complex (ACC) were analyzed. The evoked N1 and N1' responses to the fricative sounds significantly differed in the unaided condition. The fricative contrast also elicited distinct N1-P2 responses in the aided condition. While the aided condition increased and delayed the N1 and ACC responses, significant differences in the P1-N1-P2 and ACC components were still observed, which would support fricative contrast perception at the cortical level. Despite significant alterations in the ERP responses by the aided condition, normal-hearing adult listeners showed distinct neural coding patterns for the voiceless fricative contrast, "s" and "sh," with or without a hearing aid.