Asymmetries in vowel perception

Asymmetries in vowel perception occur such that discrimination of a vowel change presented in one direction is easier compared to the same change presented in the reverse direction. Although such effects have been repeatedly reported in the literature there has been little effort to explain when or why they occur. We review studies that report asymmetries in vowel perception in infants and propose that these data indicate that babies are predisposed to respond differently to vowels that occupy different positions in the articulatory/acoustic vowel space (defined by F1–F2) such that the more peripheral vowel within a contrast serves as a reference or perceptual anchor. As such, these asymmetries reveal a language-universal perceptual bias that infants bring to the task of vowel discrimination. We present some new data that support our peripherality hypothesis and then compare the data on asymmetries in human infants with findings obtained with birds and cats. This comparison suggests that asymmetries evident in humans are unlikely to reflect general auditory mechanisms. Several important directions for further research are outlined and some potential implications of these asymmetries for understanding speech development are discussed