# Investigating the Potential Use of EEG for the Objective Measurement of Auditory Presence
## 4 Discussion  
In Section 3, it was found that an increase in the presence score was correlated with a decrease in the PAF. The underlying neurological mechanism of this correlation remains unclear. However, we found some clues that might shed light on research into this mechanism. It was found in the previous study that an increase in the subjective presence level was correlated with an increase in the theta/beta ratio [21]. Neurologically, both the theta/beta ratio and the alpha-band oscillations have been demonstrated to be associated with attentional processes [24, 50, 51, 52]. [PERSON] and [PERSON] [2] stated that a person's presence in a virtual environment depends on them shifting their attention from the physical environment to the virtual environment. Hence, it is likely that changes in the theta/beta ratio and the PAF are closely related to changes in attention. In addition, the theta/beta ratio was found to be negatively correlated with the PAF [53, 54]. Combined with the results of [21] showing that the presence level is positively correlated with the theta/beta ratio, it can be deduced that the presence level is negatively correlated with the PAF, which is consistent with the findings of the present study. Furthermore, an increase in theta/beta ratio and a decrease in PAF were observed simultaneously in patients with attention deficit hyperactivity disorder (ADHD) [32, 33], which further supports the results of this study. Considering that there are relatively few studies that investigate auditory presence exclusively, particularly using EEG, it is useful to note that the findings of these two studies are in agreement with each other. It is interesting to note that an increase in PAF has been found to be associated with good performance [35, 55, 56] or an increase in cognitive load (or task demand) [38, 39]. We assume by intuition that when the program that stimulated greater presence was played, the participants' attention would rise and the cognitive load would also increase. However, the results would be just the opposite of those in this study if they were built on this assumption. We suppose this discrepancy arises from the difference between the brain's \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Participant** & **Group** & \
\begin{tabular}{c} **Presence** \\ **Score (A)** \\ \end{tabular} &
\begin{tabular}{c} **Presence** \\ **Score (B)** \\ \end{tabular} & **PAF (A)/Hz** & **PAF (B)/Hz** \\ \hline
1 & I & 25 & 18 & 11.250 & 11.500 \\
2 & I & 34 & 35 & 10.250 & 10.250 \\
3 & I & 35 & 28 & 10.078 & 10.750 \\
4 & I & 34 & 26 & 9.500 & 9.778 \\
5 & I & 34 & 29 & 9.641 & 9.385 \\
6 & I & 39 & 34 & 8.313 & 11.500 \\
7 & I & 36 & 34 & 10.437 & 10.639 \\
8 & I & 36 & 28 & 10.286 & 10.500 \\
9 & I & 39 & 21 & 9.250 & 9.750 \\
10 & II & 29 & 35 & 11.150 & 11.400 \\
11 & II & 34 & 28 & 10.750 & 10.842 \\
12 & II & 35 & 30 & 7.450 & 7.750 \\
13 & II & 36 & 35 & 10.316 & 10.533 \\
14 & II & 35 & 34 & 12.743 & 13.000 \\
15 & II & 29 & 34 & 10.710 & 10.467 \\
16 & II & 35 & 34 & 9.000 & 9.750 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Presence scores and PAF estimates for Programs A and B in Experiment 2.  
top-down processing system and bottom-up processing system, which is reflected in the experimental design. Top-down processing is related to directed attention, which focuses on task-relevant information and inhibits the processing of non-essential information [57]. In the above-mentioned studies, the participants were required to complete tasks with various difficulties, where a better performance (i.e., better memory or shorter reaction time) should result from an increase in intentional attention. In other words, the causal relationship should be \"the more attention assigned to the tasks, the higher the cognitive load, and consequently the higher the PAF\". Furthermore, alpha oscillations have been found to be associated with top-down processing [57; 58], which may account for the relationship between PAF and task-relevant performance.