Aural Harmonics: A Possible Relation to Loudness

Abstract

Two aspects of auditory function vary as frequency is lowered: (1) the rate of loudness growth for pure tones increases, and (2) at equivalent SLs, the magnitude of harmonic distortion (CM) is greater. Noting these relationships, Wever, hypothesized that the central summator yields a sensation of loudness based on its total input and that the neural responses caused by a pure tone fundamental (f1) are incompletely differentiated from the excitation of its aural harmonics. Such reasoning also suggests that dissimilarities in loudness growth rates between individuals at any particular f1 may be directly related to differences in their aural harmonic magnitudes. Four normals performed ratio (double/half) sealing at 1 and 2 kHz. Using these frequencies as f1's, the second and third harmonics were also estimated from tone-on-tone masking measurements [60–90 db (SPL) at 10-dB intervals]. These distortion estimates further support description of aural harmonic growth by the power law. The covariation of aural harmonic magnitudes and loudness growth rates are not clear for f1 = 2 kHz. For f1 = 1 kHz, however, an inverse relationship is evident. This finding suggests that for intensities at which aural harmonics are masked, their contribution to the loudness of f1 may be subtractive rather than additive.