Doctoral Dissertation Research: Incomplete Neutralization: The Loss and Maintenance of Contrast

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Languages are not always pronounced the way they are written. Over time, the pronunciation of a language changes, but its orthography remains fixed. This poses problems for standardized spelling, language teaching and learning, and even speech recognition technologies, which need to process and convert spoken language into orthographic representations and vice versa. This dissertation addresses the problem of pronunciation change over time, looking specifically at cases where a distinction between two sounds that was previously present and represented orthographically begins to be lost. Changes like this happen gradually, where differences in the acoustics ("acoustic cues") slowly disappear, sometimes without speakers even realizing it. For example, "t" and "d" are different sounds in Dutch, but over time, the difference between "t" and "d" was lost at the ends of words; "bot" (bone) and "bod" (offer) are both pronounced like the English word "bought". This type of sound change, called "neutralization", is not always complete; small but measurable acoustic differences may remain between the two sounds, despite sounding identical to the naked ear. Studies have shown that listeners are able to perceive these differences subconsciously, as they can tell two seemingly-identical words apart (e.g. Dutch "bot" and "bod") at a rate better than chance, even without additional context. It is unknown what causes this incompleteness, how this process unfolds over time, and what social characteristics affect it. Additionally, it is unclear how speakers can tell these sounds apart, and what the necessary acoustics are for distinguishing between them. This dissertation will examine two cases of apparently incomplete neutralization in Dutch and Afrikaans. Both languages are losing the distinction between "t" and "d" and between "p" and "b", both word-initially and word-finally, though they are at different stages of the neutralization process. In four experiments, participants will read words and stories that have these consonants, and then listen to the sounds with manipulated acoustics and see if they can tell them apart. As we discover what differences listeners can hear, we are able to understand more about our cognitive capabilities and how social characteristics can affect our speech and hearing. This knowledge can be used to inform speech recognition technologies to better understand variability in speech production. Additionally, we will have a better understanding of language pronunciation change over time, which can help us develop curricula for teaching foreign languages, especially focusing on the link between reading and pronunciation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.