Asymmetric discrimination of nonspeech tonal analogues of vowels.

Directional asymmetries reveal a universal bias in vowel perception favoring extreme vocalic articulations, which lead to acoustic vowel signals with dynamic formant trajectories and well-defined spectral prominences because of the convergence of adjacent formants. The present experiments investigated whether this bias reflects speech-specific processes or general properties of spectral processing in the auditory system. Toward this end, we examined whether analogous asymmetries in perception arise with nonspeech tonal analogues that approximate some of the dynamic and static spectral characteristics of naturally produced /u/ vowels executed with more versus less extreme lip gestures. We found a qualitatively similar but weaker directional effect with 2-component tones varying in both the dynamic changes and proximity of their spectral energies. In subsequent experiments, we pinned down the phenomenon using tones that varied in 1 or both of these 2 acoustic characteristics. We found comparable asymmetries with tones that differed exclusively in their spectral dynamics, and no asymmetries with tones that differed exclusively in their spectral proximity or both spectral features. We interpret these findings as evidence that dynamic spectral changes are a critical cue for eliciting asymmetries in nonspeech tone perception, but that the potential contribution of general auditory processes to asymmetries in vowel perception is limited. (PsycINFO Database Record (c) 2018 APA, all rights reserved).