Directional Hearing Capacity in Hearing Disorders

Abstract

Jongkees & Groen investigated from which direction a test person with closed eyes would estimate that a sound is coming. In order to obtain objective and measurable results they used a graduated circle (radius 50 cm) along which the sound source could be moved and on which the test person was requested to indicate where he thought the source was situated. As a diagram of his directional hearing, the subjective place, as indicated by the test person, was plotted as a function of the objective place, both in degrees as marked on the arc graduation. Directional hearing is examined in a group of patients suffering from various types of loss of hearing. The results are compared with the diagram for directional hearing in the horizontal plane as found in a series of normal test subjects. Statistically a probable limit value for directional hearing in the horizontal plane is obtained by using Wilcoxon's symmetry test. Otitis media chronica, atresia, nerve deafness, otosclerosis, fenestration, tympanoplasty and unilateral total deafness were the groups examined in this investigation. It was evident from these examinations that neither a conduction deafness, nor a difference in hearing acuity of the two ears necessarily resulted in an impairment of directional hearing. Patients from the perception deafness group often had impaired directional hearing. However, no relationship between the types of audiograms neither in a.c. nor in b.c. and the degree of loss in directional hearing could be found. Otosclerosis patients (subjected to a fenestration or not) all showed strongly disturbed directional hearing. The hypothesis is submitted that in these patients a change in time and phase pattern may cause the loss in directional hearing. Unilateral total deafness does not necessarily prevent directional hearing. In our series of 10 patients two had normal directional hearing and one a slight impairment only. Only a few patients spontaneously complained about the loss of directional hearing in daily life.