cerebral palsy is a nonprogressive disorder that occurs during early brain development and 
 presents with abnormal movement and posture1 , 2 .
previous studies indicated that 90% of 
 patients with cerebral palsy exhibit impaired gait patterns due to excessive muscle 
 weakness , altered joint kinetics , and diminished postural reactions3 .
the impairments cause abnormal gait , including 
 developmental disability in the upper and lower extermities4 , a wide base of support , decreased step and stride lengths , reduced 
 time in single stance , and a slower walking velocity5 .
therefore , a common goal of rehabilitation in children with 
 cerebral palsy is the recovery of functional gait6 , 
 7 .
certain aspects of gait control in humans are generated by integration of visual , 
 proprioceptive , and vestibular information8 .
visual information input is essential for detecting and identifying 
 sensory information from the surrounding environment , thus enabling appropriate 
 spatiotemporal anticipation , before initiating and completing movement9 .
hence , many studies involving rehabilitation of patients 
 demonstrating a hemiplegic gait pattern have employed visual information techniques such as 
 visual feedback therapy and virtual reality training methods11,12,13 .
yang et al . investigated the effects of virtual reality treadmill training on functional 
 gait in hemiplegic stroke patients , and the results of this training appeared to demonstrate 
 improvement of gait function and patient mobility13 .
baram et al . reported that visual feedback improved walking speed 
 and stride length in patients with hemiplegic cerebral palsy14 .
optic flow is the pattern of motion perceived at the retina , which specifies the direction 
 of locomotion15 and provides vital 
 feedback concerning patient regulation of walking velocity16 .
reported that modulation of optic flow resulted in 
 changes in gait parameters such as gait velocity , cadence , and stride length in human 
 subjects17 .
reported 
 that a fast optic flow speed resulted in increased walking velocity and cadence in 
 hemiplegic stroke patients18 .
moreover , 
 kang et al . reported that treadmill training , along with modulation of optic flow , improved 
 gait velocity in hemiplegic patients following a stroke8 .
several such studies concerning the effects of optic flow alterations on gait parameters 
 are found in the literature .
however , the majority of these studies assessed both hemiplegic 
 stroke patients and healthy adults .
therefore , in the present study , we examined the 
 alterations in gait parameters due to modulation of the optic flow speed specifically in 
 patients with hemiplegic cerebral palsy .
in the present study , we examined 10 children with hemiplegic cerebral palsy who visited 
 the community rehabilitation welfare center , korea .
general characteristics of the children with hemiplegic cerebral palsysubjectgenderage ( years , months)height ( cm)paretic limbgmfcs levels1male5 , 5109ris2male6 , 1117ris3female4 , 1084lis4male5 , 8103riis5female4 , 695ris6male5 , 2112ris7male4 , 196lis8male6 , 1124lis9male3 , 997ris10female4 , 299rir , right ; l , left ; gmfcs , gross motor function classification system .
all subjects and guardians signed an informed consent form after they 
 understood the contents of the study .
the inclusion criteria were as follows : a current 
 diagnosis of hemiplegic cerebral palsy , ability to walk unassisted or with only minimal 
 assistance for more than 10 m , patient motor function consistent with level i and ii 
 according to the gross motor function classification system ( gmfcs ) , and no visual deficit . 

the study was approved by the human research ethics committee of all the participating 
 institutions .
r , right ; l , left ; gmfcs , gross motor function classification system this study design is cross - sectional .
each subject was evaluated during application of optic 
 flow speeds at 3 different levels , as follows : slow ( 0.25 times the normal speed ) , normal , 
 and fast ( 2 times the normal speed ) .
the visual information was projected on a screen via a 
 connected notebook with virtual reality software , which mimicked walking in a park .
patient procedural parameters were established as follows : first , all subjects walked at a 
 self - selected speed on the gaitrite system , without visual program input information . 

second , prior to recording flow speed and gait effects , all subjects adapted their gait to 
 the visual information during a 10-min trial of the 3 levels of optic flow speed , which were 
 randomly applied .
third , the subjects who had watched the screen playing the visual 
 information with one of the 3 optic flow speeds and a self - selected gait speed , walked 
 across the walkway of the gaitrite system . the subjects walked 5 times at each optic flow 
 speed , and the data was reduced to a mean value for each subject examined .
a 3-min rest 
 period was allowed between each intervention , to minimize the effects of muscular fatigue . 

any subject who required assistance was provided minimal assistance by a therapist who was 
 not informed about the purpose of the subject s activity or the purpose of the study . the gaitrite system ( cir systems inc . ,
this device has an electronic walkway measuring approximately 700  90  cm , with 
 pressure sensors placed in a horizontal grid along the walking surface ; the device is 
 connected via an interface cable to a notebook running the ms windows xp operating system . 

the recording area of the device generally measures 61  cm in width and 732  cm in length . 

sensors are maintained at a distance of 1.27  cm from each other ( totaling 27,648 sensors ) , 
 and a recording frequency of 80  hz is used with temporal resolutions of 11  ms .
the gaitrite 
 gold , version 3.2b , software was used for spatiotemporal data analysis .
the procedure for 
 evaluation using the gaitrite system was as follows : each subject stood in front of the mat , 
 and when cued by the evaluator , the subject walked onto and along the mat at a self - selected 
 walking speed . the collected data consisted of temporal gait characteristics such as 
 velocity , cadence , single support time , double support time , and spatial gait 
 characteristics including step length and stride length .
the measurement reliability of this 
 system is r = 0.90 , and the icc is 0.9610 , 19 .
repeated measure 
 anova was used to compare spatiotemporal gait parameters for each optic flow speed .
the fast optic flow speed ( 2 times the normal speed ) significantly increased walking 
 velocity , cadence , normalized step length , base of support , and single support cycle of both 
 the paretic and non - paretic lower limbs as compared with the other flow conditions applied 
 ( p > 0.05 ) .
moreover , the slow optic flow speed ( 0.25 times the normal speed ) induced 
 significantly decreased walking velocity , cadence , normalized step length , base of support , 
 and single support cycle of both the paretic and non - paretic lower limbs as compared with 
 the other flow speed conditions applied ( p > 0.05 ) ( table 2table 2 .
comparison of gait parameter among the different optic flow speedsparametersslow ofnormal offast ofvelocity ( cm / sec)48.72.356.92.969.32.8cadence ( step / min)109.22.5122.82.3134.42.5normalized step length ( step length / leg length)affected side0.70.10.70.10.80.2non - affected side0.70.10.70.10.80.1base of support ( cm)affected side 12.50.311.40.510.10.7non - affected side13.20.312.00.49.40.4single support ( % gait cycle)affected side32.70.435.20.437.30.3non - affected side36.11.138.21.340.21.6all variables are presented as meanstandard deviation values .
statistically significant difference between normal of and 
 fast of ( p<0.05 ) . ) .
this study compared the alteration in spatiotemporal gait parameters according to the 
 application of slow , normal , and fast optic flow speeds in patients with hemiplegic cerebral 
 palsy .
after occurrence of an incongruity 
 between alteration of the optic flow speed and the resulting proprioceptive information 
 observed in the lower extremity , the subjects decreased the incongruity by altering movement 
 in the lower extremity8 , 17,18 .
konczak et al . 
 reported that an increased optic flow speed in healthy adults induced an increase in walking 
 velocity more quickly than that induced by a reduced optic flow21 .
reported that alterations of optic flow 
 speed in healthy adults resulted in modulation of stride length and walking velocity because 
 optic flow interpretation by the brain played a major role in the regular gait pattern and 
 gait control17 .
therefore , changes in the 
 gait patterns of healthy adults were induced by altering the optic flow speed . in previous studies involving subjects with several spatiotemporal orientation types , 
 schubert et al . reported that patients with parkinson s disease , tested through application 
 of various optic flow speeds ranging from 1 to 3 times the normal speed , changed their gait 
 speed and cadence more quickly than elderly adults and healthy adults .
this phenomenon was 
 attributed to the fact that patients with parkinson s disease experience excessive reliance 
 on visual feedback due to the impairment of proprioceptive guidance during voluntary 
 movement and damage noted as sensory scaling associated with altered kinesthesia22 .
reported that 
 poststroke hemiplegic patients demonstrated altered gait speed and cadence when influenced 
 by large differences in optic flow speed18 .
thus , changes in gait control in patients with parkinson s disease 
 and patients with hemiplegic stroke were both influenced by alterations in optic flow 
 speed .
this study indicated that the fast optic flow speed in hemiplegic cerebral palsy subjects , 
 generated altered temporal parameters in gait speed , cadence , single support time of the 
 affected and non - affected side , and double support time of the affected and non - affected 
 side more quickly than application of the slow optic flow speed , self - selected gait speed , 
 or normal optic flow speed .
moreover , the fast optic flow speed induced alterations of 
 spatial parameters in stride length in the hemiplegic cerebral palsy subjects , on the 
 affected and non - affected sides as well as step length on the affected and non - affected 
 sides , for an extended period of time when compared with the alterations produced by all the 
 other applied optic flow speeds . in a previous study ,
alteration of optic flow speeds in 
 hemiplegic stroke patients resulted in gait alterations similar to those found in hemiplegic 
 cerebral palsy subjects .
kang et al . reported that the application of a fast optic flow 
 speed in hemiplegic stroke patients induced spatial and temporal parameters more quickly 
 than the application of slow and normal optic flow speeds .
the most prominently observed 
 deficits in patients with hemiplegic cerebral palsy were noted in gait velocity , decreased 
 step and stride lengths , and reduced time in single stance , although self - selected gait was 
 not affected5 .
therefore , a rehabilitation 
 program including alterations of the optic flow speed in children with hemiplegic cerebral 
 palsy may improve gait parameters .
moreover , alterations of gait parameters , as a result of alterations of the optic flow 
 speed , in children with hemiplegic cerebral palsy were found to be similar to those produced 
 in hemiplegic stroke patients .
such gait alterations in both patient groups are generated by 
 changes in lower limb response patterns due to the patient s intention to decrease the 
 incongruity between proprioceptive information of the lower limbs and the optic flow 
 speed .
limitations of the present this study include the relatively small group of eligible 
 subjects available and the absence of control group data .
therefore , further similar studies 
 involving a larger subject population and a non - affected control group are needed . 

furthermore , studies documenting the effects of a rehabilitation program using variable 
 optic flow speeds in the treatment of children with hemiplegic cerebral palsy , are 
 considered to be a necessary prerequisite to the addition of variable optic flow movement 
 therapies in rehabilitation hospitals .
   [ purpose ] we investigated the effects of modulation of the optic flow speed on gait 
 parameters in children with hemiplegic cerebral palsy . [ methods ] we examined 10 children 
 with hemiplegic cerebral palsy . 
 the children underwent gait analysis under 3 different 
 conditions of optic flow speed : slow , normal , and fast optic flow speed . 
 the children 
 walked across the walkway of a gaitrite system , while watching a virtual reality screen , 
 and walking velocity , cadence , stride length , step length , single support time , and double 
 support time were recorded . 
 [ results ] compared with the other applied flow speed 
 conditions , the fast optic flow speed ( 2 times the normal speed ) significantly increased 
 walking velocity , cadence , normalized step length , base of support , and single support 
 cycle of both the paretic and non - paretic lower limbs . moreover , compared with the other 
 applied flow speed conditions , the slow optic flow speed ( 0.25 times the normal speed ) 
 yielded a significantly decreased walking velocity , cadence , normalized step length , base 
 of support , and single support cycle for both the paretic and non - paretic lower limbs . 
 
 [ conclusion ] the gait parameters of children with hemiplegic cerebral palsy are altered by 
 modulation of the optic flow speed . 
 thus , we believe that gait training involving 
 modulation of the optic flow speed is feasible and suitable for resolving abnormal gait 
 patterns in children with hemiplegic cerebral palsy . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION