# Sound Effects on Standing Postural Strategies in the Elderly via Frequency Analysis Approach
## 3 Results  
The effects of sound and group on the percent COP displacements for the three bands (low-, medium-, and high-frequency) in the AP and ML directions are shown in Figure 1. The main effect of sound significantly affected the low-frequency and medium-frequency in both directions (Table 1). In the AP direction, the main effect of sound was significant for the low-frequency band (F(3,84) = 5.185,  
Figure 1: The flowchart of the experimental protocol. \(p=0.002\)) and the medium-frequency band (F(3,84) = 4.851, \(p=0.004\)). In the ML direction, the main effect of sound was significant for the low-frequency band (F(3,84) = 4.802, \(p=0.004\)) and the medium-frequency band (F(3,84) = 5.011, \(p=0.003\)). While comparing the silence and other sound conditions, a significant decrease percentage of the low-frequency band and a significant rise percentage of the medium-frequency band in both directions were seen in the silence condition (Figure 2). For the comparison of the group effect, the percentages of the three bands were not significantly different between the older and young groups in the AP direction. In the ML direction, the older group showed a significantly smaller percentage of the low-frequency band and larger medium-frequency band compared to the young group (Figure 2). The main effect of sound was not significant for the total COP excursion and COP velocity in both directions but significant for the sway area (Table 2). A significant decrease in the sway area was observed in the silence condition (10.92 \(\pm\) 1.62 cm\({}^{2}\)) compared to the 1000 Hz (14.92 \(\pm\) 1.81 cm\({}^{2}\)) and 4000 Hz (16.37 \(\pm\) 2.23 cm\({}^{2}\)) conditions. While pairwise comparisons of the group effect, the total COP excursion and COP velocity in the AP direction were not significantly different between the older and young groups. The grand mean of total COP excursion and the COP velocity in the AP direction was 217.79 \(\pm\) 4.92 cm and 5.45 \(\pm\) 0.12 cm/s. In the ML direction, the total COP excursion and the COP velocity were significantly larger in the older group (235.41 \(\pm\) 7.82 cm; 5.89 \(\pm\) 0.20 cm/s) compared to the young group (204.51 \(\pm\) 7.82 mm; 5.11 \(\pm\) 0.20 mm/s). The grand mean of the sway \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**AP Direction**} & \multicolumn{3}{c}{**ML Direction**} \\  & **Low** & **Medium** & **High** & **Low** & **Medium** & **High** \\ \hline \multicolumn{6}{c}{Sound (within-subject Factor)} \\ F(3,84) & 5.185 & 4.851 & 1.435 & 4.802 & 5.011 & 0.415 \\ \(p\) & **0.002** & **0.004** & 0.238 & **0.004** & **0.003** & 0.743 \\ \multicolumn{6}{c}{Group (between-subject Factor)} \\ F(1,28) & 0.995 & 0.768 & 1.400 & 4.236 & 4.759 & 0.102 \\ \(p\) & 0.327 & 0.388 & 0.247 & **0.049** & **0.038** & 0.752 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The results of repeated measure ANOVA for the low-frequency, medium-frequency, and high-frequency band in the anterior-posterior and medial-lateral directions. Figure 2: The effects of sound and group on the low-frequency (LF), the medium-frequency (MF), and the high-frequency (HF) bands of the center of pressure (COP) power spectrum in the anterior-posterior (AP) (upper panels) and medial-lateral (ML) (lower panels) directions. Mean and standard errors are shown. * shows statistical significance (\(p<0.05\)). area was \(14.87\pm 2.53\) cm\({}^{2}\) in the older group and not significantly different from the young group (\(13.44\pm 2.53\) cm\({}^{2}\)). The task performance was significantly affected by the effect of sound (F(3,84) = 8.149, \(p<0.001\)) and the number of pins were significantly more in the silence condition (\(20.26\pm 0.32\)) compared to the other sound conditions (\(250\) Hz: \(19.59\pm 0.31\); \(1000\) Hz: \(19.38\pm 0.32\); \(4000\) Hz: \(19.80\pm 0.31\)). However, the task performance was not significantly different between the older and young groups and the number of pins was \(19.49\pm 0.41\) in the older and \(20.03\pm 0.41\) in the young groups.