SEARCH · PubMed Health

Results for “visual feedback”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 739 records · Page 41Linked to original sources

PubMed2001

Excitatory actions of experimental muscle pain on early and late components of human jaw stretch reflexes.

It has recently been shown that a slow stretch evokes a short-latency (probably monosynaptic) and a long-latency (polysynaptic) reflex response in human jaw-closing muscles. The effect of nociceptive muscle input on the fusimotor system has not been investigated in detail. In order to investigate the effect of sustained muscle pain on the jaw stretch reflex, two main experiments were performed. Stretch reflex responses were evoked in the masseter and temporalis muscles by slow stretches (1-mm displacement, 40-ms ramp time) before, during and 15 min after a period of experimentally induced muscle pain. In experiment I, a dose of 1.0 M hypertonic or 154 mM isotonic (control) saline was infused in random order into the left masseter for up to 15 min (n=12). The level of excitation of the left masseter at 15% maximal voluntary contraction was controlled by visual feedback of the surface EMG (sEMG). In experiment II, a dose of 1.0 M saline was infused into the left masseter but with feedback from the sEMG of the right masseter (n=12). In a control experiment, both sEMG and intramuscular EMG (imEMG) were recorded from the left and right masseters; the feedback was from imEMG of the left masseter (n=12). The early (onset: 9--10 ms) and late (duration from 25 to 40 ms) reflex components were recorded and analysed in all experiments. Infusion of 1.0 M saline caused moderate pain (mean score on a Visual Analogue Pain Scale: 4.9--5.0 cm). The peak-to-peak amplitude of the early reflex component in the painful masseter normalized to the pre-stimulus EMG activity was significantly higher during the pain than the pre- and post-infusion conditions in all experiments. The normalized area of the late reflex component in the painful masseter was significantly larger than in the pre-infusion condition in all experiments. Isotonic saline had no significant effect on the jaw stretch reflexes. These results indicate that experimental jaw-muscle pain in humans facilitates the early as well as the late component of the jaw stretch reflex response as revealed by both sEMG and imEMG. This effect appears to be independent of the level of excitation of the muscle and not related to volume effects of the injected saline. A change in the sensitivity of the fusimotor system during muscle pain is suggested as an explanation.

Adult↗

PubMed2006

Alcohol-induced suppression of BOLD activity during goal-directed visuomotor performance.

The neurophysiological influence of alcohol produces deficits of many cognitive functions, including executive and motor control processes. This study examined the acute effects of alcohol in the context of goal-directed visuomotor performance during functional magnetic resonance imaging (fMRI). Subjects consumed alcohol-laced gelatin during one scan session and non-alcoholic placebo gelatin in another. During each session, subjects performed a visuomotor target capture where they received continuous or terminal positional feedback information. Blood-oxygen level-dependent (BOLD) activity in the cerebellum was suppressed in the presence of alcohol, consistent with the known ethanol sensitivity of the cerebellum. A fronto-parietal network was identified as most affected by alcohol consumption, with differential patterns of BOLD contingent on visual feedback. Results indicate that alcohol selectively suppresses cognitive activity in frontal and posterior parietal brain regions that, in conjunction with cerebellar nuclei, are believed to contribute to the formation of internal cognitive models of motor representation and action.

Adult↗

PubMed2005

The effect of conscious control on handwriting in children with attention deficit hyperactivity disorder.

Two experiments were performed regarding the effect of conscious control on handwriting fluency in healthy adults and ADHD children. First, 26 healthy students were asked to write a sentence under different conditions. The results indicate that automated handwriting movements are independent from visual feedback. Second, the writing performance of 12 children with ADHD was examined on their usual medication with methylphenidate and under placebo. In comparison to placebo, medication with methylphenidate resulted in a reduced fluency of handwriting. Automated handwriting movements could be elicited in children with ADHD on medication. The results suggest that both visual and mental control of handwriting movements affect the automation of handwriting movements. Furthermore, a simple training procedure was designed and performed in a case study of a boy with ADHD.

Adult↗

PubMed2005

Activity patterns of the masticatory muscles during feedback-controlled simulated clenching activities.

In 10 normal subjects, the electromyographic (EMG) activities of the masseter, anterior and posterior temporalis, medial pterygoid, inferior lateral pterygoid, as well as the anterior digastric, were bilaterally recorded during clenching with various resulting force vectors. The intraoral force transfer was achieved with a three-component force transducer. The direction and magnitude of the force vectors were controlled by visual feedback. The goal of the study was to investigate how various clenching directions at constant magnitude of force influence the EMG activity in the masticatory muscles during gradual increase of the horizontal force component. Depending on the force direction and the individual muscle, an increase or decrease of activity was observed during clenching with increasing horizontal force components at constant magnitude of force. The inferior lateral pterygoid exhibited the highest activation (about 80% of maximal voluntary clenching) of all masticatory muscles. The medial pterygoid showed the greatest range of variation in activation behavior, and it was the most active muscle in relation to all clenching directions. In conclusion, the results show that with growing horizontal force components at constant magnitude of force, all muscles demonstrated an increase or decrease of activity in several clenching directions.

Adult↗

PubMed2003

First-trial adaptation to prism exposure.

Terminal target-pointing error on the 1st trial of exposure to optical displacement is usually less than that expected from the optical displacement magnitude. Such 1st trial adaptation was confirmed in 2 experiments (N = 48 students in each) comparing pointing toward optically displaced targets and toward equivalent physically displaced targets (no optical displacement), with visual feedback delayed until movement completion. First-trial performance could not be explained by ordinary target undershoot, online correction, or reverse optic flow information about true target position and was unrelated to realignment aftereffects. Such adaptation might be an artifact of the asymmetry of the structured visual field produced by optical displacement, which induces a felt head rotation opposite to the direction of the displacement, thereby reducing the effective optical displacement.

Adaptation, Psychological↗

PubMed1999

Perception of self-generated movement following left parietal lesion.

Three apraxic patients with lesions in the left parietal cortex were required to execute finger movements with either hand, while the visual feedback they received about the movement was manipulated systematically. We used a device which allowed us to present on a video monitor either the patient's hand or the examiner's hand simultaneously performing an identical or a different movement. In each trial, patients were required to decide whether the hand shown on the screen was their own or not. Hand movements produced in response to verbal command included simple (single-finger extension) and complex gestures (multi-finger extension). Ownership judgements were analysed and compared with those produced by six normal controls and two non-apraxic neurological patients. Apraxic patients and controls accurately recognized their own hand on the screen (own movement condition) and correctly identified the viewed hand as the examiner's when it performed a movement different from their own movement (incongruent movement condition). However, when the viewed hand was the examiner's hand executing their own movement (congruent movement condition), apraxic patients were significantly more impaired than controls. When the results were analysed as a function of gesture type, the number of correct responses was significantly lower for apraxic patients with respect to controls only for complex gestures. Interestingly, when patients executed the finger gestures inaccurately, they still failed to recognize the examiner's hand as alien, and claimed that the correct movement presented on the screen was their own. These results confirm that parietal lesions alter the representational aspects of gestures, and suggest a failure in evaluating and comparing internal and external feedback about movement. We conclude that the parietal cortex plays an important role in generating and maintaining a kinaesthetic model of ongoing movements.

Aged↗

PubMed2002

Effect of short-term saccadic adaptation on saccades evoked by electrical stimulation in the primate superior colliculus.

The brain maintains the accuracy of visually guided movements by using visual feedback to correct for changes in the nervous system and musculature that would otherwise result in dysmetria. In monkeys, evidence suggests that an adaptive mechanism can compensate for weakness in an extraocular muscle by changing the gain of the neural signal to the weakened muscle. The visual effects of such neuromuscular changes have been simulated using a short-term saccade adaptation paradigm, in which the target spot jumps to a new location during the initial saccade. Under these circumstances, over several hundred trials, monkeys gradually change the amplitude of their saccades so that the eye lands closer to the final location of the target spot. There is considerable evidence from lesion and single-unit recording studies that the locus of such saccade adaptation is downstream of the superior colliculus in the cerebellum. Paradoxically, previous research has indicated that saccades evoked by electrical stimulation in the superior colliculus are not modified by short-term saccade adaptation, suggesting that adaptation occurs in the oculomotor system upstream of the superior colliculus or else in a pathway that bypasses the superior colliculus. We tested whether this result was due to using suprathreshold stimulation currents. Stimulating at 44 low-threshold sites in the superior colliculi of three monkeys revealed that using low current levels evoked saccades that were modified by adaptation. Adaptation for visually guided and electrically evoked saccades had similar time courses and tended to be accomplished by a reduction in saccade velocity rather than a decrease in duration. Moreover, the more similar the velocity of electrically evoked and visually guided saccades prior to the start of saccadic adaptation the greater the effect of adaptation on electrically evoked saccades. These results suggest that the superior colliculus is indeed upstream of the locus of adaptation, corroborating previous lesion and single-cell recording studies, but that the mechanism mediating saccade adaptation is sensitive to the parameters of electrical stimulation.

Adaptation, Physiological↗

PubMed1990

Procedure-specific estimates of structural and strategic factors in the Horizontal-Vertical illusion.

The present study examined potential differences in structural and strategic factor estimates involved in the Horizontal-Vertical (HV) illusion. Performance on adjustment and production-task forms of the illusion was examined under the conditions of intertrial feedback, continued visual inspection, combined feedback and visual inspection, as well as control procedures. Estimates of structural and strategic factors were procedure-specific and, for each task, the correction of inaccurate strategic factors was significantly greater for the feedback than the visual-inspection and control groups. There were no significant additive effects when feedback was combined with visual inspection. The illusion results from an overestimation of the length of vertical lines, seems to be predominantly cognitive in nature, and exists in the absence of line bisection and a comparison line.

Adolescent↗

PubMed2003

Effects of visual center of pressure feedback on postural control in young and elderly healthy adults and in stroke patients.

The goal of this study was to compare young and elderly healthy individuals and elderly stroke patients in their capacity to use visual CP feedback (VF) in controlling both quiet standing and weight shifting and to assess their sensory re-weighing when this VF is withdrawn. A total of 40 participants were involved in this study. Participants were asked to either quietly stand on a force platform for a period of 45 s with eyes open (EO), using visual feedback (VF) or without visual feedback (No VF) or to perform a dynamic weight shifting task while using VF or No VF. During the quiet standing trials with VF, only the young (YO) were able to decrease the amplitude and increase the frequency of their sway in either plane. Removal of the VF resulted in a 'destabilizing' effect in both healthy elderly (EL) and stroke patients (ST) in the sagittal plane. With regard to the dynamic task, both the YO and EL were generally more successful at weight shifting in terms of speed and control when compared to the ST. Yet, when VF was removed, only the YO were able to largely maintain speed and precision of control. Hence, providing or removing visual CP feedback during quiet standing or removing VF during visually controlled weight shifting can discriminate healthy young participants from healthy elderly, but does not clearly discriminate healthy elderly from stroke patients in the same age group. Results revealed that sagittal plane imbalance in healthy elderly and stroke patients may be largely due to the effects of aging, whereas frontal plane imbalance is much more specific for the postural problems associated with stroke.

Adult↗

PubMed1997

Spatial learning by rats across visually disconnected environments.

Two spatial tasks were designed to test specific properties of spatial representation in rats. In the first task, rats were trained to locate an escape hole at a fixed position in a visually homogeneous arena. This arena was connected with a periphery where a full view of the room environment existed. Therefore, rats were dependent on their memory trace of the previous position in the periphery to discriminate a position within the central region. Under these experimental conditions, the test animals showed a significant discrimination of the training position without a specific local view. In the second task, rats were trained in a radial maze consisting of tunnels that were transparent at their distal ends only. Because the central part of the maze was non-transparent, rats had to plan and execute appropriate trajectories without specific visual feedback from the environment. This situation was intended to encourage the reliance on prospective memory of the non-visited arms in selecting the following move. Our results show that acquisition performance was only slightly decreased compared to that shown in a completely transparent maze and considerably higher than in a translucent maze or in darkness. These two series of experiments indicate (1) that rats can learn about the relative position of different places with no common visual panorama, and (2) that they are able to plan and execute a sequence of visits to several places without direct visual feed-back about their relative position.

Animals↗

PubMed2001

Sensorimotor adaptation to rotated visual input: different mechanisms for small versus large rotations.

The present study investigates if sensorimotor adaptation to large visual rotations is achieved by a continuous angular change of the internal representation of space. Human subjects performed manual tracking movements under rotated visual feedback in two sessions; the magnitude of rotation in the second session was 45 degrees larger or smaller than in the first. We found mostly a facilitatory effect of the first adaptation on the second, which supports the view that the internal representation can gradually shift from one angular transformation to another. However, no facilitation was found for visual rotations in the 80-120 degrees range, suggesting that the internal model changes gradually only up to a limiting angle. A subsidiary experiment, employing small stepwise changes of visual rotation throughout a testing session, confirmed this view and placed the limiting angle near 120 degrees for an increasing, and near 70 degrees for a decreasing visual rotation. We conclude that adaptation to large-magnitude rotations may be achieved in two stages: a polarity inversion of both axes (=180 degrees rotation), followed by a "backward" shift toward somewhat smaller angles.

Adaptation, Physiological↗

PubMed1980

Saccadic eye movements and body sway.

Different conditions of moving retinal images show differential influences on postural stability. A surrounding pattern moved during steady fixation increases body sway, but similar image motions generated by voluntary saccades do not. Mechanisms for postural control do not respond to visual feedback during saccades. Analogous principles in saccadic suppression and space constancy are discussed.

Biofeedback, Psychology↗

PubMed1997

Visual sensation during pecking in pigeons.

During the final down-thrust of a pigeon's head, the eyes are closed gradually, a response that was thought to block visual input. This phase of pecking was therefore assumed to be under feed-forward control exclusively. Analysis of high resolution video-recordings showed that visual information collected during the down-thrust of the head could be used for 'on-line' modulations of pecks in progress. We thus concluded that the final down-thrust of the head is not exclusively controlled by feed-forward mechanisms but also by visual feedback components. We could further establish that as a rule the eyes are never closed completely but instead the eyelids form a slit which leaves a part of the pupil uncovered. The width of the slit between the pigeon' eyelids is highly sensitive to both, ambient luminance and the visual background against which seeds are offered. It was concluded that eyelid slits increase the focal depth of retinal images at extreme near-field viewing-conditions. Applying pharmacological methods we could confirm that pupil size and eyelid slit width are controlled through conjoint neuronal mechanisms. This shared neuronal network is particularly sensitive to drugs that affect dopamine receptors.

Animals↗

PubMed1987

Eye movements and vestibulo-ocular reflex in the blind.

To assess the effect of chronic deprivation of visual feedback, 21 blind patients underwent clinical and electronystagmographical examination. Patients with congenital blindness were characterized by spontaneous eye movements, inability to consciously move the eyes and absence of the vestibulo-ocular reflex (VOR), whereas eye movement abnormalities were practically absent in those with blindness acquired late in life. Active visual experience, at least in early life, seems to be crucial for the development of eye movements and VOR adjustment.

Adult↗

PubMed2006

Parkinsonian deficits in sensory integration for postural control: temporal response to changes in visual input.

This study investigated the effect of Parkinson's disease (PD) on the time course for postural control following the removal and reinsertion of visual information. Twelve medicated PD patients (PD) and 12 age matched control (CTRL) subjects performed two 45-s quiet standing trials, during which visual feedback was available (0-15s), deprived (15-30s), and then restored (30-45s). The 45s test trial was divided into 5s time bins to compare the time-based effect of sensory reorganization during deprivation and reintegration. Results revealed an increase in Elliptical Sway Area (ESA) following visual deprivation for both groups; this increased ESA remained significantly higher than the baseline level for the duration of the deprivation period among PD patients and returned to baseline the level among CTRL. Despite elevated ESA at the end of visual deprivation among PD patients, neither group showed a change in ESA after visual information was restored. These results indicate a PD-associated deficit with the reorganization of sensory priorities for postural control, and may implicate the basal ganglia as being critical for integration of sensory information for postural control.

Aged↗

PubMed2005

Functional properties of grasping-related neurons in the ventral premotor area F5 of the macaque monkey.

We investigated the motor and visual properties of F5 grasping neurons, using a controlled paradigm that allows the study of the neuronal discharge during both observation and grasping of many different three-dimensional objects with and without visual guidance. All neurons displayed a preference for grasping of an object or a set of objects. The same preference was maintained when grasping was performed in the dark without visual feedback. In addition to the motor-related discharge, about half of the neurons also responded to the presentation of an object or a set of objects, even when a grasping movement was not required. Often the object evoking the strongest activity during grasping also evoked optimal activity during its visual presentation. Hierarchical cluster analysis indicated that the selectivity of both the motor and the visual discharge of the F5 neurons is determined not by the object shape but by the grip posture used to grasp the object. Because the same paradigm has been used to study the properties of hand-grasping neurons in the dorsal premotor area F2, and in the anterior intraparietal area (AIP), a comparison of the functional properties of grasping-related neurons in the three cortical areas (F5, F2, AIP) is addressed for the first time.

Action Potentials↗

PubMed2000

Disparity vergence double responses processed by internal error.

Disparity vergence eye movements occasionally exhibit two high-velocity components to a single step stimulus (Alvarez, T. L., Semmlow, J. L. & Yuan, W. (1998). Journal of Neurophysiology, 79, 37-44). This research investigates the neural strategy used to trigger the second component of double high-velocity vergence eye movements. Vergence doubles evoked by an experimental protocol that induces post-movement visual error were compared to doubles that occur normally. The second component of a visually evoked response double occurred later, and with slower dynamics, than that of a naturally occurring double. These differences in timing and dynamics indicate that natural double responses are mediated, at least in part, by a mechanism other than visual feedback. The faster dynamics and timing of natural doubles suggest that an internal monitoring process triggers these movements.

Adolescent↗

PubMed2002

Adaptation to Coriolis force perturbation of movement trajectory; role of proprioceptive and cutaneous somatosensory feedback.

Subjects exposed to constant velocity rotation in a large fully-enclosed room that rotates initially make large reaching errors in pointing to targets. The paths and endpoints of their reaches are deviated in the direction of the transient lateral Coriolis forces generated by the forward velocity of their reaches. With additional reaches, subjects soon reach in straighter paths and become more accurate at landing on target even in the absence of visual feedback about their movements. Two factors contribute to this adaptation: first, muscle spindle and golgi tendon organ feedback interpreted in relation to efferent commands provide information about movement trajectory, and second, somatosensory stimulation of the fingertip at the completion of a reach provides information about the location of the fingertip relative to the torso.

Acceleration↗