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At least 271 records · Page 15Linked to original sources

PubMed1995

On-line visual control of aiming movements?

Two experiments are reported which addressed the flexibility of visuo-motor processing by manipulating the availability of visual information while executing a discrete aiming movement. The flexibility of visuo-motor processing was tested by unexpectedly changing the proportion of the movement trajectory that visual feedback was present. Visual feedback was manipulated for a short (0.30), medium (0.60) or long (0.90) proportion of the trajectory within a block of trials. Each of these three proportions of vision occlusion (Experiment 1) or visual disclusion (Experiment 2) during the initial trajectory was examined. Within a visual condition, one of the three visual feedback proportions occurred with a high probability (p = 0.72), whereas the remaining two proportions each occurred with a low probability (p = 0.14). The results clearly indicated that spatial accuracy was determined by the actual vision period, independent of its probability of occurrence. The data are consistent with a model of continuous on-line control of movement execution.

Adult↗

PubMed2000

Muscle involvement during intermittent contraction patterns with different target force feedback modes.

OBJECTIVE: Assess the effect of different feedback modes during intermittent contractions on primary and assessory muscle activity. BACKGROUND: Intermittent contractions and physiological responses have been studied in laboratory settings. However, the feedback given to the subjects regarding timing and force level is generally not specified. DESIGN: Repeated measure design in which six subjects in randomized order performed two experimental conditions only differing in feedback mode. METHODS: Intermittent static elbow flexion was performed against either a fixed-force transducer (visual feedback) or a weight to be held in position (proprioceptive feedback) both corresponding to 30% maximal voluntary contraction. Contraction and relaxation timing of 6 and 4 s, respectively, was shown on a VDU screen as colour code identical in both conditions. RESULTS: Test contractions performed before and following 30 min of intermittent contractions showed larger fatigue development with proprioceptive feedback than visual feedback. Also rating of perceived exertion increased more during proprioceptive feedback than visual feedback. This may in part be explained by small differences in the mechanics during the two different feedback modes. In line with this, EMG recorded from four shoulder/arm muscles analyzed for amplitude and frequency showed similar activity initially; but later, during the 30 min contraction larger amplitudes were attained during proprioceptive feedback than visual feedback. CONCLUSIONS: Feedback mode significantly effects the muscle involvement and fatigue during intermittent contractions. RelevanceIntermittent contractions are common in many work places and various feedback modes are being given regarding work requirements. The choice of feedback may significantly affect the muscle load and consequently the development muscle fatigue and disorders.

Biomechanical Phenomena↗

PubMed1999

Visuo-motor adaptation in smokeless tobacco users.

Ten smokeless tobacco (ST) users and 11 non-smokers participated in a visuo-motor adaptation experiment in which the visual feedback of point-to-point horizontal arm movements, displayed in real-time on a computer screen, was rotated by 45 degrees counterclockwise for some trials. Visuo-motor performance between smokers and non-smokers was compared on three occasions, once after at least 8 h of tobacco abstinence (Session 1), a second time following ST intake (Session 2), and a third time 45 min after the original ST intake (Session 3). Non-smokers were tested at the same relative times as the smokers in the absence of any tobacco. Both groups performed the three conditions during each session: baseline (normal visual feedback), rotated visual feedback (45 degrees visual feedback rotation), and post-adaptation (normal visual feedback immediately following feedback rotation). Compared with non-smokers, ST users had significantly larger normalized jerk scores (a measure of movement smoothness) after ST intake during the adaptation and post-adaptation conditions in Sessions 2 and 3, but not during the baseline conditions, implying a differential effect of ST use specific to rotated visual feedback. Movement duration was also longer for smokers than for non-smokers after ST intake, but only in the post-adaptation condition. Overall the results suggest that ST use, and hence nicotine, has a detrimental effect on visuo-motor performance, particularly on movement smoothness.

Adaptation, Physiological↗

PubMed2003

On-line feedback control of human visually guided slow ramp tracking: effects of spatial separation of visual cues.

Visual feedback control of tracking movements is dependent upon a visual comparison of the guiding target and moving limb positions but the human fovea greatly restricts the area of high acuity vision. The effect of vertically separating the target and movement cues in a slow movement task is investigated. Subjects track a slow constant velocity target in the horizontal plane with wrist flexion controlled cursor movements. The effects of changes in the vertical distance between the two cues upon tracking performance were observed. When both cursors were at the same level, tracking was most accurate but showed significant intermittency around 2 Hz in frequency. Increased separation of cues reduced significantly both accuracy and intermittency; tracking was smoother but less accurate. Thus, feedback control is dependent upon the efficiency of positional comparison and hence becomes less effective as the cue separation increases. These results also support previous studies suggesting each cue makes an equal contribution to visuomotor feedback control, each acting as a reference to the other.

Adult↗

PubMed2005

Intermittent visuomotor processing in the human cerebellum, parietal cortex, and premotor cortex.

The cerebellum, parietal cortex, and premotor cortex are integral to visuomotor processing. The parameters of visual information that modulate their role in visuomotor control are less clear. From motor psychophysics, the relation between the frequency of visual feedback and force variability has been identified as nonlinear. Thus we hypothesized that visual feedback frequency will differentially modulate the neural activation in the cerebellum, parietal cortex, and premotor cortex related to visuomotor processing. We used functional magnetic resonance imaging at 3 Tesla to examine visually guided grip force control under frequent and infrequent visual feedback conditions. Control conditions with intermittent visual feedback alone and a control force condition without visual feedback were examined. As expected, force variability was reduced in the frequent compared with the infrequent condition. Three novel findings were identified. First, infrequent (0.4 Hz) visual feedback did not result in visuomotor activation in lateral cerebellum (lobule VI/Crus I), whereas frequent (25 Hz) intermittent visual feedback did. This is in contrast to the anterior intermediate cerebellum (lobule V/VI), which was consistently active across all force conditions compared with rest. Second, confirming previous observations, the parietal and premotor cortices were active during grip force with frequent visual feedback. The novel finding was that the parietal and premotor cortex were also active during grip force with infrequent visual feedback. Third, right inferior parietal lobule, dorsal premotor cortex, and ventral premotor cortex had greater activation in the frequent compared with the infrequent grip force condition. These findings demonstrate that the frequency of visual information reduces motor error and differentially modulates the neural activation related to visuomotor processing in the cerebellum, parietal cortex, and premotor cortex.

Adult↗

PubMed1996

Practice and Component Submovements: The Roles of Programming and Feedback in Rapid Aimed Limb Movements.

An experiment is reported in which subjects (N = 30) practiced rapid aimed limb movements (wrist rotations), with either full visual feedback, no visual feedback, or delayed visual feedback. Previous research has indicated that, with practice, subjects increase the distance and duration of ballistic primary submovements and decrease the distance and duration of corrective secondary submovements. The design of the present experiment permitted the determination of whether these practice-related changes are results of improved programming of the primary submovement or of more efficient processing involved in the production of secondary submovements. The results suggest that improved programming occurs with practice. Furthermore, it appears that visual feedback is not solely responsible for the production of secondary submovements.

Journal Article↗

PubMed1997

Adaptation to altered visual-vestibular feedback: mechanisms of maintenance and recovery.

Adaptation of perceived movement during head motion (apparent concomitant motion, ACM) and the subsequent elimination of adaptation were studied in two experiments. During the adaptation phase of both experiments, subjects performed voluntary 1-Hz head oscillations for 6 min while fixating a stimulus moving either in the same (with) direction as or the opposite (against) direction of head movements. In Experiment 1, ACM adaptation was measured following either a 1- or a 4-min delay after the adaptation phase. Results indicated some loss of adaptation during the additional 3-min delay, demonstrating a tendency of the system linking head and image to return to its preadaptation state following removal of an adaptation stimulus. In Experiment 2, subjects viewed a stimulus after adaptation that appeared to move minimally in the same manner as the adaptation stimulus during 3 min of head oscillations. No loss of adaptation was measured in these subjects between the beginning and the end of the 3-min interval. In another condition, subjects viewed a stimulus that appeared to move alternately in the same direction as and in the opposite direction of the adaptation stimulus during a similar 3-min interval following adaptation. ACM adaptation was substantially reduced during this 3-min interval. These results implicate two mechanisms that operate to either maintain or eliminate the short-term adaptation. One is passive and operates in the absence of visual feedback to eliminate the short-term adapted state, and the other responds to postadaptation visual feedback.

Adaptation, Psychological↗

PubMed2004

The parietal role in the sense of self-ownership with temporal discrepancy between visual and proprioceptive feedbacks.

One hypothesis on how we recognize an image of, for example, an arm as our own is through the co-occurrence of multiple sensory feedbacks, especially visual and proprioceptive feedbacks, in this process. It has been suggested that the parietal lobe is the region where proprioceptive and visual information of one's own body is integrated. This study investigated parietal cortical activity during a visual-proprioceptive synchrony judgment task in which visual feedback of the subjects' own passively moving hand was delayed. The subjects were required to judge whether or not there was a delay between the proprioceptive and visual feedbacks. Parietal cortical activity, which was measured using a 48-channel near-infrared spectroscopy (NIRS) apparatus, appeared to be modulated by the length of the delay between the visual and proprioceptive feedbacks. The bilateral superior/middle parietal areas were involved in experiencing the synchrony between the visual and proprioceptive feedbacks, whereas the right inferior parietal areas were strongly activated when discrepancy between the two feedbacks was detected. We postulate that the superior portion of the parietal lobe is essential for maintaining one's own body image, while the right inferior portion is involved in detecting movements of others.

Adolescent↗

PubMed2001

Visual control of isometric force in Parkinson's disease.

The current article reports an investigation of the influence of visual feedback on force production in Parkinson's disease (PD) that required subjects to maintain a constant amount of isometric force with their index finger and thumb with and without visual feedback. Eight PD and eight matched control subjects produced force at 5, 25 and 50% of their maximal voluntary contraction for 20 s. In conditions of full vision, the force trajectory and force target were viewed on the computer monitor. In the no visual feedback condition, visual feedback of the force trajectory vanished after the initial 8 s of the trial. The results showed that under the vision condition PD subjects produced levels of maximal and submaximal force that were similar to controls. Approximately 1.5-2.5 s following the removal of visual feedback, the force level in both subject groups decreased to steady-state levels. There was no difference in the time between visual feedback removal and the beginning of force decay in PD. There was a larger amount and faster rate of force decay after visual feedback removal in PD subjects compared to the controls. It is proposed that the increased force decay in PD does not result from sensory reflex deficits but from higher order sensory-motor memory processes.

Aged↗

PubMed1999

Visual control of automated handwriting movements.

This study provides new insight into the subtle interaction between visual feedback and automated handwriting movements. To separate effects of visual feedback from effects of speed/accuracy trade-off, subjects were trained to perform the tasks with rapid and automated movements. To control the visual feedback the written trace was presented only on a computer screen. In the first experiment the visual feedback of script size was manipulated. Subjects had to write the character combination "ll" onto a pattern of squares. In some trials the script size was unpredictably enlarged by 133% or reduced by 66%. Results showed that the ongoing "l" was not affected by the manipulation, but subjects adapted script size in the following "l" without any change in the kinematic characteristic of the movements. In a second experiment trajectory correction strategies in perturbed writing movements were studied. Two small boxes had to be connected by rapid and single-stroke movements. In some of the trials the position of the target box was changed unpredictably to a new position. Kinematic analysis revealed that the initial movement was not aborted, but rather a second independent movement was added to correct the trajectory to the new target. Thus, this proves that a distortion of visual feedback does not directly slow down open-loop movements to allow control of the motor output in a closed-loop mode. The ballisticity and automation was maintained during movement correction. Our findings fit perfectly well with recent theories of kinematic organization where complex movements are composed by elemental movement strokes.

Adolescent↗

PubMed1997

Prediction of complex two-dimensional trajectories by a cerebellar model of smooth pursuit eye movement.

A neural network model based on the anatomy and physiology of the cerebellum is presented that can generate both simple and complex predictive pursuit, while also responding in a feedback mode to visual perturbations from an ongoing trajectory. The model allows the prediction of complex movements by adding two features that are not present in other pursuit models: an array of inputs distributed over a range of physiologically justified delays, and a novel, biologically plausible learning rule that generated changes in synaptic strengths in response to retinal slip errors that arrive after long delays. To directly test the model, its output was compared with the behavior of monkeys tracking the same trajectories. There was a close correspondence between model and monkey performance. Complex target trajectories were created by summing two or three sinusoidal components of different frequencies along horizontal and/or vertical axes. Both the model and the monkeys were able to track these complex sum-of-sines trajectories with small phase delays that averaged 8 and 20 ms in magnitude, respectively. Both the model and the monkeys showed a consistent relationship between the high- and low-frequency components of pursuit: high-frequency components were tracked with small phase lags, whereas low-frequency components were tracked with phase leads. The model was also trained to track targets moving along a circular trajectory with infrequent right-angle perturbations that moved the target along a circle meridian. Before the perturbation, the model tracked the target with very small phase differences that averaged 5 ms. After the perturbation, the model overshot the target while continuing along the expected nonperturbed circular trajectory for 80 ms, before it moved toward the new perturbed trajectory. Monkeys showed similar behaviors with an average phase difference of 3 ms during circular pursuit, followed by a perturbation response after 90 ms. In both cases, the delays required to process visual information were much longer than delays associated with nonperturbed circular and sum-of-sines pursuit. This suggests that both the model and the eye make short-term predictions about future events to compensate for visual feedback delays in receiving information about the direction of a target moving along a changing trajectory. In addition, both the eye and the model can adjust to abrupt changes in target direction on the basis of visual feedback, but do so after significant processing delays.

Animals↗

PubMed2005

Supplementary motor area encodes reward expectancy in eye-movement tasks.

Neural activity signifying the expectation of reward has been found recently in many parts of the brain, including midbrain and cortical structures. These signals can facilitate goal-directed behavior or the learning of new skills based on reinforcements. Here we show that neurons in the supplementary motor area (SMA), an area concerned with movements of the body and limbs, also carry a reward expectancy signal in the postsaccadic period of oculomotor tasks. While the monkeys performed blocks of memory-guided and object-based saccades, the neurons discharged a burst after a approximately 200-ms delay following the target-acquiring saccade in the memory task but often fired concurrently with the target-acquiring saccade in the object task. The hypothesis that this postsaccadic bursting activity reflects the expectation of a reward was tested with a series of manipulations to the memory-guided saccade task. It was found that although the timing of the bursting activity corresponds to a visual feedback stimulus, the visual feedback is not required for the neurons to discharge a burst. Second, blocks of no-reward trials reveal an extinction of the bursting activity as the monkeys come to understand that they would not be rewarded for properly generated saccades. Finally, the delivery of unexpected rewards confirmed that in many of the neurons, the activity is not related to a motor plan to acquire the reward (e.g., licking). Thus we conclude that reward expectancy is represented by the activity of SMA neurons, even in the context of an oculomotor task. These results suggest that the reward expectancy signal is broadcast over a large extent of motor cortex, and may facilitate the learning of new, coordinated behavior between different body parts.

Action Potentials↗

PubMed2001

Intermittency in the visual control of force in Parkinson's disease.

Studies on the variability of motor output in Parkinson's disease have found contrasting results depending on the speed-accuracy constraints of the task. The first goal of this study was to determine if Parkinson's disease subjects are more variable than control subjects. The second goal of the study was to examine the limitations on visual and motor processing that contribute to the changes in force variability in Parkinson's disease. Eight mild to moderate Parkinson's disease (age: 68-80 years) and eight matched control (age: 68-80 years) subjects maintained a constant level of force at 25% of their maximum voluntary contraction with their index finger and thumb (grip precision task) for 20 s while online visual feedback of the total force was viewed on a computer monitor. During the force task, subjects received visual feedback at varying frequencies. The sampled visual feedback levels were presented at intervals as slow as every 5 s to as fast as every 0.04 s (0.2, 0.4, 0.8, 1.6, 3.2, 6.4, 12.8, 25.6 Hz). Force variability decreased over sampled visual feedback according to hyperbolic decay functions. The minimal visual processing time for both the Parkinson's disease and control subjects was approximately 160 ms. Motor output corrections were generated in both groups at a frequency of 1 Hz over a wide range of sampled visual feedback levels. However, the amplitude of the 1-2 Hz visuo-motor corrective process was amplified in Parkinson's disease, and this related to increases in force-output variability. The findings suggest that the basal ganglia are important for adjusting the amplitude of motor output at 1-2 Hz during visuo-motor feedback control.

Aged↗

PubMed1991

Kinaesthetic acuity of stutterers and non-stutterers for oral and non-oral movements.

Six adult stutterers and six normal speakers were instructed to make the smallest possible movements of the jaw, lower lip, tongue and right index finger, both with and without continuous visual feedback. In the non-visual (kinaesthetic) condition, the stutterers showed significantly larger minimal displacements (MDs) than did the non-stutterers for oral but not for finger movements. However, movements made in the presence of visual feedback were consistently smaller for all subjects than those made without, and no differences in MD were found between the stutterers and the non-stutterers when visual feedback was provided. The results suggested the presence of a sensorimotor deficit among at least some adult stutterers that is confined to oral movements. Given the importance of somatic sensory feedback during speech production, these observed orosensory deficiencies among stutterers may provide important insights into causal factors which contribute to the breakdowns in stutterers' speech.

Adult↗

PubMed1993

On-line versus off-line control of rapid aiming movements.

Recent studies have shown the importance of visual feedback during the rapid initial phase of aiming movements for the control of direction (e.g., Bard, Paillard, Fleury, Hay, & Larue, 1990; Blouin, Teasdale, Bard, & Fleury, in press; Teasdale, Blouin, Bard, & Fleury, 1991). In most of these studies, visual feedback conditions were presented in blocked sessions. Consequently, higher-order processes (e.g., feedforward and/or learning processes), along with on-line processing of visual feedback, might have contributed to the better accuracy found when subjects had visual feedback of only the initial portion of the movements (compared with movements without visual feedback). To test this possibility, we studied subjects' performance of rapid arm movements under different types of presentation (random, precued, and blocked) of the visual feedback conditions of the trajectory (no vision, initial portion only, and vision of the entire trajectory). Directional errors were larger in the no-vision condition than in both conditions with visual feedback. There were no differences among the presentation conditions, suggesting that on-line processing of visual information contributed to the control of the arm movements.

Journal Article↗

PubMed2002

Visual influence on postural control, with and without visual motion feedback.

Body sway was investigated in 20 healthy subjects to determine whether visual input must contain motion feedback information from the surroundings in order to influence postural control. Posturography was used to record body sway under the following visual conditions: eyes open with or without a restricted visual field; eyes open in ganzfield white light; eyes open in darkness with a head-fixed visual target; eyes open in darkness; and eyes closed in darkness. Stance was perturbed by means of a pseudorandomly applied vibratory stimulation to the calf muscles. Least sway was found with eyes open in an unrestricted visual field but increased in a restricted visual field. Greatest sway was found without visual motion feedback, i.e. under the following conditions: eyes closed; eyes open in darkness; eyes open in ganzfield white light; and with a head-mounted fixation point. Sway was significantly (p < 0.05) greater with eyes open in darkness compared with eyes closed during the initial 50 s with perturbations. After 150 s, sway was almost identical under the four test conditions without visual motion feedback. Standing with eyes open in darkness was initially a disadvantage compared with having the eyes closed. The postural control system may be programmed to expect visual feedback information when the eyes are open, which may delay changes in postural strategy.

Adaptation, Physiological↗

PubMed2004

A feedback model of visual attention.

Feedback connections are a prominent feature of cortical anatomy and are likely to have a significant functional role in neural information processing. We present a neural network model of cortical feedback that successfully simulates neurophysiological data associated with attention. In this domain, our model can be considered a more detailed, and biologically plausible, implementation of the biased competition model of attention. However, our model is more general as it can also explain a variety of other top-down processes in vision, such as figure/ground segmentation and contextual cueing. This model thus suggests that a common mechanism, involving cortical feedback pathways, is responsible for a range of phenomena and provides a unified account of currently disparate areas of research.

Algorithms↗

PubMed1999

Distributed Control in Rapid Sequential Aiming Responses.

The preparation and on-line control of short, rapid sequential aiming responses were studied in 3 experiments. Participants (N = 12 in Experiments 1 and 2, and 20 in Experiment 3) produced 3-segment responses (a) within self-initiation, simple reaction time (RT), and choice RT paradigms (Experiment 1); (b) without visual feedback under self-initiation conditions (Experiment 2); and (c) with and without visual feedback under simple RT conditions (Experiment 3). In all conditions in which participants initiated movement in response to an external imperative signal, the 2nd response segment was performed consistently slower than preceding and succeeding response segments. That pattern of segmental movement times was found whether or not visual feedback was available but was not evident when participants self-initiated their responses with or without visual feedback. The findings rule out the possibility that subjects' use of visual feedback is responsible for the slowing of the 2nd response segment under RT conditions and suggest that the programming of rapid sequential aiming responses can be distributed in pre- and postinitiation intervals.

Journal Article↗