1. Visually-Induced Postural Sway in Children
Aged 7-12: Effect of Frequency and
Surface Support
Sparto PJ, Redfern MS, Furman JM,
Mandel EM, Casselbrant ML
Depts of Physical Therapy, Otolaryngology, Bioengineering
University of Pittsburgh, PA, USA
Sponsors: Eye and Ear Foundation,
NIH: DC02490, DC05205, K25 AG001049

2. Introduction
Integration of sensory inputs for balance control occurs throughout childhood
Children are more visually dependent for balance control in preschool years
Although others have reported more adult patterns of balance control during the pre-teen years, we have observed greater visual dependence in children aged 7-12

3. Purpose
Examine magnitude of visually-induced postural sway responses in children, as a function of frequency and support surface
Compare these responses to healthy adults

6. Experimental Design Independent Variables
Frequency of Optic Flow Stimulation
0.1, 0.25, 0.4, 0.7 Hz (16 cm p-t-p amp)
Support Surface
Fixed and Sway-referenced
Dependent Variable
Anterior – Posterior (A-P) Head Sway

7. Subjects Children 19 children aged 7 –12, 10 Female Healthy Adults
8 adults aged , 3 Female

8. Procedure
30 seconds of no movement followed by at least 9 cycles of optic flow
Sway-referencing performed by pitching platform up or down to maintain constant angle of ankle with the platform

9. Scene A-P Translation (cm) Head Platform: Fixed, Freq: 0.4 20 15 10 5
RMS : 3.0 cm -5
-10 10 20 30 40 50 60

10. Data Analysis
A-P Head Position sampled at 20 Hz using electromagnetic tracker
Data processed using phaseless digital bandpass filter
Bandpass at stimulus frequency, Hz
RMS sway computed during optic flow stimulus

11. Sway v. Freq & Surface RMS Head (cm) Frequency (Hz) 3 Sway-Ref Fixed 21 PF
Freq
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Frequency (Hz)
N=19 children

12. Sway v. Freq & Age RMS Head (cm) Frequency (Hz) 2.5 Kids Adults 2 1.5
Age * Freq PF
Age * PF
0.5
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
Frequency (Hz)

13. Sway v. Freq & Age Sway/Fixed Ratio Frequency (Hz) 6 Kids Adults 5 4 32 1
Age
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
Frequency (Hz)

14. Discussion
Optic flow stimuli elicit postural responses in children that are frequency and surface dependent, with a peak around 0.25 Hz
The same stimuli in adults elicit responses that are relatively flat over 0.1 – 0.4 Hz

15. Discussion
Across all conditions, the amount of visually induced sway in children is 1.5 – 2.0 times greater than in adults
The ratio of the amount of sway during sway-referenced platform conditions to fixed platform conditions is less in children

16. Discussion
Taken together, these results indicate that children are more visually dependent and less surface dependent than adults for balance control.

17. 35 31