# Sound Effects on Standing Postural Strategies in the Elderly via Frequency Analysis Approach
## 4 Discussion  
The current study was conducted to investigate how sound influences COP displacement during a hand task in standing via spectral analysis. The sound effect was observed in the low-frequency and medium-frequency band in the AP and ML direction. The LF\({}_{\text{AP}}\) and LF\({}_{\text{ML}}\) were decreased and MF\({}_{\text{AP}}\) and MF\({}_{\text{ML}}\) were increased in the silence condition compared to the other three sound frequency conditions. The smaller percentage of the low-frequency band and the larger percentage of the medium-frequency band in the ML direction were observed in the older group and significantly different from the young group. The larger number of pins and small sway area were also observed in the silence condition than the other conditions. The hand task was aimed to simulate daily activities and increase the challenges as a dual-task to postural control. The hand task produced in the present experiment was the Purdue Pegboard test, which was designed to evaluate finger/hand dexterity and has been employed in neuropsychological assessments in older adults as a clinical measurement [25]. According to the user instructions of the Purdue Pegboard test, the number of pins was 15.44 in the age group of 21-25 and 14.6 in the age group of 60-69 when performing in 30 s. It was comparable with 20.69 in the young groups and 19.83 in the older group for performing 40 s in the silence condition. This comparison confirmed that the participants correctly executed the Purdue Pegboard test. The comparable performances of Purdue Pegboard test with previous studies could indicate changes in the COP displacements, postural regulation, and task performance were due to the factor of sound or age in performing the dual-task. During quiet standing without conducting a dual-task, it has been reported that sound and sound frequency substantially affect the postural sway length and the position variability of COP [8] and significantly decrease the sway area during extreme loudness [4]. In the current study, the sway area was decreased and improved task performance with a greater number of pins was observed in the silence condition compared to the other sound conditions. Likewise, when individuals were exposed to a noisy environment, worsened task performance, such as the scores of the balance error scoring system, has been reported [26]. Therefore, the sound did not act positively to the vestibular system as expected on the medium-frequency band. On the contrary, it might be considered as an external disturbance to sensory integration, which further resulted in the increased postural sway [27]. On the other hand, potential benefits of sound frequency influencing the vestibular system might also be compromised. The frequency analysis revealed changes in postural regulations in the sound conditions. It showed that the low-frequency and medium-frequency bands in both directions were significantly different \begin{table}
\begin{tabular}{l c c c c c c} \hline  & \multicolumn{2}{c}{**Sound**} & \multicolumn{2}{c}{**Silence**} & \multicolumn{2}{c}{**250 Hz**} & \multicolumn{2}{c}{**1000 Hz**} & \multicolumn{2}{c}{**4000 Hz**} \\  & **F(3,84)** & \(p\) & & & & \\ \hline excursion\({}_{\text{AP}}\) (cm) & 2.059 & 0.112 & 216.83 (4.96) & 217.25 (4.82) & 218.48 (5.06) & 218.61 (4.97) \\ excursion\({}_{\text{ML}}\) (cm) & 0.615 & 0.607 & 220.19 (5.73) & 219.38 (5.46) & 220.32 (5.59) & 219.96 (5.39) \\ velocity\({}_{\text{AP}}\) (cm/s) & 2.059 & 0.112 & 5.42 (0.12) & 5.43 (0.12) & 5.46 (0.12) & 5.47 (0.12) \\ velocity\({}_{\text{ML}}\) (cm/s) & 0.615 & 0.607 & 5.51 (0.14) & 5.48 (0.14) & 5.51 (0.14) & 5.60 (0.14) \\ sway area (cm\({}^{2}\)) & 6.284 & **0.001** & 10.92 (1.62) & 14.43 (2.12) & 14.92 (1.81) * & 16.37 (2.23) * \\ \hline \end{tabular}  
* \(p<0.01\) compared to the silence condition.  
\end{table} 
Table 2: The results of repeated measure ANOVA for excursion\({}_{\text{AP}}\), excursion\({}_{\text{ML}}\), velocity\({}_{\text{AP}}\), velocity\({}_{\text{ML}}\), and sway area.