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Hearing of Speech by Bone Conduction
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1937
Year
Vibrator ButtonSpeech KinematicsElectroglottographySpeech ScienceOrthopaedic SurgeryKinesiologyAuditory ScienceAcoustic AnalysisHealth SciencesAuditory ProcessingAural RehabilitationAudiologyArtsSpeech AcousticAuditory ResearchHearing ConservationHuman HearingBone ConductionPercent ArticulationSpeech CommunicationArticulation ListsHearing SciencesHearing LossSpeech AcousticsAuditory PhysiologySpeech Perception
A method for testing hearing of speech by bone conduction has been developed on the basis of Fletcher and Steinberg's articulation testing methods. High quality recordings of the articulation lists were substituted for callers. A special induction type electrodynamic bone conduction vibrator was developed from the original Barany-Schwarz Knochentelefon. It is linear over a wide intensity range for all speech frequencies and has a frequency response characteristic which allows clear transmission of speech. The method and apparatus have been tested by a comprehensive series of measurements on an individual with hearing slightly above normal. The force of application of the vibrator necessary for best understanding of speech was found to be approximately 350–400 grams-weight. The best area of vibrator button varied with conditions; for open ear canals a button of 0.7 sq. cm area gave higher articulations than larger ones and as high scores as smaller, less comfortable ones; for closed ear canals a larger button gave better results. Speech was heard best by bone conduction when the observer's mouth was closed, his teeth touching but not clenched, and his ear canals occluded. The variation of percent articulation with level-above-threshold was studied for bone conduction with both open and occluded canals and for air conduction with one ear and two. The curves obtained were coincident within observational error, indicating the same functional relation in all four cases. (The intensity levels at threshold varied for the four cases, being greater for bone conduction than for air conduction and greater for open-canal bone conduction than closed-canal.) A large amount of frequency distortion was tolerable without seriously affecting the articulation as long as there was no nonlinear distortion. Finally, all the results have revealed that the hearing of speech by bone conduction may attain as high a degree of perfection as that attained by the more usual method of air conduction.