# Age related postural responses during repeated virtual stimulation: traditional analysis and analysis of the complexity

Marie-Philippine Séba, Pauline Maillot, Sylvain Hanneton, Gilles Dietrich

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Marie-Philippine Séba, Pauline Maillot, Sylvain Hanneton, Gilles Dietrich. Age related postural re-
sponses during repeated virtual stimulation: traditional analysis and analysis of the complexity. In-
ternational Society of Posture & Gait Research, Jul 2022, Montréal, Canada., 2022. hal-03707245

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Submitted on 28 Jun 2022

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# Age related postural responses during repeated virtual stimulation: traditional analysis and analysis of the complexity

Marie-Philippine Séba*, Pauline Maillot*, Sylvain Hanneton*, Gilles Dietrich*

*Institut des Sciences du Sport-Santé, Université Paris Cité, F-75015 Paris, France

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STAPS
Sociétés et Humanités
Université Paris Cité

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## BACKGROUND

The aging of the sensorimotor system alters the perception of our environment and reduces our ability to react quickly to stimuli. This phenomenon contributes to increase the risk of falling in older adults. One way to artificially induce sensory conflicts is to expose individuals to virtual environments, causing conflicts between visual and sensory signals. Postural control reflects the central nervous system's processing of sensory conflicts. A traditional analysis uses the postural parameters resulting from the center of pressures such as the length of the trajectory of the center of pressures or even the mean velocity. It allows to observe the repercussions of sensory conflicts. On the other hand, a complexity analysis uses postural parameters such as fractal dimension or entropy. Complexity is a marker of sensory state. A decrease in complexity and variability may be due to a pathological condition. Complexity is an estimator of fall risk in older adults (Seigle et al., 2009, Zhou et al., 2017). On the other hand, repetitive patterns are adaptation markers (Riley, Balasubramaniam & Turvey, 1999).

This is why this study addresses the following question: are age, repetition and translations influencing traditional and complexity-based postural parameters when exposed to repeated virtual stimulation?

## IN BRIEF

### WHAT IS A TRADITIONAL COP TRAJECTORY ANALYSIS?

Observing the variability of the system in proportion to the disturbance experienced in postural control

<figure><img src="image_5.png" /></figure>

### WHAT IS A COP TRAJECTORY COMPLEXITY ANALYSIS?

Quantifying exploratory postural strategies. Identifying repeating patterns.

<figure><img src="image_6.png" /></figure>

## PURPOSE Investigate the effects of age on postural responses during virtual reality stimulation using traditional analysis and complexity analysis

## METHODS

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84 healthy adults aged 21 to 86
M : 42.41 SD : 18.00

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Oculus Rift (CV1)

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Wii Balance Board

### INDEPENDANT VARIABLES

* Virtual stimulation: Translation direction (forward or backward)
* Number of repeated exposure x 5
* Age

### DEPENDANT VARIABLES

* Mean Velocity
* Surface
* Fractal Dimension
* Percent Recurrence in the AnteroPosterior axis (AP)
* Sample Entropy AP

<figure><img src="image_10.png" /></figure>

Note. The analyses here focus only on the sequences before and after the forward and backward translations.

## RESULTS

<figure><img src="image_11.png" /><figcaption>Translation effect on Mean Velocity</figcaption></figure>

### REPEATED MEASURES ANCOVAS

<figure><img src="image_12.png" /><figcaption>Repetition effect on Fractal Dimension</figcaption></figure>

<figure><img src="image_13.png" /></figure>

## CORRELATIONS WITH AGE AND POSTURAL PARAMETERS

Exposure number

Translation

Mean Velocity

Surface

Fractal Dimension

Sample Entropy AP

Percent Recurrence AP

1

<table><thead><tr><th>Pre-forward translation</th><th>Post-forward translation</th><th>Pre-backward translation</th><th>Post-backward translation</th></tr></thead><tbody><tr><td>0.22*<br>p = .04</td><td>0.17<br>p = .13</td><td>0.20<br>p = .08</td><td>0.20<br>p = .06</td></tr></tbody></table>

<table><tbody><tr><td>0.40*</td><td>p = .0002</td></tr><tr><td>0.29*</td><td>p = .007</td></tr><tr><td>- 0.28*</td><td>p = .01</td></tr></tbody></table>

<table><thead><tr><th>Pre-forward translation</th><th>Post-forward translation</th></tr></thead><tbody><tr><td>0.20*<br>p = .06</td><td>0.15<br>p = .19</td></tr></tbody></table>

<table><tbody><tr><td>0.43*</td><td>p = .0001</td></tr><tr><td>0.26*</td><td>p = .02</td></tr><tr><td>- 0.34*</td><td>p = .001</td></tr></tbody></table>

<table><thead><tr><th>Pre-forward translation</th><th>Post-forward translation</th></tr></thead><tbody><tr><td>0.29*<br>p = .006</td><td>0.15<br>p = .19</td></tr></tbody></table>

<table><tbody><tr><td>0.13<br>p = .22</td><td>0.10<br>p = .34</td></tr><tr><td>0.09<br>p = .40</td><td>- 0.03<br>p = .78</td></tr><tr><td>- 0.03<br>p = .81</td><td>- 0.04<br>p = .75</td></tr></tbody></table>

5

<table><thead><tr><th>Pre-backward translation</th><th>Post-backward translation</th></tr></thead><tbody><tr><td>0.10<br>p = .35</td><td>0.22*<br>p = .047</td></tr><tr><td>- 0.02<br>p = .89</td><td>0.05<br>p = .68</td></tr></tbody></table>

<table><tbody><tr><td>0.08<br>p = .48</td><td>0.18<br>p = .10</td></tr><tr><td>0.17<br>p = .11</td><td>0.08<br>p = .48</td></tr><tr><td>- 0.19<br>p = .09</td><td>- 0.05<br>p = .62</td></tr></tbody></table>

## DISCUSSION

According to the mean velocity, the visual disturbance have indeed caused a sensory conflict. Before the visual disturbance, aging led to an increase in mean velocity, but after the disturbance, all participants appeared to be equally affected. Complexity analysis (Sample Entropy and Percent Recurrence) showed that after the disturbance, participants restricted their postural oscillations. It is by looking at the complexity of the signal according to the age of the participants that differences emerged after visual disturbance. There was an increase in fractal dimension with age, an increase in sample entropy, and a decrease in percent recurrence. But with repetition, the age of the participants no longer correlated with the complexity of the signal. Five repetitions allowed adaptation to the visual disturbance (translations) with aging (Fransson et al., 2019).

## CONCLUSION

Traditional analyzes and the complexity of the center of pressure allow to observe the impact of a sensory conflict on posture and quality of adaptation. With age, visual disturbances cause a restriction of postural oscillations, but repetition allows adaptation to the stimulus through a relaxation of postural oscillations.

## KEY POINTS

* Studying aging and sensory conflicts with Virtual Reality
* 5 identical exposures to forward and backward translations
* Age as a continuous variable (21 to 86 y.o.)

* Traditional analysis and analysis of the complexity of CoP data
* Increase of mean velocity after visual disturbance
* The fractal dimension, the entropy and the percentage of recurrence reveal the influence of age on postural adaptation to visual disturbances

## REFERENCES

de Vassimon-Barroso, V., Catai, A. M., Buto, M. S. D. S., Porta, A., & Takahashi, A. C. D. M. (2017). Linear and nonlinear analysis of postural control in frailty syndrome. Brazilian Journal of Physical Therapy, 21(3), 184-191.
Fransson, P. A., Patel, M., Jensen, H., Lundberg, M., Tjernström, F., Magnusson, M., & Ekvall Hansson, E. (2019). Postural instability in an immersive Virtual Reality adapts with repetition and includes directional and gender specific effects. Scientific reports, 9(1), 1-10.
Riley, M. A., Balasubramaniam, R., & Turvey, M. T. (1999). Recurrence quantification analysis of postural fluctuations. Gait & posture, 9(1), 65-78.
Seigle, B., Ramdani, S., & Bernard, P. L. (2009). Dynamical structure of center of pressure fluctuations in elderly people. Gait & Posture, 30(2), 223-226.
Zhou, J., Habtemariam, D., Iloputaife, I., Lipsitz, L. A., & Manor, B. (2017). The complexity of standing postural sway associates with future falls in community-dwelling older adults: the MOBILIZE Boston Study. Scientific reports, 7(1), 1-8.