Evaluation of peripheral compression and auditory nerve fiber intensity coding using Auditory Steady-State Responses (ASSR)

Description

The compressive nonlinearity of the auditory system is assumed to be an epiphenomenon of a healthy cochlea and particularly, outer-hair cell function. Auditory steady-state responses (ASSR) reflects coding of the stimulus envelope. Recent research in animals shows that noise over-exposure, producing temporary threshold shifts, can cause auditory nerve fiber (ANF) deafferentation in predominantly low-spontaneous rate (SR) fibers. It is hypothesized here that deafferentation of low-SR fibers can lead to a reduction of ASSR amplitude at supra-threshold levels. ASSR input/output (I/O) functions were measured in two groups of normal-hearing adults at stimulus levels ranging from 20 to 90 dB SPL. First, multi-frequency ASSR I/O functions were obtained using a modulation depth of 85%. Secondly, ASSR were obtained using a single sinusoidally amplitude modulated (SAM) tone at four modulation depths (25, 50, 85 and 100%). Results showed that ASSR growth functions exhibit compression of about 0.25 dB/dB. The slope for levels above 60 dB SPL showed more variability across subjects. The slope of ASSR I/O functions could be used to estimate peripheral compression simultaneously at four frequencies below 60 dB SPL, while the slope above 60 dB SPL might be used to evaluate the integrity of intensity coding of low-SR fibers.

Period	27 Aug 2015
Event title	5th International Symposium on Auditory and Audiological Research
Event type	Conference
Conference number	5
Location	Nyborg, Denmark