Similarity of vowel-formant ensembles in phonetic contexts: a vowel-axis shift in perspective

Systematic effects of phonetic context on vowel-formant ensembles (VFEs) are uncovered using the hypothesis that, for a given formant and a given speaker, the relative spacing between vowels is unaffected by consonantal context or by location within a syllable. The invariance in inter-vowel spacing implies that, within and between contexts, VFEs will be geometrically similar to and, therefore, linearly-scaled copies of one another. Here we explain this vowel-axis shift in perspective and, then, describe the sequence of steps leading to scale factors, with which one can compare the relative strengths of different contexts or normalise for context effects. This is illustrated using formant-frequency data measured at onglides and steady-states of 5 Arabic vowels in 13 fricative contexts.