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PubMed1998

Effects of variation in system responsiveness on user performance in virtual environments.

System responsiveness (SR) is defined as the elapsed time until a system responds to user control. SR fluctuates over time, so it must be described statistically with mean (MSR) and standard deviation (SDSR). In this paper, we examine SR in virtual environments (VEs), outlining its components and methods of experimental measurement and manipulation. Three studies of MSR and SDSR effects on performance of grasp and placement tasks are then presented. The studies used within-subjects designs with 11, 12, and 10 participants, respectively. Results showed that SDSR affected performance only if it was above 82 ms. Placement required more frequent visual feedback and was more sensitive to SR. We infer that VE designers need not tightly control SDSR and may wish to vary SR control based on required visual feedback frequency. These results may be used to improve the human-computer interface in a wide range of interactive graphical applications, including scientific visualization, training, mental health, and entertainment.

Data Display↗

PubMedDate not supplied

Optical merger of direct vision with virtual images for scaled teleoperation.

Scaled teleoperation is increasingly prevalent in medicine, as well as in other applications of robotics. Visual feedback in such systems is essential and should make maximal use of natural hand-eye coordination. This paper describes a new method of visual feedback for scaled teleoperation in which the operator manipulates the handle of a remote tool in the presence of a registered virtual image of the target in real time. The method adapts a concept already used successfully in a new medical device called the Sonic Flashlight, which permits direct in situ visualization of ultrasound during invasive procedures. The Sonic Flashlight uses a flat-panel monitor and a half-silvered mirror to merge the visual outer surface of a patient with a simultaneous ultrasound scan of the patient's interior. Adapting the concept to scaled teleoperation involves removing the imaging device and the target to a remote location and adding a master-slave control device. This permits the operator to see his hands, along with what appears to be the tool, and the target, merged in a workspace that preserves natural hand-eye coordination. Three functioning prototypes are described, one based on ultrasound and two on light microscopy. The limitations and potential of the new approach are discussed.

Algorithms↗

PubMed2006

Determinants of offline processing of visual information for the control of reaching movements.

The authors investigated the use of visual feedback as a form of knowledge of results (KR) for the control of rapid (200-250 ms) reaching movements in 40 participants. They compared endpoint accuracy and intraindividual variability of a full-vision group (FV) with those of no-vision groups provided with KR regarding (a) the endpoint in numerical form, (b) the endpoint in visual form, or (c) the endpoint and the trajectory in visual form (DEL). The FV group was more accurate and less variable than were the no-vision groups, and the analysis of limb trajectory variability indicated that their superior performance resulted primarily from better movement planning rather than from online visual processes. The FV group outperformed the DEL group even though both groups were obtaining the same amount of spatial visual information from every movement. That finding suggests that the effectiveness with which visual feedback is processed offline is not a simple function of the amount of visual information available, but depends on how that information is presented.

Adult↗

PubMed2001

Feedback-dependent modulation of isometric force control: an EEG study in visuomotor integration.

The primary purpose of this investigation was to examine the cortical mechanisms underlying visuomotor integration in an experiment directly manipulating visual feedback (control-signal gain) as participants executed a grasping task. This was accomplished by assessing human electroencephalograms in both time and frequency domains and relating these measures to the performance accuracy of isometric force control. The basic experimental manipulation consisted of subjects controlling a grip dynamometer and the subsequent force trace displayed on a computer monitor at various magnitudes of force output and control-signal gain. Several findings from this study were of interest. First, the effects of control-signal gain and its interplay with the magnitude of force were most evident across the parietal and frontocentral electrode locations--areas specifically related to multi-modal sensory evaluation (parietal lobe) and higher-order movement control (supplementary and mesial premotor areas). Second, electroencephalography (EEG) measures in the time domain, i.e., slow-wave potentials, were sensitive to control-signal gain only during the ramp phase of force production (period of reaching the target force), not the static phase (period of maintaining the target force level). Third, EEG measures within the frequency domain (event-related desynchronization), unlike the slow-wave potential measures, were sensitive to control-signal gain during the static phase of force production--a sensitivity that was directly related to improvements in the accuracy of isometric force control. The findings of this investigation are described in relation to the existent literature on human visuomotor integration with special attention paid to the distinct spatial and temporal electrocortical patterns exhibited under varying degrees of visual feedback and magnitudes of force output during grasping.

Adult↗

PubMed2004

On-line vs. off-line utilization of peripheral visual afferent information to ensure spatial accuracy of goal-directed movements.

Manual aiming movements are often initiated when one gazes at the target, while the hand is seen in peripheral vision. The objective of the present study was to determine whether vision of one's hand in peripheral vision and/or central vision as it progresses towards the target can be used to modulate the direction and the extent components of the initial movement impulse. Participants performed video aiming movements while vision of the cursor they were moving was permitted for its whole trajectory, 40 degrees to 15 degrees of visual angle, 15 degrees to 0 degrees of visual angle, or not visible at all. Movements were to be completed within prescribed movement times varying between 300 ms and 900 ms. The results did not reveal endpoint accuracy or variability differences between the 40 degrees -15 degrees and the 15 degrees -0 degrees visual feedback conditions. Both conditions yielded lower endpoint bias and variability than the no-vision condition from early on after movement initiation. This indicates that the visual afferent information available in the 40 degrees -15 degrees and the 15 degrees -0 degrees visual feedback conditions could be used to better plan upcoming movements than the no vision condition. From these data, it appears very unlikely that different portions of the retina are specialized for processing different movement attributes as has been suggested in the past (Paillard 1980; Paillard and Amblard 1985). Both the peripheral and central retina are apt at detecting on-line extent and direction errors in one's movement. In addition, the data cast serious doubts on the widely accepted proposition that the movement initial impulse is essentially ballistic.

Adult↗

PubMed2004

Deficits in the evolution of hand preshaping in Parkinson's disease.

Parkinson's disease (PD) results in various types of motor impairments including bradykinesia, tremor and rigidity. Recent research has implicated more fundamental processes at the source of the observed motor deficits. Among these, problems in the sequencing and/or timing of complex movements and in the execution of internally-guided tasks. Furthermore, PD patients exhibit procedural learning deficits which may complicate the interpretation of experimental results of studies involving novel sensorimotor tasks. The reach-to-grasp movement is a complex, overlearned sensorimotor task consisting of two semi-independent components, a relatively simple reach or transport phase and a more complex manipulation or prehension phase. In the present study, we used a novel technique in order to study the evolution of hand preshaping during the reach-to-grasp movement of PD patients and age-matched controls to objects of different shapes in three different spatial locations. Our results indicate that while PD patients are able to specify movement direction as well as controls, their hand preshaping exhibits substantial impairments. Other prehension measures, such as the time to peak aperture (TPA), indicate that PD patients delayed execution of the grasp until visual feedback of their hand was available. Overall, our results suggest that PD patients' internal guidance processes are severely disrupted, having to rely on visual feedback in order to modulate their hand shape to fit the contours of the target objects during a reach-to-grasp movement.

Aged↗

PubMed2001

Interactive 3-dimensional segmentation of MRI data in personal computer environment.

We describe a method of interactive three-dimensional segmentation and visualization for anatomical magnetic resonance imaging (MRI) data in a personal computer environment. The visual feedback necessary during 3-D segmentation was provided by a ray casting algorithm, which was designed to allow users to interactively decide the visualization quality depending on the task-requirement. Structures such as gray matter, white matter, and facial skin from T1-weighted high-resolution MRI data were segmented and later visualized with surface rendering. Personal computers with central processing unit (CPU) speeds of 266, 400, and 700 MHz, were used for the implementation. The 3-D visualization upon each execution of the segmentation operation was achieved in the order of 2 s with a 700 MHz CPU. Our results suggest that 3-D volume segmentation with semi real-time visual feedback could be effectively implemented in a PC environment without the need for dedicated graphics processing hardware.

Adult↗

PubMed1991

Vestibulo-ocular reflex suppression during high velocity head-free pursuit in normal subjects.

Recordings of head and smooth pursuit eye movement were made during head-free pursuit of a pseudo-random target motion stimulus. The pseudo-random stimulus was composed of 2 high velocity sinusoids, of frequency 0.4 and 1.3 Hz, with the velocity of the higher frequency being varied as a ratio of the lower frequency velocity between 0 and 2. Slow-phase gaze velocity gain for the lower frequency component decreased significantly with an increase in velocity ratio, and with an increase in target velocity above 60 degrees/s. Gaze velocity gain was frequently less than head displacement gain which remained fairly constant, indicating that the eyes had been driven in the opposite direction to head movement as a result of inability of suppress the vestibulo-ocular reflex. Similar effects were seen when visual feedback was degraded by tachistoscopic illumination of a target composed of 2 low velocity sinusoids (0.11 and 0.13 Hz). These results indicate that visual feedback, rather than head displacement, is essential for suppression of slow-phase vestibular eye movement during head-free pursuit, even at high stimulus velocities.

Feedback↗

PubMed2001

'Arm-reaching' neurons in the parietal area V6A of the macaque monkey.

In previous experiments we have found that several cells of area V6A in the macaque superior parietal lobule were activated by small and stereotyped movements of the arms (C. Galletti, P. Fattori, D. F. Kutz & P. P. Battaglini, Eur. J. Neurosci., 1997, 9, 410). This behaviour was not accounted for by retinal information, nor by somatosensory inputs from the arms. We now want to investigate whether V6A neurons are modulated by purposeful movements aimed at reaching visual targets or targets located outside the field of view. V6A neuronal activity was collected while monkeys performed arm movements during an instructed-delay reaching task in darkness. The task required the animal to reach out for a visual target in the peripersonal space and to bring the hand back to its body. Quantitative analysis of neuronal activity carried out on 55 V6A neurons showed that: (i) the great majority of neurons (71%) was significantly modulated during the execution of arm movements; (ii) 30% of neurons were significantly modulated during preparation of reaching; and (iii) modulations during both execution and preparation of reaching occurred in the absence of any visual feedback and were not due to eye movements. V6A reach-related neurons could be useful in guiding the hand to reach its target with or without visual feedback.

Action Potentials↗

PubMed2003

Matching different levels of isometric torque in elbow flexor muscles after eccentric exercise.

Human subjects generated a specified level of isometric torque with elbow flexor muscles of one arm, the reference arm, under visual feedback. They were then asked to generate what they perceived to be the same level, with the other arm, the indicator, but with no visual feedback. A number of torque levels, between 2% and 30% of maximum were used in the matching trials. Elbow flexors of one arm were then exercised eccentrically on a dynamometer. Immediately after the exercise, there was a large (40%) drop in maximum voluntary torque, as well as some soreness and swelling 24 h later, indicative of muscle damage. When the torque-matching experiment was repeated after the indicator arm had been exercised, the indicator signalled torque levels significantly below the reference level (P<0.05). When the reference arm was exercised, errors were in the opposite direction. Over the 4 days of testing post-exercise, errors became less as torque levels returned to normal. When errors were expressed in terms of maximum torque post-exercise, they were significantly reduced. This suggested that subjects were using as a matching cue the perceived effort required to generate a given level of torque rather than the level of torque itself. Persisting matching errors, from 24 h onwards after the eccentric contractions, were proposed to include a component attributable to the muscle soreness. Changes in electromyogram recorded after eccentric exercise were consistent with the effort-matching hypothesis. The muscle's torque-angle relationship was used to estimate matching ability in the absence of fatigue. One forearm was placed at various angles and its reference torque was matched by the other, the indicator, always at 90 degrees. Again, matching errors were consistent with an interpretation based on a match of effort rather than torque.

Adolescent↗

PubMed2004

Online control of the direction of rapid reaching movements.

Online visual control of the direction of rapid reaching movements was assessed by evaluating how human subjects reacted to shifts in seen hand position near movement onsets. Participants ( N=10) produced saccadic eye and rapid arm movements (mean duration = 328 ms) towards a peripheral visual target in complete darkness. During the saccade, visual feedback of hand position could be shifted by 1, 2, 3 or 4 cm perpendicularly to the main movement direction. The resulting discrepancies between visual and proprioceptive information about hand position were never consciously perceived by the subjects. Following the shifts, hand trajectories deviated from those produced in a control condition (without shift) in order to bring seen hand position closer to the target. Globally, the deviations corresponded to 45% of the shifts, regardless of their magnitude or movement duration. This finding highlights not only the efficiency of visual feedback processing in online motor control but also underlines the significant contribution of limb proprioception.

Adult↗

PubMed2004

Development of visuomotor representations for hand movement in young children.

The stability and adaptability of visuomotor representations for hand movement in young children was investigated using a visuomotor adaptation paradigm in which the real-time visual feedback of pen movement was rotated 45 degrees clockwise during exposure trials. Four, six, and eight-year-old children performed line drawings to visual targets, from a common centered position ("center-out task"), in the horizontal plane under normal (pre-, and post-exposure), and rotated (exposure) visual feedback conditions. Analysis of pre-exposure trials indicated that older children performed faster, straighter, smoother, and showed more patterned movements than the younger children. Initial direction of movement, computed at 80 ms after movement onset, showed a progressive tuning of movement direction with increasing age. On introduction of the screen cursor rotation, all age group children showed improvement in their planning (initial directional error) and execution (movement time, movement length, root mean square error, and normalized jerk) error scores from early to late-exposure trials, but the 4-year-olds were less affected than older age children by the distortion during the early exposure period. Moreover, only the oldest group of children showed significant after-effects during post-exposure trials indicating that only this age group learned the internal model of the distorted environment. The absence of after-effects for initial movement direction observed in the two younger age groups suggest that these children might have less developed (i.e. more broad) internal visuomotor representations for hand movements, and that their internal representations are sharpened (i.e. tuned) with visuomotor experience.

Age Factors↗

PubMed2006

The effect of the Müller-Lyer illusion on the planning and control of manual aiming movements.

Two experiments used Müller-Lyer stimuli to test the predictions of the planning-control model (S. Glover, 2002) for aiming movements. In Experiment 1, participants aimed to stimuli that either remained the same or changed upon movement initiation. Experiment 2 was identical except that the duration of visual feedback for online control was manipulated. The authors found that the figures visible during movement planning and online control had additive effects on endpoint bias, even when participants had ample time to use visual feedback to modify their movements (Experiment 2). These findings are problematic not only for the planning-control model but also for A. D. Milner and M. A. Goodale's (1995) two visual system explanation of illusory bias. Although our results are consistent with the idea that a single representation is used for perception, movement planning, and online control (e.g., V. H. Franz, 2001), other work from our laboratory and elsewhere suggests that the manner in which space is coded depends on constraints associated with the specific task, such as the visual cues available to the performer.

Adult↗

PubMedDate not supplied

[Use of biological feedback in persons with complete new dental prostheses during the initial period of functional adaptation].

Adductor muscles muscular tone of new complete denture wearers in the period of initial functional adaptation was investigated as well as the use of visual feedback with EMG method for more efficient use of dentures. Thirteen persons of 63 years average were investigated. Action potential of masseter muscle surface layers and pterigoid muscles anterior layers on both sides were registered. Subjects were instructed how to adjust the mandible from the rest position to the full contact with upper denture teeth and to keep it that way for 5 minutes, 3 times a day. Intensity of measured muscle activity was controlled immediately after denture insertion as well as 7, 14 and 21 days after insertion. The greatest amplitude values of all of four examined muscles were registered after denture insertion. Expected changes due to the use of visual feedback had favorable effect on muscular tone lowering during the following period. Maximal therapeutic tone was reestablished.

Action Potentials↗

PubMed2005

The use of non-motion-based cues to pre-programme the timing of predictive velocity reversal in human smooth pursuit.

Human smooth pursuit eye movements are principally driven by visual feedback and cannot normally be initiated at will. However, when tracking periodic motion, smooth eye movements reverse direction prior to target reversal, driven by anticipation, not visual feedback. Here, we investigate cognitive control over such eye reversals. Target stimuli were discrete double ramps-constant speed (30 degrees /s) rightwards followed by similar leftward movement, reversal time ranging from 420 ms to 840 ms. Three experimental conditions were examined. In the precued condition, double ramps of randomised reversal time were presented. Prior to ramp presentation audio precues were given with an interval indicating start and reversal time of the unseen, upcoming double ramp. Subjects were able to use these cues to voluntarily control timing of anticipatory eye reversal, so that when occasional false precues gave underestimates of target reversal time, eye reversal occurred before target reversal. Precued eye reversal times were comparable to those in a second, predictable condition, in which double ramps with identical reversal time were given repeatedly without precues. In contrast, reversal occurred much later in a third, reactive condition, also without precues, when unexpected early target reversals occurred sporadically within a series having identical, predictable reversal times. The findings provide evidence that timing of anticipatory smooth eye movement, both at the start of the double-ramp and at its reversal, can be independently controlled at will using non-motion-based timing cues.

Brain↗

PubMed1988

Patterns of rotary pursuit performance in clumsy and normal children.

The present study is concerned with the development of motor programs in clumsy children. In order to investigate this, the performance of clumsy and normal children on a rotary pursuit tracking task was compared. The performance of the clumsy group was inferior to that of the control group in terms of time on target, but the pattern of performance across successive trials was broadly similar for the two groups, suggesting a progression from control by visual feedback to control by motor programs. It was concluded that the performance of clumsy children on the rotary pursuit task may be limited more by impaired visual feedback control than by an impairment in the ability to develop motor programs.

Attention↗

PubMed1999

Dissociation of 'on-line' and 'off-line' visuomotor control of the arm by focal lesions in the cerebellum and brainstem.

Visuomotor control of the arm was assessed in a single case study of a subject with focal lesions in the cerebellum and brainstem. A dissociation between 'on-line' and 'off-line' visuomotor control was revealed: impairments in 'on-line' visuomotor control included inaccuracy of tracking velocity, increase in spatial pointing variability and a delay in simple reaction time; whereas the patient was able to adapt to a gain change in 'off-line' visual feedback during a pointing task, and his adaptation was less affected than that of control subjects by trial-to-trial random fluctuations in 'off-line' visual feedback. We conclude that focal damage in the cerebellar peduncles may be principally responsible for this dissociation.

Adaptation, Physiological↗

PubMed1988

Endurance tests of the masticatory system on different bite force levels.

Endurance tests of the masticatory system were performed in three different groups of healthy volunteers in order to investigate the relation between bite force and endurance time on different force levels. The subjects clenched a bite fork until exhaustion. Some tests were performed with and others without visual feedback of the exerted force. It was found that the subjects could sustain the maximal bite force practically at the same level during the recording time with visual feedback. The exerted force varied during the non-feedback recordings and generally decreased on the forceful levels. The average endurance time increased at lower bite force levels and the relation between force and endurance time is described. The average integrated time-force areas did not differ between the test levels. It is concluded that endurance tests in the clinic may be performed on submaximal bite force levels.

Adult↗