[Sound localization in patients with asymmetrical hearing loss]

Good directional hearing ability demands good and symmetrical hearing in both ears. We report the effect of impaired hearing on the directional hearing ability of 98 patients, especially of patients with bilateral asymmetrical hearing loss. The directional testing device included 12 loudspeakers placed at 30 degree intervals in a circle with a diameter of 3.25 m, whose centre lay between the ears of the patient. In included an audiometer for producing the signals, an amplifier and a PDP11/23 computer interfaced to a loudspeaker switch bank. The subject's answers to 60 directionally randomized stimuli were recorded. During the presentation of the signal the patients were not allowed to turn their head. The patients had to name the number of the loudspeaker on the circle that they thought was producing the sound. In addition to the directional hearing test a pure-tone audiogram was done, and the middle- and high-frequency hearing loss estimated. The records of the directional hearing test were analysed in two new ways: firstly, vector analysis of the errors; secondly, averaging of the difference between the true interaural time delay and the virtual time difference, which was implicated in the possibly incorrect answer of the patient (effective delta-t-parameter). This average gives a score for the uncertainty in defining the correct "cone of confusion". In addition to the statistical analysis, two cases are reported showing the directional hearing ability of two patients with neuromas treated by transtemporal surgery, with some residual hearing.(ABSTRACT TRUNCATED AT 250 WORDS)