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Results for “visual feedback”

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PubMed1999

Vestibular information contributes to update retinotopic maps.

In order to investigate the contribution of the vestibular system to spatial orientation, we studied memory-guided saccades in three conditions: visual-memory guided saccades (ViC), saccades to the remembered spatiotopic position of a visual target, after whole-body rotation (SVeC) and saccades to the remembered retinotopic position of a visual target, after whole-body rotation (RVeC). Visual feedback presented after each trial allowed eye position correction. The error was larger in SVeC, but the performance improved throughout the experiment (learning) in that condition only. As learning occurred over the first four trials, we omitted these trials from the average computation, and the significant difference between the conditions disappeared. It is concluded that vestibular information does contribute to update the internal spatial representation of visual information when a visual feedback is provided.

Feedback↗

PubMed2005

Perceptual-motor adaptations in a synchronization task: the joint effects of frequency and motion coherence manipulations.

Two experiments were conducted to examine the human ability to adapt to a perturbation in a synchronization task. Five experimental signal conditions were tested using random-dot kinematograms, representing four conditions with different coherence levels (100%, 50%, 30% and 10%) and one target-alone condition. Within one trial, increasing or decreasing the frequency of the sinusoidally moving signal dots abruptly in the midst of each trial provoked a perturbation. The first experiment was aimed to clarify the process of adaptation to the new frequency situation. The second experiment explored the role of visual feedback about the arm's position on the participants' ability to adapt after the perturbation had occurred. The results clearly demonstrated that the synchronization performance gradually declined in function of the increasing number of randomly moving noise dots. In the 50% coherence condition, the participants were not or only partially able to adjust their arm movements to the new frequency situation. In addition, the provision of enhanced visual feedback about the arm's failed to improve one's adaptive ability. In general, these findings provided evidence for the important role of perceptual constraints on perception-action coupling in this type of synchronization task.

Adaptation, Physiological↗

PubMed2005

Differential progression of proprioceptive and visual information processing deficits in Parkinson's disease.

Indirect evidence suggests that patients with Parkinson's disease (PD) have deficits not only in motor performance, but also in the processing of sensory information. We investigated the role of sensory information processing in PD patients with a broad range of disease severities and in a group of age-matched controls. Subjects were tested in two conditions: pointing to a remembered visual target in complete darkness (DARK) and in the presence of an illuminated frame with a light attached to the index finger (FRAME). Differences in pointing errors in these two conditions reflect the effect of visual feedback on pointing. PD patients showed significantly larger constant and variable errors than controls in the DARK and FRAME condition. The difference of the variable error in the FRAME and DARK condition decreased as a function of the severity of PD. This indicates that any deficits in the processing of proprioceptive information occur already at very mild symptoms of PD, and that deficits in the use of visual feedback develop progressively in later stages of the disease. These results provide a tool for early diagnosis of PD and shed new light on the functional role of the brain structures that are affected in PD.

Adult↗

PubMed1983

Programming precision in repetitive tapping.

The present paper reports an experiment using the Fitts' tapping paradigm. It is concerned with a comparison of movement times and accuracy during blind and visual repetitive tapping. A blind condition was used to investigate rapid aiming movements under motor program control, whilst visual aiming was used to assess the role of visual feedback for control purposes. Subjects in the blind conditions were able to replicate the amplitude specifications of the task, whereas effective target width was constant for a set amplitude and did not reflect specified target width. Subjects, furthermore, responded more rapidly when tapping blind. These results are discussed in terms of the magnitude of forces being attempted as a result of performing a set amplitude, and the role of visual feedback.

Journal Article↗

PubMed2000

Using time domain characteristics to discriminate physiologic and parkinsonian tremors.

Tremor amplitude and frequency do not always clearly differentiate subjects with particular pathologies from control subjects or from subjects with other pathologies, especially in early stages of a disease. For patients with early stages of Parkinson's disease (PD) the discriminative power of amplitude was compared with that of other time domain characteristics of tremor recordings that are probably not evident clinically. Postural tremor with and without visual feedback and rest tremor were recorded in both hands of a group of patients with Parkinson's disease (n = 21) and a group of healthy control subjects (n = 30) using displacement lasers. Velocity and acceleration data were derived from displacement data. Twelve time domain characteristics were calculated on each recording and the discriminating power of each was evaluated using the worse hand in each case. Postural tremor with no visual feedback separates the two groups of subjects most efficiently, especially in velocity and acceleration. Tremor in Parkinson's disease (in comparison to normal physiologic tremor) has a specific morphology, has a distinctive histogram, is more periodic, and contains indications of nonlinearity in the underlying dynamics. There may also be greater difference in amplitude between the two hands and time asymmetry in tremor of patients with PD. A series of finger flexions seems to enhance normal tremor but not tremor in PD and may thus aid in discrimination. Discrimination of tremor attributable to PD from normal physiologic tremor can be enhanced by measuring time domain characteristics subtler than amplitude, particularly when amplitude itself is not large. Tremor measurement should not be limited to acceleration data because some information is more visible in other variables.

Aged↗

PubMed2004

Different modes of grip force control: voluntary and externally guided arm movements with a hand-held load.

OBJECTIVE: When we move hand-held objects that exhibit stable physical properties grip force is regulated in anticipation of movement-induced inertial loads. In contrast, when the object's behaviour is unpredictable, grip force is adjusted in response to sensory feedback with the consequence that grip tends to lag behind load. Previous studies analysed reactive and predictive grip force behaviour by systematically varying the predictability of the physical object properties. METHODS: This study examines if anticipatory force control also depends on the predictability of the limb dynamics interfering with external objects. The coupling between grip and load force profiles was comparatively analysed during voluntary and externally guided vertical arm movements with an instrumented hand-held object. Voluntary and externally guided movements were performed with and without visual feedback. RESULTS: During voluntary arm movements grip force was precisely regulated in anticipation of movement-induced inertial load fluctuations with grip force increasing in parallel with load force without an obvious time delay. In contrast, during externally guided movements grip force was regulated in reaction to the imposed load fluctuations. However, the reflex-mediated grip force responses were still flexible to account for the differential loading requirements of movement direction. There was no difference of grip force performance between movements performed with and without visual feedback. CONCLUSIONS AND SIGNIFICANCE: The results suggest that predictability of both the external object and the dynamics of the own body is essential to establish an anticipatory mode of grip force regulation. Unpredictability of the own limb dynamics results in a reactive mode of grip force control. Reactive grip force control appears to be both highly automatised and flexible reflecting differential loading requirements of movement direction.

Adult↗

PubMed1987

Interactive visual optimization of SPECT prereconstruction filtering.

A number of factors must be considered when forming a digital filter to two-dimensionally filter single photon emission computed tomographic (SPECT) acquisition images. In an effort to provide subjectively optimal filtering, a program has been developed which provides "real-time" visual feedback. This allows a user to select from among a family of Metz filters tailored for the imaging conditions (i.e., formed to deconvolve scatter, septal penetration, and combined collimator and intrinsic spatial resolution losses). Also, a guideline for assisting the user in selecting from among the possible Metz filters has been formulated. This guideline is based upon knowledge of the probability distribution of the noise power spectrum, and consists of choosing the filter which has a value of 1.0 when the one-dimensional compression of the image power spectrum equals the 90% confidence limit for noise fluctuations. The program starts by filtering a planar reference image with the Metz filter computed for the radionuclide, collimator, magnification, and count-level of the image. This filter is displayed beside the image where it is overlayed on a plot of the logarithm of the one-dimensional compression of the image power spectrum. The user is then allowed to vary the filter parameters through movement of a joystick. By doing the filtering using an array processor, a new filtered image is formed and displayed less than a second after movement of the joystick. Visual feedback from the series of filtered images thus produced as well as the plots of the filter overlayed on the estimated blurred object power spectrum are used to obtain a visually "optimal" filter. The filter can be adapted to the visual preferences of the individual reader, and serves as a useful teaching tool on the effects of filtering.

Evaluation Studies as Topic↗

PubMed2006

Deficits in movement planning and intrinsic coordinate control in ideomotor apraxia.

Two central issues in the field of motor control are the coordinate frame in which movements are controlled and the distinction between movement planning and online correction. In this study we used these issues to frame several hypotheses about the deficits underlying ideomotor apraxia (IMA). In particular, we examined whether ideomotor apraxics exhibited (1) deficits in movement control in intrinsic (body relative) coordinates with better control in extrinsic (workspace relative) coordinates, (2) deficits in movement planning that are compensated for by an overreliance on online correction, or (3) both deficits. Patients with IMA and two comparison groups performed movement tasks that relied preferentially on either intrinsic or extrinsic coordinate control when online correction was either possible or impossible. Participants performed posture imitation and grasp imitation movements to body- and object-relative end positions in the presence or absence of visual feedback. Consistent with the intrinsic coordinate control hypothesis, patients with IMA showed a significantly greater disparity than the other two groups between movements made to body-relative and object-relative targets as well as between imitation of meaningless postures and grasping. Consistent with the correction overreliance hypothesis, the IMA group was more disrupted than the other groups by the removal of vision. Thus, IMA patients exhibit behavioral patterns consistent with both deficient intrinsic coordinate control and overreliance upon visual feedback. Finally, lesion analysis suggests that damage to the left inferior parietal lobe (Brodmann's areas 39 and 40) may play a key role in both behavioral deficits.

Acoustic Stimulation↗

PubMed1998

Pointing to remembered targets in 3-D space in Parkinson's disease.

A three-dimensional tracking system was used to examine whether subjects with Parkinson's disease (PD) would show characteristic performance deficits in an unconstrained pointing task. Five targets were presented in a pyramidal array in space to 11 individuals with mild to moderate PD and 8 age-matched controls. After the target was indicated, subjects closed their eyes and pointed to the remembered target locations without vision. Despite the absence of visual feedback during movement, PD subjects were as accurate overall as controls. However, PD subjects showed greater variable errors, more irregular trajectories, and a vertical endpoint bias in which their endpoints were significantly lower than controls. They also showed deficiencies in the compensatory organization of joint rotations to ensure consistency in azimuthal (horizontal) positioning of the arm endpoint. We concluded that, under appropriate task conditions, PD subjects may not show overall deficits in accuracy even when making targeting movements at normal speed without visual feedback. Nevertheless, our findings indicate that there are certain dimensions of performance which are selectively altered in Parkinson's disease even when overall performance is normal.

Aged↗

PubMed2004

Plasticity and tuning of the time course of analog persistent firing in a neural integrator.

In a companion paper, we reported that the goldfish oculomotor neural integrator could be trained to instability or leak by rotating the visual surround with a velocity proportional to +/- horizontal eye position, respectively. Here we analyze changes in the firing rate behavior of neurons in area I in the caudal brainstem, a central component of the oculomotor neural integrator. Persistent firing could be detuned to instability and leak, respectively, along with fixation behavior. Prolonged training could reduce the time constant of persistent firing of some cells by more than an order of magnitude, to <1 s. Normal visual feedback gradually retuned persistent firing of integrator neurons toward stability, along with fixation behavior. In animals with unstable fixations, approximately half of the eye position-related cells had upward or unstable firing rate drift. In animals with leaky fixations, two-thirds of the eye position-related cells showed leaky firing drift. The remaining eye position-related cells, generally those with lower eye position thresholds, showed a more complex pattern of history-dependent/predictive firing rate drift in relation to eye drift. These complex drift cells often showed a drop in maximum persistent firing rate after training to leak. Despite this diversity, firing drift and the degree of instability or leak in firing rates were broadly correlated with fixation performance. The presence, strength, and reversibility of this plasticity demonstrate that, in this system, visual feedback plays a vital role in gradually tuning the time course of persistent neural firing.

Animals↗

PubMed2007

The acquisition and implementation of the smoothness maximization motion strategy is dependent on spatial accuracy demands.

We recently showed that extensive training on a sequence of planar hand trajectories passing through several targets resulted in the co-articulation of movement components and in the formation of new movement elements (primitives) (Sosnik et al. in Exp Brain Res 156(4):422-438, 2004). Reduction in movement duration was accompanied by the gradual replacing of a piecewise combination of rectilinear trajectories with a single, longer curved one, the latter affording the maximization of movement smoothness ("global motion planning"). The results from transfer experiments, conducted by the end of the last training session, have suggested that the participants have acquired movement elements whose attributes were solely dictated by the figural (i.e., geometrical) form of the path, rather than by both path geometry and its time derivatives. Here we show that the acquired movement generation strategy ("global motion planning") was not specific to the trained configuration or total movement duration. Performance gain (i.e., movement smoothness, defined by the fit of the data to the behavior, predicted by the "global planning" model) transferred to non-trained configurations in which the targets were spatially co-aligned or when participants were instructed to perform the task in a definite amount of time. Surprisingly, stringent accuracy demands, in transfer conditions, resulted not only in an increased movement duration but also in reverting to the straight trajectories (loss of co-articulation), implying that the performance gain was dependent on accuracy constraints. Only 28.5% of the participants (two out of seven) who were trained in the absence of visual feedback from the hand (dark condition) co-articulated by the end of the last training session compared to 75% (six out of eight) who were trained in the light, and none of them has acquired a geometrical motion primitive. Furthermore, six naive participants who trained in dark condition on large size targets have all co-articulated by the end of the last training session, still, none of them has acquired a geometrical motion primitive. Taken together, our results indicate that the acquisition of a geometrical motion primitive is dependent on the existence of visual feedback from the hand and that the implementation of the smoothness-maximization motion strategy is dependent on spatial accuracy demands. These findings imply that the specific features of the training experience (i.e., temporal or spatial task demands) determine the attributes of an acquired motion planning strategy and primitive.

Adolescent↗

PubMed1994

Visual control of arm movement in Parkinson's disease.

Patients with Parkinson's disease (PD) are more dependent on visual information during movements than normals. To investigate the mechanisms underlying deterioration of movement under nonvisual conditions, we studied two-dimensional pointing movements to randomly occurring targets. The experimental design allowed us to systematically manipulate visual feedback during the movement by removing vision of the target, of the moving hand, or of both. Execution of pointing movements in PD deviated most severely from that of normals when PD patients moved without vision of their own moving hand. Under this condition, undershooting of the target appeared, and movements were particularly slow. In contrast, with complete vision or when only vision of the target was occluded, pointing movements of PD patients were accurate and faster. PD patients had no difficulties selecting the correct movement direction. Reaction times were longer in PD patients irrespective of the availability of visual feedback. Our findings suggest that the ability of PD patients to use nonvisual feedback during execution of arm movements is impaired.

Adult↗

PubMed2000

The timing of arm-trunk coordination is deficient and vision-dependent in Parkinson's patients during reaching movements.

The role of the basal ganglia in the coordination of different body segments and utilization of motor synergies was investigated by analyzing reaching movements to remembered three-dimensional (3D) targets in patients with Parkinson's disease (PD). Arm movements were produced alone or in combination with a forward bending of the trunk, with or without visual feedback. Movements in PD patients were more temporally segmented, as evidenced by irregular changes in tangential velocity profiles. In addition, the relative timing in the onsets and offsets of fingertip and trunk motions were substantially different in PD patients than in control subjects. While the control subjects synchronized both onsets and offsets, the PD patients had large mean intervals between the onsets and offsets of the fingertip and trunk motions. Moreover, PD patients showed substantially larger trial-to-trial variability in these intervals. The degree of synchronization in PD patients gradually increased during the movement under the influence of visual feedback. The mean and variability of the intersegmental intervals decreased as the fingertip approached the target. This improvement in timing occurred even though the separate variability in the timing of arm and trunk motions was not reduced by vision. In combined movements, even without vision, the PD patients were able to achieve normal accuracy, suggesting they were able to use the same movement synergies as normals to control the multiple degrees of freedom involved in the movements and to compensate for the added trunk movement. However, they were unable to recruit these synergies in the stereotyped manner characteristic of healthy subjects. These results suggest that the basal ganglia are involved in the temporal coordination of movement of different body segments and that related timing abnormalities may be partly compensated by vision. Abnormal intersegmental timing may be a highly sensitive indicator of a deficient ability to assemble complex movements in patients with basal-ganglia dysfunction. This abnormality may be apparent even when the overall movement goal of reaching a target is preserved and normal movement synergies appear to be largely intact.

Aged↗

PubMed2005

Interlimb coordination following stroke.

Studies investigating whether simultaneous bilateral movements can facilitate performance of the impaired limb(s) of stroke patients have returned mixed results. In the present study we compared unilateral limb performance (amplitude, cycle duration) with performance during an interlimb coordination task involving both homologous (both arms, both legs) and non-homologous (one arm, one leg) limbs in stroke participants (n=7) and healthy age-matched controls (n=7). In addition, the effect of on-line augmented visual feedback on interlimb coordination was investigated. Participants performed cyclical flexion-extension movements of the arms and legs in the sagittal plane paced by an auditory metronome (1 Hz). Movement amplitudes were larger and cycle durations shorter during homologous limb coordination than non-homologous coordination. Compared with unilateral movements both groups had reduced movement amplitudes and the stroke group increased cycle duration when interlimb coordination tasks were performed. These effects were most evident during non-homologous (arm and leg) coordination. No evidence of facilitation of the impaired limb(s) was found in any of the interlimb coordination conditions. Augmented visual feedback had minimal effect on the movements of control participants but lead to an increase of cycle duration for stroke participants.

Adult↗

PubMed1983

The effects of varying lower-lip displacement on upper-lip movements: implications for the coordination of speech movements.

Upper-lip and lower-lip movements were transduced in the inferior-superior dimension in five normal-speaking subjects during four tasks. In task 1 visual feedback was used to manipulate the maximum displacement of the lower lip during speech. The upper lip elevated significantly less for the opening gesture when the amount of opening from the lower lip was increased. The upper lip moved to significantly lower positions for bilabial closure when the distance to be moved by the lower lip was increased. In task 2 the same procedures were followed with a bite block between the teeth. The bite block did not significantly change the interactions between lips for the opening gesture. The interactions were larger for bilabial closure with the bite block. In task 3 different vowels instead of visual feedback were used to manipulate lower-lip displacement. The relations between lips were similar to those found in task 1. In task 4 it was shown that these relations between lips are not found in nonspeech lower-lip movements. The interactions between lips are discussed in relation to models of speech motor control, including spatial targets, mass-spring systems, and planned trajectories.

Adult↗

PubMed1999

Latency of voluntary cancellation of the human vestibulo-ocular reflex during transient yaw rotation.

Volitional suppression of the initial vestibuloocular reflex (VOR) was studied in ten normal humans, aged 29+/-8 years (mean+/-standard deviation, SD), who were rotated about a vertical axis centered between the otoliths. Rotations consisted of steps in acceleration of 2800, 1600, 1000, or 500 degrees/S2 delivered at unpredictable times in unpredictable directions in the horizontal plane. As a test of the VOR, subjects were asked to attend to an earth-fixed target located 500 cm away that was either continuously visible or extinguished immediately before rotation. The gain of the VOR (angular eye velocity/angular head velocity) was 0.78+/-0.01 (mean+/-standard error of the mean, SE) during the period 35-45 ms after the onset of head rotation and 0.952+/-0.005 during the period 125-135 ms after the onset of head rotation. Subsequent rotations were performed during viewing of a target that moved with the head (cancellation). Cancellation was studied under three conditions of target visibility: (1) with the target always visible; (2) with the target always extinguished immediately prior to head rotation; or (3) with the target unpredictably extinguished half of the time immediately before each rotation. Cancellation responses showed individual idiosyncrasies, but certain features were common to most subjects. During cancellation, the VOR response generally differed from the earth-fixed target condition in that there was usually a small decrease in slow-phase VOR gain followed by an oppositely directed saccade. During the highest acceleration (2800 degrees/s2), the latency of the earliest statistically significant gain decrease for cancellation, as compared with the earth-fixed target condition, averaged 48+/-5 ms (mean+/-SE) from the onset of head rotation, although it was significantly shorter in one subject who had an onset at 14+/-2 ms. The latency of cancellation increased as head acceleration decreased such that, for each stimulus, cancellation began when the head was displaced an average of 1.4+/-0.1 degrees (-/+SD). Because VOR cancellation generally occurred before the availability of visual feedback or under conditions when vision was never permitted, it is inferred that cancellation is triggered by a threshold eye position or an estimate of head rotation based on integration of vestibular afferents. Cancellation occurred significantly earlier with a visible target than with an extinguished target only at the lowest peak head acceleration of 500 degrees/s2. Corrective saccades with a visible target occurred later for head accelerations of 500 and 1000 degrees/s2 than for greater head accelerations. Significant effects of target illumination on the latencies of both saccades and cancellation occurred at least 80-90 ms after the onset of head rotation, consistent with the earliest available visual feedback. This longer latency of saccades for visible as compared with extinguished targets may be analogous to a release of fixation, as occurs with express saccades. The latency difference due to target visibility was not related to prediction, since it was unchanged under conditions of random target illumination.

Acceleration↗

PubMed2003

Virtual reality simulator for vitreoretinal surgery.

AIM: To develop computer simulation of steps in vitreoretinal surgery using virtual reality technology. MATERIAL AND METHODS: A workstation with three-dimensional position tracking stylus was attached to a Pentium II desktop PC with a graphic accelerator. Computer algorithms were developed using Open GL and Microsoft Visual C++ languages to control the interaction and update the visual feedback tracking the instruments. Soft tissue computer modelling was carried out to mimic the removal of a vitreous opacity. Lens touch with the instruments was also detected. Mathematical modelling to allow for lens distortion was taken into account. RESULTS: A virtual reality computer model has been developed that can simulate initial steps of vitreoretinal surgery. Soft tissue modelling of the vitreous opacity and its removal by the vitrector was successfully simulated. The movements of the active and passive instruments in the dummy eye corresponded to the movements on the computer screen. On evaluation of the system, there was a minimal but discernable time lag between the stylus movement and the visual feedback. There was no tactile feedback when the lens touch was simulated. No further complex vitreoretinal surgery simulation was possible at this stage.

Algorithms↗

PubMed2005

Is the diaphragm motion probability density function normally distributed?

During radiotherapy treatment planning, the margins given to the clinical target volume to form the planning target volume accounts for internal motion and set-up error. Most margin formulas assume that the underlying distributions are independent and normal. Clinical data suggests that the set-up error probability density function (pdf) can be considered to have an approximately normal distribution. However, there is evidence that internal motion does not have a normal distribution. Thus, in general, a convolution of the two pdfs should be performed to determine the total geometric error. The goals of this article were to (1) determine if the internal motion pdf due to respiration can be characterized using a normal distribution, and (2) if not, determine if the total geometric uncertainty for combining internal motion and set-up error can be characterized by a normal distribution. Sixty fluoroscopy diaphragm motion data sets were obtained using three breathing training types: free breathing, audio instruction, and visual feedback. Diaphragm motion was used as a surrogate for liver and lung cancer motion. The data were analyzed with normality tests in the following groups: (1) single motion measurements, (2) combined motion measurements for each patient, and (3) combined motion measurements for all patients. Following this analysis, the diaphragm motion pdfs were convolved with a set-up error pdf, and the standard deviation of the set-up error pdf at which the total geometric error pdf became normal was determined. At set-up error standard deviation values of at least 0.27 and 0.1 cm for free breathing, 0.57 and 0.42 cm for audio instruction, and 0.55 and 0 cm for visual feedback, for single motion measurements and combined motion measurements for each patient, respectively, total geometric error pdfs became approximately normal. When the motion measurements for all the patients were combined, diaphragm motion pdfs were approximately normal for all feedback types. Therefore, for treatment planning purposes in the absence of individual patient measurements, the diaphragm motion pdf can be considered an approximately normal distribution. However, care should be taken when determining a margin based on individual patients measurements as the total geometric error will, in general, not be normally distributed.

Artifacts↗