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Results for “visual feedback”

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At least 19 recordsLinked to original sources

PubMed2004

The influence of force feedback and visual feedback in grasping tissue laparoscopically.

BACKGROUND: Due to the limited force feedback provided by laparoscopic instruments, surgeons may have difficulty in applying the appropriate force on the tissue. The aim of this study was to determine the influence of force feedback and visual feedback on the exerted pinch force. METHODS: A grasper with a force sensor in the jaws was developed. Subjects with and without laparoscopic experience grasped and pulled pig bowel with a force of 5 N. The applied pinch force was measured during tasks of 1-s and 1-min duration. Visual feedback was provided in half the measurements. Force feedback was adjusted by changing the mechanical efficiency of the forceps from 30% to 90%. RESULTS: The mean pinch force applied was 6.8 N (+/-0.5), whereas the force to prevent slippage was 3.0 N (+/-0.4). Improving the mechanical efficiency had no effect on the pinch force for the 1-s measurements. The amount of excessive pinch force when holding tissue for 1 min was lower at 30% mechanical efficiency compared with 90% (105% vs 131%, p = 0.04). The tissue slipped more often when the subject had no visual feedback (2% vs 8%, p = 0.02). CONCLUSION: Force feedback and visual feedback play a more limited role than expected in the task of grasping tissue with laparoscopic forceps.

Animals↗

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↗

PubMed1994

Effects of movement duration and visual feedback on visual and proprioceptive components of prism adaptation.

While looking through laterally displacing prisms, subjects pointed sagittally 80 times at an objectively straight-ahead target, completing a reciprocal out-and-back pointing movement ever 1, 3, or 6 s. Visual feedback was available early in the pointing movement or only late at the end of the movement. Aftereffect measures of adaptive shift (obtained after every 10 pointing trials) showed adaptive change only in limb position sense (i.e., proprioceptive adaptation) when movement duration was 1 s, regardless of visual feedback condition; but as movement duration increased, adaptive change in the eye position sense (i.e., visual adaptation) increased while proprioceptive adaptation decreased, especially for the late visual feedback condition. Regardless of visual feedback condition, proprioceptive adaptation showed the maximal rate of growth with the 1-s movement duration, whereas visual adaptation showed maximal growth with the 6-s movement duration. These results provide additional support for a model of adaptive spatial mapping in which the direction of strategically flexible coordination (guidance) between eye and limb (and consequently the locus of adaptive spatial mapping) is jointly determined by movement duration and timing of visual feedback. An additional effect of movement duration is to determine the rate of discordant inputs. Maximal growth of adaptation occurs when the input rate matches the response time of the spatial mapping function.

Journal Article↗

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↗

PubMed2005

The use of visual feedback is independent of visual awareness: evidence from visual extinction.

Milner and Goodale (The visual brain in action, Oxford Press, 1995) made a distinction between vision for perception and vision for action. In contrast to perception, many action tasks have strict temporal constraints, which can only be met if the visual information is relayed directly to the motor system without first passing through a conscious decision making process. Milner and Goodale therefore predict that visual stimuli do not have to reach visual awareness in order to guide rapid motor responses. Online visual feedback provides a good example of visual information that is used under tight temporal constraints to guide rapid motor responses. Online visual feedback provides information about the position of the moving limb. This information can be used to improve the accuracy of our movements. If vision for action operates independently of visual awareness, visual feedback should be beneficial even if the subject is unaware of this information. We tested this prediction in a patient (V.E.) with left-sided visual extinction, a condition in which a visual stimulus typically fails to reach awareness if a second stimulus is presented simultaneously at a more rightward location. V.E. was asked to point towards a central target with his left hand. In some trials a light-emitting diode (LED) provided brief visual feedback from the moving hand. However, in the majority of trials, V.E. was unaware of this LED, due to his extinction. His performance was nevertheless significantly better when visual feedback was present, regardless of whether or not the information was available for verbal report. We conclude that visual awareness is not essential for the effective use of online visual feedback.

Aged↗

PubMed2006

Discrete bandwidth visual feedback increases structure of output as compared to continuous visual feedback in isometric force control tasks.

BACKGROUND: Performance variability measures provide a partial picture of force control ability. Nonlinear analyses can reveal important information related to the randomness and complexity of the data, providing a more complete picture of the physiological process. METHODS: We investigated the effects of visual feedback on the structure and performance of the force output from isometric force control tasks. Twelve young volunteers completed isometric force control tasks using two types of visual feedback: discrete bandwidth (+/-4% maximal voluntary contraction) and continuous line matching. We determined force signal variability (standard deviation), self-similarity (fractal dimension), and complexity (approximate entropy). Analyses of variance (feedback x muscle group x force level) were conducted and P values less than 0.05 were considered significant. FINDINGS: The force signal in discrete bandwidth feedback, compared to continuous line matching, had significantly a higher standard deviation (P=.000): 2.18 Nm (SD 1.98) vs. 0.99 Nm (SD 0.91); lower fractal dimension (P=.000): 1.07 (SD 0.04) vs. 1.16 (SD 0.04); and lower approximate entropy (P=.000): 0.12 (SD 0.07) vs. 0.26 (SD 0.09). INTERPRETATION: The greater self-similarity (lower fractal dimension) and greater regularity (lower approximate entropy) of the discrete bandwidth, compared to the continuous line matching, may indicate a process that required more kinesthetic (intrinsic) feedback to modulate force. Clinicians may choose to employ visual feedback paradigms that target the use of intrinsic feedback during rehabilitation. Discrete bandwidth feedback may be useful for delineating impairments in motor skill and measuring outcomes of intervention programs.

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↗

PubMed2005

Perceptual limits for a robotic rehabilitation environment using visual feedback distortion.

Imperceptible visual distortion, in the form of a disguised progression of performance goals, may be a helpful addition to rehabilitation after stroke and other brain injuries. This paper describes work that has been done to lay the groundwork for testing this hypothesis. We have constructed and validated an experimental environment that provides controllable visual distortion and allows precise force and position measurements. To estimate the amount of visual distortion that should be imperceptible, we measured the limits for force and distance/position perception in our rehabilitation environment for young and elderly unimpaired subjects and for a single traumatic brain injury (TBI) patient. We found the Just Noticeable Difference (JND) for produced force to be 19.7% (0.296 N) and the JND for movement distance/finger position to be 13.0% (3.99 mm) for young subjects (ages 18-35). For elderly subjects (ages 61-80), the JND for force was measured to be 31.0% (0.619 N) and the JND for distance/po'sition was 16.1% (5.01 mm). JNDs of 46.0% (0.920 N) and 45.0% (14.8 mm) were found for the motor-impaired individual. In addition, a subject's rating of effort was found to be profoundly influenced by visual feedback concerning the force magnitude. Even when this feedback was distorted, it accounted for 99% of the variance of the effort rating. These results indicate that substantial visual distortions should be imperceptible to the subject, and that visual feedback can be used to influence the subject's perceived experience in our robotic environment. This means that we should be able to use imperceptible visual distortion to alter a patient's perception of therapeutic exercise in a robotic environment.

Adolescent↗

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↗

PubMed2004

Decrease in prefrontal hemoglobin oxygenation during reaching tasks with delayed visual feedback: a near-infrared spectroscopy study.

Visual feedback of hand movement is crucial to accurate reaching. Although previous studies have extensively examined spatial alteration of visual feedback (e.g., prism adaptation), temporal delay of visual feedback has been less explored. In the present study, we investigated the effect of delayed visual feedback of the moving hand in a reaching task. The prefrontal cortical activity was measured by near-infrared spectroscopy (NIRS). Twelve subjects performed reaching tasks under two conditions where visual feedback of their own hand was delayed by 200 ms (delay condition) or 0 ms (normal condition). Introducing the visual feedback delay significantly disrupted the reaching performance, although the subjects gradually adapted to the delay during the experiment. There was a clear tendency to overreach the target in the delay condition, even after the reaching movement had been practiced sufficiently in the normal condition. We observed marked oxy- and total-Hb decreases in the dorsal prefrontal area in the delay conditions. The decrease began shortly after task onset and diminished during the rest period, indicating that the decrease was task-induced. Furthermore, the oxy- and total-Hb decreases were significantly correlated with task performance--the degree of decrease was larger as the subject made more errors. We suggest that the decreases in oxy- and total-Hb at the dorsal prefrontal area are related with the visuomotor recalibration process.

Adult↗

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↗

PubMed2003

The use of visual feedback and on-line target information in catching and grasping.

Although visual feedback (i.e. seeing our hand while we move it) improves the accuracy and efficiency of grasping movements, these positive effects of visual feedback are not consistently found for catching. It was the aim of our study to compare the efficiency of the use of visual feedback in grasping and catching and to explore possible reasons why visual feedback effects have been found less consistently in catching than in grasping. The first reason might be technical. Less sensitive measurement methods have been used in catching; this might explain why some catching studies did not find visual feedback effects. This problem was avoided in our study by using the same methods for both the catching and the grasping task. The effects of visual feedback were examined under standard conditions and under conditions where subjects wore prismatic glasses. Nevertheless, visual feedback effects were obtained for grasping but not for catching movements. This confirms that the difference in the use of visual feedback is real and not due to technical differences between grasping and catching studies. The second reason relates to the different temporal demands of grasping and catching. During a catching task, subjects have less time to respond, and therefore might not have sufficient time to use visual feedback. We tested this explanation with a task that required subjects to reach for a stationary object (i.e. grasping) as quickly as they had for the moving object in the catching task. However, even in this time-constrained grasping task, significant visual feedback effects were found, suggesting that time constraints do not explain the lack of visual feedback effects in catching. In our last explanation, we suggest that possibly the mode of motor control is different for catching and grasping, more particularly while grasping allows for on-line corrections, such corrections might not be possible for catching movements. We tested this explanation with a catching task that contained perturbation trials. During those perturbation trials, the target trajectory was shifted, after the subject had already started to move. We found that subjects responded to the target shifts with an appropriate shift of their catching response. This shows that on-line corrections are possible in the case of catching movements. We conclude that neither differences in the temporal demands nor in the capacity to make on-line modifications explain why visual feedback is used less effectively in the catching than in the grasping task.

Adult↗

PubMed2006

Separating brain regions involved in internally guided and visual feedback control of moving effectors: an event-related fMRI study.

Online visual information of moving effectors plays important roles in visually guided movements. The present study used event-related functional resonance imaging to temporally separate neural activity associated with internally guided and visual feedback control of moving effectors. Using a cursor controlled by a computer mouse, participants traced curved lines on a screen. During this movement, vision of the moving cursor was occluded after tracing had begun and then was restored after variable intervals. The results showed that when visual feedback was unavailable, bilateral activation was significantly greater in the basal ganglia, thalamus, premotor cortex and mesial motor areas, peaking at the presupplementary motor area (pre-SMA). In contrast, when visual feedback was available, significantly greater activation was observed bilaterally in the posterior parietal cortex (PPC) and cerebellum and in the middle and inferior frontal gyri and occipito-temporal cortex in the right hemisphere. Pre-SMA activity was significantly negatively correlated with tracing error when visual feedback was unavailable. In contrast, right PPC activation showed a significant positive correlation with tracing error after visual feedback became available. These findings suggest that the pre-SMA is involved in internally guided movements in the absence of visual feedback, and that the PPC is related to visual feedback control by evaluating online visuomotor error. The current study clarifies the different functional roles of fronto-parietal and cerebellum circuits subserving visually guided movements regarding visual feedback control of effectors.

Adult↗

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↗