Directional Audiometry: III. The Influence of Azimuth on the Perception of Speech in Patients with Monaural Hearing Loss

Abstract

The Directional Threshold of Intelligibility (DTI) both with and without background noise has been determined in 37 patients with one-sided hearing defects ranging from a 30 dB loss to total deafness. Free field speech audiometry was done with an apparatus permitting independent radial positioning of a speech loudspeaker and a noise loudspeaker on the circumference of a horizontal circle centred on the head of the seated person examined. The DTI measured without noise not only depended upon the amount of the hearing loss in the defective ear, but also upon slight variations in the hearing ability of the good ear. A relationship between the DTI without noise and the normal ear's Pure Tone Average (PTA) in the range 500, 1 000, and 2 000 Hz was found. In the persons examined it was also found that when speech was reproduced against background noise under certain conditions the bad ear contributed to the perception oE speech if the person tested had one-sided PTA of 53 dB hearing level or less.