Aural Harmonics: Tone-on-Tone Masking at Lower Frequencies of a Fundamental

Abstract

Monaural presentation of a pure tone fundamental (f1) together with an objective second harmonic (f2) has been used to demonstrate the presence of aural harmonics. The listener's task involves tracing a Békésy-type threshold for the f2 as it is shifted through 360° relative to f1. The phase shift produces changes in threshold sensitivity described by the equation Y = A1 + A2 sin (x+φ). These results have been interpreted in terms of a model that has three major assumptions: (a) the ear generates an aural harmonic (AH); (b) the objective f2 and AH sum vectorially; (c) the listener must maintain the resultant at some perceptual threshold level. This model also successfully predicted a peculiar reversal of the usual masking effect. All previous studies have been limited, however, to f1=1000 Hz. The present experiment reports results obtained from 10 normal listeners using f1=500 Hz at intensities between 51 and 71 dB SPL. Preliminary analysis confirms that the threshold changes sinusoidally but the reversal of the usual masking effect is absent. The derived values of A1, A2, and φ will be discussed in relation to the model and previous results. [Work supported by a grant from the National Institutes of Health.]