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Results for “visual feedback”

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PubMed1996

A cane reduces loss of balance in patients with peripheral neuropathy: results from a challenging unipedal balance test.

OBJECTIVE: To test the hypothesis that use of a cane in the nondominant hand during challenging balance tasks would significantly decrease loss of balance in patients with peripheral neuropathy while transferring from bipedal to unipedal stance on an unsteady surface. DESIGN: Nonrandomized control study. SETTING: Tertiary-care institution. PARTICIPANTS: Eight consecutive patients with peripheral neuropathy (PN) and eight age- and gender-matched controls (C) with a mean (SD) age of 65 (8.2) years. METHODS: Subjects were asked to transfer their weight onto their right foot, despite a rapid +/- 2 degrees or +/- 4 degrees frontal plane tilt of the support surface at 70% of weight transfer, and balance unipedally for at least 3 seconds. The efficacy of their weight transfer was evaluated over 112 consecutive randomized and blocked trials by calculating loss of balance as failure rates (%FR) with and without visual feedback, and with and without use of a cane in the nondominant (left) hand. Results were analyzed using a 2 x 2 x 2 x 2 x 2 repeated-measures analysis of variance (rm-ANOVA) and post hoc t tests. RESULTS: The rm-ANOVA showed that the FR of the PN subjects (47.6% [18.1%]) was significantly higher than C (29.2% [15.2%], p = .036). Removing visual feedback, simulating the dark of night, increased the FR fourfold (p = .000). Use of a cane in the contralateral nondominant hand significantly reduced the FR (p = .000), particularly in the PN group (cane x disease interaction: p = .055). Post hoc t tests showed that with or without visual feedback, the cane reduced the FR of the PN group fourfold and enabled them to perform more reliably than matched controls not using a cane (p = .011). An inversion perturbation resulted in a higher FR than an eversion perturbation (p = .007). The PN group employed larger mean peak cane forces (21.9% BW) than C (13.6% BW) in restoring their balance (p = .000). CONCLUSION: Use of a cane by PN patients significantly reduced their risk of losing balance on unstable surfaces, especially under low-light conditions.

Aged↗

PubMed2004

Hemispheric asymmetries for kinematic and positional aspects of reaching.

Kinematic analyses of reaching have suggested that the left hemisphere is dominant for controlling the open loop component of the movement, which is more dependent on motor programmes; and the right hemisphere is dominant for controlling the closed loop component, which is more dependent on sensory feedback. This open and closed loop hypothesis of hemispheric asymmetry would also predict that advance planning should be dependent on the left hemisphere, and on-line response modification, which defines closed loop processes, should be dependent on the right hemisphere. Using kinematic analyses of reaching in patients with left or right hemisphere damage (LHD or RHD), we examined the ability: (i) to plan reaching movements in advance by examining changes in reaction time (RT) when response amplitude and visual feedback were cued prior to the response; and (ii) to modify the response during implementation when target location changed at the RT. Performance was compared between the stroke groups, using the ipsilesional arm, and age-matched control groups using their right (RNC) or left (LNC) arm. Aiming movements to a target that moved once or twice, with the second step occurring at the RT, were performed with or without visual feedback of hand position. There were no deficits in advance planning in either stroke group, as evidenced by comparable group changes in RT with changes in amplitude and visual feedback. Response modification deficits were seen for the LHD group in secondary velocity only. In addition, LHD produced slower initial peak velocity with prolongation of the deceleration phase and faster secondary peak velocities, and the RHD group produced deficits in final error only. These differences are more consistent with the dynamic dominance hypothesis, which links left hemisphere specialization to movement trajectory control and right hemisphere specialization to position control, rather than to global deficits in open and closed loop processing.

Aged↗

PubMedDate not supplied

Visuomotor adaptation in normal aging.

Visuomotor adaptation to a gradual or sudden screen cursor rotation was investigated in healthy young and elderly subjects. Both age groups were equally divided into two subgroups; one subgroup was exposed to 11.25 degrees step increments of visual feedback rotation, every 45 trials (up to a total of 90 degrees), whereas a second subgroup was subjected to 90 degrees rotation from the onset of exposure. Participants performed discrete, horizontal hand movements to virtual targets in four randomized directions. Targets appeared on a computer screen in front of them, and a board prevented vision of the hand at all times. Differential effects of aging on visuomotor adaptation were found, depending on the time course of the visual distortion. In both age groups, early exposure to the sudden visual feedback distortion resulted in typical spiral-like trajectories, which became straighter by late exposure. However, the final adaptation level was reduced in the aged group, although the aftereffects were similar. When subjects were exposed to the gradual distortion, no statistically significant differences in measures of adaptation with advancing age were found. In this case, both age groups appeared to adapt equally. However, after removal of the distortion, elderly subjects showed reduced aftereffects as compared with the young group. These findings suggest differential effects of aging on adaptation to gradual versus sudden visual feedback distortions, and may help to explain the conflicting results obtained in previous visuomotor adaptation studies.

Adaptation, Physiological↗

PubMed1993

Jaw-jerk reflex activity in relation to various clenching tasks in man.

In order to investigate whether the mandibular stretch (jaw-jerk) reflex is modulated in a task-dependent manner, jaw-jerk reflexes were elicited in eight subjects during clenching with unilateral and bilateral tooth support, respectively. The reflexes were examined in the electromyographic (EMG) activity recorded by means of surface electrodes and were elicited by means of small transient jaw displacements at a constant value of 80 microns. Low levels of background EMG were applied ranging from 1 to 30% maximal voluntary contraction (MVC) as controlled by means of visual feedback. Linear relationships were observed between reflex amplitude and level of background EMG. The slope in these relationships served as a measure of reflex gain. For the masseter as well as the anterior temporal muscles, the reflex gain, averaged over both sides, was larger during clenching with unilateral tooth support than with bilateral tooth support (P < 0.05). Furthermore, the gain was larger on the side without tooth support during unilateral clenching and larger on the side without visual feedback of elevator muscle activity during bilateral clenching. It can be concluded that the jaw-jerk reflex is modulated to subserve the stabilization of the mandible, with the reflex sensitivity being larger the more that alternative stabilizing factors such as mechanical tooth contact, visual feedback and feedback from periodontal pressure receptors around the teeth are lacking. The reflex modulation may be of functional importance in stabilizing the mandible during its movement in the chewing process, as the food is predominantly placed unilaterally between the antagonistic teeth during individual chewing cycles.

Adolescent↗

PubMed2006

A comparison of the reach-to-grasp movement between children and adults: a kinematic study.

In this study, the reach-to-grasp movement of 5-year-old children was compared to that of adults. Participants were required to reach out and grasp objects, with and without on-line visual feedback. Object size and distance were covaried in a within-subjects design and it was found that for both groups, grip formation and reach kinematics were affected by the manipulation of either variable. Although there are a large number of similarities, a few differences between the two groups emerge. For the reaching component, the children revealed a longer movement duration and deceleration time and a lower maximum height of wrist trajectory than in adults. For the grasp component, the children, in both the vision and no-vision condition, show a maximal finger aperture larger than the adults. Further, the children of this study were able to scale their grip aperture according to object size when visual feedback during the movement was lacking. These findings suggest that children adopt different strategies than adults when planning a reach-to-grasp movement on the basis of object size, distance, and the predictability of visual feedback. The results are discussed in terms of the neural mechanisms underlying hand action and how these mechanisms may not be fully developed by the age of 5.

Adult↗

PubMed1992

Kinematic analysis of upper limb trajectories in Parkinson's disease.

The purpose of this study was to analyze the kinematic properties of upper limb trajectories in Parkinson's disease (PD) patients and to investigate the role of visual feedback from the moving limb. Beyond the characteristic bradykinesia, PD patients differed from controls by generating hand trajectories with asymmetrical velocity profiles that lacked smoothness and were composed of a short initial accelerative phase, followed by a prolonged interval composed of alternating decelerative and accelerative phases. In both groups, the reaction times for movements directed away from the body were longer than for movements directed toward the body; this effect was accentuated in PD. In both groups, initial peak accelerations were significantly larger for distally as compared to proximally directed movements. In the absence of visual feedback from the limb a deterioration in the accuracy of reaching the target was observed in both control and PD patients only for distally directed movements. However, this deterioration and the effect of target location on final accuracy was substantially larger in PD. Taken together, our study suggests that in PD visual information is continuously relied upon for ongoing movement correction, therefore accentuating the bradykinesia. The deficit in final accuracy in the absence of visual feedback reflects the important role played by the basal ganglia in sensorimotor integration.

Acceleration↗

PubMed1998

Kinematic analysis of prehension movements in children.

The kinematics of the reach-to-grasp movement were analyzed in ten healthy children (age 6-7 years) under different experimental conditions: distance and size of the target objects, and visual feedback during the reach were varied in a within-subjects design. To assess age-related differences, the same experiments were performed in ten healthy adults. The experimental set-up was scaled according to body proportions to obtain equivalent conditions for both age groups. The temporal coupling between the transport and grasp components of prehension was very similar in children and adults. Peak transport velocity increased by the same factor in both age groups when the object distance was doubled. However, the decelerating approach phase was shorter in the children, who opened their hands relatively wider than adults. Unlike the adults, children failed to scale their grip aperture according to object size when visual feedback during the movement was lacking. The grip aperture increased with object distance in adults, but not in the children. The intrasubject variability of kinematic parameters was distinctly higher in the children. The results suggest that grip formation is not yet mature at an age of 6-7 years, depending more on visual feedback than in adult prehension.

Adult↗

PubMed1978

The effects of feedback and consequences on transitional cursive letter formation.

Twelve first-grade students were employed to analyze the effects of (1) Verbal and Visual Feedback, (2) Verbal and Visual Feedback plus immediate rewriting of trained letters with one or more incorrect letter strokes, and (3) Potential Reinforcement on cursive letter strokes. Students practised both a set of trained and a set of untrained letters during each session. Feedback and reinforcement was administered only for trained letter strokes. The percentage of correct trained letter strokes increased during all conditions. Performance on the untrained but practiced and trained letter strokes followed the same general trend in response pattern. No consistent pattern of generalization was demonstrated with untrained and unpracticed letter strokes.

Journal Article↗

PubMed1999

Altered control of submaximal bite force during bruxism in humans.

The control of bite force during varying submaximal loads was examined in patients suffering from bruxism compared to healthy humans not showing these symptoms. The subjects raised a bar (preload) with their incisor teeth and held it between their upper and lower incisors using the minimal bite force required to keep the bar in a horizontal position. Further loading was added during the preload phase. A sham load was also used. Depending on the session, the teeth were loaded by the experimenter or the subject and in one session the subject did not see the load (no visual feedback). The bite force was measured continuously using a calibrated force transducer. In all the subjects, the bite force increased with increasing load. Following the addition of the load, the level of the tonic bite force was reached rapidly with no marked overshoot. The patients with bruxism used significantly higher bite forces to hold the submaximal loads compared to the control subjects. In the control subjects, the holding forces for each submaximal load were identical in the men and the women and were independent of subject maximal bite force. Sham loading evoked no marked responses in biting force. Whether the subject or the experimenter added the load or whether the subject had visual feedback or not were not significant factors in determining the level of bite force. The results indicated that the patients with bruxism used excessively large biting forces for each given submaximal load. This study showed no evidence that the inappropriate control of bite force by patients with bruxism was due to an abnormality in the higher cortical circuits that regulates the function of trigeminal motoneurons in the brainstem. This was shown by a lack of abnormality in coordination of voluntary hand movement with biting force, a lack of abnormal anticipation response to a sham load and a lack of any effect of visual feedback. The results were in line with the hypothesis that afferent input from oral (periodontal or masticatory muscle) tissues does not provide an appropriate control of motor command in bruxism.

Adult↗

PubMed1997

Analysis of action tremor and impaired control of movement velocity in multiple sclerosis during visually guided wrist-tracking tasks.

We investigated the relationship between action tremor (AT) and impaired control of movement velocity (MV) in visually guided tracking tasks, in normal subjects and in patients with multiple sclerosis (MS) with or without motor deficits. The effects of withdrawing visual feedback of either the target or the cursor were then investigated. Visually cued simple reaction times (SRTs) were also measured. The effects of thalamotomy on motor performance in these tasks were evaluated in seven patients. In the MS patients with tremor, there was no correlation between AT and impairment in control of MV, but the latter was highly correlated with an increased delay in SRT. Withdrawal of visually guiding cues increased the error significantly in MV, but reduced AT by approximately 30% in magnitude. Frequency analysis indicated that the AT had two components: (a) non-visual-dependent, oscillatory movements, mainly at 4 Hz; and (2) visual-dependent, repetitive movements, with significant power at 1-2 Hz. Thalamotomy significantly reduced AT but hardly improved accuracy in MV. These results suggest that visual feedback of a spatial mismatch signal may provoke a visually dependent repetitive movement contributing to AT. Conduction delays along either the cortico-cerebello-cortical or the proprioceptive pathways and impaired working memory caused by MS may be responsible for the movement disorders in these patients.

Adult↗

PubMedDate not supplied

A neurodynamical model of visual attention: feedback enhancement of spatial resolution in a hierarchical system.

Human beings have the capacity to recognize objects in natural visual scenes with high efficiency despite the complexity of such scenes, which usually contain multiple objects. One possible mechanism for dealing with this problem is selective attention. Psychophysical evidence strongly suggests that selective attention can enhance the spatial resolution in the input region corresponding to the focus of attention. In this work we adopt a computational neuroscience perspective to analyze the attentional enhancement of spatial resolution in the area containing the objects of interest. We extend and apply the computational model of Deco and Schürmann (2000), which consists of several modules with feedforward and feedback interconnections describing the mutual links between different areas of the visual cortex. Each module analyses the visual input with different spatial resolution and can be thought of as a hierarchical predictor at a given level of resolution. Moreover, each hierarchical predictor has a submodule that consists of a group of neurons performing a biologically based 2D Gabor wavelet transformation at a given resolution level. The attention control decides in which local regions the spatial resolution should be enhanced in a serial fashion. In this sense, the scene is first analyzed at a coarse resolution level, and the focus of attention enhances iteratively the resolution at the location of an object until the object is identified. We propose and simulate new psychophysical experiments where the effect of the attentional enhancement of spatial resolution can be demonstrated by predicting different reaction time profiles in visual search experiments where the target and distractors are defined at different levels of resolution.

Attention↗

PubMed2006

Effect of tutorial input in addition to augmented feedback on manual dexterity training and its retention.

Virtual reality (VR) simulators can be used as tools in manual dexterity training. The visual feedback guides the subject towards proper performance but creates, at the same time, some dependency on this feedback. To overcome this drawback, the effect of adjunct tutorial input on motor learning behaviour was examined. Novice dental students were randomly assigned to one of two training groups or to a non-training control group, given the task of preparing a geometrical class 1 cavity in phantom teeth. The feedback (FB) group trained under augmented visual feedback conditions, provided by the VR system (DentSim). The feedback-plus (FB+) group received, in addition, standardised expert input to enrich the augmented feedback information. The control group, consisting of same year students, did not participate in any training programme. All preparations were evaluated by the VR scoring system. Performance analyses revealed an overall trend towards significant improvement with practice for the training groups. Performance of the FB+ group was most accurate across training. After 1 day and 3 weeks of no practice, both training groups outperformed the control group. After 4 months, however, only the FB+ condition was significantly more accurate than the control group. The same tendency was noted for the transfer tests. Consequently, cavity preparation experience on a VR system under the condition of frequently provided feedback supplemented with expert input was most beneficial to long time learning.

Computer Simulation↗

PubMedDate not supplied

Intelligent multifunction myoelectric control of hand prostheses.

Intuitive myoelectric prosthesis control is difficult to achieve due to the absence of proprioceptive feedback, which forces the user to monitor grip pressure by visual information. Existing myoelectric hand prostheses form a single degree of freedom pincer motion that inhibits the stable prehension of a range of objects. Multi-axis hands may address this lack of functionality, but as with multifunction devices in general, serve to increase the cognitive burden on the user. Intelligent hierarchical control of multiple degree-of-freedom hand prostheses has been used to reduce the need for visual feedback by automating the grasping process. This paper presents a hybrid controller that has been developed to enable different prehensile functions to be initiated directly from the user's myoelectric signal. A digital signal processor (DSP) regulates the grip pressure of a new six-degree-of-freedom hand prosthesis thereby ensuring secure prehension without continuous visual feedback.

Algorithms↗

PubMed2005

Information and force level interact in regulating force output during two and three digit grip configurations.

The experiment examined the force fluctuations during two and three digit grip configurations to investigate the relationship between task performance and inter-digit individuation as a function of force level and visual information intermittency rate over approximately 100-fold range (0.21-20 Hz). Subjects grasped an object with either the index finger (two digit grip) or the index and middle finger (three digit grip) opposing the thumb and produced isometric force to match a low and high total force level target. Force accuracy was lower at the large visual intermittency conditions and the higher force level. The force variability was lower in the three digit grip. Inter-digit individuation increased as a function of visual intermittency rate and was greater at the low force level. There was no improvement in performance or inter-digit individuation when visual feedback intermittency was greater than approximately 6 Hz (approximately 150 ms). Linear regression between the measures of task performance and inter-digit individuation yielded a significant negative relationship that was only present in the two digit grip when visual feedback rate was 1.67 Hz or lower and in the three digit grip when the feedback rate was 10 Hz or lower. The greater biomechanical degrees of freedom in the three digit grip configuration enable the subject to use, more effectively, visual information feedback at faster timescales in maximizing task performance by increasing digit independence. The shift from visual to nonvisual dominated motor control processes is dependent on the interaction of informational and biomechanical degrees of freedom.

Adult↗

PubMed1995

Impairments of reaching movements in patients without proprioception. I. Spatial errors.

1. This paper introduces a series of studies in which we analyze the impairments in a planar reaching task in human patients with severe proprioceptive deficits resulting from large-fiber sensory neuropathy. We studied three patients, all of whom showed absence of discriminative tactile sensation, position sense, and stretch reflexes in the upper extremities. Muscle strength was normal. We compared the reaching movements of the patients with those of normal control subjects. The purpose of this first paper was no characterize the spatial errors in these patients that result primarily from impairments in the planning and execution of movement rather than in feedback control. This was done by using a task in which visual feedback of errors during movement was prevented. 2. Subjects were instructed to move their hand from given starting positions of different targets on a horizontal digitizing tablet. Hand position and targets were displayed on a computer screen. Subjects could not see their hand, and the screen display of hand position was blanked at the signal to move. Thus visual feedback during movement could not be used to achieve accuracy. Movement paths were displayed as knowledge of results after each trial. 3. Compared with controls, the patients made large spatial errors in both movement direction and extent. Directional errors were evident from movement onset, suggesting that they resulted from improper planning. In addition, patients' hand paths showed large curves and secondary movements after initial stops. 4. The overall control strategy used by patients appeared the same as that used by controls. Hand trajectories were approximately bell shaped, and movement extent was controlled by scaling a trajectory waveform in amplitude and time. However, both control subjects and patients showed systematic errors in movement extent that depended on the direction of hand movement. In control subjects, these systematic dependencies of extent on direction were small, but in patients they produced large and prominent errors. Analysis of the hand trajectories revealed that errors were associated with differences in velocity and acceleration for movements in different directions. In an earlier study, we showed that in subjects with normal sensation that the dependence of acceleration and velocity on direction results from a failure to take the inertial properties of the limb into account in programming the initial trajectory. In control subjects, these differences in initial acceleration are partially compensated by direction-dependent variations in movement time.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed1994

Kinematic analyses of manual asymmetries in visual aiming movements.

The right hand advantage has been thought to arise from the greater efficiency of the right hand/left hemisphere system in processing visual feedback information. This hypothesis was examined using kinematic analyses of aiming performance, focusing particularly on time after peak velocity which has been shown to be sensitive to visual feedback processing demands. Eight right-handed subjects pointed at two targets with their left and right hands with or without vision available and either as accurately or as fast as possible. Pointing errors and movement time were found to be smaller with the right hand. Analyses of the temporal components of movement time revealed that the hands differed only in time after peak velocity (in deceleration), with the right hand spending significantly less time. This advantage for the right hand, however, was apparent whether or not vision was available and only when accuracy was emphasized in performance. These findings suggest that the right hand system may be more efficient at processing feedback information whether this be visual or nonvisual (e.g., proprioceptive).

Acceleration↗

PubMed1995

The interaction of visual and proprioceptive inputs in pointing to actual and remembered targets.

Errors in pointing to actual and remembered targets presented in three-dimensional (3D) space in a dark room were studied under various conditions of visual feedback. During their movements, subjects either had no vision of their arms or of the target, vision of the target but not of their arms, vision of a light-emitting diode (LED) on their moving index fingertip but not of the target, or vision of an LED on their moving index fingertip and of the target. Errors depended critically upon feedback condition. 3D errors were largest for movements to remembered targets without visual feedback, diminished with vision of the moving fingertip, and diminished further with vision of the target and vision of the finger and the target. Moreover, the different conditions differentially influenced the radial distance, azimuth, and elevation errors, indicating that subjects control motion along all three axes relatively independently. The pattern of errors suggest that the neural systems that mediate processing of actual versus remembered targets may have different capacities for integrating visual and proprioceptive information in order to program spatially directed arm movements.

Adult↗

PubMedDate not supplied

Effects of asymmetric vergence on compensatory eye movements during active head rotation.

The kinematics of the horizontal VOR for near fixation demand that VOR gain should change dependent on the target distance and the orientation of the head with respect to the target, or, equivalently, the amount of ocular vergence and the asymmetry of this vergence. Across two experiments, the gain of the VOR was measured in the right eye of humans who rotated their heads to the right or left while viewing a target placed either 22, 32.5 or 200 cm from the center of head rotation, in conditions with and without visual feedback. When the eye was in-line with the target, the measured VOR gain was up to 43% greater than when the eye was in an eccentric position. However, in the eccentric position, higher VOR gains were achieved with visual feedback of the target than without feedback, indicative of a visual component in the compensatory eye movement. Also, by changing the posture of the left eye but keeping the right eye constant, the VOR gain in the right eye was changed substantially during a subsequent head rotation. Hence, the positions of both eyes in their orbits determine the gain of the VOR in each eye.

Adaptation, Ocular↗