These people created stimuli that are supposed to sound like the steps between a Proto-Germanic monophthong and the corresponding Old English diphthong, i.e., the x-axis is the degree of monophthongization to dipthongization. They then made listeners judge whether they heard a dipthong or monophthong (after som training).
Figure 3: Mean responses to stimuli for all fifteen vowel continua. Grey squares: Monophthongal ("unchanging") responses. Black circles: Diphthongal ("changing") responses.
Hudson, Toby, Jonathan Wei & John Coleman. 2024. Using acoustic-phonetic simulations to model historical sound change. Diachronica (not assigned issue/volume yet). https://doi.org/10.1075/dia.23019.hud.











