«Year: 2016 On the origin of post-aspirated stops: production and perception of /s/ + voiceless stop sequences in Andalusian Spanish Ruch, Hanna; ...»
(35; 16 women and 19 men). Of the 74 listeners, 48 also took part in the production study described above, which was conducted prior to the perception experiment. The listeners were between 18 and 86 years old. Forty-three of them had lived for their whole life in Seville or Granada; the remaining 31 subjects had lived for at least 20 years in Seville/ Granada or the respective province. Of the 74 participants, 65 reported having no hearing impairment, 7 reported having bilateral hearing impairment, and 2 having unilateral hearing impairment; all of those reporting hearing impairment were part of the older group.
3.2 Results For data analysis the remaining 74 subjects were, again, divided in an older ( 50 years;
36 subjects, mean age 67.2 years) and a younger ( 50 years; 38 subjects, mean age
26.8 years) group. Men and women were approximately equally distributed among the two dialect and age groups (see Table 4).
A generalized linear mixed model in R was used to calculate the slope and the intercept individually for each listener. The Listeners’ Judgement was set as the dependent variable (two levels: pata/pasta), the VOT Step as fixed factor (9 levels), and the Listener (74 levels) and the Continuum (two levels: pasta-/pata-continuum) as random factors.3 The speakerspecific slope m and intercept k were then used to calculate a psychometric curve for each listener.4 It turned out that for five listeners the cross-over point (i.e., the 50% decision boundary) was situated outside the stimuli range, meaning that their answers were not consistently influenced by VOT. They were all over 50 years of age, one was from Granada and four from Seville of which one reported having hearing problems. The data of these five listeners were excluded from further analysis.
Figure 8 displays the decision boundaries for all four listener groups. As expected, older listeners needed a longer VOT to perceive pasta than younger subjects, that is, they show a higher value for the cross-over point. No difference can be seen between EAS and WAS listeners in what refers to the cross-over point. An ANOVA with the Cross-over Point as the dependent variable and Age and Variety as between-subject factors showed a highly significant effect of Age (F[1,65] = 37.6, p 0.001) on the dependent variable; the effect of Variety was not significant and there was no interaction between the factors.
Figure 9 shows the psychometric curves separately for age and variety. The endpoints of the VOT-continua were identified consistently as /pata/ or /pasta/ by all four listener groups. The mean psychometric curves of the younger listeners appear to be steeper than those of the older listeners. At the same time, Eastern Andalusian subjects show a flatter psychometric curve than Western Andalusian subjects, this difference
Table 4: Distribution of the participants in the forced-choice perception experiment.
The following model was fitted to the perception data: o = lmer(input ~ step + ( 1 + step | listener) + (1 | continuum), family = “binomial”) Formula for calculation of the speaker-specific slope and intercept of the psychometric curve: p = emx+k /
Figure 8: Cross-over point (50% decision boundary) in the perception experiment (one value per listener), separately for old (dark grey) and young (white) speakers of EAS (left two boxplots) and WAS (right two boxplots).
Figure 9: The mean psychometric curves in the perception experiment. Dashed lines refer to young speakers, solid lines to old speakers; black lines refer to WAS and grey lines to EAS speakers.
Art. 2, page 24 of 36 Ruch and Peters: On the Origin of Post-Aspirated Stops being more marked for younger than for older subjects. An ANOVA with the speakerspecific Slope as the dependent variable and Age and Variety as between-subject factors showed a significant effect of Age (F[1,65] = 33.4, p 0.001) and Variety (F[1,65] = 19.6, p 0.001) and an interaction between them (F[1,65] = 6.3, p 0.05). In a post-hoc Tukey test, Age turned out to be significant only among WAS (padj 0.001), but not among EAS listeners, and there was no significant effect of Variety among the older listeners.
As explained in Section 3.1, the stimuli for this perception experiment were generated based on two different productions: /pata/ [ˈpata] and /pasta/ [ˈpatha]. As displayed in Table 3, the first of the two naturally produced baseline tokens contains additional cues to /pata/, the latter additional cues to /pasta/. Although the main aim of the perception experiment lays on the role of VOT, a comparison between the two continua—the pata- and the pasta-continuum—may give some indication of whether other acoustic cues besides post-aspiration potentially play a role in the perceptual distinction between pata and pasta. The psychometric curves were again calculated for all 74 listeners, but this time separately for each of the two continua. The data of 8 listeners had to be removed because they did not converge in one or in both continua.
Figure 10 shows the psychometric curves separately for EAS and WAS listeners, and separately for the two continua. In both varieties, the curves of the pasta-continuum are slightly left-shifted, meaning that the participants gave fewer pata answers than when the continuum was generated based on [ˈpata]. This trend seems to be more pronounced for older than for younger listeners. A repeated-measures ANOVA with Cross-over Point as the dependent variable, Continuum as within-subject factor, and Age and Variety as between-subject factors showed a highly significant effect of Continuum (F[1,62] = 115.3, p 0.001) and a significant interaction between Age and Continuum (F[1,62] = 32.3, p 0.001). In post-hoc t-tests with Bonferroni correction, Continuum appeared significant in both older (padj 0.001) and younger listeners (padj 0.001). Age turned out to be significant only in the pata- (padj 0.001), but not in the pasta-continuum. There was no influence of Continuum on the slope of the psychometric curve, and no significant interaction.
3.3 Discussion The results showed that younger and older listeners of Eastern and Western Andalusian Spanish were able to distinguish the minimal pair pata-pasta that differed only in VOT of /(s)t/.
The age-dependent differences in the cross-over point suggest that younger listeners are more sensitive to post-aspiration as a cue for /st/ than older listeners. The differences between EAS and WAS listeners in the slope of the psychometric curves, on the other hand, indicate that the latter have a more categorical perception of post-aspiration in this minimal pair, i.e., they distinguish more consistently between stimuli containing either a short or a long VOT.
Stimuli that had been resynthesized based on an original pasta token were more likely to be perceived as pasta. When the cross-over point was calculated separately for each continuum, age appeared to be significant only in the pata-continuum. This finding underlines the importance of additional cues to /st/. It is possible that older listeners based their judgements primarily on the C:V1-ratio, and not on VOT. The measurements in Table 3 demonstrate that the C:V1-ratio was greater in the stimuli of the pasta- than in those of the pata-continuum (1.05 for VOT-step 1 in the pata-continuum, 1.35 for VOT-step 1 in the pasta-continuum).
As hearing is known to decline with age (Boenninghaus & Lenarz, 2005, p. 109), the question arises whether the reported age-dependent differences in the perception of post-aspiration are due to hearing loss in the elderly subjects. Additional analyses were conducted in order to address this question. The 9 subjects with self-reported hearing problems (all of them older than 50 years) and all other 16 subjects older than 65 years5 were excluded for these tests. The same statistical tests as described above were performed on the data of the remaining 48 listeners. For this reduced dataset the same significant effects of Age on the Cross-over Point (F[1,44] = 14.9, p 0.001) and on the Slope of the psychometric curve (F[1,44] = 7.7, p 0.01) were found.
The fact that continuum had a significant effect also among older listeners suggests that older listeners did perceive the phonetic details that distinguished the two continua, and thus supports the interpretation that the differences between older and younger listeners in crossover-point and slope of the psychometric curve do not have to be attributed to hearing-loss, but can be interpreted as a sound change in progress. In order to fully exclude hearing degradation as an artefact to listener age, future perception experiments with Age as an independent variable should include a control continuum (e.g. /x/-/f/) or a same-different test on the stimuli.
With the caveat that the effect of hearing loss may not be entirely excluded, the results of the forced-choice perception experiment suggest that the sound change in progress from pre- to post-aspiration also affects perception.
Except for 5 out of 74 listeners, the endpoint of the continua with a VOT of 55 ms was identified very consistently as /pasta/ even by the older EAS subjects. This result is surprising when it is considered that older EAS subjects in the production task did not use post-aspiration for distinguishing hC- and intervocalic C-sequences.
Still, on a whole, there seems to be a relationship between production and perception of post-aspiration such that the group of younger Western Andalusians displaying the longest VOT in production showed also a more categorical perception of post-aspiration in the forced-choice perception experiment, and older Eastern Andalusians producing the From the age of 60, a significant decline of hearing in the frequencies relevant for spoken language comprehension is reported to take place (Boenninghaus & Lenarz, 2005, p. 109). In the present study, only five participants were aged between 50 and 60, and eight between 60 and 65. The reason for excluding participants over 65—and not 60 years—was to keep a sufficiently high number of older participants to run the statistical tests.
Art. 2, page 26 of 36 Ruch and Peters: On the Origin of Post-Aspirated Stops shortest VOT were also the least sensitive to post-aspiration in the perception experiment.
The more abrupt psychometric curves of the younger WAS listeners suggest that the postaspirated stop [th] is for this group, to a certain degree, phonologized. The next section tests whether this group relationship also holds true at an individual speaker-listener level.
4 The relationship between production and perception of post-aspiration If there is a relationship between perception and production of post-aspiration, then speakers who produced /s/ + voiceless stops with a long post-aspiration should also be more sensitive to post-aspiration as a cue to /st/ in perception. This means that there should be a correlation between VOT in production and the cross-over point and the slope of the psychometric curve in perception, respectively. Since in the perception experiment only a minimal pair of /t/ vs. /st/ was tested, and production-perception comparison will only be based on ht-words. The analysis in this section is based on the data of those 48 listeners who also participated in the production task.
The VOT-difference between ht- and t-words was calculated for each speaker-listener by subtracting the speaker-wise mean value of VOT in t-words from the mean value in ht-words. This procedure was chosen in order to get per speaker one value that discloses to what extent a speaker uses VOT for distinguishing between ht- and t-words.6 The scatterplots in Figure 11 display the VOT-difference and its relationship to the cross-over point (a) and the psychometric curve (b) for each speaker-listener. As is apparent from Figure 11, there is a negative relationship between the VOT-difference and the perception data: Speakers who distinguished ht- from t-words by VOT in production displayed a lower cross-over point and a steeper psychometric curve (i.e., higher slope values).
Two linear regression models in R were then applied to test whether (1) the individual cross-over point and (2) the slope of the psychometric curve can be predicted from the VOT difference in production. In both models Age and Variety and the interaction between them were included as fixed factors in order to test whether the relationship between production and perception differed across age and variety. The first model showed a significant effect of VOT-difference (F[1,34] = 13.8, p 0.001) and a significant effect of Age on the Cross-over Point (F[1,34] = 4.3, p 0.05). There was no significant interaction effect.
The second model showed, similarly to the first, a significant effect of VOT-difference on the Slope of the psychometric curve (F[1,34] = 9.4, p 0.01). This indicates that there is a relationship between the production and the perception data. Age did not significantly influence the Slope and there was no interaction effect.
At first glance, these results might be counterintuitive since it would be expected that speakers who produced a longer VOT should also use a longer VOT in perception to distinguish the minimal pair pata-pasta. However, taking into account that a lower crossoverpoint and a steeper slope in perception indicate that the subjects were more sensitive and showed a more categorical perception of post-aspiration, the results are compatible with the predictions.
5 General discussion This paper investigated the production and perception of /s/ + voiceless stops in two varieties and two age groups of Andalusian Spanish. One of the aims of this study was to assess if the finding of a sound change in progress for /st/-sequences of a previous study It has to be noted that absolute VOT in production and perception are only comparable indirectly, since the production data are based on trisyllabic words with stress on the second syllable (e.g., /esˈtado/), while the perception data are based on the bisyllabic word /ˈpasta/.
Ruch and Peters: On the Origin of Post-Aspirated Stops Art. 2, page 27 of 36 Figure 11: Scatterplot to show the relationship between the production data (x-axis; VOT-difference between ht- and t-words) and the perception data (y-axis; a. cross-over point, b. slope of the psychometric curve, cf. Figures 8 and 9) within one speaker-listener. Circles stand for younger, dots for older speaker-listeners; black for WAS, grey for EAS subjects.