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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↗

PubMed2003

Effects of object shape and visual feedback on hand configuration during grasping.

Normal subjects gradually preshape their hands during a grasping movement in order to conform the hand to the shape of a target object. The evolution of hand preshaping may depend on visual feedback about arm and hand position as well as on target shape and location at specific times during the movement. The present study manipulated object shape in order to produce differentiable patterns of finger placement along two orthogonal "dimensions" (flexion/extension and abduction/adduction), and manipulated the amount of available visual information during a grasp. Normal subjects were asked to reach to and grasp a set of objects presented in a randomized fashion at a fixed spatial location in three visual feedback conditions: Full Vision (both hand and target visible), Object Vision (only the object was visible but not the hand) and No Vision (vision of neither the hand nor the object during the movement). Flexion/extension angles of the metacarpophalangeal and proximal interphalangeal joints of the index, ring, middle and pinkie fingers as well as the abduction/adduction angles between the index-middle and middle-ring fingers were recorded. Kinematic analysis revealed that as visual feedback was reduced, movement duration increased and time to peak aperture of the hand decreased, in accord with previously reported studies. Analysis of the patterns of joint flexion/extension and abduction/adduction per object shape revealed that preshaping based on the abduction/adduction dimension occurred early during the reach for all visual feedback conditions (approximately 45% of normalized movement time). This early preshaping across visual feedback conditions suggests the existence of mechanisms involved in the selection of basic hand configurations. Furthermore, while configuration changes in the flexion/extension dimension resulting in well-defined hand configurations occurred earlier during the movement in the Object Vision and No Vision conditions (45%), those in the Full Vision condition were observed only after 75% of the movement, as the moving hand entered the central region of the visual field. The data indicate that there are at least two control mechanisms at work during hand preshaping, an early predictive phase during which grip selection is attained regardless of availability of visual feedback and a late responsive phase during which subjects may use visual feedback to optimize their grasp.

Adult↗

PubMed1990

Effects on prism adaptation of duration and timing of visual feedback during pointing.

In two experiments, we investigated the effects of duration of visual feedback of the pointing limb and the time (early to late) in the movement when the limb first becomes visible (timing of visual feedback). Timing, rather than duration of visual feedback, proved to have the greater effect on the relative magnitude of visual and proprioceptive adaptation. Visual adaptation increased smoothly with feedback delay, but corresponding decreases in proprioceptive adaptation underwent an additional sharp change when feedback was delayed until about three-fourths of the way to the terminal limb position. These results are consistent with the idea that visual and proprioceptive adaptation are mediated by exclusive processes. Change in the limb position sense (i.e., proprioceptive adaptation) may be produced by visual guidance of the pointing limb, and view of the limb early in the pointing movement seems to be critical for such visual guidance. The limb may be ballistically released as it nears the terminal position, and, thereafter, any opportunity for visual guidance (i.e., view of the limb) is not effective. On the other hand, change in the eye position sense (i.e., visual adaptation) may be mediated by proprioceptive guidance of the eye; the eyes may track the imaged position of the nonvisible limb. Such proprioceptive guidance seems to be solely a function of the distance moved before the limb becomes visible.

Journal Article↗

PubMed2003

Visual feedback induces opposite effects on elementary centre of gravity and centre of pressure minus centre of gravity motions in undisturbed upright stance.

OBJECTIVE: To evaluate the instantaneous effects of visual feedback on undisturbed stance control mechanisms. DESIGN: The controlling variable, the centre of pressure trajectories, recorded using a force platform, were decomposed into two elementary motions: (1) the horizontal displacements of the centre of gravity and (2) the vertical projection of the difference between centre of pressure and the centre of gravity. These motions were processed through frequential analysis and modelled as fractional Brownian motion. BACKGROUND: Even though visual feedback protocols are advantageously used for rehabilitation purposes, their immediate effects from biomechanical and motor control points of view need to be assessed. METHODS: Twelve healthy adult subjects were tested through eyes open and visual feedback conditions. RESULTS: A significant amplitude increase in the difference between the centre of pressure and the centre of gravity motions and a decrease in the centre of gravity motions are observed during visual feedback. The fractional Brownian motion modelling analysis reveals an enhanced control of these elementary motions. The point at which the corrective process is initiated is increased with visual feedback whereas the time delay remains the same. CONCLUSIONS: The decrease of the centre of pressure displacements classically observed through visual feedback protocol initially results in a reduction of the centre of gravity motions and an augmentation of the difference between centre of pressure and centre of gravity motions, hence suggesting increased muscular activity. RELEVANCE: Precise knowledge of the effects generated by such feedback protocol should allow to optimise it as a rehabilitation tool.

Adult↗

PubMed1998

Persistence in visual feedback control by the elderly.

Young and elderly subjects performed aiming movements to a visual target with a manipulandum to determine whether the elderly reduce their reliance on visual feedback after extended practice. Reliance on visual feedback was assessed by performance on trials in which the cursor displaying arm movement was unpredictably extinguished. Movements were divided into two subcomponents: a primary, ballistic submovement and a secondary, corrective submovement. For both age groups, removal of visual feedback prior to practice resulted in a decrease in the distance covered in the primary submovement, an increase in the distance of the secondary submovement, and a decrease in endpoint accuracy. After extensive practice with the cursor present, the proportion of distance traveled with the primary submovement was again assessed under trial conditions in which the cursor randomly disappeared. Following practice, the young demonstrated that they were capable of extending the primary submovement distance closer to the target. In addition, primary submovement distance was unaffected by the removal of vision following practice. After practice the elderly did not show evidence of lengthening the primary submovement, and submovement distance and endpoint accuracy continued to be altered by the removal of vision. This suggests that, unlike the young, the elderly do not benefit from practice so that they can place a greater proportion of the movement under program control. Thus, on a relative basis, a greater proportion of their overall movement requires corrective adjustments.

Adult↗

PubMed1986

Visual feedback during speech production.

The question of whether visual information can affect ongoing speech production arises from numerous studies demonstrating an interaction between auditory and visual information during speech perception. In a preliminary study, the effect of delayed visual feedback on speech production was examined. Two of the 13 subjects demonstrated speech errors that were directly related to the delayed visual signal. However, in the main experiment, providing immediate visual feedback of the articulators did not diminish the effects of delayed auditory feedback for 11 speakers.

Feedback↗

PubMed2005

Kinematic and EMG characteristics of simple shoulder movements with proprioception and visual feedback.

The objective of this study was to determine if simple, shoulder movements use the dual control hypothesis strategy, previously demonstrated with elbow movements, and to see if this strategy also applies in the absence of visual feedback. Twenty subjects were seated with their right arm abducted to 90 degrees and externally rotated in the scapular plane. Subjects internally rotated to a target position using a custom shoulder wheel at three different speeds with and without visual feedback. Kinematics were collected with a motion analysis system and electromyographic (EMG) recordings of the pectoralis major (PECT), infraspinatus (INFRA), anterior and posterior (ADELT, PDELT) deltoid muscles were used to evaluate muscle activity patterns during movements. Kinematics changed as movement speed increased with less accuracy (p<0.01). Greater EMG activity was observed in the PECT, PDELT, and INFRA with shorter durations for the ADELT, PDELT and INFRA. Movements with only kinesthetic feedback were less accurate (p<0.01) and performed faster (p<0.01) than movements with visual feedback. EMG activity suggests no major difference in CNS control strategies in movements with and without visual feedback. Greater resolution with visual feedback enables the implementation of a dual control strategy, allowing greater movement velocity while maintaining accuracy.

Adult↗

PubMed1997

Distorted visual feedback effects on drawing in Parkinson's disease.

We investigated the effects of distorted visual feedback on the drawing performance of a group with Parkinson's disease (PD) and a control group. Twenty older healthy adults and 20 PD patients copied figures onto a digitizer tablet with a pen under normal and distorted visual feedback conditions. PD patients were less able than controls to adjust the size of their drawing to compensate for distortions in visual feedback. The effect was particularly pronounced when patients were required to draw smaller than normal. Nevertheless, with practice. PD patients showed a similar degree of improvement in size as controls, although they did not match the control group's level of performance. Overall, these findings support the notion that PD may have specific difficulty adjusting to a change in gain (or discrepancy) between visual and kinesthetic feedback when they must alter the size of their drawing. These findings point to the putative role of the basal ganglia in adjusting for the intermodal discrepancy between sensory feedback, and re-scaling the size of movements.

Aged↗

PubMed2007

Electrophysiological and hemodynamic evidence for late maturation of hand power grip and force control under visual feedback.

Several human imaging studies have described the neural network involved in power grip under visual control and the subset of cortical areas within this network that are sensitive to force modulation. As there is behavioral evidence for late maturation in even simple hand motor tasks involving visual feedback, we aimed at identifying the neural correlates of these developmental changes. Subjects from three developmental age groups (9-11, 15-17, and adults) performed the same power grip task in both a functional magnetic resonance imaging and an event-related potential (ERP) session. Trials started with a visual target indicating whether to squeeze at 20%, 40%, or 75% of their maximum and online visual feedback on the actual amount of force was provided. Longer reaction times and more shallow slopes of the force curve characterized the behavior of the younger age groups, especially the children. Both neurophysiological methods detected both general as well as force modulation-specific maturational changes. General development was characterized by decreasing ERP amplitudes and increasing deactivation of an extended network, closely resembling the so-called "default" network. The most pronounced developmental changes specific for force control were observed in an ERP component and brain regions involved in feedback processing. In contrast to adult subjects, we found evidence for a stronger dependency on visual feedback information in the younger age groups. Our results also suggest that the ability to deactivate task-irrelevant networks might be a late developmental achievement.

Adolescent↗

PubMed1994

Influence of visual feedback on human isometric bite-force tremor.

In contrast to recent reports, during an isometric short forceful bite, visual feedback had a significant influence on the force tremor spectrum. The value of a 'half-value frequency', being the frequency f1/2 at which, with increasing frequency, the amplitude of the spectrum for the first time drops to half its initial value, was used as an indicator for the spectral behavior. Under visual feedback, the amplitude contribution to the force spectrum in the 3-5 Hz frequency range was much larger than after deprivation of visual feedback. Elevations in the frequency range between 3 and 5 Hz in the force spectrum are interpreted as an expression of a visual feedback loop with a tau between 100 and 200 ms. This is supported by the visual/oral reaction times recorded, which were between 110 and 190 ms.

Adult↗

PubMed1984

Dependence of cerebellar tremor on proprioceptive but not visual feedback.

We studied the influence of proprioceptive and visual feedback on cerebellar tremor which occurred after arm perturbations and after voluntary elbow flexions. Cerebellar tremor was produced in monkeys by reversibly cooling through two probes implanted lateral and medial to the dentate nucleus. Cerebellar tremor was synchronized in different trials to torque pulse onset and to the end, but not the start, of voluntary movements. Addition of loads to the handle held by the monkey (increases in spring stiffness, viscosity, constant torque, and inertial load) changed the amplitude and frequency of tremor that follows arm perturbations or voluntary movements in the same way. In both situations EMG activity in each cycle of tremor followed stretch of its own muscle and attained a peak near peak velocity irrespective of the mechanical load. Removal of visual feedback did not alter the characteristics of the tremor or the associated EMG activity. We concluded that cerebellar intention tremor, which occurs when attempting to hold the arm in an intended position, is driven by stretch-evoked peripheral feedback and not by voluntary corrections based on vision.

Animals↗

PubMed1986

Visual feedback and lip-positioning skills of children with and without impaired hearing.

Interplay between visual feedback and lip-positioning skill was studied in 10 5- to 14-year-old children with normal hearing and 10 with severe to profound hearing impairment. With visual feedback, the subjects in both groups had similar response times and accuracy in matching six visually specified lip separation "targets." Special skill in processing visual information by the hearing-impaired subjects was suggested by higher velocities of lip movement toward the targets and shorter latencies in reaching the goal positions. In the responses of the hearing children, lip-closing movements were executed more accurately than opening movements both with and without visual feedback. In general, the findings showed that, given visually displayed lip-position targets and feedback from positioning actions, children can achieve the targets with high accuracy regardless of hearing status or prior speaking experience.

Adolescent↗

PubMed1996

Task-dependent changes in visual feedback control: a frequency analysis of human manual tracking.

Prominent components in the frequency spectrum of human manual tracking responses are thought to reflect the visual feedback control loop and have been used in estimations of the visual feedback loop delay. The frequency structure of human tracking was therefore examined here in two tasks: visually guided tracking of slow and fast pseudorandom targets. Visually related frequency components were identified by testing, in each condition, the effect of adding additional feedback delays on the frequency spectrum. The major frequency components of the responses consisted of a fundamental component and its odd harmonics. These components were related to the visual feedback loop delay and shifted in concert toward lower frequencies as the feedback delay was increased. Furthermore, there were no differences in responses between 3 normal subjects and 1 subject with peripheral sensory loss. This implies that the frequency structure is dominated by the visual feedback control loop, without significant influence from proprioceptive control loops. However, the feedback-loop delay was shown to decrease from around 341 to 264 ms as the task speed doubled. Thus the estimates of visual feedback delays are influenced by the target being followed, and this suggests that the subjects can lquot;tunerquot: their feedback system to suit the demands of the tracking task.

Journal Article↗

PubMed1999

Characteristics of visual feedback in postural control during standing.

In the present study, the visual feedback system in postural control was investigated. To suppress the vestibular and proprioceptive feedback paths, a subject stood on a force-measuring plate with a fixed back support. Because the subject's body was immovable under these conditions, the subject controlled a computer model which simulated body dynamics. Information on the sway angle of the model was fed visually. Under this condition, frequency response functions for the ankle moment in response to the sway angle were calculated. The experimental results suggest that the visual feedback system contains a large time delay and, consequently, the visual system does not by itself allow a subject to maintain an upright posture. Index Terms- Feedback control, frequency characteristics, identification, posture, visual sensory feedback.

Adult↗

PubMed2003

The utilization of visual feedback in the control of movement direction: evidence from a video aiming task.

The purpose of the present study was to establish the contribution of visual feedback in the correction of errors during movement execution (i.e., online) and the utilization of visual feedback from a completed movement in the programming of upcoming trials (i.e., offline). Participants performed 2 dimensional sweeping movements on a digitizing tablet through 1 of 3 targets, which were represented on a video monitor. The movements were performed with and without visual feedback under 4 criterion movement times (150, 250, 350, 450 msec). We analyzed the variability in directional error at 25%, 50%, 75%, and 100% of the distance between the home position and the target. There were significant differences in variability between visual conditions at each movement time. However, in the 150-msec condition, 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 250-, 350-, and 450-msec conditions, there was evidence for both online and offline control, as the form of the variability profiles differed between the vision and no vision conditions.

Adolescent↗

PubMed1997

Processing of artificial visual feedback in the walking fruit fly Drosophila melanogaster.

A computerized 360 degrees panorama allowed us to suppress most of the locomotion-induced visual feedback of a freely walking fly without neutralizing its mechanosensory system ('virtual open-loop' conditions). This novel paradigm achieves control over the fly's visual input by continuously evaluating its actual position and orientation. In experiments with natural visual feedback (closed-loop conditions), the optomotor turning induced by horizontal pattern motion in freely walking Drosophila melanogaster increased with the contrast and brightness of the stimulus. Conspicuously striped patterns were followed with variable speed but often without significant overall slippage. Using standard open-loop conditions in stationary walking flies and virtual open-loop or closed-loop conditions in freely walking flies, we compared horizontal turning induced by either horizontal or vertical motion of appropriately oriented rhombic figures. We found (i) that horizontal displacements and the horizontal-motion illusion induced by vertical displacements of the oblique edges of the rhombic figures elicited equivalent open-loop turning responses; (ii) that locomotion-induced visual feedback from the vertical edges of the rhombic figures in a stationary horizontal position diminished the closed-loop turning elicited by vertical displacements to only one-fifth of the response to horizontal displacements; and (iii) that virtual open-loop responses of mobile flies and open-loop responses of immobilized flies were equivalent in spite of delays of up to 0.1 s in the generation of the virtual stimulus. Horizontal compensatory turning upon vertical displacements of oblique edges is quantitatively consistent with the direction-selective summation of signals from an array of elementary motion detectors for the horizontal stimulus components within their narrow receptive fields. A compensation of the aperture-induced ambiguity can be excluded under these conditions. However, locomotion-induced visual feedback greatly diminished the horizontal-motion illusion in a freely walking fly. The illusion was used to assay the quality of open-loop simulation in the new paradigm.

Animals↗

PubMed2002

Age-related differences and the role of augmented visual feedback in learning a bimanual coordination pattern.

The purpose of this study was to investigate the effects of aging and the role of augmented visual information in the acquisition of a new bimanual coordination pattern, namely a 90 degrees relative phase pattern. In a pilot study, younger and older adults received augmented visual feedback in the form of a real-time orthogonal display of both limb movements after every fifth trial. Younger adults acquired this task over three days of practice and retained the task well over periods of one week and one month of no practice while the older adults showed no improvement at all on the task. It was hypothesized that the amount of augmented information was not sufficient for the older adults to overcome the strong tendency to perform natural, intrinsically stable coordination patterns, which consequently prevented them from learning the task. The present study evaluated the age-related role of augmented visual feedback for learning the new pattern. Participants were randomly assigned within age groups to receive either concurrent or terminal visual feedback after every trial in acquisition. In contrast to the pilot study, all of the older adults learned the pattern, although not to the same level as the younger adults. Both younger and older adults benefitted from concurrent visual feedback, but the older adults gained more from the concurrent feedback than the younger adults, relative to terminal feedback conditions. The results suggest that when learning bimanual coordination patterns, older adults are more sensitive to the structure of the practice conditions, particularly the availability of concurrent visual information. This greater sensitivity to the learning environment may reflect a diminished capacity for inhibitory control and a decreased ability to focus attention on the salient aspects of learning the task.

Adult↗

PubMed2005

Obstetric forceps training using visual feedback and the isometric strength testing unit.

OBJECTIVE: This is a descriptive study that tested the maximum traction residents could apply to forceps during simulations. Visual feedback was then used to reinforce an optimal range of traction, and the ability of residents to reproduce this pull when blinded was assessed. METHODS: Fifty-five residents participated in 6 pulling exercises using an isometric strength testing unit with a real-time computer printout of the force applied. Maximum traction was determined for male and female residents in standing and sitting positions. Visual feedback was then used to estimate whether residents could be trained to reproduce an optimal force range of 30-45 pounds. Data were analyzed using a repeated measures analysis of variance. RESULTS: When asked to produce a maximum pull, male residents could generate significantly more force than females in the standing and sitting positions (P < .001). In general, all residents of both sexes generated more traction in the sitting position than in the standing position. The mean maximum traction produced by men in the standing and sitting positions was 69.5 and 85.8 pounds, respectively. For women, the mean maximum force generated was 45.5 pounds in the standing position and 61.3 pounds in the sitting position. Residents could easily reproduce an appropriate force in the short term after training by computer-assisted visual feedback. CONCLUSION: Motor learning tasks using visual feedback can be useful in training practitioners to produce appropriate traction forces during obstetric forceps deliveries. Residents of both sexes, but especially men, can generate traction forces exceeding the recommended limit. Unless tempered by training, forces generated from the sitting position in particular can often exceed the preferred range. LEVEL OF EVIDENCE: II-3.

Adult↗