On a dynamic threshold for the perception of diphthongization

This research investigates the minimal amount of spectral change beyond which a vocalic segment is perceived as diphthongized. Perceptual experiments based on both natural and synthetic stimuli are presented. The results of these experiments lead to a first tentative definition of a threshold for the perception of diphthongization. Moreover, it will be shown that this threshold is not static, but rather varies as a function of duration. A formula that allows us to predict the values of the threshold for vocalic segments of different durations will therefore be proposed. Lastly, the theoretical implications of these findings will be discussed in relation to the processes of spontaneous diphthongization documented in many Italo-Romance dialects.