postural control refers to the sensorimotor control that maintains center of pressure ( cop ) 
 within the base of support when postural sway occurs due to active or external forces1 .
patients with stroke show a pattern of 
 increased postural sway during quiet standing due to motor , sensory , and cognitive 
 impairments2 , 3 , which increases the risk of falls , as well as limits their ability 
 to independently perform daily life activities4,5,6 .
many studies have reported that providing additional sensory information to patients with 
 balance impairment results in improved postural control7,8,9 .
one of the methods is using a computer screen to provide visual 
 feedback on the displacement of cop .
however , this method has its limitations for home - use 
 because of its high cost10 .
visual feedback training using a mirror is a method that can lead to improvements in 
 postural control by providing feedback on induced movements through a reflection of the body 
 image in the mirror11 .
hlavackova et 
 al.12 reported that when visual 
 feedback was obtained by transfemoral amputees from a mirror placed in front of them , a 
 significant decrease was observed in the subsequent measurement of sway distance .
moreover , 
 a study of the elderly that measured the effects of visual feedback from a mirror reported 
 significant improvement in the mediolateral postural sway10 .
many studies have reported that mirror therapy is effective for motor learning in patients 
 with stroke13,14,15,16 .
few studies have been conducted on the effects of visual feedback 
 from a mirror on the balance ability of patients with stroke .
in addition , most of the 
 studies only measured the effect on stable surfaces .
hence , there is a need for studies on 
 the effects of visual feedback on unstable surfaces .
this study aimed to measure the effects 
 of visual feedback from a mirror on the balancing ability of patients with stroke on various 
 supporting surfaces .
fifteen patients with hemiparetic stroke were recruited for this study from myongii 
 chonnhey hospital .
the inclusion criteria for subjects were as follows : patients who were 
 diagnosed with first onset of unilateral hemisphere stroke , could stand independently for 1 
 minute on a stable surface , had no visual deficit , had no vestibular deficit , and were able 
 to understand and follow simple verbal instructions .
table 1table 1.subject characteristics ( n=15)meansdgender ( male / female)9/6age ( years)54.9  10.9height ( cm)165.7  8.3weight ( kg)63.7  8.0post - stroke duration ( mo)12.9  4.7paretic side ( right / left)8/7lesion type ( hemorrhage / ischemia)7/8mmse26.15  1.83mmse : mini mental state examination shows a list of general characteristics of the subjects . after being informed 
 about the study , all subjects agreed to participate and signed a consent form .
mmse : mini mental state examination the subjects were asked to stand , barefoot and with their heels separated by a distance of 
 8.4 inch on a force plate .
experimental 
 trials included three visual ( eyes closed , eyes open , and mirror feedback ) and two support 
 surface ( stable and unstable ) conditions . in the eyes
open condition , the subjects were 
 asked to fix their gaze on the wall 1  m in front of them , at the eye level . in the mirror 
 feedback condition ,
the subjects were able to visualize their frontal reflected image in a 
 mirror placed on the wall 1  m in front of them12 . for the trials on an unstable surface , the subjects stood on a 
 balance pad ( airex , aalen , germany)17 .
the foot positions were marked on the forceplate and maintained 
 constant between the trials .
the effect of muscle 
 fatigue was minimized by providing a 1-minute rest between measurements .
all subjects wore a 
 harness and a therapist stood behind each of them for safety .
the subject s balance ability was measured using a force platform ( wii balance board [ wbb ] , 
 nintendo , kyoto , japan ) .
the size of the wbb with four load cells was 45  cm  26.5  cm .
this 
 instrument is reported to have a high test - retest reliability ( intraclass correlation 
 coefficient [ icc ] = 0.660.94 ) and construct validity ( icc=0.770.89)18 .
data was exchanged between the wbb and a laptop using the 
 built - in bluetooth and balancia software ( balancia v2.0 , mintosystems , seoul , republic of 
 korea ) .
the sampling rate was set at 50  hz , and 12  hz low pass filtering was performed .
balancia 
 software is reported to have a high interrater reliability ( icc=0.890.79 ) and intrarater 
 reliability ( icc=0.920.70)19 . in order to compare balance ability in different conditions
, data were analyzed using 
 one - way repeated measures analysis of variance ( anova ) .
the least significant difference 
 post hoc test was used to examine the differences within each trials .
for all directions , cop distance and speed increased when the subjects stood on the stable 
 surface with their eyes closed . during stance on the stable surface
, no significant 
 differences were observed in cop distance and speed between the eyes open and mirror 
 feedback conditions ( table 2table 2.center of pressure ( cop ) in patients with stroke during stance under three 
 conditions on a stable surfaceeyes closedeyes openmirror feedbackcop distance ( cm)anteroposterior58.324.036.813.036.911.3mediolateral43.612.836.28.936.19.3total 80.827.657.716.758.916.2cop speed ( cm / s)anteroposterior2.91.21.80.71.80.6mediolateral2.20.61.80.51.90.5total4.01.42.90.82.90.8values are expressed as meansd . * significant difference compared with the eyes 
 closed condition .
significant difference compared with the mirror feedback 
 condition during stance on the unstable surface , an effect of condition was observed along the 
 mediolateral direction with a smaller mediolateral cop distance in the mirror feedback than 
 in the eyes open and eyes closed conditions , whereas no effect of condition was observed 
 along the anteroposterior direction .
cop speed was significantly reduced by mirror feedback 
 when the subjects stood on the unstable surface ( table 
 3table 3.center of pressure ( cop ) in patients with stroke during stance under three 
 conditions on an unstable surfaceeyes closedeyes openmirror feedbackcop distance ( cm)anteroposterior84.924.647.914.643.910.3mediolateral74.123.348.513.742.18.3total 125.237.175.820.867.513.5cop speed ( cm / s)anteroposterior4.92.532.40.731.80.6mediolateral3.71.22.40.72.10.4total6.82.93.81.03.40.7values are expressed as meansd . * significant difference compared with the eyes 
 closed condition .
values are expressed as meansd . * significant difference compared with the eyes 
 closed condition .
in this study we examined the effects of visual feedback from a mirror for patients with 
 stroke in a standing position on various supporting surfaces . the sway distance and speed 
 were the highest when the subjects were standing on a stable surface with their eyes closed , 
 whereas no significant difference was observed in all directions when the mirror feedback 
 was obtained with their eyes open . in a study of amputees that examined the effect of visual 
 feedback from a mirror ,
this was 
 attributed to the improved balance ability through the visual information reflected in the 
 mirror that acted as a sensory substitution for diminished proprioception from the injured 
 limb12 .
furthermore , visual feedback 
 from a mirror helps in learning accurate motions through adjustment of errors observed 
 during task performance20 . a study that 
 used visual feedback in conducting balance training in patients with stroke also reported 
 that such training improved weight distribution and balance ability21 .
however , in this study , no significant improvement effect was observed from visual feedback 
 for subjects who could maintain a standing position on their own for at least 1 minute on 
 the stable surface with relatively small postural sway .
horak et al.22 indicated that dependency on the vestibular organs and 
 vision increased for postural control as the surface became more unstable .
a study on the 
 effects of providing additional somatic sensory information for balance in the elderly also 
 reported that greater improvements were observed on a more unstable surface with increased 
 postural sway23 .
accordingly , the effect of visual feedback from a mirror on the postural sway on unstable 
 surfaces was observed in this study .
it has been reported that mediolateral sway is 
 significantly correlated with falls and can be a predictive factor for falls24 , 25 . therefore , improving postural control in this direction is important 
 for reducing the incidence of falls26 .
mediolateral sway can be recognized as the error associated with the movement that deviates 
 from the body s centerline , while anteroposterior sway can be visually recognized through 
 changes in the sizes of images reflected in the mirror .
10 reported that when visual feedback from a mirror was 
 obtained by the elderly , significant improvement was observed only in the mediolateral 
 direction , and the authors attributed this to the threshold difference in the visual 
 recognition of mediolateral and anteroposterior sway .
decreased mediolateral sway distance 
 and speed was observed when visual feedback was obtained from a mirror , compared to the 
 condition in which the eyes were either closed or open , but the findings were not 
 statistically significant . moreover , since the anteroposterior sway was not large enough to 
 show changes in the size of the image , a significant difference based on the visual feedback 
 was not exhibited .
the visual feedback from a mirror for patients with stroke led to a significant decrease in 
 the postural sway on surfaces that are more unstable , where the sway distance and speed had 
 increased .
however , generalization of the result is difficult due to the small number of 
 subjects .
in addition , because the subjects were recruited regardless of fall experience , a 
 correlation of visual feedback with falls could not be determined .
therefore , future studies 
 should examine the effects of visual feedback from a mirror in dynamic states such as sit to 
 stand , and visual feedback training using a mirror on balance and falls in patients with 
 fall experience .
 [ purpose ] this study aimed to examine the effects of a visual feedback obtained from a 
 mirror on balance ability during quiet standing in patients with stroke . 
 [ subjects ] 
 fifteen patients with stroke ( 9 males , 6 females ) enrolled in the study . 
 [ methods ] 
 experimental trials ( duration , 20s ) included three visual conditions ( eyes closed , eyes 
 open , and mirror feedback ) and two support surface conditions ( stable , and unstable ) . 
 
 center of pressure ( cop ) displacements in the mediolateral and anteroposterior directions 
 were recorded using a force platform . 
 [ results ] no effect of condition was observed along 
 all directions on the stable surface . 
 an effect of condition was observed on the unstable 
 surface , with a smaller mediolateral cop distance in the mirror feedback as compared to 
 the other two conditions . 
 similar results were observed for the cop speed . 
 [ conclusion ] 
 visual feedback from a mirror is beneficial for improving balance ability during quiet 
 standing on an unstable surface in patients with stroke . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION