Cross-linguistic investigation of neutralization
The extent to which phonological contrasts are phonetically maintained has been actively pursued over the past 30 years. Our research contributes to this debate in a number of ways. In an early study (Kim and Jongman, 1996), we investigated neutralization of manner of articulation instead of word-final voicing, the focus of most studies of neutralization. This research explored the underlying three-way distinction among word-final fricatives, plain stops, and aspirated stops in Korean. Results suggest that Korean manner neutralization offers a perhaps rare instance of the standard view of neutralization, producing outputs which are not distinguished in either production or perception.
A detailed acoustic and perceptual investigation of word-final devoicing in Dutch showed that there are small but consistent differences in the duration of the final consonant and its preceding vowel and that, under certain circumstances, listeners can use these differences to determine the underlying voicing of the consonant (Warner, Jongman, Sereno, and Kemps, 2004). This research also showed that a wide variety of factors, in addition to underlying form, can induce speakers to produce slight durational differences which listeners can also use in perception.
Our recent investigation of flapping in American English which neutralizes the underlying distinction between pairs such as ‘leader’ and ‘liter’ showed a similar pattern in that vowels preceding /d/ were significantly longer than those preceding /t/ English (Herd, Jongman, and Sereno, J. Phonetics, in press). Flap frequency was analyzed based on a new and non-arbitrary method of distinguishing flapped from unflapped stops on a speaker-by-speaker basis. Contrary to past research, neither word frequency nor morphological complexity affected flap frequency in the present study. Perceptually, vowel duration alone did not predict the listeners’ perception of flapped /t/ and /d/; word frequency, where high frequency words were identified correctly more often than low frequency words, and a d-bias, where /d/ flaps were identified correctly more often than /t/ flaps, did prove significant.
Finally, we have begun to explore neutralization by second language learners. Specifically, we investigated the extent of word-final devoicing in Russian for monolingual native Russian speakers, native Russian speakers with knowledge of English, and American English learners of Russian (Dmitrieva, Jongman, and Sereno, J. Phonetics, 2010). Acoustic analysis indicates the absence of complete neutralization of underlying voicing for all three groups. Moreover, correlations indicated that speakers with higher English proficiency produced greater differences for vowel duration. In addition, native speakers of English learning Russian also distinguished final obstruents in terms of preceding vowel duration, closure/frication duration, duration of voicing into closure/frication, and duration of release portion, with greater durational differences for these second language learners than for Russian native speakers. The more proficient speakers of Russian decreased the durational differences and the most proficient second language learners were closer to complete neutralization than monolingual speakers of Russian.