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●
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−4
−2 0 2 4
cailleach duilleag leabhar leugh Word
Random effect
Figure 6.9: Random word effects from the regression model in Table 6.3. n = 4.
6.3.2 Static acoustic analysis
This Section reports the results of the F2-F1 static acoustic measure taken at lateral steady state midpoint (excluding the tokens found to have no laterality at all - see above). Overall, the data suggest formant differences for each of the phonemic categories reported in the previous literature. Figure 6.10 shows the F2-F1 values for the three laterals in word-initial (left panel) and word-medial (right panel) position. The exact values of the first three formants in Hertz are tabulated in Table 6.4 for ease of comparison with other languages.
Word-initial Word-medial
palatalised alveolar velarised palatalised alveolar velarised
F1 333 384 369 380 393 451
(77) (103) (111) (115) (124) (123)
F2 1825 1429 1023 1771 1513 1056
(615) (399) (263) (447) (442) (165)
F3 3199 3174 3162 3097 3138 3172
(358) (322) (308) (299) (301) (311)
Table 6.4: Mean Hertz values for the first three formants of Gaelic laterals. Standard deviation in brackets. Values rounded to the nearest Hertz.
The boxplots show that the greatest values of F2-F1 are in the palatalised laterals, followed by the alveolar laterals, and the lowest values for F2-F1 are in the velarised laterals. This was
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palatalised alveolar velarised palatalised alveolar velarised Lateral phonemic category
F2−F1 (Bark)
Figure 6.10: F2-F1 values for the three different phonemic laterals in Scottish Gaelic, with data from all the speakers. Left panel shows word-initial laterals n = 668, right panel shows word-medial n = 640.
predicted above considering the described articulations for Gaelic laterals and compared to previous acoustic studies of laterals (Lehiste 1964; Espy-Wilson 1992; Stevens 1998; Carter
& Local 2007). Statistical testing was employed to see whether these apparent differences were statistically significant. One of the assumptions of parametric regression and ANOVA is that the data are normally distributed within groups (Field, Miles & Field 2012, 169).
From looking at the distributions of these data it was clear that the palatalised lateral data were not normally distributed. Distributions of these laterals are displayed in Figure 6.11 as density plots (smoothed histograms). The figure is split by speaker group and word position:
word-initial palatalised laterals are on the left, and word-medial palatalised laterals are on the right. The bimodal distributions in the data from the Glasgow teachers, Lewis young people and Glasgow young people may be indicative two different production strategies with some speakers producing palatalised laterals and some speakers producing non-palatalised laterals.
The Shapiro-Wilk test for normal distribution was carried out on the palatalised lateral data. A significant result from this test indicates that the data are non-normally distributed.
Each group of speakers (Lewis old, Lewis young, Glasgow teachers, Glasgow young) in word-initial and word-medial place was tested, and only the results from the Lewis older speakers were non-significant (normally distributed). The exact results are shown in Table 6.5.
Speaker group Word-initial Word-medial
W p W p
Lewis old 0.94 .31 0.94 .26
Glasgow teachers 0.81 <.001 0.80 <.001
Lewis young 0.95 .03 0.93 .02
Glasgow young 0.95 <.001 0.95 .001
Table 6.5: Results from the Shapiro-Wilk test for normal distributions on the word-initial and word-medial palatalised laterals. W is the test statistic from this statistical test.
Lewis old Glasgow teachers
Figure 6.11: Density plots showing the non-normal distribution of the palatalised lateral F2-F1 values. Left panel shows word-initial laterals n = 203; and right panel shows word-medial laterals n = 180.
Due to these non-normal distributions, the non-parametric Kruskal-Wallis test was used to test for differences between lateral categories. This test can only test one independent variable at once, and cannot test for interactions. Two models were therefore run, the first on the word-initial laterals and the second on word-medial laterals. In each case the dependent variable was F2-F1 in Bark and the independent variable was lateral phonemic category. The Kruskal-Wallis test results indicate whether the data are significantly different according to lateral category or not, but the test does not indicate which categories are different from each other. Post hoc Mann-Whitney tests were used to answer this question. As explained in Section 6.2.3 the Mann-Whitney, the p values of the Mann-Whitney test were corrected to avoid family-wise errors. The threshold for significant is set at the equivalent of p < .05 with the correction applied. I therefore adopt the recommendations for reporting in Field, Miles
& Field (2012, 686) and do not report the exact p values, as they would be misleading. The differencereported is the mean difference between mean ranks of the two sets of data being compared. The larger the value, the more different the two sets of data.
In word-initial position the Kruskal-Wallis test showed significant differences according to lateral phonemic category: H(2) = 220.71, p < .001. Focused comparisons using the Mann-Whitney test indicated that palatalised and alveolar laterals were different (difference = 116.10), palatalised and velar laterals were different (difference = 272.73), and alveolar and velarised laterals were different (difference = 156.63).
In word-medial position there were also significant differences in the data according to lateral phonemic category: H(2) = 260.69, p < .001. Comparisons indicated that palatalised laterals are different to alveolar laterals (difference = 68.97). Palatalised laterals are also different to velarised laterals (difference = 279.53), and alveolar laterals are different to velarised laterals (difference = 210.55).
!!
palatalised alveolar velarised palatalised alveolar velarised Lateral phonemic category
palatalised alveolar velarised palatalised alveolar velarised Lateral phonemic category
Figure 6.12: F2-F1 (Bark) values split according to speaker group. Top panel shows word-initial laterals; and bottom panel shows word-medial laterals.
The results of the Kruskal-Wallis test indicate that across the whole dataset, the three phonemic laterals are phonetically distinct. The test does not, however, look at whether distinctions are made within the four groups of speakers: older Lewis speakers, younger Lewis speakers, teachers from the Glasgow school, and young Glasgow speakers. Due to the small number of tokens in some groups, reliable statistical testing could not be carried out on each group. Instead I present box plots of the F2-F1 data for each group in Figure 6.12.
Word-initial laterals are in the top panel, and word-medial laterals in the bottom panel.
The laterals appear mostly phonetically distinct within the different groups. In word-initial position however, there is a lot of overlap between palatalised and alveolar laterals for the Glasgow school teachers and the Glasgow young people. The same is true in word-medial position for the Glasgow young speakers and the Lewis young speakers. This provides acoustic evidence in support of the auditory analysis concentrating on palatalised laterals, which found a high degree of variability in the data (see above Section 6.3.1).
When comparing the acoustics of lateral productions within each lateral category, there are clear acoustic differences across the different groups of speakers. Again, low token counts made statistical comparison inappropriate, but the results are displayed graphically in Figure 6.13. Overall, the older Lewis speakers have the most distinct lateral phonemes, producing the highest F2-F1 in palatalised laterals, and the lowest F2-F1 in the velarised laterals. This is also clear from looking at the formant values for individual speakers, which are in Figure 6.14. This Figure shows a clear separation of values among the older speakers, especially for the velarised laterals compared to the alveolar and palatalised laterals.
!!
Lewis old Glasgow teachers Lewis young Glasgow young Lewis old Glasgow teachers Lewis young Glasgow young Lewis old Glasgow teachers Lewis young Glasgow young
F2−F1 (Bark)
Lewis old Glasgow teachers Lewis young Glasgow young Lewis old Glasgow teachers Lewis young Glasgow young Lewis old Glasgow teachers Lewis young Glasgow young
F2−F1 (Bark)
n = 236 n = 180
n = 224
Figure 6.13: Static F2-F1 measures per group for each lateral phonemic category. Top panel shows word-initial lateral; bottom panel word-medial laterals.
The young people, especially in Glasgow, display lower F2-F1 for palatalised and higher F2-F1 for the velarised laterals indicating less acoustically distinct phonemic categories.
Among the palatalised laterals in particular, Figure 6.13 again highlights the high degree of variability in the production of palatalised laterals, especially in Glasgow (see Section 6.3.1). Among the alveolar laterals, the distribution of tokens among the Glasgow young people is clearly different from the other speaker groups, with the Glasgow speakers having a lower F2-F1 (equating to a lateral produced with more tongue backing/retraction). In word-initial position, there appear to be differences between the groups in the production of the velarised laterals: the older Lewis speakers produce laterals with the lowest F2-F1 (most tongue backing/retraction), and the Lewis younger speakers produce laterals with the highest F2-F1 (least tongue backing/retraction). Lewis old Lewis young GlasgowTeachers
Figure 6.14: F2-F1 measures for individual speakers. Left panel word-initial laterals; right panel word-medial laterals.