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Visually-Induced Postural Sway in Children Aged 7-12: Effect of Frequency and Surface Support

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,

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Visually-Induced Postural Sway in Children Aged 7-12: Effect of Frequency and Surface Support

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  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

  4. 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

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

  6. 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

  7. 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

  8. 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

  9. 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) N=19 children

  10. 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)

  11. 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)

  12. 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

  13. 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

  14. 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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