Bone-Conducted Speech Reception ThresholdAn Investigation with the Oticon a 20 Bone Vibrator Calibrated on the Brüel & Kjær Artificial Mastoid

Abstract

This study proposes a new clinical parameter, the bone—conducted speech reception threshold, and hypothesises its correlation with other clinical variables, viz. the three frequency pure—tone averages of air—and bone—conducted thresholds, and the air—conducted speech reception threshold. Three groups of population were studied: (1) Normal—hearing group, (2) Conductive hearing loss group, and (3) Sensorineural hearing loss group. The audiometer was calibrated to ISO standards for air conduction and to B.S. draft proposal values for bone conduction. The Oticon A 20 bone vibrator was used (conforming to IEC R 373, 1971), calibrated on a Brüel & Kjær artificial mastoid 4930 (conforming to IEC R 373, 1971 and B. C. 4009: 1966). The study confirms the reproducibility of the British Standard for bone conduction threshold and proves the utility of the Brüel & Kjær artificial mastoid as well as of the Oticon bone vibrator. The results indicate significant correlations between the bone—conducted speech reception threshold and the other variables studied, thus supporting the hypothesis. The clinically useful construct of “Air—bone gap for speech”, is evolved. In both pathological groups, a significant correlation between the air—bone gap for speech and the air—bone gap for pure—tone averages was found. However, some patients exhibited a considerably (up to 25 dB) larger air—bone gap for verbal than for tonal stimuli. This was particularly found in cases with sloping bone conduction curves. Larger populations will be studied.