Psychoacoustical and electrophysiological investigation of the relative masking levels for narrowband chirps

Objective hearing diagnostics in asymmetric hearing often require masking the better ear. Currently, no guideline for masking levels for narrowband chirps used in evoked response audiometry is available. The present study investigated which levels of a broadband noise are required to mask narrowband chirps. In a psychoacoustic experiment with 12 normal-hearing adults and an electrophysiological experiment using auditory steady-state responses with 12 single-sided deaf adults, air-conducted and bone-conducted narrowband chirp trains were presented at a repetition rate of 40 Hz. Both experiments showed similar results. Masking levels depended on the center frequency of the narrowband chirps as well as the transducer used to present the chirps. In the psychoacoustic experiment, noise levels of 36.0, 27.4, 28.3, and 30.6 dB above the chirp level were measured for air-conducted chirp trains of center frequencies 500, 1000, 2000, and 4000 Hz, respectively. For bone-conducted chirp trains, noise levels of 53.4, 38.1, 29.1, and 42.2 dB above the chirp level were necessary to mask the signals. The masker levels measured in this study can be used in the clinical routine to enhance the diagnostic quality of hearing assessments in patients with asymmetric hearing loss.