Effects of masker harmonicity on masked threshold

Abstract

The role of masker harmonicity in auditory masking is not yet fully understood. This paper compares the effect of harmonic and inharmonic maskers on the simultaneous masked thresholds of narrow bandwidth noise probes using a three-alternative, forced-choice method. The harmonic masker had an 88-Hz fundamental and 45 consecutive partials (random starting phases). The inharmonic masker differed in that the partial frequencies were adjusted to nearby prime numbers. Maskers were presented at several levels, and the probe at several frequencies. Thresholds were consistently lower for the harmonic masker (4–8 dB). The masking release persisted when masker and probe bandwidths were equal, so it is not due to comodulated auditory filter outputs. The difference between maskers disappeared when the harmonic partials were separated by more than 176 Hz, suggesting that the effect may be related to critical bandwidth. Further, the threshold of noise probes located between two partials was always lower for the harmonic masker. However, the threshold for a tonal probe at the frequency of an omitted partial was higher with the harmonic masker than with the inharmonic masker. The results are consistent with a harmonic template model that proposes inhibition at the template frequencies and disinhibition between those frequencies.