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PubMed1995

Effect of age and training schedules on balance improvement exercises using visual biofeedback.

There has been a growing popularity and success rate of balance rehabilitation programs, and this success is paralleled by the growth of technology, making available instruments that provide objective, quantitative, and immediate results. The Balance Master is such a commercially available instrument, consisting of a dual-force platform connected to a micro-computer that provides visual feedback of the centre of gravity (COG) in relation to the theoretical limits of stability. Spontaneous body sway can be measured in a static central position, or in peripheral positions around the limits of stability (peripheral sway area). The trajectory between targets can also be analyzed in terms of time (transition time) and accuracy (path error) of transition, which gives a quantitative measure of dynamic movement of the COG. This study examined the practice effect that occurs while using this instrument over repeated sessions for two schedules of training (daily and weekly) and over two age groups (20-35 years, and 60-75 years). Each group completed a series of postural exercises, with an assessment of static and dynamic postural variables before and after training, and at approximately 3 and 6 weeks post-training. Spontaneous body sway was measured with eyes open, eyes closed, and with visual feedback of the COG. No significant changes were observed in these variables as measured over the four standard assessment occasions. Peripheral sway area and path error decreased significantly for both the daily and weekly training groups from pre- to post-training, and these skills were retained over both retention tests, whereas the tendency toward decreasing transition time was not significant.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1983

Acquisition of frication by severely hearing-impaired children.

The ability of severely deaf school children to master fricative production and the fricative-affricate distinction was studied over a period of 6 months. The children were given daily speech therapy and half of them received, in addition, visual feedback from a microprocessor-based speech training aid - the 'Fricative and Timing Aid'. The speech of a third group of children, who received no training from us, was also monitored. Results were analysed in terms of the acquisition of fricatives and affricates, and of their position in a word. Results yielded by perceptual tests showed a substantial increase in the intelligibility of all trained children for almost all phonemes at the end of the training programme. Retention scores, i.e. intelligibility scores obtained by re-testing the children after a 2-moth period of non-practice, showed that practically no forgetting of articulatory skills occurred during this interval. Comparisons between children trained with or without visual feedback in general showed no difference between them; however, the former were more intelligible when producing affricates. No improvement in intelligibility was found when no systematic speech training was available. It was concluded that while frication may not be acquired spontaneously, it is a task within the reach of severely deaf children when adequately trained.

Adolescent↗

PubMed2004

Non-invasive assessment of single motor unit mechanomyographic response and twitch force by spike-triggered averaging.

A method for non-invasive assessment of single motor unit (MU) properties from electromyographic (EMG), mechanomyographic (MMG) and force signals is proposed. The method is based on the detection and classification of single MU action potentials from interference multichannel surface EMG signals and on the spike-triggered average of the MMG (detected by an accelerometer) and force signals. The first dorsal interosseous (FDI) and abductor digiti minimi (ADM) muscles were investigated at contraction levels of 2% and 5% of the maximum voluntary contraction (MVC) force. A third contraction was performed by selective activation of a single MU with surface MU action potential visual feedback provided to the subject. At 5% MVC, the mean (+/-standard error) single MU MMG peak-to-peak value was 11.0+/-1.8 mm s(-2) (N= 17) and 32.3+/-6.5 mm s(-2) (N=20) for the FDI and ADM muscles, respectively. The peak of the twitch force was, at the same contraction level, 7.41+/-1.34 mN and 14.42+/-2.92 mN, for the FDI and ADM muscles, respectively. The peak-to-peak value of the MMG was significantly different for the same MU at different contraction levels, indicating a non-linear summation of the single MU contributions. For the FDI muscle, the MMG peak-to-peak value of individual MUs was 21.5+/-7.8 mm s(-2), when such MUs were activated with visual feedback provided to the subject, whereas, for the same MUs, it was 11.8+/-3.8 mm s(-2), when the subject maintained a constant force level of 2% MVC. The method proposed allows the non-invasive assessment of single MU membrane and contractile properties during voluntary contractions.

Action Potentials↗

PubMed1996

Role of physical countermaneuvers in the management of orthostatic hypotension: efficacy and biofeedback augmentation.

OBJECTIVE: To evaluate the efficacy of various physical countermaneuvers in reducing orthostatic hypotension and its associated symptoms and to assess the efficacy of biofeedback training in enhancing the effectiveness of physical countermaneuvers. MATERIAL AND METHODS: In nine study subjects with neurogenic orthostatic hypotension, four training sessions on physical countermaneuvers were performed after tilt-up, three with visual feedback on the effect of physical countermaneuvers on blood pressure and other cardiovascular variables. Blood pressure change and orthostatic symptoms during tilt-up were determined, as were the changes in total peripheral resistance, stroke index, and heart rate. RESULTS: The five female and four male patients had a mean age of 53 years and a mean duration of symptoms of 4.2 years. On an orthostatic symptom scale of 0 to 10, these patients had a mean symptom score of 7.3. The increment in systolic blood pressure was better for some maneuvers (such as leg crossing and a combination) than others (such as neck flexion and abdominal contraction). Three patterns of responses to biofeedback were found. Simple maneuvers such as squatting did not improve with training; visual feedback was needed for maneuvers such as thigh contraction, and performance declined without biofeedback; the third pattern, seen in maneuvers such as leg crossing, showed continued improvement with training, even without biofeedback. A survey at 3 to 4 months after training revealed continued use of physical maneuvers (3.8 +/- 3.1 per day), increased standing time with each episode of presyncopal symptoms (8.3 +/- 5.8 minutes), and continued global symptomatic improvement. Total peripheral resistance, but not heart rate or stroke index, showed significant regression with blood pressure improvement. CONCLUSION: Physical countermaneuvers are efficacious in reducing orthostatic hypotension, can be augmented by use of biofeedback, and may significantly improve the functional outcome. The major mechanism of improvement is an increase in total peripheral resistance, presumably by reducing the vascular capacitance.

Adult↗

PubMed1980

A no-stimulus, no-response, event-related potential of the human cortex.

Brain macropotentials related to self-paced uni- or bimanual, unskilled or skilled movements were recorded from the motosensory cortical areas from 26 subjects. EMG of the active muscles, respiration, GSR, ECG and potentials generated by eye movements were also recorded. Subjects triggered the sweep of an oscilloscope with self-paced thumb movements in the following, unskilled, conditions: left-hand press (LHP), right-hand press (RHP), pressing with both hands simultaneously. They then performed a skilled performance task (SPT) during which the sweep was initiated by an LHP and was terminated within 40--60 msec by an RHP. Ten of the tested subjects participated in a variation of the skilled performance task during which no visual feedback was provided about their performance. All movements were preceded by sustained negativities known as N, component or Bereitschaftspotential (BP). All actions were followed by the motor cortex potential (MCP) with a latency of 32 msec from the EMG peak and a positivity with a latency of 200 msec from movement execution and initiation of the oscilloscope trace. Only the movements during SPT were followed by an additional positivity with a latency of 460 msec from the movement, having a centroparietal distribution and a mean amplitude at the vertex of 12.7 muV and S.D. of 5.0 muV. This skilled performance positivity (SPP) was independent of the amplitude of the previous BP and MCP and it was absent when the subject executed a variation of the SPT test during which visual feedback was not provided. Thus the SPP potential seems to be independent of stimulus or response characteristics and develops under experimental circumstances in which the subject expects and receives information about the outcome of coordinated self-placed movements.

Adult↗

PubMed1983

Acquisition of the voicing distinction by profoundly hearing-impaired children.

The ability of profoundly deaf schoolchildren to learn the voicing distinction was studied over a period of 6 months. The children were given daily speech therapy and half of them received, in addition, visual feedback from a microprocessor-based speech training aid - the Fricative and Timing Aid. Their performance was analysed in terms of the acquisition of voiced v. voiceless stop consonants and of their position in a word. Results yielded by perceptual tests showed a substantial increase in the intelligibility of stop consonants at the end of the training programme. Retention scores, i.e. intelligibility scores obtained by re-testing the children after a 2-month period of non-practice, showed that practically no articulatory skills were forgotten during this interval. Measurements of vowel duration in word-final stop consonants indicated a considerable decrease in vowel length with training, and although this remained higher than for hearing children it probably contributed to higher intelligibility scores. Comparisons between children trained with or without visual feedback showed a definite advantage for the former. No improvement in intelligibility was found when no systematic speech training was available. It was concluded that while the voicing distinction may not be acquired spontaneously, it is a skill within reach of profoundly deaf children when they are trained adequately.

Adolescent↗

PubMed1997

Influence of lift moment in determining MAWL.

An experiment was performed to determine whether maximum acceptable weight of lift (MAWL) estimates were consistent with previously reported values when the MAWL was determined without visual feedback during the weight adjustment period. Twelve healthy male students performed four lifting tasks similar to those often performed in previous psychophysical studies: floor to knuckle at 1 lift per min, floor to knuckle at 4.3 lifts per min, knuckle to shoulder at 1 lift per min, and knuckle to shoulder at 4.3 lifts per min. When compared with the previous studies with similar box dimensions, similar trends between the conditions were present, but a slight reduction in weight was usually chosen by the participant in this study. However, the results of this study agreed with previous psychophysical studies when the distance of the load from the spine (moment arm) was taken into consideration by either comparing the MAWLs with those of a large box or by comparing load moments. Hence this study shows that eliminating visual feedback during the adjustment periods did not significantly alter the MAWLs from previous studies. It also indicates that one must use caution when applying the MAWL in the workplace because the MAWL is very sensitive to moment arm.

Analysis of Variance↗

PubMed2003

Development of isometric force and force control in children.

Fifty-six children between 5 and 12 years of age and 15 adults performed a task (pressing on a lever with the index finger of the preferred hand), in which a force had to be maintained constant at five levels with on-line visual feedback. Since this is a simple isometric task, the hypothesis is that optimal performance (in terms of force variability control) closely matches the maturation of the corticospinal tract up to age 10. It was found that maximum voluntary contraction (MVC) matured over the full range of the examined age groups. In contrast, the coefficient of variation of force showed maturation mainly up to the age of 9-10, as hypothesised. Gender differences were found for MVC but not for the other force control parameters. Power spectral density analysis revealed developmental differences in the lower (1-6 and 7-12 Hz) and higher frequencies bands (13-18 and 19-24 Hz). In the lowest frequency range the amount of energy decreased with age, presumably because young children (5-8 years of age) rely more heavily on control from proprioceptive and visual feedback. It is argued that with increasing neural maturation the control processes become more dependent upon internal representation manifested by feed forward control that starts to substitute feedback-based control.

Adult↗

PubMed2001

Ocular oscillations on eccentric gaze.

Many normal individuals show ocular oscillations on eccentric gaze. This study was designed to investigate the effect of visual disengagement and visual feedback on the nature of these end point oscillations. Three test conditions were examined: target present, target absent and when the target position was determined by the subject's eye position via a variable feedback control system. Feedback gains (i.e. target velocity/eye velocity) ranged from 0, where the target position was decoupled from the subject's eye movements (i.e. the target is stationary on the screen), to +1.0 where the retinal image was stabilised (i.e. the target is driven by the subject's eye movements). Only subjects who exhibited sustained end-point oscillations with no latency were included in the study (n=6). Seven different oscillations including square-wave jerks were recorded in the abducting eye during eccentric gaze of a stationary target. The three most common oscillations were the jerk oscillations, with decelerating, linear or pendular slow phases. A number of additional previously unreported waveforms were also recorded. On removal of the target, the mean drift velocity of the slow phase was greatly reduced. The response to the introduction of a change in the visual feedback was specific to each subject, although in all cases, the end-point oscillations generally were of a lower velocity, and gaze was shifted by up to 8 deg in the direction of the slow phase within the first two seconds. The important role of slow eye movement control for maintaining gaze holding is discussed.

Adult↗

PubMed2002

Effects of balance training on hemiplegic stroke patients.

BACKGROUND: The purpose of this study was to evaluate the delayed effects of balance training program on hemiplegic stroke patients. METHODS: A total of 41 ambulatory hemiplegic stroke patients were recruited into this study and randomly assigned into two groups, the control group and trained group. Visual feedback balance training with the SMART Balance Master was used in the trained group. Bruunstrom staging of affected limb scores and Functional Independent Measure (FIM) scores of each patient were recorded. Quantitative balance function was evaluated using the SMART Balance Master. Data were collected before training and 6 months after completing the training program. RESULTS: Significant improvements in dynamic balance function measurements were found for patients in the trained group at 6 months after completing the training program. The ability of self-care and sphincter control also improved for patients in the trained group. On the other hand, no significant differences were found in static balance functions between the trained group and control group at 6 months of follow up. The locomotion and mobility scoring of FIM also revealed no differences between the groups. CONCLUSION: Dynamic balance function of patients in the visual feedback training group had significant improvements when compared with the control group. Activities of daily living (ADL) function in self-care also had significant improvements at 6 months of follow up in the trained group. The results showed that balance training was beneficial for patients after hemiplegic stroke.

Adult↗

PubMed1986

Evidence that a disordered servo-like mechanism contributes to tremor in movements during cerebellar dysfunction.

The characteristics of discontinuities and tremor that occurred in elbow flexions during cooling of the lateral cerebellar nuclei were investigated in five Cebus monkeys. Discontinuities in movements appeared as rhythmical oscillations (kinetic tremor) when movements were slow or when movements were made with a constant force that loaded the antagonist. These oscillations had similar properties to cerebellar terminal tremor following movements; e.g., their amplitude and frequency were decreased by addition of mass to the handle and they occurred in the absence of visual feedback. The abnormal initial decrease in velocity that initiated oscillations in flexion movements was associated with abnormally early or large antagonist (triceps) electromyogram (EMG) activity. This abnormal EMG activity did not follow the normal inverse relation between initial velocity and antagonist latency from onset of movement. The initial deflection from the expected trajectory was opposed by a second burst of EMG activity in the agonist (biceps). This second burst was not the continuation of a step of EMG activity because its amplitude was often larger than the amplitude of the first agonist burst. The second agonist burst had the properties of a servo-like response: it occurred when biceps shortening was slowed (but biceps was not stretched), its magnitude was proportional to the magnitude or the deflection in velocity, its latency was 50-80 ms from onset of the abnormal decrease in velocity, and it occurred in the absence of visual feedback. However, this servo-like response was disordered because it did not return the limb accurately to the expected trajectory. The servo-like mechanism was studied further by applying torque pulse perturbations during elbow flexions. When the cerebellar nuclei were cooled, agonist responses to the perturbation were proportional to the size of the velocity deflection, but they were prolonged and onset of antagonist activity was delayed. It is suggested that discontinuities and tremor in movements during cerebellar dysfunction result from the same mechanism: alternation between disordered stretch reflexes and disordered servo-assistance mechanisms, both partly involving transcortical pathways.

Animals↗

PubMed2004

Predictive smooth ocular pursuit during the transient disappearance of a visual target.

When a moving target disappears and there is a complete absence of visual feedback signals, eye velocity decays rapidly but often recovers to previous levels if there is an expectation the target will reappear further along its trajectory Given that eye velocity cannot be maintained under such circumstances, the anticipatory recovery may function to minimize the developing velocity error. When there is a change in target velocity during a transient, any recovery should ideally be scaled and hence predictive of the expected target velocity at reappearance. This study confirmed that subjects did not maintain eye velocity close to target velocity for the duration of the inter-stimulus interval (ISI). The majority of subjects exhibited an initial reduction in eye velocity followed by a scaled recovery prior to target reappearance. Eye velocity during the ISI was, therefore, predictive of the expected change in target velocity. These behavioral data were simulated using a model in which gain applied to the visuomotor drive is reduced after the loss of visual feedback and then modulated depending on subject's expectation regarding the target's future trajectory.

Adult↗

PubMed2006

Virtual reality cues for improvement of gait in patients with multiple sclerosis.

OBJECTIVE: To study the effects of visual cues, provided through a portable visual-feedback virtual reality (VR) apparatus, on the walking abilities of patients with multiple sclerosis (MS). METHODS: On-line (display-on) and residual short-term therapeutic effects on walking speed and stride length were measured in 16 randomly selected patients with gait disturbances predominantly due to cerebellar ataxia. RESULTS: Patients whose baseline walking speed (BWS) was below the median showed an average on-line improvement of 13.46% in their walking speed, while patients whose BWS was above the median improved their speed by 1.47%. The average short-term residual therapeutic improvement in walking speed was 24.49% in patients with BWS below the median, and 9.09% in patients with BWS above the median. Similar results were obtained for improvements in stride length. These results of improved functions in patients are particularly noteworthy when compared with the lack of change in healthy control subjects. CONCLUSIONS: Patients with multiple sclerosis showed improvement in walking abilities using virtual reality visual-feedback cues.

Adult↗

PubMed2004

[The study of photorefractive keratectomy induced defocus on emmetropization in infant monkeys].

OBJECTIVE: To investigate the effect of photorefractive keratectomy (PRK) induced defocus on emmetropization in infant rhesus monkeys and to determine the role of visual feedback on emmetropization. METHODS: PRK was performed in 8 healthy rhesus monkeys age ranging from 2 to 3 months. Either 3.00 D of relative hyperopic or myopic defocus was produced in one eye and the fellow eye as controls. The eyes were examined periodically with corneal topography, cycloplegic retinoscopy, A-scan ultrasonography, and slit-lamp biomicroscopy. RESULTS: All operated eyes demonstrated re-epithelialization within 3 days post-surgically and maintained transparent. Compensating axial length growth occurred throughout the observation period. The rate of vitreous chamber elongation varied with the post-PRK refractive status of the eye. The hyperopia-induced eyes exhibited a vitreous chamber elongation faster than the fellow eyes (t = 3.656, P = 0.0354), whereas myopia-induced eyes demonstrated a vitreous chamber elongation slower than the fellow eyes (t = 3.576, P = 0.0374). CONCLUSIONS: PRK-induced-defocus altered axial growth rates and emmetropization in infant monkeys predictably. These results indicate that primate emmetropization is regulated by visual feedback and correction of refractive error on children should be careful. PRK-induced-defocus is a promising method for myopic animal model and for the investigation of vision science.

Animals↗

PubMed2006

Online movement control in multiple sclerosis patients with tremor: effects of tendon vibration.

Patients with intention tremor due to multiple sclerosis (MS) exhibit an increased reliance on visual feedback in the sensorimotor control of slow goal-directed movements. In the present study, the use of proprioceptive information was investigated in MS patients with intention tremor compared to MS patients without tremor and healthy controls. Tendon vibration was applied to the wrist extensor muscles during a memory-guided slow wrist step-tracking task to investigate the use of muscle spindle afferent information in online movement control. A significant reduction of movement amplitude was induced by tendon vibration in all three groups, but the effect was found to be smaller in MS patients with tremor (28%) than in subjects without tremor (50%). Vibration also induced an increase of overall tremor amplitude in the MS tremor group; however, its effect on movement amplitude was not directly related to (changes in) tremor severity. The results suggest that the decreased online use of proprioceptive information in MS patients with tremor reflects an adaptation over time to cope with a tremor-related noisy background. Abnormalities in proprioceptive processing may explain why MS patients with tremor show an increased reliance on visual feedback for online motor control.

Adult↗

PubMed2003

The role of vision on hand preshaping during reach to grasp.

During reaching to grasp objects with different shapes hand posture is molded gradually to the object's contours. The present study examined the extent to which the temporal evolution of hand posture depends on continuous visual feedback. We asked subjects to reach and grasp objects with different shapes under five vision conditions (VCs). Subjects wore liquid crystal spectacles that occluded vision at four different latencies from onset of the reach. As a control, full-vision trials (VC5) were interspersed among the blocked vision trials. Object shapes and all VCs were presented to the subjects in random order. Hand posture was measured by 15 sensors embedded in a glove. Linear regression analysis, discriminant analysis, and information theory were used to assess the effect of removing vision on the temporal evolution of hand shape. We found that reach duration increased when vision was occluded early in the reach. This was caused primarily by a slower approach of the hand toward the object near the end of the reach. However, vision condition did not have a significant effect on the covariation patterns of joint rotations, indicating that the gradual evolution of hand posture occurs in a similar fashion regardless of vision. Discriminant analysis further supported this interpretation, as the extent to which hand posture resembled object shape and the rate at which hand posture discrimination occurred throughout the movement were similar across vision conditions. These results extend previous observations on memory-guided reaches by showing that continuous visual feedback of the hand and/or object is not necessary to allow the hand to gradually conform to object contours.

Adult↗

PubMed2000

Intermittency in the control of continuous force production.

The purpose of the current investigation was to examine the influence of intermittency in visual information processes on intermittency in the control continuous force production. Adult human participants were required to maintain force at, and minimize variability around, a force target over an extended duration (15 s), while the intermittency of on-line visual feedback presentation was varied across conditions. This was accomplished by varying the frequency of successive force-feedback deliveries presented on a video display. As a function of a 128-fold increase in feedback frequency (0.2 to 25.6 Hz), performance quality improved according to hyperbolic functions (e.g., force variability decayed), reaching asymptotic values near the 6.4-Hz feedback frequency level. Thus, the briefest interval over which visual information could be integrated and used to correct errors in motor output was approximately 150 ms. The observed reductions in force variability were correlated with parallel declines in spectral power at about 1 Hz in the frequency profile of force output. In contrast, power at higher frequencies in the force output spectrum were uncorrelated with increases in feedback frequency. Thus, there was a considerable lag between the generation of motor output corrections (1 Hz) and the processing of visual feedback information (6.4 Hz). To reconcile these differences in visual and motor processing times, we proposed a model where error information is accumulated by visual information processes at a maximum frequency of 6.4 per second, and the motor system generates a correction on the basis of the accumulated information at the end of each 1-s interval.

Adult↗

PubMed1992

Three-dimensional drawings in isometric conditions: planar segmentation of force trajectory.

Normal human subjects grasped an isometric handle with an unrestrained, pronated hand. They were asked to exert forces continuously to draw lemniscates (figure eights) in specified or self-chosen planes and in the presence or absence of a three-dimensional visual feedback cursor and a visual template. In every condition, the mean plane orientation in the force space differed appreciably between the two loops of the figure, as described previously by Soechting and Terzuolo (1987a) for free drawing arm movements. These findings suggest that the planar segmentation of the motor trajectory is not a consequence of joint motion but arises from central constraints related to the production of motor trajectory in space.

Feedback↗