Calculating the Hearing Threshold from the Stapedius Reflex Threshold for Different Sound Stimuli

Abstract

The acoustic stapedius reflex depends not only on stimulus intensity, but also on stimulus frequency, as far as reflex threshold, amplitude of response and reflex decay are concerned. The stapedius reflex threshold (SRT) for wide-band noise has been proved lower than that for pure tones. Our own investigations dealt with the relation between the SRTs for pure tones, white noise, and a 24-tone mixture (one single tone at every critical band width) in normal-hearing persons and patients suffering from sensorineural hearing loss

In normal hearing, the SRT for pure tones was measures at 70-85 dB (73-105 dB SPL) above the normal-hearing threshold in a free sound-field, the SRT for white noise (average) at 46.5 dB (68.5 dB SPL) and the SRT for the 24-tone mixture at 47.0 dB (67.2 dB SPL). In 125 patients (223 ears), the difference level between the mean SRT for tones of 0.5-4 kHz and the SRT for white noise (dl 2) was correlated with the difference level between the mean SRT for tones of 0.5-4 kHz and the mean hearing threshold for tones of 0.5-4 kHz (dl 1). The functions were found to be roughly linear: dl 2 = dl 1/2.5 and dl 1 = 2.5 dl 2. Validity: 73% ∼ 10 dB; 17% ∼ 15 dB, and 10% ∼ 20 dB. Since the dB-value of the mean SRT for pure tones of 0.5-4 kHz can be read from the audiogram, it is possible to calculate the mean hearing threshold for 0.5-4 kHz from dl 2 with equal validity: mean hearing threshold 0.5-4 kHz = SRT tones -2.5 dl 2

In cases of falling threshold curves the results become less exact and in addition to the SRT for white noise and pure tones, the SRT for two tone-mixtures was determined, namely for one low-pass noise consisting of 12 sine waves of 100-1 600 Hz, and for one high-pass noise consisting of 12 sine waves of 1.8-13.5 kHz. In normal hearing, the dl 2 for the low-pass noise is ∼ 15 dB and for the high-pass noise ∼ 20 dB (3:4). In falling audiograms, the dl 2 for the high-pass noise was found to be equal or lower than that for the low-pass noise. Investigations in sleeping children indicated that these relations were practically unchanged

A correlation of the free-field findings with the loudness calculated by Zwicker's procedure showed that the triggering of the stapedius reflex by wide-band sounds is due to the centrally summated loudness and not the SPL

Key Words:

• Objective audiometry
• Formation of loudness
• Loudness calculation
• White noise
• Critical band width
• Acoustic reflex
• Intra-aural reflex