Figure 3: Comparison of average F2 and F3 formants for epenthetic and full vowels.
3.2. Results on the perception test In general, three tasks were completed with average accuracy rates of 88.4%, 81.6% and 61.3% by the five Mandarin speakers, and 66.7%, 67.5% and 67.4% by English speakers. For Mandarin speakers, the second and third tasks witnessed a substantial drop of accuracy rates [F(3, 617)=8.719, p<.0001], but not for English speakers[F(3, 617)=1.249, p=.576]. For Mandarin speakers, Tukey’s post-hoc test showed that the difference lied in the third task, with tone modified as the constant [Task 1: md=.27, std.E=.214; p=.438; Task 2: md=.27, std.E=.214, p<.001; Task 3: md=.27, std.E=.214, p<.0001]. Consonant differences were drastic across all three tasks. (86.6%, 96.1% and 83.3% for the first task; 85.4%, 100% and 81.7% for the second task, 56.7%, 99.1% and 56.7% for the third task [F(2, 617)=9.467, p<.0001]). Tukey’s post-hoc test showed that the difference lies in the alveolar cluster /tr/. Similar situation exists for English speakers as well. Without the tasks with /tr/ cluster, the percentages were quite different. The three tasks were completed with average accuracy rates of 80.4%, 74.6% and 49.7% by the five speakers for Mandarin speakers and 51.4%, 47.7%, and 46.9% for English speakers. The inter-task difference for Mandarin speakers was even larger and the chance-level of the third experiment was even more salient [F(3, 617)=6.275, p<.0001]. For post-hoc tests, [Task 1: md=.45, std.E=.178; p=.438; Task 2: md=.45, std.E=.178, p<.001; Task 3: md=.45, std.E=.178, p<.0001] (See Figure 4). For both Mandarin and English speakers, between-group differences of vowel and speaker were not significant. As for Mandarin speakers, the average accuracy rates by vowels in the order of /i, /ɑ/, and /u/ were 87.5%, 91.4% and 88.5%, and accuracy rates by individual speaker were 81.55%, 82.2%, 74.4%, 78.8% and 81.5%. For English speakers, accuracy rates by vowel were 51.8%, 42.8%, and 47.7% respectively, and the difference by speaker were 65.67%, 68.6%, 59.4%, and 68.6%, and 70.2%. These differences were all insignificant.
Figure 4: Comparison of mean perceptual accuracy rates by tasks (with /tr/ condition excluded).
4. General Discussions In the production test, the epenthetic and full vowels showed significant differences in duration, but not in F1 and F2 values. We could interpret the insignificant difference in F1 and F2 as evidence for lack of spectral difference for the epenthetic and full vowel. The longer durations for full vowels could be interpreted as longer duration of glottal opening. More importantly, the production results showed evidence that tone can be a salient cue for perceptual distinction for L2 segments. It echoes back to our hypothesis that L1 suprasegmental traits may also influence L2 perception. In the perception test, the substantial gap of overall accuracy between Mandarin and English speakers had shown that Mandarin speakers could distinguish actual and epenthesis in a minimal context, while native English speakers could not. Noticeably, the high accuracy rate for Mandarin perception of original productions showed that Mandarin listeners could distinguish the target pair (CrVt and CerVt) with ease. The contrast between high and low accuracy in the original task by Mandarin and English listeners indicated that Mandarin speakers may had utilized some L2-specific cues in perceiving L2 speech. But in the second and third test, where duration and tone were manipulated, accuracy rates substantially dropped for Mandarin speakers. This showed that tone and duration were the cues Mandarin speakers used to perceive epenthetic vowels. However, the weightings of the two cues were not equal. Duration may not be a heavily weighted cue because the perceptual accuracy was somewhat high in the second task as well (especially in /p/ condition). However, the cue of tonal variations was more significant than duration because of a larger drop of accuracy rate was found in the third task. We could hence infer that Mandarin listeners would allocate much of their attention to the pitch variations in their peers ’ productions to decide whether there was a phonological vowel in between two consonant members in stop-/r/ clusters. For English speakers, perceptual accuracy was similarly low across three tasks. It suggested that the durational and tonal cues did not significantly help English speakers in perceiving the difference. However, we did see a minor drop of accuracy rates in the second task, showing that duration may be of insignificant help in English speakers’ successful perception of epenthetic vowels. This suggests that duration can be a universal cue for perceiving epenthetic vowels, which is predictable.