Binaural minimum audition in a subject with ranges of deficient acuity.

Abstract

While working on the problem of the bone transmission of sound, the writers found several peculiar effects. At certain pitches, pulsating ringing tones were heard synchronous with the heart beat. Other frequency ranges showed evidences of diplacousis. In determining in which ear a sound was apparently being heard, when the sound was being applied to both ears, “cross-over” effects from one ear to the other occurred as the pitch was changed without referable cause in so far as the acuity curves for the two ears was concerned. Inasmuch as bone transmission is necessarily conveyed to both ears, it was thought essential that binaural acuity for air transmitted sounds be tested as well as monaural. It was also considered important to find out whether or not any reinforcing effect due to the use of the two ears which might be shown in the ranges of normal hearing, would similarly be found in abnormal ranges.

The type of apparatus used has been described elsewhere. 1 Alternating electrical currents were generated by means of a vacuum-tube oscillator and sounds were produced from these currents by the use of the thermophone. The frequencies and intensities were regulated by electrical means. For binaural tests, two exactly similar thermophones were used in series, so that the measured current ran through both of them and the same intensity of sound was applied to the two ears. The absolute intensities were calculated from the currents and from the characteristics of the thermophones.

The results obtained are shown graphically in the accompanying sketches where the sensitivities are given for each ear and also both together. The difference between any two adjacent horizontal lines, as 8 and 9, represents a factor of 10 in the intensity of the applied sounds.