Comparative studies of masking by harmonic complexes in several species of birds

Abstract

Studies of masking by harmonic complexes have been useful in identifying some of the mechanisms that may contribute to the processing of complex sounds. In humans, for instance, harmonic complexes constructed in positive and negative Schroeder phase are differentially effective as maskers even though they have identical temporal envelopes and long-term spectra — a result that may reflect the phase response of the mammalian basilar membrane. Recent experiments on budgerigars show significant differences from the responses observed in humans [Dent et al., J. Acoust. Soc. Am. 104, 1811 (1998)]. Here, we extend the generality of the budgerigar masking results to three other bird species. Masked thresholds for tones embedded in Schroeder-phase maskers were measured in budgerigars, canaries, zebra finches, and fire finches using operant conditioning and the method of constant stimuli. All species produced similar masking results to those reported earlier for budgerigars: none of the birds showed greater masking by the negative than the positive-phase waveforms, and in some cases the positive waveform was the more effective masker. These results may reflect general differences in the processing of complex sounds in avian versus mammalian cochleas. [Supported by NIH R01 DC00198 and NRSA DC00046.]