Tóth József (szerk.): Nyelv, kultúra, megértés: új kutatási módszerek a humán tudományok területén
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1. Nyelvi rendszerek és jelentésleírás
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Production and perceptual representation of American English vowels by monolingual and bilingual Iranian Learners • Naeimeh Afshar, Vincent J. van Heuven
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3. Perceptual representation of the AE vowels in L1 and L2
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3.3. Results
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3.3.1. Perceptual representation: centroids and dispersion ellipses

3.3.1. Perceptual representation: centroids and dispersion ellipses

Jegyzet elhelyezéséhez, kérjük, lépj be.!

Figure 7 presents the centroids and dispersion ellipses in the F1 by F2 plane (both axes in Barks) for the responses obtained from the three listener groups. The centroids are located in the middle of each phonetic symbol in the figure. Ellipses were drawn such that they include the most typical 25% of the vowel qualities associated with each category.1 The panels in the upper row are based on the short stimulus vowels (200 ms), while the bottom panels are based on the long vowel stimuli (300 ms). The left-hand panels (A, D) show the monolingual EFL learners, the middle panels (B, E) the early bilinguals, and the right-most panels (C, F) present the responses collected for the American native listeners. There is no breakdown by gender, since all stimuli were synthesized to suggest a male voice.

Jegyzet elhelyezéséhez, kérjük, lépj be.!

Figures 7/A–7/D show that the qualities of the synthesized stimuli were interpretable by the monolingual Persian learners of English. Stimuli with /i/, /u/ and /æ/-like vowel qualities end up in the left-top, right-top and mid-bottom part of F1-by-F2-plane. We also observe that the learners make a clear distinction, with a large distance between the centroids and no overlap between the spreading ellipses, between AE /ε/ and /æ/, which is what one would expect given the presence of near-equivalents in the learners’ L1 – whereas this particular contrast is a well-known problem for many other EFL speakers (e.g., Van Heuven, 2016). What immediately strikes the eye is the absence of a contrast between the tense and lax (mid-) high front vowels /i-ɪ/ and between the high back vowels /u/~/ʊ/. The centroids are virtually in the same locations and the spreading ellipses show almost complete overlap. We also see very little difference in the configuration of the vowel responses between the two panels – no effects of the difference in vowel duration are apparent.

Jegyzet elhelyezéséhez, kérjük, lépj be.!

The observations that were made for the monolingual EFL learners equally apply to the early bilingual learners. There is almost complete overlap between the location of the centroids and the dispersion ellipses for the short/lax and long/tense counterparts in the pairs /ɪ-i/ and /ʊ-u/ but a clear distinction between mid and low front vowels /ε-æ/ is maintained. The (mid)- high back vowels are poorly separated, as are the (mid-)low back vowels. The centralized mid-low back vowel /ʌ/, however, seems to be better separated from the other (mid-)low back vowels (/ɔ, ɑ/) than was seen in the monolingual results.
 

Jegyzet elhelyezéséhez, kérjük, lépj be.!

Figure 7. Centroids and spreading ellipses obtained from vowel identification of 86 synthesized vowel tokens differing in F1, F2 (Barks) and duration (see Figure 6). Ellipses include the 25% central-most datapoints around the category centroid. Separate panels show the responses given by 21 monolingual Persian EFL learners (A, D), 27 early bilingual Azerbaijani/Persian EFL learners (B, E), and 20 American native listeners (C, F).
 

Jegyzet elhelyezéséhez, kérjük, lépj be.!

The results for the American native listeners are shown in Figure 7, panels C and F. The most striking difference between the foreign and the native representation of the AE vowel system is that the L1 listeners maintain a clear difference between the long/tense versus short/lax counterparts, /i/~/ɪ/ and /u/~/ʊ/. There is a large distance between the centroids associated with the members of these pairs, and there is no, or only relatively little, overlap between the spreading ellipses. Notice that the centroids of the lax vowels, especially those of /ɪ/, /ʊ/ and /ʌ/ are rather centralized when computed for the long stimulus vowels, but assume more peripheral locations (closer to the tense counterparts) when heard with short duration. This would be a first indication that vowel quality and duration are in a trading relationship in the native speakers’ mental representation of the tense-lax vowels. For a phonetically long vowel to be perceived as a lax member of a contrast, it has to be very clearly centralized. When a less centralized vowel is short (enough), it will still be perceived as lax. It is also apparent that the native listeners do not maintain distinct vowel categories for pair of tense vowels /ɑ/~/ɔ/ and for the lax vowels /ʊ/~/ʌ/.2
 
1 The plots were produced with Visible Vowels (Heeringa, Van de Velde, 2018) – with some post-editing. We narrowed the ellipses to include only 25% central-most data points to avoid visual clutter. Since some of the synthesized vowels assume extreme positions in the vowel space, and the task was forced choice, the scatter in the responses is much larger than what was seen in the corresponding vowel production data in section 2.
2 Most Californian speakers, and speakers in the western half of the USA, do not distinguish between /ɔ/ and /ɑ/ (the vowel sounds in caught versus cot), characteristic of the cot–caught merger (Labov et al., 2006; see also Ladefoged, Johnson, 2011: 212–213). Also, /ʊ/ is moving towards [ʌ] (so that, for example, book and could in the California dialect start to sound, to a GA speaker, more like buck and cud), /ʌ/ is moving beyond [ɜ].
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