Visually-Induced Postural Sway in Children

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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
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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

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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

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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

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Subjects

• Children
• 19 children aged 7 12, 10 Female
• Healthy Adults
• 8 adults aged 25 - 70, 3 Female

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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

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Platform Fixed, Freq 0.4
20
15
Scene
10
5
A-P Translation (cm)
Head
0
-5
-10
0
10
20
30
40
50
60
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Data Analysis

• A-P Head Position sampled at 20 Hz using
  electromagnetic tracker
• Data processed using phaseless digital bandpass
  filter
• Bandpass at stimulus frequency, 0.05 Hz
• RMS sway computed during optic flow stimulus

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Sway v. Freq Surface
3
Sway-Ref
Fixed
2
RMS Head (cm)
1
PF Freq
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Frequency (Hz)
N19 children
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Sway v. Freq Age
2.5
Kids
Adults
2
RMS Head (cm)
1.5
1
Age Age Freq PF Age PF
0.5
0
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
Frequency (Hz)
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Sway v. Freq Age
6
Kids
Adults
5
4
Sway/Fixed Ratio
3
2
1
Age
0
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
Frequency (Hz)
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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

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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

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Discussion

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

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