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Results for “visual feedback”

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PubMed1999

Using frequency domain characteristics to discriminate physiologic and parkinsonian tremors.

The manner in which characteristics of time series in the frequency domain can enhance discrimination between physiologic and parkinsonian tremor when tremor amplitude is low was examined. Rest tremor and postural tremor with and without visual feedback were recorded twice in the two hands of a group of patients with Parkinson's disease (PD) (n = 21) and a group of healthy control subjects (n = 30) using displacement laser systems. Recordings were analyzed quantitatively using amplitude and seven frequency domain characteristics. Postural tremor with no visual feedback allowed the most efficient discrimination between the two groups of subjects especially in velocity and acceleration (derived from displacement) and allowed identification of more patients with PD as separate from the range observed in the control group. Moreover, the frequency domain characteristics that were investigated identified the majority of the patients even when amplitude did not. After eliminating redundant (correlated) characteristics, it was found that the frequency composition of tremor in PD can be described adequately with four characteristics, which are the most reliable, independent, and discriminative elements for detecting early or subtle modifications in tremor. Also, a series of finger flexions was found to enhance physiologic tremor but not tremor in PD. Discrimination of low-amplitude tremor in PD from normal physiologic tremor is enhanced by examining the median frequency of oscillations, the concentration of power in the power spectrum, and the distribution of power in particular ranges. Tremor measurement should not be limited to acceleration data as some information is more visible in velocity time series.

Acceleration↗

PubMed1989

Trajectories of reaches to prismatically-displaced targets: evidence for "automatic" visuomotor recalibration.

The present study examined the kinematics of unrestricted reaches to prismatically-displaced targets. The kinematic analysis allowed us (1) to document how and where in the reach adjustments were made to compensate for the prismatic displacement. (2) to detail the changes that occur in the characteristics of reaches during the course of adaptation to the prisms, and (3) to look at the effects of providing information (or not) to the subject about the presence and nature of the prismatic distortion. The experiment differed from classic studies of prism adaptation in that subjects were permitted full visual feedback of their moving limb at all times, and entire reaching movements were recorded in addition to terminal errors. Experimental subjects were tested either with large-displacement prisms of the sort typically used in such experiments (20 diopters) or with small-displacement prisms (5 diopters) the properties of which went undetected in uninformed subjects. By using small displacements, it was possible to examine the process of visuomotor recalibration directly, free of contamination by "conscious" correction strategies. There were no differences in the terminal accuracies of the reaches made by subjects in any of the conditions. The availability of visual feedback allowed subjects to place their finger accurately on the target, despite the fact that in some cases their vision was displaced by as much as 11.4 degrees to the right. When the entire reach was examined, however, it was found that the amount of curvature in the path increased when large or small diopter prisms were unexpectedly introduced, with the subjects showing large deviations to the right. This rightward deviation was corrected in the final approach with a larger terminal correction. On some occasions, nonetheless, corrections were observed very early in the course of the reaching movement and appeared to be part of a natural process of trajectory fine-tuning. Uninformed subjects exposed to either large or small prismatic displacements also showed evidence of adaptation through an increased number of on-line corrections which compensated for a tendency to reach into the side of space opposite to the direction of the displacement (a "negative after-effect" in the path of the reach). Moreover, when questioned after the experiment, it became clear that uninformed subjects exposed to small prismatic displacements had apparently failed to detect any visual displacement whatsoever. Taken together, these results suggest that visuomotor recalibration can take place "automatically" without feedback from terminal errors and without the use of conscious strategies.(ABSTRACT TRUNCATED AT 400 WORDS)

Adaptation, Physiological↗

PubMed2003

Adapting the fluoroscope to image-guided surgery.

Image-guided techniques have been well established in all surgical disciplines for years. To achieve an optimised work flow during image-guided surgery, the surgeon should be able to manipulate the visual feedback and therefore the imaging unit. C-arm fluoroscopy is the imaging modality routinely used for intraoperative imaging in orthopaedic surgery. The C-arm fluoroscope is positioned and handled by a radiographer on vocal commands, which means that the surgeon depends on external help to manipulate the visual feedback and the work flow is not optimised. The MEPUC interface adapts the C-arm fluoroscope to the needs of image-guided orthopaedic procedures. MEPUC is an acronym for Motorised Exact-Positioning Unit for C-arm. In the hardware component of the MEPUC a conventional C-arm fluoroscope is equipped with stepping motors. The software component allows the surgeon to control the motorised movements of the fluoroscope. The MEPUC interface enables the surgeon to position the C-arm fluoroscope independently in the operating room. Further advantages are achievable when the MEPUC interface is combined with surgical navigation, as this combination allows fully automatic reproduction of former projections. Clinical experience with the MEPUC interface suggests that the work flow for intraoperative imaging is improved and personal requirements reduced.

Fluoroscopy↗

PubMed1989

Task-based methods for evaluating electrically stimulated antagonist muscle controllers.

Single-joint motor neural prosthesis control algorithms were tested in a novel animal model. The model consisted of a human subject who provided joystick inputs to a controller. The controller output determined the stimulus activation levels of two antagonist muscles which manipulated the ankle joint of an intact, anesthetized cat. Using visual feedback, the subject manipulated the system to perform positioning tasks which simulated normal activity of an intact limb. Three controllers were evaluated, open-loop reciprocal control, P-D closed-loop reciprocal control, and open-loop cocontraction control. The results demonstrated that in the presence of visual feedback, open-loop cocontraction control compared favorably in performance to a P-D closed loop controller. This has a practical value for the implementation of clinical neural prostheses since it suggests that in some cases, feedback transducers may not be required for fine control.

Animals↗

PubMed2005

Reaching in children with and without developmental coordination disorder under normal and perturbed vision.

The aim of this study is to describe the reaching action of children with developmental coordination disorder (DCD) and to investigate whether their use of visual feedback during the time course of this action differs from that of normally developing children. Fifty-two children subdivided into 2 age bands (7-8 and 9-10 years) within 2 groups (with and without DCD) participated in this experiment. They were asked to reach for a target positioned either ipsilaterally or contralaterally to the reaching hand in 2 visual conditions: a condition where vision was unrestrained (normal vision) and a condition where they wore glasses with prismatic lenses (perturbed vision). An analysis of the experimental data indicates that the trajectories followed by the DCD group were longer and more curved than those of the control group. Further, the deceleration times were longer for the DCD group than for the normally developing children. The introduction of the prismatic lenses supports the idea that the use of visual feedback by children with DCD may be different from that in children without DCD.

Age Factors↗

PubMed2003

Limb position drift: implications for control of posture and movement.

In the absence of visual feedback, subject reports of hand location tend to drift over time. Such drift has been attributed to a gradual reduction in the usefulness of proprioception to signal limb position. If this account is correct, drift should degrade the accuracy of movement distance and direction over a series of movements made without visual feedback. To test this hypothesis, we asked participants to perform six series of 75 repetitive movements from a visible start location to a visible target, in time with a regular, audible tone. Fingertip position feedback was given by a cursor during the first five trials in the series. Feedback was then removed, and participants were to continue on pace for the next 70 trials. Movements were made in two directions (30 degrees and 120 degrees ) from each of three start locations (initial shoulder angles of 30 degrees, 40 degrees, 50 degrees, and initial elbow angles of 90 degrees ). Over the 70 trials, the start location of each movement drifted, on average, 8 cm away from the initial start location. This drift varied systematically with movement direction, indicating that drift is related to movement production. However, despite these dramatic changes in hand position and joint configuration, movement distance and direction remained relatively constant. Inverse dynamics analysis revealed that movement preservation was accompanied by substantial modification of joint muscle torque. These results suggest that proprioception continues to be a reliable source of limb position information after prolonged time without vision, but that this information is used differently for maintaining limb position and for specifying movement trajectory.

Adult↗

PubMed1997

Visuo-motor adaptation: evidence for a distributed amplitude control system.

We investigated the constraints for visuo-motor adaptation in human pointing movements. Subjects pointed at sequentially presented visual targets while visual feedback about their finger position was either absent (pre- and post-period), or was manipulated such as to require a gradual reduction of response amplitude (per-period). We found that response amplitudes were smaller during the post- than during the pre-period, which documents the existence of adaptation to distorted visual feedback. We further found that adaptation can transfer fully to untrained amplitudes (Exp. 1), although the amount of transfer may be reduced if trained and untrained amplitudes are substantially different (Exp. 2). However, selective adaptation of one amplitude but not another can also be yielded if the paradigm explicitly asks for it (Exp. 3), and if the two amplitudes differ by more than about 10 cm (Exp. 4). We conclude from these findings that the adapted mechanism consists of amplitude-specific elements, tuned to amplitude spans of some 10 cm.

Adaptation, Physiological↗

PubMed1986

Modifications in deaf children's vowel production: perceptual evidence.

This study examined the perceived changes in vowel articulation by profoundly deaf children as a function of the method of teaching: with visual feedback provided by the Computer Vowel Trainer (CVT) vs conventional methods. The assessment carried out by experienced listeners consisted in marking the sounds heard on the vowel quadrilateral. It was found that changes in perception were feedback and age dependent: younger children taught with the CVT were perceived as displaying more mobility in articulation and they approximated more closely the target vowels than their control counterparts or older children. Progress was evident in particular for back and central vowels. Analysis of perceived discrepancies between target and judged vowels, too, suggested that visual feedback was beneficial: perception of experimental children's utterances showed a marked reduction in substitutions with central vowels, a characteristic pattern of deaf speech. Comparison of these findings with the results yielded by the judgement of the same items by naive listeners indicated broad agreement between the two categories of assessors. Results were discussed in terms of the perceptual and articulatory intervening variables with reference to the specific advantages and constraints imposed by evaluating vowel quality on the vowel plane.

Articulation Disorders↗

PubMed1988

Vestibulo-ocular (VOR) abnormalities at high rotational frequencies in patients with Menière's disease.

Although visual feedback is required to maintain gaze stability during low-frequency rotations (below 1 Hz) because of suboptimal VOR gain in this frequency range, such behavior is not as evident at higher frequencies. Benson and Hydén et al. noted a steady increase in VOR gain in the higher-frequency range (2 to 5 Hz), where visual feedback has little effect. Similar behavior has also been reported in the monkey models. Eleven patients with diagnoses of Meniere's disease had tests of VOR and VOR cancellations performed with the use of pseudorandom oscillations as high as 5 Hz. The responses at various frequencies were compared with normal data from 17 subjects. The VOR gain in patients exhibited a more rapid rise at high frequencies than that observed in normal subjects. For example, at 3.5 Hz the normal gain was 1.09, whereas patients exhibited a gain of 1.35 (mean of 11 subjects). When the performance during VOR cancellation tasks was compared, Meniere's patients appeared to be less able to perform these tasks; however, when the values were compared by use of a cancellation index that compensates for any difference in VOR gain, this apparent difference disappeared.

Adult↗

PubMed1993

Contribution of vision to the stabilization of body sway in patients with spinocerebellar degeneration.

Body sway was recorded with closed eyes, open eyes and visual feedback for 30 s each. Thirteen patients with spinocerebellar degeneration and 17 age-matched normal controls underwent the examination. Four parameters (area, length, sums of frequency spectrum in the anterior-posterior and lateral directions) were computed. Furthermore, Romberg ratios between closed and open eye conditions [Romberg c/o] and Romberg ratios between closed eyes and visual feedback conditions [Romberg c/f] were computed. Four parameters were significantly greater in the patients with spinocerebellar degeneration than in the normal controls. However, three of eight Romberg ratios were significantly greater in the patients with spinocerebellar degeneration than in the normal controls. The results implied that the proprioceptive-posture loop was mainly disordered while the visuo-postural loop was intact in patients with spinocerebellar degeneration.

Cerebellum↗

PubMed1998

The effect of pre-movement delays on pointing accuracy in middle childhood.

In adults, the introduction of a pre-response delay has been shown to affect accuracy in pointing tasks while leaving accuracy in perceptual matching tasks unaffected. Here, we report on the effect of pre-movement delays on pointing accuracy in 6-10-year-old children. Children of this age group are of particular interest as their reliance on visual cues to monitor and correct their reaches appears to change during this period of development. Nineteen children were asked to point to the location of a target light after a delay of 0, 1, 2, or 4 s following target extinction. Performance was measured in two conditions: (i) open-loop, where the child reproduced the target locations in complete darkness, and (ii) with visual feedback, where information about hand position was available. Errors in the direction and in the amplitude of each reaching movement were recorded separately. The results show that temporal delay significantly affects the pointing movements of these children. Accuracy (mean) deteriorated after only 1 s whereas the precision (standard deviation) of the responses deteriorated after 4 s. Errors in amplitude, but not errors in direction, were reduced by the provision of visual feedback. Taken together, the findings suggest that amplitude and directional components of pointing in childhood utilise different sources of information, which differ in the extent to which temporal constraints operate.

Child↗

PubMed1995

Kinematic properties of upper limb trajectories in idiopathic torsion dystonia.

The kinematic properties of upper limb trajectories of simple reaching movements have been analysed in patients with idiopathic torsion dystonia (ITD). The velocity profiles differed from those of neurologically healthy subjects by being less symmetric. In several patients movement execution was slow due to a longer deceleration time. This phenomenon was even more conspicuous in the absence of visual feedback from the limb and was accompanied by a significant decrease in the final accuracy. These findings show that patients with ITD have deficits in central motor mechanisms beyond abnormal muscle activation patterns. Similarities between kinematic properties of patients with ITD and patients with Parkinson's disease including the deterioration of motor performance in ITD in the absence of visual feedback from the limb, suggest the existence of abnormalities in sensorimotor integration in both diseases.

Adult↗

PubMed2006

Imitation of facial expressions in schizophrenia.

Diminished facial expressivity is a common feature of schizophrenia that interferes with effective interpersonal communication. This study was designed to determine if real-time visual feedback improved the ability of patients with schizophrenia to imitate and produce modeled facial expressions. Twenty patients with schizophrenia and 10 controls viewed static images of facial expressions and were asked to imitate them. Half of the images were imitated with the use of a mirror and half were imitated without the use of a mirror. In addition, we examined whether practice in imitating and producing expressions improved the ability of participants to generate facial expressions on their own, without the aid of a model or mirror. Participants' facial expressions were photographed with a digital camera and each was rated for accuracy in producing characteristic facial expressions. Patients with schizophrenia were less accurate in imitating and producing facial expressions than controls, and real-time visual feedback did not improve accuracy in either group. Preliminary findings suggest that exposure to model expressions and practice in generating these expressions can improve the accuracy of certain posed expressions in schizophrenia.

Adult↗

PubMedDate not supplied

Cortical feedback increases visual information transmitted by monkey parvocellular lateral geniculate nucleus neurons.

We studied the effect of cooling the striate cortex on parvocellular lateral geniculate nucleus (PLGN) neurons in awake monkeys. Cooling the striate cortex produced both facilitation and inhibition of the responses of all neurons, depending on the stimulus presented. Cooling the striate cortex also altered the temporal distribution of spikes in the responses of PLGN neurons. Shannon's information measure revealed that cooling the striate cortex reduced the average stimulus-related information transmitted by all PLGN neurons. The reduction in transmitted information was associated with both facilitation and inhibition of the response. Cooling the striate cortex reduced the amount of information transmitted about all of the stimulus parameters tested: pattern, luminance, spatial contrast, and sequential contrast. The effect of cooling was nearly the same for codes based on the number of spikes in the response as for codes based on their temporal distribution. The reduction in transmitted information occurred because the differences among the responses to different stimuli (signal separation) were reduced, not because the variability of the responses to individual stimuli (noise) was increased. We conclude that one function of corticogeniculate feedback is to improve the ability of PLGN neurons to discriminate among stimuli by enhancing the differences among their responses.

Animals↗

PubMed2001

Modulating semantic feedback in visual word recognition.

According to the interactive activation framework proposed by McClelland and Rumelhart (1981), activation spreads both forward and backward between some levels of representation during visual word recognition. An important boundary condition, however, is that the spread of activation from lower to higher levels can be prevented (e.g., explicit letter processing during prime processing eliminates the well-documented semantic priming effect). Can the spread of activation from higher to lower levels also be prevented? This question was addressed with a choice task procedure in which subjects read a prime word and then responded to a target, performing either lexical decision or letter search depending on the color of the target. A semantic context effect was observed in lexical decision, providing evidence of semantic-level activation. In contrast, there was no semantic context effect in the letter search task, despite evidence of lexical involvement: Words were searched faster than nonwords. Further evidence of lexical involvement in the letter search task appeared in Experiment 2 in the form of greater identity priming for words than for nonwords. The results of these experiments are consistent with the conclusion that feedback from the semantic level to the lexical level can be blocked. Hence, between-level activation blocks can be instantiated in both bottom-up and top-down directions.

Adult↗

PubMed2002

Kinematics and dynamics are not represented independently in motor working memory: evidence from an interference study.

Our capacity to learn multiple dynamic and visuomotor tasks is limited by the time between the presentations of the tasks. When subjects are required to adapt to equal and opposite position-dependent visuomotor rotations (Krakauer et al., 1999) or velocity-dependent force fields (Brashers-Krug et al., 1996) in quick succession, interference occurs that prevents the first task from being consolidated in memory. In contrast, such interference is not observed between learning a position-dependent visuomotor rotation and an acceleration-dependent force field. On the basis of this finding, it has been argued that internal models of kinematic and dynamic sensorimotor transformations are learned independently (Krakauer et al., 1999). However, these findings are also consistent with the perturbations interfering only if they depend on the same kinematic variable. We evaluated this hypothesis using kinematic and dynamic transformations matched in terms of the kinematic variable on which they depend. Subjects adapted to a position-dependent visuomotor rotation followed 5 min later by a position-dependent rotary force field either with or without visual feedback of arm position. The force field tended to rotate the hand in the direction opposite to the visuomotor rotation. To assess learning, all subjects were retested 24 hr later on the visuomotor rotation, and their performance was compared with a control group exposed only to the visuomotor rotation on both days. Adapting to the position-dependent force field, both with and without visual feedback, impaired learning of the visuomotor rotation. Thus, interference between our kinematic and dynamic transformations was observed, suggesting that the key determinant of interference is the kinematic variable on which the transformation depends.

Adolescent↗

PubMed1995

Automated instrument tracking in robotically assisted laparoscopic surgery.

This paper describes a practical and reliable image analysis and tracking algorithm to achieve automated instrument localization and scope maneuvering in robotically assisted laparoscopic surgery. Laparoscopy is a minimally invasive surgical procedure that utilizes multiple small incisions on the patient's body through which the surgeon inserts tools and a videoscope in order to conduct an operation. The scope relays images of internal organs to a camera, and the images are displayed on a video screen. The surgeon performs the operation by viewing the scope images rather than performing the traditional "open" procedure, where a large incision is made on the patient's body for direct viewing. The current mode of laparoscopy employs an assistant to hold the scope and position it in response to the surgeon's verbal commands. However, this results in suboptimal visual feedback, because the scope is often aimed incorrectly and vibrates due to hand trembling. We have developed a robotic laparoscope positioner to replace the assistant. The surgeon commands the robotic positioner through a hand/foot controller interface. To further simplify the human-machine interface that controls the robotic scope positioner, we report here a novel scope-positioning scheme using automated image analysis and robotic visual servoing. The scheme enables the surgeon to control visual feedback and to perform surgery more efficiently without requiring additional use of the hands.

Algorithms↗

PubMed2006

Afferent contributions to digit force coupling and force level variation during performance of non-lift pinch.

Afferent contributions to the coordination of thumb and index finger forces during non-lift pinch were studied using an anesthetization case study design. Two subjects, one performing with and without digital anesthetization and one with intact sensation, produced dynamic pinch forces against a stable object, with and without visual feedback. Error corrections were less frequent post-anesthetization, and the cross correlation between digit forces was lower when sensation was removed. However, this decrease in cross correlation between digit forces seemed to reflect a loss in the magnitude of tightly coupled error corrections when sensation was removed, rather than more frequent deviations of force magnitude between the digit forces. Force-time output without visual feedback lacked these error corrections, and the correlation between digit forces remained high, irrespective of sensory status. Additionally, with vision occluded, the time rate of force change did not vary in a gradual manner as would be expected from a neural representation of a sinusoidal target, but was instead marked by sudden abrupt reversals of force rate of change, invariant of somatosensory status. The coupling of digit forces and rates of force change during non-lift pinch appear to be controlled primarily with feedforward mechanisms, where the lack of proprioceptive feedback does not seem to disrupt this coupling.

Adult↗