Aural Harmonics: The Tone-on-Tone Masking vs. The Best-Beat Method in Normal and Abnormal Listeners

Abstract

Amplitude distortion is revealed through the generation of harmonics when a pure tone signal of sufficient intensity is presented to the ear. The psychophysical procedure most commonly used to detect the onset of aural harmonics, called the threshold of the aural harmonic, is the method of best-beats. This technique, however, is difficult to use clinically: Complex time-consuming judgements are required and the obtained measurements have an overestimation bias due to masking. A tone-on-tone masking procedure is described and suggested as a simpler alternative for obtaining the same information.

Two experiments have been performed to demonstrate the similarity between the harmonic threshold and the masking threshold. In the first, the thresholds of masking at one octave above the fundamental (= 1000 Hz) and tlie second harmonic thresholds are shown to be within a few dB SL of each other in normal ears. In addition, both techniques tend to rank the two ears of the same listener in a similar way. The second study shows that the masking thresholds for a small sample of abnormal listeners are lower than for a comparable group of normals. Also, the mean masking threshold of tlie abnormals, 26 dB SL, is within the range of harmonic thresholds, 13 to 30 dB SL, reported by previous investigators. Thus, these preliminary results indicate that the diagnos- tic information obtained by the tone-on-tone masking technique is equivalent to the harmonic thresholds measured by the best-beat method. The masking procedure is both simpler and quicker than tlie best-beat method and, therefore, more practical for use in the clinic.