## 3 Results  
### Auditory-Perceptual Data  
Once all listeners had completed the experimental task, their ratings of strain and listening effort were first analyzed for reliability. Two sets (i.e., test and retest) of strain and listening effort ratings  
Figure 1: (**a**) Screenshot of the user interface for assessing the “strain” and “listening effort” using visual analog sliders. The label of the “Start!” button was changed to “Next” once the first stimulus was played back. (**b**) Participant positioned on the EyeLink 1000 tower in front of the monitor displaying the ratings screen set-up. (**c**) A secondary display showing the EyeLink 1000 tracker parameters and pupil image, which was monitored by the experimenter to ensure proper data collection during the experiment. that could range between 1 and 100 were generated for each talker sample and listener. Intra-rater reliability for both strain and listening effort was obtained for each listener by computing the Pearson correlation coefficient between the test and retest session ratings across all talkers. These correlation values ranged from 0.56 to 0.96 for strain and from 0.58 and 0.90 for listening effort, indicating moderate-to-high intra-rater reliability. Interrater reliability was calculated separately with [PERSON]'s \(\alpha\) in SPSS (Version 24, IBM, Armonk, NY, USA, 2020) for each of the two rated features. The [PERSON]'s \(\alpha\) was 0.98 for strain and 0.97 for listening effort, indicating very high reliability among listeners for the rating tasks. The strain and listening effort ratings for each AdSD talker were subsequently averaged across all listeners and the test-retest sessions. These averaged ratings along with their standard errors are displayed in Figure 2a. It can be seen from Figure 2a that Talkers 8 and 10 were rated to have the least and Talkers 1 and 18 were rated to exhibit the highest degrees of both perceived strain and effort. In addition, the strain and listening effort ratings appeared to vary in a similar pattern across talkers. This association is confirmed through the scatter plot shown in Figure 2b, where a linear regression fit to the strain-listening effort data accounted for 80% of the variance. In addition, linear mixed-effects models (LMMs) were developed to further probe the relationship between strain and listening effort. The LMMs were implemented using the R statistical software (v4.0.2, R Foundation for Statistical Computing, Vienna, Austria, 2020) using the _nlme_ package. The basic LMM model included listening effort as the dependent variable, strain as the fixed effect, and the talker and listener variables as random effects. Results showed that strain was a significant predictor of listening effort (F (1, 298.71) = 184.04, \(p\) < 0.001), with a correlation of 0.53 (t (298.7087) = 13.566, \(p\) < 0.001). A more complex LMM model, which allowed different slope coefficients for each talker, revealed statistically similar results (x\({}^{2}\) (1) = 0.244, \(p\) = 0.622). Thus, these results indicate a consistent relationship between the vocal strain and listening effort ratings. A repeated measures ANOVA was conducted to statistically assess the effects of the auditory-perceptual features (i.e., vocal strain and listening effort), talkers, and any potential interaction between the features and talkers. The a priori significance level was set to 0.05 for all statistical tests, and the Greenhouse-Geisser correction was applied when sphericity condition was violated. Significant effects were found for the auditory-perceptual features (F (1, 19) = 37.13, \(p\) < 0.001, \(\eta_{p}^{2}\) = 0.662), and talkers (F (6.41, 121.73) = 72.08, \(p\) < 0.001, \(\eta_{p}^{2}\) = 0.791). In addition, a significant interaction between auditory-perceptual features and talkers was found (F (4.04, 76.66) = 12.88, \(p\) < 0.001, \(\eta_{p}^{2}\) = 0.404). Post-hoc comparisons using the Bonferroni correction revealed that Talkers 5 and 20 were rated differently on the auditory-perceptual features than the others.