Relations Between Perceptual Measures of Temporal Processing, Auditory-evoked Brainstem Responses and Speech Intelligibility in Noise

This study investigates behavioural and objective measures of temporal auditory processing and their relation to the ability to understand speech in noise. The experiments were carried out on a homogeneous group of seven hearing-impaired listeners with normal sensitivity at low frequencies (up to 1 kHz) and steeply sloping hearing losses above 1 kHz. For comparison, data were also collected for five normal-hearing listeners. Temporal processing was addressed at low frequencies by means of psychoacoustical frequency discrimination, binaural masked detection and amplitude modulation (AM) detection. In addition, auditory brainstem responses (ABRs) to clicks and broadband rising chirps were recorded. Furthermore, speech reception thresholds (SRTs) were determined for Danish sentences in speech-shaped noise. The main findings were: (1) SRTs were neither correlated with hearing sensitivity as reflected in the audiogram nor with the AM detection thresholds which represent an envelope-based measure of temporal resolution; (2) SRTs were correlated with frequency discrimination and binaural masked detection which are associated with temporal fine-structure coding; (3) The wave-V thresholds for the chirp-evoked ABRs indicated a relation to SRTs and the ability to process temporal fine structure. Overall, the results demonstrate the importance of low-frequency temporal processing for speech reception which can be affected even if pure-tone sensitivity is close to normal.