Measurement of hearing-protector attenuation using auditory steady state responses

Abstract

There is a need to assess hearing protection device (HPD) attenuation to ensure that individuals receive adequate protection from noise. Present methods of attenuation measurement have limitations. Objective measurements such as field microphone in real ear (F-MIRE) do not assess bone conducted sound. Psychophysical measurements such as real ear attenuation at threshold (REAT) are biased due to the low frequency masking effects from test subjects' physiological noise, and the variability of measurements based on subjective response. We explored using auditory steady state responses (ASSR) as a technique that may overcome these limitations. ASSRs were recorded in ten normal hearing adults, using both “normal” and “occluded” conditions. Stimuli included both narrow band noises and pure tones (500 and 1000 Hz), amplitude modulated at 40 Hz. Stimuli were presented through either loudspeakers or headphones, at 45, 55, and 65 dB SPL. “Physiological attenuation” was calculated as the difference between ASSR values (both amplitude and phase) for normal and occluded conditions. Physiological attenuation estimates were compared to in-ear (objective) and psychophysical (subjective) measurements. Grand mean ASSR data complied well with in-ear and subjective measurements. Further work is needed to provide accurate assessment of ASSR-based physiological attenuation for individual subjects.