Reduction of unstressed central and back vowels in Contemporary Standard Bulgarian

This paper reports two experiments that examine unstressed vowel reduction and neutralisation in Contemporary Standard Bulgarian. Stress-dependent F1 and F2 frequency variation was measured for the central and back vowel pairs in careful speech. The results reveal a less unequivocal picture of the pairwise convergence of formant frequencies than has previously been reported: the data confirm a high degree of acoustic overlap only for the unstressed back vowels, /O – u/, whereas the differences in the unstressed central vowels, /a – @/, remain statistically significant. A perception experiment consisting of an identification and a discrimination task was designed to test whether the existing differences in unstressed vowels are perceptually significant. The correct-response rates in both tasks were not significantly higher than chance. This partial mismatch between acoustic and perceptual data points to incomplete, rather than categorical neutralisation.