Neutralisation and the perception of close-mid and open-mid vowels: the gradient between phonological categories

Abstract

A prototype theoretical framework was the basis of a study on the impact of neutralisation on the perception of Portuguese close-mid and open-mid vowels and the gradient between phonological categories. Fifteen Portuguese listeners from Lisbon participated in identification and goodness rating tasks of 20 random repetitions of 31 stimuli from a /i/-/e/-/ε/-/a/ continuum. Boundaries between categories were explored using logistic regression curves and analysis of variance. Results from the identification task revealed four vowel categories marked by three statistically distinct boundaries. The prototype of a category, i.e., the stimulus with the highest goodness rating score, was approximately in the centroid and the goodness score decreased as the stimulus moved away from this centroid. The boundary between /e/ and /ε/, the underlying opposition that neutralises at surface level, was less steep than between /ε/ and /a/, the opposition that never neutralises, a possible influence of the phonological system on speech perception.