# Changes in Articulatory Contact Pressure as a Function of Vocal Loudness
## 3 Results  
Figure 2 displays the ACP group data in each loudness condition. There was a statistically significant difference in ACP for the phoneme /t/ as a function of loudness, \(\chi^{2}(3)=40.886\), \(p<0.001\). In the post hoc testing (Table 1), all paired comparisons of ACP for /t/ were statistically significant and indicated the highest values for loud, followed by habitual, whisper, and then soft. For each pairwise comparison, the effect sizes were large (0.58-0.62) using [PERSON]'s (1988) [45] criteria. ACP also differed significantly across the loudness conditions for the phoneme /d/, \(\chi^{2}(3)=36.429\), \(p<0.001\). For the post hoc tests, all paired comparisons except one were statistically significant (Table 1) and had large effect sizes (0.60-0.62). The habitual and whisper conditions did not differ significantly for /d/ (medium effect of 0.46), but in all other cases, ACP descended from the highest values for loud, followed by habitual, whisper, and soft. Lastly, there was a statistically significant difference in ACP for the phoneme /s/, \(\chi^{2}(3)=33.000\), \(p<0.001\). The post hoc testing indicated that ACP was significantly greater in the loud condition compared to the habitual, soft, and whisper conditions (large effect of 0.62 for each compared to loud). However, the habitual, soft, and whisper conditions did not differ from one another, although the effect sizes were medium to large (habitual-soft = 0.55, habitual-whisper = 0.44, soft-whisper = 0.53). Figure 2: _Cont._  
In order to capture the magnitude of change in ACP as a function of loudness, the percentage change in the loud, soft, and whisper conditions relative to an individual \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Phoneme**} & \multirow{2}{*}{**Loudness Condition**} & \multirow{2}{*}{**Statistic**} & \multicolumn{4}{c}{**Loudness Condition**} \\ \cline{3-6}  & & & **Soft** & **Habitual** & **Loud** \\ \hline /t/ & Whisper & Z & \(-\)3.296 & \(-\)3.297 & \(-\)3.296 \\  & & p & \(<\)0.001 & \(<\)0.001 & \(<\)0.001 \\  & Soft & Z & \(-\) & \(-\)3.297 & \(-\)3.297 \\  & & p & \(-\) & \(<\)0.001 & \(<\)0.001 \\  & Habitual & Z & \(-\) & \(-\) & \(-\)3.233 \\  & & p & \(-\) & \(-\) & \(0.001\) \\ /d/ & Whisper & Z & \(-\)3.297 & \(-\)2.417 & \(-\)3.296 \\  & & p & \(<\)0.001 & \(0.016\) & \(<\)0.001 \\  & Soft & Z & \(-\) & \(-\)3.170 & \(-\)3.297 \\  & & p & \(-\) & \(0.002\) & \(<\)0.001 \\  & Habitual & Z & \(-\) & \(-\) & \(-\)3.170 \\  & & p & \(-\) & \(-\) & \(0.002\) \\ /s/ & Whisper & Z & \(-\)2.794 & \(-\)2.323 & \(-\)3.297 \\  & & p & 0.005 & \(0.020\) & \(<\)0.001 \\  & Soft & Z & \(-\) & \(-\)2.88 & \(-\)3.296 \\  & & p & \(-\) & \(0.004\) & \(<\)0.001 \\  & Habitual & Z & \(-\) & \(-\) & \(-\)3.297 \\  & & p & \(-\) & \(-\) & \(<\)0.001 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Wilcoxon signed-rank test results for all paired comparisons of the articulatory contact pressure (ACP) mean across loudness conditions for /t/, d/, and /s/. Probability values \(<\) 0.00278 (_p_) were considered statistically significant. \(Z\) = statistic for the Wilcoxon signed-rank test. Figure 2: Box-and-whisker plots for articulatory contact pressure (ACP) for each phoneme in the four loudness conditions. participant's habitual condition was calculated. Group data for the percent differences are presented in Figure 3. Based on the median percent differences, ACP in the loud condition was approximately 38% higher than the habitual condition for /t/, 36% higher for /d/, and 90% higher for /s/. In contrast, ACP in the soft condition was 53% lower than the habitual condition for /t/, 52% lower for/d/, and 37% lower for /s/. Likewise, ACP was lower in the whisper condition compared to the habitual condition by 33% for /t/, 27% for/d/, and 11% for/s/. Figure 3: _Cont._  
To gain insight regarding the changes in ACP at the level of the individual, the ACP values for each participant are plotted in Figure 4 by the phoneme and loudness condition.