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At least 91 records · Page 5Linked to original sources

PubMed2004

Augmented visual feedback increases finger tremor during postural pointing.

Physiological tremor in the upper limb of eight adults was examined during the performance of a unilateral pointing task under conditions where the visual feedback, limb used and target size were altered. All subjects were required to aim a hand-held laser pointer at a circular target 5.5 m away with the goal of keeping the laser emission within the centre of the target. Visual feedback was defined as either normal vision (NV) of their limb tremor, where the laser was switched off, or augmented vision (AV) where the laser was switched on. Postural tremor from the segments of the upper limb, forearm muscle EMG activity, and target accuracy measures were recorded and analysed in the time and frequency domains. Accuracy-tremor relations were assessed using cross correlation and linear regression. Results revealed a high degree of similarity in the general pattern of the tremor output seen for each limb segment across conditions with only scalar (amplitude) changes being seen as a function of the different constraints imposed. For any single condition the tremor amplitude increased from proximal to distal segments. The frequency profile for the tremor in any segment displayed two prominent frequency peaks (at 2-4 Hz and 8-12 Hz). A third, higher frequency peak (18-22 Hz) was observed in the index fingers only. Across all conditions significant coupling relations were observed only between the hand-finger and forearm-upper arm segment pairs. Altering the visual feedback was shown to have the greatest effect on limb tremor with increased tremor and EMG activity and decreased coupling being seen under AV conditions. In trying to reduce tremor output when the augmented feedback was provided novice subjects instead increased muscle activity which resulted in increased tremor. Overall these results indicate that the physiological tremor output observed in neurologically normal subjects is not simply the product of intrinsic oscillations but is influenced by the nature of the task being performed.

Adult↗

PubMed1997

An elbow joint movement control model with visual feedback.

A motor program generator control model is proposed to simulate neuromuscular control. Three muscles (Biceps, Triceps, Brachialis) driving elbow joint flexion in a plane are simulated by integrating their nonlinear dynamic property and spinal neural circuitry. The motor descending commands are described by a visual feedback signal from the joint and an excitation signal for the motor neuron pool. The visual feedback signal mimics the gamma command whereas the excitation signal mimics another descending co-activation command. The gamma command is expressed as the output of a PID controller with the visual feedback error signal as the input. The gamma command and the motoneuron pool background activity are the inputs to the motoneuron pool model coupled with the Renshaw cell recurrent inhibitions. The output of the motoneuron pool model mimics the alpha command feeding directly to the muscle dynamics. A movement is produced by reducing the error signal between goal position and actual position and altering excitation signal properly. The simulation results show that a burst pattern of excitation signal and a PID controller can accurately trace the terminal goal and generate a smooth movement with a bell shaped velocity profile. The muscle activation signals have the characteristic similar to the smoothed EMG. Changing different parameters of the PID can cause the same effects as the stimulus pulse intensity or duration modulation.

Elbow Joint↗

PubMed1996

ALBERT: a real-time visual feedback computer tool for professional vocal development.

This paper considers the nature of real-time visual feedback for vocal analysis and development and presents a new software tool, called ALBERT (acoustic and laryngeal biofeedback enhancement in real time), designed for use with those developing their voices professionally. This tool embodies several important issues in the provision of real-time visual feedback, including: (a) support for user-configurable visual displays, (b) the ability to use colour as a complementary or sole medium for the presentation of information, (c) the ability to combine algorithmically any number of vocal parameters to create a new single parameter representative of some aspect of vocal measurement which may be displayed and updated in real time, and (d) a rate of information update which may be altered by the user at any point for the most appropriate use according to the context of the feedback task. Several examples of system use are given, including the real-time display of fundamental frequency, jitter, and larynx closed quotient (CQ) parameters in a variety of visual configurations. Several examples are given relating to developing professional voice users, including the derivation of a new parameter which reflects the measure of progress of subjects along a linear correlation line between CQ and the level of energy in the singer's formant region.

Computers↗

PubMed1990

Arm-tracking performance with and without visual feedback in children and adults: developmental changes.

Tracking performance was investigated in children (aged 6-7 and 10-11) and in adult subjects. Target signals, moving unpredictably along a straight line, were tracked with the preferred arm, alternately with and without visual feedback. Qualitative observations indicate that tracking is based on continuous adjustments of the ongoing response to the continuously changing target position. No step-and-hold strategy could be detected in any of the three age groups. Tracking performance was described with four simple parameters, derived from linear systems analysis: (a) the delay between target signal and tracking movement (DL); (b) performance at the low-frequency range (LF), (c) performance at the high-frequency range (HF); and (d) a measure of tracking quality or overall similarity in the shape of target signal and tracking movement (Q). There was a considerable improvement in tracking performance with age, even after the age of 10-11, which was mainly demonstrated by a decrease in DL and increases in HF and Q. Tracking performance decreased only to a small extent when visual feedback was withdrawn. Age-related differences in the contribution of visual feedback to tracking performance could not be demonstrated.

Journal Article↗

PubMed1991

Visuomotor performance of normal and clumsy children. II: Arm-tracking with and without visual feedback.

Tracking performance was investigated in normal and clumsy children in two age-groups, six to seven and 10 to 11 years. Target signals moving unpredictably along a straight line had to be tracked, both with and without visual feedback. Performance was described in three ways: (1) performance in the low-frequency range (LF); (2) the delay between target signal and tracking movement (DL); and (3) a measure of tracking quality or over-all similarity in the shape of target signal and tracking movement (Q). Clumsy children in both age-groups had a lower tracking quality (Q) and longer delay (DL) than the normal children. Disturbances in the regulation of attention seemed to affect tracking performance, particularly of the six- to seven-year-old clumsy children. There was no significant difference between normal and clumsy children in the effect of visual feedback on tracking performance. This suggests that clumsiness is not linked to disturbance of integration of visual feedback information and motor processes.

Attention↗

PubMed1983

Target location and visual feedback as variables determining accuracy of aiming movements.

The accuracy of a long aiming movement was studied as a function of whether it was performed toward or away from the midline of the subject's body in the presence or absence of visual feedback. 30 right-handed, male university students (19-26 yr.) served as subjects. With movement distance and duration controlled, the mean percentage of error was 6.34% less for movements made toward the body's midline than for those performed away from the midline. The mean percentage of error was also 48% less in the presence of visual feedback than in its absence. However, contrary to our expectation, movements executed toward the body's midline were not appreciably less disrupted in the absence of visual feedback than movements performed away from the midline.

Adult↗

PubMed2000

Adaptation to visual feedback delays in a human manual tracking task.

The time-course of human adaptation to spatial perturbations of visuomotor function (e.g. with prisms) is very short. However, it is not clear how rapid the adaptation to other aspects of perturbed feedback is. In this paper we report the adaptation to delayed visual feedback. Three groups of six subjects tracked unpredictable, continuously moving targets using a hand-held joystick while visual feedback of the joystick position was delayed (0 ms, 200 ms or 300 ms). Subjects clearly adapted to the delay, with a significant drop in tracking error, but changes in more subtle aspects of their tracking behaviour (such as changes in intermittency and their "impulse response functions") were not consistently observed. We suggest that the adaptation seen was consistent with the idea of there being a "delay component" in the internal processes used in manual tracking, as proposed in models such as the Smith predictor model.

Adaptation, Physiological↗

PubMed1993

Children's and adults' learning of a visuomanual coordination: role of ongoing visual feedback and of spatial errors as a function of age.

The role of ongoing visual feedback and of spatial errors in learning a target-aimed task was investigated in 6-, 8-, and 11-yr.-old children, and young adults. In each of the four age groups, 16 subjects were randomly assigned to one of three conditions of learning (either with or without vision of the limb or with vision of final spatial error). All the subjects were tested without vision of the limb before and after the learning session. Before learning, directional bias was larger for 8-yr.-old children and target undershooting was greater for adults. After learning with vision of final spatial error, amplitude and direction improved for all age groups. Nevertheless, directional accuracy during the learning session increased more slowly for children than for adults. After learning with vision of the limb, direction improved for 6- and 8-yr.-old children only, demonstrating a specific role of ongoing visual feedback during learning at these ages. Further, an analysis of movement paths suggests a poorer capability for integrating proprioception by children than by adults.

Adult↗

PubMed2004

Spontaneous eye movements in goldfish: oculomotor integrator performance, plasticity, and dependence on visual feedback.

To quantify performance of the goldfish oculomotor neural integrator and determine its dependence on visual feedback, we measured the relationship between eye drift-velocity and position during spontaneous gaze fixations in the light and in the dark. In the light, drift-velocities were typically less than 1 deg/s, similar to those observed in humans. During brief periods in darkness, drift-velocities were only slightly larger, but showed greater variance. One hour in darkness degraded fixation-holding performance. These findings suggest that while visual feedback is not essential for online fixation stability, it may be used to tune the mechanism of persistent neural activity in the oculomotor integrator.

Animals↗

PubMed2003

Online versus offline processing of visual feedback in the production of component submovements.

The present authors tested the assumptions in R. S. Woodworth's (1899) 2-component model regarding the specific roles of vision in the production of both the initial impulse and the error-correction phases of movement. Participants (N = 40) practiced a rapid aiming task (1,500 trials), with either no visual feedback, vision of only the 1st 50% of the movement, vision of only the 1st 75% of the movement, or vision of the entire movement. Consistent with previous research, the availability of vision over the 1st half of the movement had no effect on aiming accuracy during acquisition. In contrast, when visual feedback was available over the 1st 75% of the movement and the entire movement, initial impulse endpoints were less variable and the efficiency of the error-correction phase was improved. Analysis of spatial variability at various stages in the movement revealed that participants processed visual feedback offline to improve programming of the initial impulse and processed it online in regulating the deceleration of the initial impulse.

Computers↗

PubMed1998

Sinusoidal forearm tracking with delayed visual feedback. II. Dependence of the relative phase on the relative delay.

The influence of delayed visual feedback on the phase relationships between target and response signal during a sinusoidal tracking task was analysed in five normal subjects. Target frequency was varied systematically between 0.3 and 1.5 Hz, and the delay between 0 and 120% of the target cycle duration. For each subject, 63 trials were recorded. Phase parameters (relative phase, absolute relative phase and percentage of positive relative phases) revealed a clear dependence on relative delay but not on target frequency. With relative delays close to 0 and 100% of the target cycle duration, subjects successfully tracked the target signal with a small phase lag. With delays in the 30-90% range, larger phase differences were observed. Furthermore, the (delayed) response signal usually preceded the target signal in this delay range. These findings provide further evidence for a dependence of tracking error on external delays in the visual feedback loop, and indicate that delays of about 50% of the movement cycle are more difficult to handle than are smaller or larger delays. The results are discussed with regard to the influence of different control strategies (feedback, feedforward) and different types of feedback (such as vision and proprioception) on motor control.

Adult↗

PubMed2006

The influence of advance information about target location and visual feedback on movement planning and execution.

This study was designed to determine if movement planning strategies incorporating the use of visual feedback during manual aiming are specific to individual movements. Advance information about target location and visual context was manipulated using precues. Participants exhibited a shorter reaction time and a longer movement time when they were certain of the target location and that vision would be available. The longer movement time was associated with greater time after peak velocity. Under conditions of uncertainty, participants prepared for the worst-case scenario. That is, they spent more time organizing their movements and produced trajectories that would be expected from greater open-loop control. Our results are consistent with hierarchical movement planning in which knowledge of the movement goal is an essential ingredient of visual feedback utilization.

Adult↗

PubMed2005

Mobile in vivo camera robots provide sole visual feedback for abdominal exploration and cholecystectomy.

The use of small incisions in laparoscopy reduces patient trauma, but also limits the surgeon's ability to view and touch the surgical environment directly. These limitations generally restrict the application of laparoscopy to procedures less complex than those performed during open surgery. Although current robot-assisted laparoscopy improves the surgeon's ability to manipulate and visualize the target organs, the instruments and cameras remain fundamentally constrained by the entry incisions. This limits tool tip orientation and optimal camera placement. The current work focuses on developing a new miniature mobile in vivo adjustable-focus camera robot to provide sole visual feedback to surgeons during laparoscopic surgery. A miniature mobile camera robot was inserted through a trocar into the insufflated abdominal cavity of an anesthetized pig. The mobile robot allowed the surgeon to explore the abdominal cavity remotely and view trocar and tool insertion and placement without entry incision constraints. The surgeon then performed a cholecystectomy using the robot camera alone for visual feedback. This successful trial has demonstrated that miniature in vivo mobile robots can provide surgeons with sufficient visual feedback to perform common procedures while reducing patient trauma.

Abdomen↗

PubMed1987

The effects of practice and visual feedback on mandibular border movements.

Twenty healthy subjects were studied on the effects of training on mandibular border movements. Maximum left (LL) and right (RL) lateral excursions, maximum protrusive movement (PT), maximum mouth opening (MO), the difference between left and right excursions (R-L), midline deflection (DF) during opening and closing and midline deviation of the jaw (MOD) at maximum opening position of mandibular border tracing with or without practicing and visual feedback were compared among various sessions. No significant difference has been found on the amount of border extension under the influence of training. However, 70 to 85% of the subjects had some improvement after verbal instruction practicing, while only 50 to 65% of the same subjects showed improvement through visual feedback. It is suggested that doing research related to the jaw border movement on healthy subjects does not have to train them to obtain comparable data. On the other hand, since repeated border tracing in healthy subjects did not worsen the results, practicing or visual feedback training might ascertain a repeatable border tracing.

Adult↗

PubMed2001

Peripheral visual feedback: a powerful means of supporting effective attention allocation in event-driven, data-rich environments.

Breakdowns in human-automation coordination in data-rich, event-driven domains such as aviation can be explained in part by a mismatch between the high degree of autonomy yet low observability of modern technology. To some extent, the latter is the result of an increasing reliance in feedback design on foveal vision--an approach that fails to support pilots in tracking system-induced changes and events in parallel with performing concurrent flight-related tasks. One possible solution to the problem is the distribution of tasks and information across sensory modalities and processing channels. A simulator study is presented that compared the effectiveness of current foveal feedback and two implementations of peripheral visual feedback for keeping pilots informed about uncommanded changes in the status of an automated cockpit system. Both peripheral visual displays resulted in higher detection rates and faster response times, without interfering with the performance of concurrent visual tasks any more than does currently available automation feedback. Potential applications include improved display designs that support effective attention allocation in a variety of complex dynamic environments, such as aviation, process control, and medicine.

Adult↗

PubMed2000

Superposition of independent units of coordination during pointing movements involving the trunk with and without visual feedback.

Previous studies addressing the problem of the control of multiple degrees of freedom have examined the influence of trunk movement on pointing movements within the arm's reach. Such movements may be controlled by two functionally independent units of coordination (synergies): one involving only arm joints and producing the hand trajectory to the target (the transport synergy), and the other coordinating trunk and arm movements leaving the hand trajectory unchanged (the compensatory synergy). The question of whether or not this functional subdivision depends on visual feedback was addressed in the present study. We also tested whether or not the motor effects of different synergies are summated as independent components, a control strategy called "superposition." Finally, we investigated whether or not the relationship between different degrees of freedom within each synergy could be considered linear resulting in proportional changes in different joint angles. Seated subjects produced fast, uncorrected arm movements to an ipsi- or a contralateral target in the direction of +/-45 degrees to the sagittal midline of the trunk. Targets could be reached using the arm alone (control trials) or by combining the arm motion with a forward or backward trunk motion produced by hip flexion or extension (test trials), with and without visual feedback. The shape of the hand trajectory, its direction and tangential velocity, movement precision, joint angles and the sequence of the trunk and hand recruitment and de-recruitment were measured. In both visual conditions, the direction of the hand trajectory observed in control trials was generally preserved in test trials. In terms of sequencing, even in the absence of vision, the trunk movement was initiated before the onset of and outlasted the hand shift, indicating that the potential influence of the trunk on the hand movement was compensated by rotations in the elbow and shoulder joint. The analysis of other variables also implied that the effects of trunk recruitment on the hand trajectory were minor compared to those which could be observed if these effects were not compensated by appropriate changes in the arm joint angles. It was concluded that an arm-trunk compensatory synergy is present in pointing movements regardless of visual feedback. Principal component analysis showed that the relationship between elbow, shoulder and hip joint angles in individual arm and combined arm-trunk movements cannot be considered linear, implying that this relationship is adjusted according to the changing arm geometry. The changes in each arm joint angle (elbow, shoulder) elicited by a forward trunk bending in one block of trials were compared with those elicited by a backward bending in another block, whereas the hand moved to the same target in both blocks. These changes were opposite but of similar magnitude. As a result, for each moment of movement, the mean joint angle obtained by averaging across two directions of trunk motion was practically identical to that in control trials in which the trunk was motionless. It is concluded that the transport and arm-trunk compensatory synergies are combined as independent units, according to the principle of superposition. This principle may simplify the control of the coordination of a redundant number of degrees of freedom.

Adult↗

PubMed2005

Visual feedback therapy to enhance medication adherence in psychosis.

Adherence to antipsychotic medications is key to enhancing maximum responses to medication and to decreasing relapse rates among those with psychotic disorders. Visual feedback therapy used electronic monitoring to provide visual feedback of daily medication-taking behaviors, combined with supportive counseling and education components. Twenty-three participants with DSM-IV diagnoses of psychotic disorders were recruited from community and inpatient settings. No statistical significance was found for intervention weekly for 1 month, followed by monthly for 2 months, although a majority of participants either maintained or increased adherence rates at 1 month. Additional findings included associations between low insight and low adherence and descriptive data on medication adherence behaviors.

Adult↗

PubMed2000

Visual feedback has differential effects on reaching movements in Parkinson's and Alzheimer's disease.

We examine the role of visual feedback in the programming and execution of reaching movement in patients with Parkinson's disease without cognitive impairment and patients with Alzheimer's disease without extrapyramidal signs. Controls were normally aging subjects. All subjects moved a cursor to targets on a digitizing tablet without seeing their limb. Starting and target positions were always visible on a screen while, during movement, cursor position was either visible or blanked. They were instructed to make uncorrected movements, as fast and as accurate as possible without minimizing reaction time. In absence of visual feedback, movement accuracy in patients with AD was severely impaired. Hand paths of parkinsonian patients were as accurate as normal subjects' with similar temporal velocity profiles and movement speed. With cursor feedback, accuracy was the same in the three groups, although movement speed and transport phase in patients with Alzheimer's disease were significantly reduced compared to the other groups. Also, movements of parkinsonian patients showed shorter transport phase and lower mean velocity than controls'. The different characteristics of the motor performance suggests that in the two diseases visual information is used differently for both motor programming and execution: patients with Alzheimer's disease, while scarcely using feed forward commands, relied on continuous on-line external cues. The correlation of motor performance with cognitive impairment argues against the hypothesis of basal ganglia involvement in AD. The motor abnormalities we found may represent early subclinical manifestation of apraxic disturbance. Parkinsonian patients showed higher reliance on feedback commands only with cursor feedback: this could be explained by their difficulty in engaging effectively automatic routines when distractors are present.

Aged↗