Although phonologists acknowledge the phonemic contrast between oral and nasal vowels in Portuguese, few studies examine their acoustic and articulatory differences. Some of these include Kelm (1989), which focuses on the acoustic differences between /a/ and /~/ and Gigliotti de Sousa (1994), which investigates acoustic characteristics of nasal and oral monophthongs in southern Brazil. Two studies which measure nasal airflow of nasal(ized) vowels are Medeiros (2011) and Fails (2011), which both provide evidence for different acoustic targets for nasal (contrastive) and nasalized (allophonic) vowels in Brazilian Portuguese (Medeiros 2011) and between Portuguese nasal and Spanish nasalized vowels (Fails 2011).
The current study contributes to the investigation of Portuguese vowels with an acoustic analysis of oral and nasal vowels in six L1 Brazilian Portuguese speakers and four Spanish-English bilinguals who learned Portuguese as an L3. Real words containing all Portuguese vowels (see Table 1) were embedded in naturalistic sentences as well as the carrier sentence “Diga ____ também” (“Say ____ as well”). Real words1 containing Spanish vowels in oral and nasalized contexts were also included in a Spanish reading passage (see Table 2) to allow for comparisons of the L3 Portuguese group‟s Spanish and Portuguese production.
An analysis of the Portuguese vowels formants (F1 and F2) revealed no significant differences between groups except for /~/, which had higher tongue height when produced by the L1 Portuguese group. Results for vowel duration revealed a significant effect for type of vowel (oral or nasal) for all cases except /a/, in which nasal vowels were longer than oral vowels in both L1 groups, suggesting that both groups used duration as a mechanism for differentiating oral and nasal vowels. The comparison between the L3 Portuguese group‟s Spanish and Portuguese vowels also revealed few differences in formants and vowel duration, but longer nasal consonant duration in Spanish than Portuguese. These results provide evidence not only for positive transfer, facilitated by cross-linguistic similarity, but also the creation of a new phonetic category (Flege 1995) concerning the nasal consonant that follows the vowel in these contexts.
Work currently in progress considers additional acoustic correlates of nasalization, specifically the A1-P0/P1 technique used in Chen (1997) in which nasality is calculated by the difference between the amplitude of the first formant (A1) and the harmonic near a nasal pole (P0 or P1). Preliminary results, similar to Chen (1997), revealed differences in nasal and nasalized vowels, suggesting the phonemic status of nasal vowels as a source of these differences in acoustic targets. The current study measures the A1-P0/P1 for both Spanish and Portuguese tokens with two main objectives: (i) to measure differences in the levels of nasality between Spanish nasalized and Portuguese nasal vowels for comparison to the results of both Medeiros (2011) and Fails (2011), and (ii) to determine if the L3 Portuguese speakers make a level of nasality distinction between Spanish nasalized and Portuguese nasal vowels in their speech, which would also provide insight to acquiring new contrasts in a typologically similar language. Implications for both the acquisition of phonology and underlying representations of nasal/nasalized vowels will be discussed.

¹ All Spanish tokens except “Pento” (a character's name in the reading task) were real words

References
Chen, Marilyn. 1997. Acoustic correlates of English and French nasalized vowels. Journal of the Acoustical Society of America 102 (4): 2360-2370
Fails, Willis. 2011. O grau de nasalização das vogais oronasais no português paulistano e no espanhol mexicano: Um estudo experimental comparativo. Hispania 94 (3): 442-461.
Flege, James. 1995. Second language speech learning: Theory, findings, and problems. In Winifred Strange (ed.), Speech perception and linguistic experience: Issues in cross-linguistic research, 101-131. Mahwah, NJ: Lawrence Erlbaum Associates.
Gigliotti de Sousa, Elizabeth Maria. 1994. Para a caracterização fonético-acústico da nasalidade no português do Brasil. Campinas, SP: Universidade Estadual de Campinas thesis.
Kelm, Orlando. 1989. Acoustic characteristics of oral vs. nasalized /a/ in brazilian portuguese: Variation in vowel timbre and duration. Hispania 72 (4) (Dec): 853,853-861.
Medeiros, Beatriz Raposo de. 2011. Nasal coda and vowel nasality in Brazilian Portuguese. In Scott Alvord (ed), Selected Proceedings of the 5th Conference on Laboratory Approaches to Romance Phonology, 33-45. Cascadilla Proceedings: Somerville, MA.