Adult listeners’ processing of indexical versus linguistic differences in a pre-attentive discrimination paradigm

The human ability to comprehend speech regardless of variation across speakers and accents has long puzzled researchers. Human listeners appear to employ separate mechanisms to cope with speaker versus accent variation. The present study uses event-related potentials (ERP) to test whether such different mechanisms exist at a pre-attentive level of speech processing.
We assessed Australian English monolinguals’ and bilinguals’ perceptual sensitivity to four types of variation in vowels: namely, variation in speaker identity, gender, accent, and vowel category. Interestingly, listeners showed similar results regardless of their linguistic background. As expected, listeners showed large sensitivity to accent changes. Rather surprisingly, however, they were more sensitive to changes in speaker gender than to changes in vowel category. These results are not in line with those of overt vowel classification but are explained by adults’ sensitivity to large differences in voice quality when discriminating speech sounds.