it is difficult to determine the center of mass of the human body while in the standing 
 posture , as the base of support is narrow ; therefore , it is hard to maintain the standing 
 posture , and this posture is fundamentally unstable1 . in order to maintain the upright posture , the ability to control 
 posture is constantly required2 . while 
 maintaining posture , sensory information from the vestibular , visual , and somatosensory 
 systems is integrated in the central nervous system2 . the upright standing posture is maintained when afferent 
 information is integrated in the central nervous system through the vestibular , visual , and 
 somatosensory systems and induces reflexive control of eye and extremity movement3 . all three sensory systems are required for 
 optimal postural stability ; thus , impairment of any of these sensory systems may increase 
 sway while standing . postural sway increases by 2070% under visually blocked 
 conditions , as the ability to control posture declines under these blocked conditions6 . stroke patients usually experience 
 impairments such as motor paralysis , sensory loss , and muscle tone change9 , and these impairments usually occur in the 
 trunk and extremity of the affected side , causing imbalance with the unaffected side . the 
 imbalance between the affected and unaffected sides results in asymmetric weight 
 distribution , with 6090% of the weight supported by the unaffected side10 , 11 , and this increases postural sway , thus disturbing postural 
 control10 . this imbalance affects gait , 
 causes an abnormal gait pattern , and restricts functional activities12 . therefore , it is important to improve postural control 
 using these methods that improve the elements described above9 . a previous study found that pelvic stability of stroke patients improved with light cane 
 support13 . additionally , previous 
 studies have suggested that light support with a fixed handrail using fingers improves 
 postural stability while walking on an unstable support14 . this sensory information , called the 
 light touch cue , may provide latent support to postural control16 . previous studies reported that light touch cue increases 
 sensory feedback about body movement during postural control17 . in particular , light touch with a force under 1 n provides tactile 
 stimulation instead of mechanical support that decreases postural sway18 . many previous studies have reported on the effects of 
 active touch , which reduces postural sway and improves postural stability . another study 
 found that active touch reduces perturbation not only during normal standing posture but 
 also during the romberg posture1 . additional studies have applied active touch to healthy adults with muscle fatigue19 , patients with muscle vibration in the 
 neck and lower extremity20 , 21 , the elderly22 , patients with peripheral neuropathy23 , patients with vestibular dysfunction on both sides4 , and patients with visual dysfunction2 . however , studies on the effect of light 
 touch instead of mechanical support on postural sway during the static standing posture in 
 stroke patients and the range of the relevant effects are limited . therefore , the current study aimed to investigate the influence of light tactile 
 stimulation under 1 n , instead of mechanical support , on the stability or postural sway in 
 stroke patients . the current study investigated whether tactile feedback from a fingertip 
 cue , regardless of mechanical support , decreases postural sway caused by active touching 
 during the static standing posture and the extent of improvement in postural sway . the subjects were 
 recruited through the hospital bulletin board , and 21 patients were screened from among 30 
 volunteers . the inclusion criteria were patients who were diagnosed with a stroke in the 
 past 6 months , those with hemiparesis , those who could walk 10  m independently without 
 assistive devices , those without hearing and visual impairments , those without neurologic or 
 orthopedic diseases that may influence the results of the experiment , and those not taking 
 medicines that may affect their stability . the characteristics of the subjects are shown in table 1table 1.characteristics of the subjectsngender(male / female)age(years)etiology(i / h)affected side(r / l)disease duration(month)2111/1072.27.814/711/10109.759.1values are frequencies or meanssd . i : infarction ; h : hemorrhage ; r : right ; l : left 
 . after screening the subjects , the aim and procedure were thoroughly explained 
 to the subjects , and written consent forms were signed . i : infarction ; h : hemorrhage ; r : right ; l : left 
  the current study was a cross - sectional study design . the characteristics of the subjects 
 were obtained from interviews and medical charts . the subjects participated in an experiment 
 that measured postural sway during the static standing posture and postural sway during the 
 static standing posture with light touch . the assessor provided an adequate explanation 
 about the procedure of the fingertip cue to all the subjects and asked them to practice . 
 additionally , all the subjects practiced the standing posture five times on the ground in 
 order to learn the process and procedure before measurement and took adequate rest after the 
 practice . before measurement , reference points were marked on the force platform in order to 
 minimize changes in reference points that might occur during repeated measurements . the 
 subjects stood on the force platform after the calibration was performed . when the  ready signal was given , the subjects were to stand on the force platform in an upright posture . the 4 conditions used were as follows : visual information not blocked without light touch , 
 visual information blocked without light touch , visual information blocked with light touch 
 using fingertips , and visual information not blocked with light touch using fingertips . each trial took 30 seconds , and subjects had a 3-min 
 break between each trial to minimize the adaptation effect on the measurement occurring 
 through the test - retest process . for the light touch with the fingertips , the subjects stood 
 upright , abducted the upper extremity slightly to the side of the trunk , flexed the elbow to 
 90 , and flexed all the fingers except the index finger to touch a piece of fabric with the 
 index finger . the subjects stood focusing on the fingertip and maintained the position of 
 touching the fabric for 30 seconds . the pressure of the light touch was set under 1 n 
 because external force under 1 n is at the non - mechanically supportive force level that does 
 not affect postural sway21 . all subjects 
 wore eye patches in order to eliminate confounding variables for the measurement conditions 
 with blocked vision . the assessor and subjects were alone in the experiment room to control 
 variables that may influence the subject . changes in postural sway during the light fingertip touch were measured using a force 
 platform that records the center of pressure ( cop ) ( good balance , metitur ltd , finland ) . the 
 force platform used in the study was composed of a triangular board connected to 3 
 amplifiers and a computer with built - in bluetooth . the signals recorded on the force 
 platform were amplified into measurable signals through the amplifier . the signals were 
 transferred to the computer through bluetooth and digitalized through a 12-bit converter so 
 that data could be saved on the computer . the computer transformed the signals using a 50  hz 
 sampling rate , performed filtering using a 12  hz low frequency filter , and analyzed the 
 saved values . the variables of postural sway include sway velocities of the cop in the 
 anterior and posterior directions and medial and lateral directions , and sway velocity 
 moments . the reliabilities of the force platform were found to be 0.51 and 0.74 in the 
 anterior and posterior directions , respectively , and 0.63 and 0.83 in the medial and lateral 
 directions , respectively24 . normality tests of the variables 
 were performed by using the kolmogorov - smirnov method , and descriptive statistics were used 
 to analyze the mean and standard deviation of all the variables . an independent t - test was 
 used to compare the influence of the light fingertip touch . the level of statistical 
 significance (  ) the results of the study are shown in table 
 2table 2.comparison of the postural sway in without light touch and with light 
 touchvariablewithout light touchwith light touchchangeseyes open(mm / s)ap sway velocity7.03.02.00.95.0*ml sway velocity8.93.54.31.54.6*velocity moment16.78.43.82.412.9*eyes closed(mm / s)ap sway velocity10.53.43.11.37.4*ml sway velocity13.85.46.13.47.7*velocity moment25.812.65.93.419.8*values are frequencies or meanssd . ap : anterioposterior ; ml : mediolateral * statistically significant at p<0.05 between without light touch and with light 
 touch . the sway velocity of the cop and moment velocity under the eyes open and 
 closed conditions were significantly decreased in the state with light touch compared to the 
 state without light touch ( p<0.05 ) ( table 2 ) . the rates of decrease of the sway velocity and moment velocity under the eyes closed 
 condition were higher compared with those under the eyes open condition ( table 2 ) . ap : anterioposterior ; ml : mediolateral * statistically significant at p<0.05 between without light touch and with light 
 touch the present study aimed to investigate the influence of active light touch on the 
 improvement of postural stability in chronic stroke patients . the study showed that the sway 
 velocity of the cop and moment velocity improved significantly during active light touch 
 compared with without light touch . cunha et al.13 found that the 
 cop decreased because of light touch provided additional sensory information for decreasing 
 postural sway of patients with hemiparesis resulting from stroke . dickstein et al.23 found a significant decrease in the cop of 
 32 patients with peripheral neuropathy compared with a control group because of fingertip 
 touch that was used for improvement in postural stability . the decrease in postural sway due to tactile feedback through active touch also occurs 
 during the application of passive touch such as rubbing the lower extremity or shoulder in 
 the standing position25 . the tactile 
 stimulation from passive touch may provide additional sensory input for decreasing postural 
 sway . previous studies found that passive touch at various parts of the lower extremity 
 improved postural stability while standing through tactile stimulation26 . the equipment used for passive touch was for tactile feedback rather than for mechanical 
 support . considering this , the study of menz et the decrease in tactile feedback from tactile stimulation without mechanical support 
 increased postural sway27 . these previous 
 studies found that compressive ischemia in the upper arm during active light touch decreased 
 tactile feedback , which then increased postural sway . a few studies found that haptic cues 
 input through a fingertip touch decreased postural sway19 , 28 . for stability while in 
 the standing posture , in terms of mechanical aspects , strong supports are needed1 , but various studies found that a light 
 touch cue can decrease postural sway in a manner similar to a strong touch cue23 , 29 . the results of previous studies and the current study confirm that 
 an increase in tactile feedback , instead of mechanical support , through active touch with a 
 force under 1 n may change postural sway . additionally , the current study results showed higher rates of decrease of sway velocity 
 and moment velocity under the eyes closed condition compared with under the eyes open 
 condition with and without active touch . although interferential statistics were not 
 performed , the descriptive statistical analysis showed a decrease of 4.98  mm / s in the 
 anterior and posterior directions , a decrease of 4.57  mm / s in the medial and lateral 
 directions , and a decrease of 12.92  mm / s in the velocity moment under the eyes open 
 condition , as well as a decrease of 7.42  mm / s in the anterior and posterior direction , a 
 decrease of 7.68  mm / s in the medial and lateral directions , and a decrease of 19.84  mm / s 
 during velocity moment under the eyes closed condition . balance is the ability to maintain 
 the center of gravity in the body with minimum postural sway on the base of support6 . the ability to maintain balance may 
 decrease due to increased postural sway under the eyes closed condition when visual 
 information is blocked30 . horvat et 
 al.31 and ray et al.32 found that patients with visual 
 dysfunction had increased postural sway compared with healthy adults , which resulted in an 
 increased risk of falls . the result showed that the rate of decreased of postural sway was 
 higher when light touch was available under the eyes closed condition . patients were highly 
 dependent on the somatosensory system in order to compensate for impaired vision , and the 
 increased somatosensory system improved the efficiency of light touch28 . in addition , when people with visual impairment tightly 
 held a cane , an assistive device , and when people held a cane lightly , static postural sway 
 decreased , which supports the assertion that the effect of light touch on postural sway 
 under the eyes closed condition is greater2 . stroke patients were to perform a light fingertip touch with a 
 force under 1 n while postural sway with and without touch was measured for comparison . the 
 results of the current study were similar to the results of previous studies that found that 
 light touch decreases postural sway16 , 28 . light fingertip touch does not act as a 
 mechanical support , rather it creates tactile feedback that improves balance2 . the present results show that active light touch contributes to improvement of balance and 
 decreases postural sway . however , the current study has limitations ; that is , due to the 
 small sample size , it is difficult to generalize the results , and we did not investigate the 
 changes in postural sway with touch involving various other body parts . therefore , future 
 studies should be conducted in order to provide useful information to patients with 
 neurologic diseases .
[ purpose ] the purpose of this study was to investigate the influence of fingertip light 
 touch on the postural control in poststroke patients . [ subjects ] in the study 
 , the 
 subjects were recruited through a rehabilitation hospital , and 21 patients were screened 
 from among 30 volunteers . [ methods ] the subjects participated in an experiment that 
 measured postural sway during the static standing posture without light touch and postural 
 sway during the static standing posture with light touch as follows : visual information 
 not blocked without light touch , visual information blocked without light touch , visual 
 information blocked with light touch using fingertips , and visual information not blocked 
 with light touch using fingertips . 
 the measurements were performed using a force platform . 
 the variables measured by the force platform included sway velocities of the cop in the 
 anterior and posterior directions and , medial and lateral directions and sway velocity 
 moments . 
 [ results ] in the results of the study , there were significant differences between 
 the state without light touch and state with light touch in terms of the postural sway 
 velocity and velocity moment under all conditions . 
 the rate of decease of the sway 
 velocity and moment velocity under the eyes closed condition were higher compared with 
 those under the eyes open condition . 
 [ conclusion ] through this study , we confirmed the 
 influence of fingertip light touch on the decrease in postural sway . 
 the results show that 
 active light touch may be supplemental means of improving postural sway in stroke 
 patients .