## 3 Results and Discussion
### Reading  
In the reading part of the experiment, 34 listeners gave three responses each, thus yielding a total of 102 observations in the form of A-weighted level of read speech as the dependent variable. As described earlier, during this part of the experiment, the listeners were asked to read a few lines of text for three different levels of the visual stimulus, identical to the ones in the listening part of the experiment. To statistically analyze the obtained data and determine the possible influence of visual stimulus as the independent factor on the A-weighted level of read speech as the \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Speaker Voice** & **Voice 1** & **Voice 2** & **Voice 2** & **Voice 4** \\ \hline Mean A-weighted level (dBA) & 51.9 & 52.5 & 53.7 & 52.0 \\ Standard deviation (dB) & 7.6 & 7.4 & 7.6 & 7.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Marginal means and standard deviations of the groups at four different levels of speaker voice in the listening part of the experiment. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Visual Stimulus** & **No Visual Stimulus** & \
\begin{tabular}{c} **Dummy Head at** \\ **85 cm** \\ \end{tabular} &
\begin{tabular}{c} **Dummy Head at** \\ **280 cm** \\ \end{tabular} \\ \hline Mean A-weighted level (dBA) & 53.0 & 52.9 & 51.6 \\ Standard deviation (dB) & 7.4 & 7.4 & 7.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Marginal means and standard deviations of the groups at three different levels of the visual stimulus in the listening part of the experiment. dependent variable, a one-way repeated measures ANOVA was implemented. The data in all three groups satisfied the condition of normality, as examined with the Shapiro-Wilk test and the corresponding QQ plots. Two outliers have been found, but not deemed extreme. [PERSON]'s test of sphericity was performed, and the Greenhouse-Geisser correction was applied. The resulting ANOVA table obtained from R is shown below as Table 7, with effect size expressed as eta-squared \(\eta^{2}\). Estimated power was added to the table as well. The results of this test indicate that there is a statistically significant effect of the visual stimulus on the A-weighted level of read speech. In terms of effect size expressed with the calculated eta-squared, the effect of visual stimulus is a medium-sized one. Power analysis confirms that the test has high power in the given conditions. A closer look at the mean values for the three groups shown in Table 8 reveals that the lowest value was obtained when the subjects were asked to read to the virtual person placed within their personal space, while the highest one was obtained with the virtual person positioned at a distance, i.e., far from the speaker, but still within their social space. The post hoc pairwise comparison test reveals that the differences between all three pairs of mean values are statistically significant. In practical terms, regarding the calibration method proposed below, the two conditions with the visual stimulus present in the room (placed close and far from the reader) are the important ones, and they show the difference of the average A-weighted levels of 2.9 dB. This 3-dB difference suggests that the readers will tend to raise their voice a bit to \"reach\" the virtual person positioned farther away from them. In study [31], optimum speech level has been found constant if the background noise level is kept below 40 dBA. This condition was fulfilled in our test room, yielding a reasonably constant and consistent level of read speech. The average A-weighted level of 55 dBA at 1 meter, found for the visual stimulus placed within the personal space of the listener is consistent with the one reported in [27] for face-to-face communication at the distance of 1 meter performed with background noise level lower than 45 dBA.