Perceptual sensitivity to spectral change in Australian English close front vowels : an electroencephalographic investigation

Speech scientists have long noted that the qualities of naturally-produced vowels do not remain constant over their durations" regardless of being nominally "monophthongs" or "diphthongs". Recent acoustic corpora show that there are consistent patterns of first (F1) and second (F2) formant frequency change across different vowel categories. The three Australian English (AusE) close front vowels /iË, ɪ, ɪə/ provide a striking example: while their midpoint or mean F1 and F2 frequencies are virtually identical, their spectral change patterns distinctly differ. The present study utilizes a pre-attentive discrimination paradigm with electroencephalography to assess AusE listeners' perceptual sensitivity to close front vowels with different F1 × F2 trajectory lengths (TLs) and directions (TDs). When TLs are modest, there is an asymmetry in perceptual sensitivity: closing vowels, e.g., /iË/ whose trajectory terminates high in the F1 × F2 vowel space, are perceptually prominent, whereas centering vowels, e.g., /ɪ, ɪə/ whose trajectories end more centrally, are not. However, when TLs are exaggerated, the asymmetry in the perceptual sensitivity to the two TDs is substantially reduced. The results indicate that, despite the distinct patterns of spectral change of AusE /iË, ɪ, ɪə/ in production, its perceptual relevance is not uniform, but rather vowel-category dependent.