«Year: 2016 On the origin of post-aspirated stops: production and perception of /s/ + voiceless stop sequences in Andalusian Spanish Ruch, Hanna; ...»
In a second step all /sC/-tokens were removed that had been produced with a full alveolar fricative [s], i.e., where /s/ was not weakened. This was achieved by separating the /sC/-tokens into two groups — [s] and [h] — entirely based on acoustic parameters (cf. Ruch & Harrington, 2014, p. 15). First, all /sC/-tokens for which the automatically detected /s/-duration was smaller than 5 ms were assigned to the category [h] (lenited tokens). For the remaining /sC/-tokens, k-means clustering (Hartigan & Wong, 1979) was applied to the mean zero-crossing rate calculated over the automatically detected interval between V1.Offset and Cl.Onset. The group with higher zero-crossing density was assigned to the [s]-group (unlenited tokens); the other group was assigned to the [h]-group (lenited tokens). The choice of this parameter was motivated by the fact that alveolar fricatives usually have energy concentrated in a higher frequency range than glottal fricatives, which is reflected in a higher zero-crossing rate in alveolar fricatives (see Ruch & Harrington, 2014, p. 15). This procedure was verified by a comparison between the auditive and the acoustic labels of /sC/-tokens: there was agreement between the acoustically and the auditorily labelled tokens in 92.2% of cases. With the auditive procedure, 255 out of 1,467 were categorized as [s]; by the automatic procedure using k-means clustering, only 221 tokens were assigned to this category.
2.2 Results 2.2.1 The production of pre- and post-aspiration in Andalusian Spanish 22.214.171.124 Voice termination time Figure 2 shows the mean values for voice termination time (VTT) as a function of age, variety, and place of articulation, separately for hC-words (e.g., estado, escapa, espada) and C-words (e.g., etapa, secaba, separa). As is apparent from Figure 2, VTT mean values per speaker for hC-words are mostly positive which means that voicing ends prior to the oral closure, i.e., they are pre-aspirated. VTT values for C-words, on the other hand, are mostly negative, i.e., voicing extends into the oral closure (see Torreira & Ernestus, 2011, for similar results on conversational Madrid Spanish). A mixed model with VTT as the dependent variable, Sequence (hC-words vs. C-words), Age (older vs. younger speakers), Art. 2, page 12 of 36 Ruch and Peters: On the Origin of Post-Aspirated Stops
Table 2: Recorded, discarded, and analyzed tokens in the production study.
Figure 2: Voice termination time (VTT) in hC-words (green) and C-words (yellow), separately for variety (EAS vs. WAS), age group (older vs. younger), and place of articulation (/p/ vs. /t/ vs. /k/).
Each boxplot contains one mean value per speaker.
and Variety (EAS vs. WAS speakers) as fixed factors, and Speaker and Word as random factors showed a significant three-way interaction (χ2 = 23.2, p 0.001). Post-hoc Tukey tests showed that younger and older speakers did not differ significantly in C-words, while younger and older speakers did differ significantly in hC-words in WAS (p 0.001), but Ruch and Peters: On the Origin of Post-Aspirated Stops Art. 2, page 13 of 36 not in EAS (although the same trend is observable from Figure 2 also for this variety).
This means that younger speakers of Western Andalusian Spanish produced a shorter preaspiration than older speakers in hC-words. The difference between hC- and C-words was significant in all four speaker groups (p 0.001).
Furthermore, Figure 2 shows that VTT varies with age and place of articulation: VTT is longest before velar stops, and longer for older than for younger speakers. Because of the three-way interaction mentioned above between Age, Variety, and Sequence, further statistical tests were conducted separately for hC- and C-words.
A mixed model on the hC-data with VTT as the dependent variable, with Age, Variety, and Stop Type as fixed factors, and Speaker and Word as random factors showed a significant effect of Age (χ2 = 13.1, p 0.05) and Stop Type (χ2 = 39.4, p 0.001) on VTT. There was no significant difference in VTT between Eastern and Western Andalusian speakers. The results of post-hoc Tukey tests showed that among hC-words, velar and bilabial stops (EAS: p 0.001; WAS: p 0.001) as well as velar and dental stops (EAS: p 0.001; WAS: p 0.001) differed significantly between younger and older speakers of both varieties. The difference between dental and bilabial stops was not significant.
126.96.36.199 Voice onset time It has been shown for numerous languages that voice onset time varies with place of articulation (Cho & Ladefoged, 1999). If we find the same VOT pattern in hC- and in C-words, it could very likely be attributed to articulatory or aerodynamic principles. A different VOT pattern in hC- compared to C-words on the other hand will improve understanding of which factors favour the emergence of post-aspiration, and how it spreads from one place of articulation to the other. As is apparent from Figure 3, we find the typical VOT pattern in C-words and in hC-words: bilabial stops show the shortest voice onset time, velar stops the longest. Among younger WAS speakers, however, VOT in dental stops exceeds that of velar stops in hC-words. At the same time, VOT is generally longer in hC-words than in C-words, with younger and WAS speakers showing the longest VOT.
A mixed model with VOT as the dependent variable, Sequence, Age, and Variety as fixed factors, and Speaker and Word as random factors showed a significant three-way interaction (χ2 = 30.4, p 0.001). Post-hoc Tukey tests confirmed that hC- and C-words differed in terms of VOT among younger (WAS: p 0.001; EAS: p 0.05), but not among older speakers. This means that younger speakers of both varieties produced hC-words with a longer post-aspiration than C-words, while older speakers of both varieties did not differ in their VOT.
In order to test the influence of Age, Variety, and Place of Articulation, a second mixed model was applied to hC-words. Among hC-words there was a significant three-way interaction (χ2 = 10.2, p 0.01) among Place of Articulation, Age, and Variety, so that post-hoc Tukey tests were conducted. Age turned out to be significant among all three stop types in WAS (hp: p 0.001; ht: p 0.001; hk: p 0.001) and in EAS among ht (p 0.001), but not among hp- and hk-words. Thus, in EAS, younger speakers produced a longer VOT duration than older speakers only in one particular stop type (ht-sequences). The above-mentioned observation that VOT is longer in velar than in alveolar stops was confirmed statistically: there was a significant difference in VOT between velar and bilabial (p 0.001), alveolar and bilabial (young WAS: p 0.001;
old WAS: p 0.001; young EAS: p 0.001; old EAS: p 0.05), and between velar and
alveolar stops in all speaker groups (old WAS: p 0.001; young EAS: p 0.05; old EAS:
p 0.001) except in young WAS speakers. This is in line with what is evident from Figure 3 that the VOT of velar and alveolar hC-sequences does not differ in young WAS speakers.
Art. 2, page 14 of 36 Ruch and Peters: On the Origin of Post-Aspirated Stops Figure 3: Voice onset time (VOT) in hC-words (green) and C-words (yellow), separately for variety, age group, and place of articulation. Each boxplot contains one mean value per speaker.
Although the number of words presented per second was controlled in the experimental setting, variation in speech rate cannot be excluded. To ascertain that the observed differences in VTT and VOT are not a result of a variation in speech rate between the varieties and age groups, an analysis of total word duration was carried out. The average word durations per speaker and stop sequences are displayed in Figure 4. Younger WAS speakers exhibit slightly shorter word durations (i.e., a faster speech rate) than the other three speaker groups. However, a mixed model with Word Duration as the dependent variable, Age and Variety as fixed factors, and Word
and Speaker as random factors revealed no significant effects. If the age- and varietydependent differences in VTT and VOT are due to differences in speech rate, then similar patterns should be found for word duration, VTT, and VOT. This was not the case:
older and younger speakers displayed different VTT in both EAS and WAS, although in EAS there was no difference in word duration. Young WAS speakers showed a longer VOT, but shorter word duration.
To exclude the possibility that the effect of stop type on VOT and VTT was due to differences in lexical frequency of the target words, an additional test was conducted. If the sound change is favoured by lexical frequency, more frequent target words should show a longer VOT and a shorter VTT than less frequent words.
The lexical frequency of target words was classified as “high” and “low” according to the frequency table based on the movie subtitles corpus for Spanish (Cuetos et al., 2011).
Ruch and Peters: On the Origin of Post-Aspirated Stops Art. 2, page 15 of 36 Figure 4: Word duration in hC- and C-words according to variety and age group (one mean value per speaker).
A token frequency count of higher than 25 within a million words was categorized as “high”, a count less than 25 as “low”. There was no effect of lexical frequency on VOT or VTT for any of the varieties and age groups.
188.8.131.52 Discussion hC-sequences and intervocalic stops clearly differed in terms of voice termination time, the former displaying mostly positive, the latter mostly negative values.
Overall, younger speakers produced hC-sequences with a shorter VTT than older speakers, but this difference was significant only in WAS, not in EAS, suggesting that in WAS pre-aspiration is fading in apparent-time. Within hC-sequences, VTT was significantly longer in the velar than in the bilabial and the dental context.
There was no interaction among place of articulation, age, and variety indicating that pre-aspiration is shortening to an equal degree across stop types. The finding of a longer VTT preceding velar than preceding bilabial/dental stops is consistent with dialectological studies on Andalusian Spanish as well as with phonetic studies of pre-aspiration in languages that have it segmentally such as Icelandic or Scottish Gaelic (see Section 1.3).
Voice onset time was much more variable across phonological sequences, varieties, and age groups. VOT in hC-sequences was longest for young WAS speakers, and generally longer for WAS and younger than for EAS and older speakers. These results indicate that in Andalusian /s/ + voiceless stop sequences VOT is lengthening in apparent-time and therefore confirm the findings of a previous study (Ruch & Harrington, 2014) for a larger data set. A subsequent analysis of place of articulation, age, and variety indicated that younger and older speakers differed in terms of VOT for all three stop types /sp, st, sk/ in WAS, and only for /st/ in EAS. This pattern suggests that the sound change is more advanced in WAS than in EAS, and is in line with previous studies that found long post-aspiration in Western Andalusian varieties (e.g., Parrell, 2012; Torreira, 2012), and differences between WAS and EAS varieties in terms of VOT (O’Neill, 2010). Furthermore, Art. 2, page 16 of 36 Ruch and Peters: On the Origin of Post-Aspirated Stops the observed pattern suggests that, at least in EAS, the sound change first affects /st/sequences, and only later might generalize to /sp, sk/-sequences. As expected by phonetic principles and VOT data from many different languages (Cho & Ladefoged, 1999), velar stops displayed the longest, and bilabial stops the shortest VOT in C- as well as in hC-sequences on average. Interestingly, this pattern did not hold for hC-sequences in young WAS speakers, where /st/ displayed a post-aspiration duration as long as /sk/. It seems, though very unlikely, that long post-aspiration in /st/ is the result of universal principles or coarticulatory overlap in the speech of younger WAS speakers. The found pattern instead suggests that a long post-aspiration is intended by the speakers as an articulatory target for /st/-sequences. Although not significantly so, the measured VOT in hC-sequences in older speakers of both varieties slightly exceeded the VOT in singleton stops. It is possible that this extended VOT arises as a result of coarticulation or a looser coupling between the glottal adduction and the oral release of the stop. This idea will be discussed in further detail in Section 5.
In the next paragraph three more durational parameters of C- and hC-sequences will be investigated in our production data: the total duration of the voiceless interval, the duration of the preceding vowel, and the oral stop closure.
2.2.2 Temporal coordination of glottal and oral gestures The aim of these subsequent analyses is to understand how glottal and oral events are coordinated temporally, and what coordination mechanism might have given rise to the diachronic change from pre-aspiration to post-aspiration. Is the diachronic change mainly due to a change in the duration and timing of the oral closure gesture, or is the timing of the glottal opening gesture itself changing over time?
In order to shed light on these questions, three additional analyses are carried out. First, the total duration of the voiceless interval in hC-sequences will be compared across age groups and varieties to see if the duration of the glottal opening changes with the sound change. Second, the timing of the onset of pre-aspiration will be analyzed relative to an anchor point, in this case, the onset of voicing in the preceding vowel. This will be done to further understand if the fading of pre-aspiration and the emergence of post-aspiration came about due to a rightwards shift of the glottal opening, and whether the sound change is associated with a change in the duration of the preceding vowel. Third, oral stop closure duration will be looked at within (h)C-sequences in both varieties and age groups and at the different places of articulation. The aim here is to understand if the fading of pre-aspiration and the lengthening of post-aspiration are associated with a change in the oral closure duration.