Binaural asymmetry for centering

Abstract

An influence of binaural hearing aids on centering phantom images from stereophonic loudspeakers was investigated. When the subject is a symmetrical receiver the location of the phantom image depends on the level difference ΔL between the two signals. A phantom image appears on the midline from both loudspeakers when ΔL is 0 dB and the listener is a symmetrical receiver. The symmetry can be altered by peripheral means such as earplugs, monaural aids, or binaural unbalanced hearing aids, or by asymmetrical hearing loss. The asymmetry of the subject, called “binaural asymmetry,” was measured for 10 normal‐hearing and 14 hearing‐impaired subjects in unaided and aided conditions. In aided conditions binaural hearing aids with identical gains (balanced) or with 10‐dB disparity between the gains (unbalanced) were used. It has been found that the normal range of binaural asymmetry in the unaided condition is ±2 dB and it is slightly greater for the aided balanced condition. Unbalanced aids introduced average ±3‐dB additional asymmetry. The variability among subjects was greater for hearing‐impaired than for normal‐hearing subjects and was greater for aided than for unaided condition. It has been postulated that difficulties in adaptation to hearing aids and errors in localization may result from additional asymmetry introduced by hearing aids. (Work supported by NIH.)