Perception of noise-vocoded tone complexes: A time domain analysis based on an auditory filterbank model

Cochlear tuning and the peripheral representation of harmonic sounds in mammals

Albert Feng was a prominent comparative neurophysiologist whose research provided numerous contributions towards understanding how the spectral and temporal characteristics of vocalizations underlie sound communication in frogs and bats. The present study is dedicated to Al's memory and compares the spectral and temporal representations of stochastic, complex sounds which underlie the perception of pitch strength in humans and chinchillas. Specifically, the pitch strengths of these stochastic sounds differ between humans and chinchillas, suggesting that humans and chinchillas may be using different cues. Outputs of auditory filterbank models based on human and chinchilla cochlear tuning were examined. Excitation patterns of harmonics are enhanced in humans as compared with chinchillas. In contrast, summary correlograms are degraded in humans as compared with chinchillas. Comparing summary correlograms and excitation patterns with corresponding behavioral data on pitch strength suggests that the dominant cue for pitch strength in humans is spectral (i.e., harmonic) structure, whereas the dominant cue for chinchillas is temporal (i.e., envelope) structure. The results support arguments that the broader cochlear tuning in non-human mammals emphasizes temporal cues for pitch perception, whereas the sharper cochlear tuning in humans emphasizes spectral cues.

Efficiency in glimpsing vowel sequences in fluctuating makers: Effects of temporal fine structure and temporal regularity

Listeners' efficiency in glimpsing the target speech in amplitude-modulated maskers may depend on whether the target is perceptually segregated from the masker and on the temporal predictability of the target. Using synthesized vowel sequences as the target, recognition of vowel sequences in simultaneous amplitude-modulated noise maskers was measured as the signal-to-noise ratio (SNR) and the masker modulation rate were systematically varied. In Experiment I (Exp. I), the temporal fine structure of the target was degraded by synthesizing the vowels using iterated rippled noise as the glottal source. In Experiment II (Exp. II), the vowel sequences were constructed so that they were not isochronous, but instead contained randomized intervals between adjacent vowels. Results were compared to the predictions from a dip-listening model based on short-term SNR. The results show no significant facilitative effect of temporal fine structure cues on vowel recognition (Exp. I). The model predictions significantly overestimated vowel-recognition performance in amplitude-modulated maskers when the temporal regularity of the target was degraded (Exp. II), suggesting the influence of temporal regularity on glimpsing efficiency. Furthermore, the overestimations by the model were greater at lower SNRs and selective to moderate masker modulation rates (between 2 and 6 Hz).