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Results for “visual feedback”

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At least 19 recordsLinked to original sources

PubMed1992

Training effects during repeated therapy sessions of balance training using visual feedback.

Visual biofeedback of postural sway is currently being investigated as a therapeutic technique to reduce postural instability in selected patient populations. Before the efficacy of this type of therapy can be determined in a clinical setting, the performance curves of a normal population doing the static and dynamic balance training exercises have to be delineated. Two groups of normal subjects were evaluated during a daily and weekly protocol of dynamic balance exercises using visual feedback of their center of gravity (COG) and theoretical limits of stability. Static stability in a central position was measured with eyes open, eyes closed, and with visual feedback of the COG in a pre-therapy to post-therapy assessment. No significant change was observed in any of these variables from the pre-therapy to the post-therapy evaluation; as well there was no difference between the scores of both groups. Dynamic variables were evaluated in both a pre-therapy to post-therapy assessment, and over the course of therapy. Each of these protocols required the subjects to track targets representing 75% of their limits of stability on a computer screen with their COG. The time taken and the accuracy to move the COG cursor from target to target, as well as the body sway upon reaching the target were evaluated. Transition time and sway area both decreased significantly (p less than 0.01) from the pre-therapy to the post-therapy assessment for both groups, with path error decreasing significantly for the daily therapy group only. No significant difference was demonstrated between groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1992

Effects of Pointing Rate and Availability of Visual Feedback on Visual and Proprioceptive Components of Prism Adaptation.

While looking through laterally displacing prisms, subjects pointed 60 times straight ahead of their nose at a rate of one complete movement every 2 or 3 s, with visual feedback available early in the pointing movement or delayed until the end of the movement. Sagittal pointing was paced such that movement speed covaried with pointing rate. Aftereffect measures (obtained after every 10 pointing trials) showed that when the limb became visible early in a pointing movement, proprioceptive adaptation was greater than visual, but when visual feedback was delayed until the end of the movement, the reverse was true. This effect occurred only with the 3-s pointing rate, however. With the 2-s pointing rate, adaptation was predominately proprioceptive in nature, regardless of feedback availability. Independent of the availability of visual feedback, visual adaptation developed more quickly with 3-s pointing, whereas proprioceptive adaptation developed more rapidly with 2-s pointing. These results are discussed in terms of a model of perceptual-motor organization in which the direction of coordinative (guidance) linkage between eye-head (visual) and hand-head (proprioceptive) systems (and consequently the locus of discordance registration and adaptive recalibration) is determined jointly by pointing rate and feedback availability. An additional effect of pointing rate is to determine the rate of discordant inputs. Maximal adaptive recalibration occurs when the input (pointing) rate matches the time constant of the adaptive encoder in the guided system.

Journal Article↗

PubMed1990

Difference between visual feedback and visual suppression upon the stabilization of body sway in normal subjects.

We developed a system to feedback the center of foot pressure by vision using a microcomputer. The subjects were instructed to adjust the center of foot pressure (displayed on the computer display at real time) to the point of intersection of the two stable (horizontal and vertical) lines on the computer display. The peak of the power spectra of body sway shifted significantly to the higher frequency range in the Y component (the lateral direction) in the visual feedback condition. Thus, we conclude that the visual feedback of body sway depends mainly on the error signals between the fovea and the image in the lateral direction to stabilize body sway.

Adult↗

PubMed1979

Study of eccentric fixation with secondary visual feedback.

Secondary visual feedback (2VFB) is a visual signal derived from continuous measurement of eye position and provides an extra artificial indication of the point of gaze. 2VFB may be eccentrically displaced and subjects are able to visually superimpose 2VFB onto a visual target signal and thus achieve and maintain eccentric fixation. Initial transient patterns of movement depend upon training but even naive subjects can achieve eccentric fixation within the first 40 s of such a task. Individual strategies and idiosyncratic patterns are exaggerations of normal control and fixational eye movements. The variance of maintained fixation increases with eccentricity and appears to be related to visual acuity as well as to precision of ocular motor control.

Biofeedback, Psychology↗

PubMed1986

Visual dominance in the cross-modal kinesthetic to kinesthetic plus visual feedback condition.

In previous studies subjects who have learned a positioning response with kinesthetic feedback tended to make greater errors when visual feedback was provided during later trials. These subjects have always performed with both kinesthetic and visual feedback available. This study determined whether subjects with only visual feedback would produce errors similar to those who received kinesthetic plus visual feedback. Blindfolded subjects learned to move a handle to a criterion location with knowledge of results following each trial. Subjects then were assigned to one of three experimental groups, with only kinesthetic feedback, with kinesthetic plus visual feedback, or with only visual feedback. Subjects had 9 trials without knowledge of results in these feedback conditions. When visual feedback was available, subjects tended to make longer response errors. This finding replicates previous studies. Also, the similarity of performances from the conditions with visual feedback indicated the dominance of visual information in the condition with kinesthetic plus visual feedback.

Feedback↗

PubMed1997

Effectiveness of visual feedback during isokinetic exercise.

Although previous investigators have observed that knowledge of performance via visual feedback tends to enhance performance during an isokinetic test, the time frame over which visual feedback remains advantageous is unclear. The purpose of this study was to compare knee extensor torques produced by visual feedback and no visual feedback groups on three occasions, completed over a 2-week period, and at 4 weeks after the third test. Healthy, sedentary subjects were each randomly assigned to either a visual feedback or a no visual feedback group (N = 10 males and 10 females per group). Visual feedback consisted of viewing a computer monitor which displayed the current and a target knee extension force. Torques produced by the visual feedback group were consistently greater (p < 0.05) and more reliable than those produced by the no visual feedback group. The effectiveness of visual feedback tended to decrease over the first three occasions, suggesting that visual feedback may not be as advantageous once a skill is well learned. Further research needs to examine the contribution of visual feedback to motor learning as well as retention and transfer of motor skills during more complex functional tasks.

Adult↗

PubMed1980

Monocular vergence movements produced by external visual feedback.

An external visual feedback procedure was used by three subjects with normal binocular vision to produce monocular lateral vergence (duction) movements. Feedback was provided by monitoring eye position with an alternating magnetic field system and by displaying the position of the monitored eye to the subject on an oscilloscope screen. Each subject was able to produce both unilateral abduction and adduction. For one subject, phorias were measured prior to several of the abduction feedback sessions, and an increase in exophoria and a decrease in the accommodative covergence/accommodation ratio was observed over the preexperimental measurement.

Accommodation, Ocular↗

PubMed1993

Role of visual feedback treatment for defective /s/ sounds in patients with cleft palate.

The role of visual feedback in the treatment of defective /s/ sounds in patients with cleft palate is described. Six patients with cleft palate who were similar in age, velopharyngeal function, and type of misarticulation were selected for this study. Treatment was provided using either visual feedback or no visual feedback. Visual feedback for tongue placement was provided by the Rion Electropalatograph (EPG). Visual feedback for frication was provided by a multi-function speech training aid (MFSTA). Improvement in /s/ sound production was assessed objectively using a method described previously (Michi et al., 1986). The results indicated that visual feedback for tongue placement and frication was especially useful in the treatment of defective /s/ sounds in patients with cleft palate who exhibited abnormal posterior tongue posturing during the production of dental or alveolar sounds.

Articulation Disorders↗

PubMed1998

Intermittency in preplanned elbow movements persists in the absence of visual feedback.

It has been observed for nearly 100 years that visually guided human movements appear to be composed of submovements, intermittently executed overlapping segments. This paper presents experiments to investigate the pervasiveness of movement intermittency and, in particular, whether it is exclusively due to visual feedback. With and without visual feedback, human subjects were asked to 1) move with constant velocity and 2) draw elliptical figures on a phase-plane display (showing velocity vs. position) that required cyclic movements at different frequencies. In both tasks, we found that removal of visual feedback did not significantly change movement intermittency. Subjects were unable to generate movements at constant speed. In addition, subjects moved less smoothly when drawing slower phase-plane ellipses. Furthermore, elliptical phase-plane figures were not always drawn at the frequency suggested by the center of the display. Instead, subjects moved more slowly than the tall (fast) ellipse displays suggested, and faster than the wide (slow) displays suggested. These results show that 1) movement intermittency is not exclusively due to visual feedback and 2) may in fact be a fundamental feature of movement behavior.

Adult↗

PubMed2000

Use of visual feedback in retraining balance following acute stroke.

BACKGROUND AND PURPOSE: Visual feedback related to weight distribution and center-of-pressure positioning has been shown to be effective in increasing stance symmetry following stroke, although it is not clear whether functional balance ability also improves. This study compared the relative effectiveness of visual feedback training of center-of-gravity (CoG) positioning with conventional physical therapy following acute stroke. SUBJECTS: Forty-six people who had strokes within 80 days before the study, resulting in unilateral hemiparesis, and who were in need of balance retraining participated. METHODS AND MATERIALS: Initially, subjects were randomly assigned to visual feedback or conventional physical therapy groups for balance retraining until 16 subjects per group were recruited. The next 14 subjects were assigned to a control group. All subjects received physical therapy and occupational therapy (regular therapy) 2 hours a day, and subjects in the 2 experimental groups received additional balance training 30 minutes a day until discharge. The visual feedback group received information about their CoG position as they shifted their weight during various activities. The conventional therapy group received verbal and tactile cues to encourage symmetrical stance and weight shifting. Static (postural sway) and activity-based measures of balance (Berg Balance Scale, gait speed, and the Timed "Up & Go" Test) were contrasted across the 3 groups at baseline, at discharge, and at 1 month following discharge using an analysis of variance for repeated measures. RESULTS: All groups demonstrated marked improvement over time for all measures of balance ability, with the greatest improvements occurring in the period from baseline to discharge. No between-group differences were detected in any of the outcome measures. CONCLUSION AND DISCUSSION: Visual feedback or conventional balance training in addition to regular therapy affords no added benefit when offered in the early stages of rehabilitation following stroke.

Acute Disease↗

PubMedDate not supplied

[The effect of visual feedback exercises on balance in normal subjects].

The effects of visual feedback exercises on balance was studied in normal individuals, to evaluate the efficacy of visual feedback of postural oscillation in improving stability. A DINAS-CAN dynamometric platform designed by the Valencian Institute of Biomechanics (IBv) was used. Before to commencing training sessions, we determined the following parameters in each individual: (a) static stability, via posturography; and (b) individual ability to displace and voluntarily maintain the center of gravity within the limits of stability. All static measures were poorer after training, but the differences were not significant (p > 0.01). In contrast, the exercises performed via visual feedback of postural control improved significantly (p < 0.01). Training by visual feedback facilitates integration of visual, somatosensory, and vestibular information. In normal individuals, stability improves under excentric conditions, but no improvement is seen in the central resting position.

Adult↗

PubMed1999

Effects of visual feedback on manual tracking and action tremor in Parkinson's disease.

Visual feedback is one of the key elements in on-line control of smooth manual tracking. To in- vestigate the effects basal ganglia dysfunction have on visual feedback control, we have tested six advanced Parkinson's disease (PD) patients in comparison with normal controls using visually guided wrist tracking tasks. Tracking performance was assessed under three visual conditions: (1) both guiding target and movement cursor were displayed continuously; (2) the target display was turned off for the second half of each trial; or (3) the cursor display, but not the target, was turned off for the second half of each trial. Thus, for the second half of each trial under conditions 2 and 3, no visual feedback of the relationship between the target and the cursor was available. Results showed that although PD patients had significantly larger tracking errors than controls, and errors significantly increased in both PD patients and controls after withdrawing either visual cue, increases in tracking errors in PD were not significantly different from those in controls. Nor were any significant changes found in the frequency (6-8 Hz) or magnitude of the PD patient's action tremor after withdrawing visual feedback. These results suggest that on-line movement control of wrist tracking movements in advanced PD is not especially reliant on visual feedback. In conjunction with our previous study of multiple sclerosis (MS) patients, the present results confirm that the basal ganglia is less involved in visual guidance of smooth manual tracking than the cerebellar circuits.

Aged↗

PubMed2003

Humans use continuous visual feedback from the hand to control fast reaching movements.

How visual feedback contributes to the on-line control of fast reaching movements is still a matter of considerable debate. Whether feedback is used continuously throughout movements or only in the "slow" end-phases of movements remains an open question. In order to resolve this question, we applied a perturbation technique to measure the influence of visual feedback from the hand at different times during reaching movements. Subjects reached to touch targets in a virtual 3D space, with visual feedback provided by a small virtual sphere that moved with a subject's fingertip. Small random perturbations were applied to the position of the virtual fingertip at two different points in the movement, either at 25% or 50% of the total movement extent. Despite the fact that subjects were unaware of the perturbations, their hand trajectories showed smooth and accurate corrections. Detectable responses were observed within an average of 160 ms after perturbations, and as early as 60% of the distance to the target. Response latencies were constant across different perturbation times and movement speed conditions, suggesting that a fixed sensori-motor delay is the limiting factor. The results provide direct evidence that the human brain uses visual feedback from the hand in a continuous fashion to guide fast reaching movements throughout their extent.

Analysis of Variance↗

PubMed2003

Online versus offline processing of visual feedback in the control of movement amplitude.

Researchers have suggested that visual feedback not only plays a role in the correction of errors during movement execution but that visual feedback from a completed movement is processed offline to improve programming on upcoming trials. In the present study, we examined the potential contribution of online and offline processing of visual feedback by analysing spatial variability at various kinematic landmarks in the limb trajectory (peak acceleration, peak velocity, peak negative acceleration and movement end). Participants performed a single degree of freedom video aiming task with and without vision of the cursor under four criterion movement times (225, 300, 375 and 450 ms). For movement times of 225 and 300 ms, the full vision condition was less variable than the no vision condition. However, the form of the variability profiles did not differ between visual conditions suggesting that the contribution of visual feedback was due to offline processes. In the 375 and 450 ms conditions, there was evidence for both online and offline control as the form of the variability profiles differed significantly between visual conditions.

Adolescent↗

PubMed2002

Adaptation of handwriting size under distorted visual feedback in patients with Parkinson's disease and elderly and young controls.

OBJECTIVE: The ability to use visual feedback to control handwriting size was compared in patients with Parkinson's disease (PD), elderly people, and young adults to better understand factors playing a part in parkinsonian micrographia. METHODS: The participants wrote sequences of eight cursive l loops with visual target sizes of 0.5 and 2 cm on a flat panel display digitiser which both recorded and displayed the pen movements. In the pre-exposure and postexposure conditions, the display digitiser showed the actual pen trace in real time and real size. In the distortion exposure conditions, the gain of the vertical dimension of the visual feedback was either reduced to 70% or enlarged to 140%. RESULTS: The young controls showed a gradual visuomotor adaptation that compensated for the visual feedback distortions during the exposure conditions. They also showed significant after effects during the postexposure conditions. The elderly controls marginally corrected for the size distortions and showed small after effects. The patients with PD, however, showed no trial by trial adaptations or after effects but instead, a progressive amplification of the distortion effect in each individual trial. CONCLUSION: The young controls used visual feedback to update their visuomotor map. The elderly controls seemed to make little use of visual feedback. The patients with Parkinson's disease rely on the visual feedback of previous or of ongoing strokes to programme subsequent strokes. This recursive feedback may play a part in the progressive reductions in handwriting size found in parkinsonian micrographia.

Aged↗

PubMed1996

Resistive eccentric exercise: effects of visual feedback on maximum moment of knee extensors and flexors.

One of the most important features of isokinetic dynamometry is the accurate assessment of muscular function. One of the main factors affecting the accuracy of isokinetic parameters during maximum activation efforts is visual feedback. The purpose of this study was the examination of the effects of visual feedback on maximum moment measurements of the knee extensors and flexors during isokinetic eccentric activations. Twenty-five males performed five maximal efforts at angular velocities of 30 degrees/sec and 150 degrees/sec with and without visual feedback on a Biodex dynamometer. Visual feedback was provided as real time display of the moment output. A three-factor analysis of variance test revealed significant differences between the moments recorded with visual feedback and the nonvisual feedback maximum moments of knee extensors and flexors at both speeds. The mean extension peak moments at 30 degrees/sec and 150 degrees/sec under visual feedback condition were approximately 7.2 and 6.4% higher than the nonvisual feedback moments, respectively. The increase for the knee flexor moment was 8.7 and 9% for slow and fast speeds, respectively. These findings suggest that visual feedback can improve maximum eccentric output and should be provided during assessment of maximum eccentric strength on an isokinetic dynamometer.

Adult↗

PubMed1992

The importance of visual feedback on the accuracy of jaw and finger positioning in man.

The anatomical position of the mandible means that direct visual feedback is not possible. To clarify the role of visual information, several jaw- and finger-positioning tasks were designed, both in a 'free-movement' and an 'isolated' (arm or head fixed) state, with or without a visual feedback display of the target position. The subjects had to position the mandible or the index finger of the preferred hand on to a movable metal bar and to maintain a defined position coinciding with the target level provided on an oscilloscope screen. The position signal was tape recorded and computer analysed off-line. Digital filtering differentiated between the drift and the oscillations around the target (root mean square). The results demonstrated a lack of precision in the free-movement, finger-positioning task after withdrawal of visual feedback. For jaw opening and closing muscles, position control was less impaired when a visual feedback display was abolished. It was suggested that the efficiency of jaw positioning is not primarily determined by visual feedback.

Adult↗

PubMed1998

PET study of pointing with visual feedback of moving hands.

This study was conducted to determine where in the human brain visual feedback of hand movements is processed to allow accurate pointing. Regional cerebral blood flow (rCBF) was measured with positron emission tomography (PET) and H2 15O in nine normal volunteers while performing one control and two reaching tasks. In all tasks, visual stimuli were presented on a head mounted display (HMD). A target board was placed in front of the subjects bearing six red light-emitting diodes (LEDs) aligned on a circle with a green LED at its center. The center green LED and one of the six red LEDs, randomly selected, were repeatedly switched on and off, alternatively. In the control task, subjects were instructed to gaze at the lit LED. In the two reaching tasks, the reaching with visual feedback (RwithF) task and the reaching without visual feedback (RwithoutF) task, they had to point to the lit red LED with their right index fingers. In the RwithF task, their right hands were visible on the HMD before touching the target, whereas in the RwithoutF task, they were not visible. For each subject, subtraction images of each reaching task minus the control and the RwithF task minus the RwithoutF task were calculated after transformation of PET images into the standard brain shape with an adjustable computerized brain atlas. These subtraction rCBF images were then averaged among the subjects, and significant changes of rCBF were identified. Significant increases in rCBF not only in the RwithF task minus control image but also in the RwithF task minus the RwithoutF task image were observed in the supramarginal cortex, the premotor cortex and the posterior cingulate cortex of the left hemisphere, the caudate nucleus and the thalamus of the right hemisphere, and the right cerebellum and vermis. These results indicate that the supramarginal cortex, the premotor cortex, and the posterior cingulate cortex of the left hemisphere and the cerebellum are involved in integrating visual feedback of hand movements and execution of accurate pointing.

Adult↗