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PubMed1999

Common 3 and 10 Hz oscillations modulate human eye and finger movements while they simultaneously track a visual target.

1. A 10 Hz range centrally originating oscillation has been found to modulate slow finger movements and anticipatory smooth eye movements. To determine if an interaction or linkage occurs between these two central oscillations during combined visuo-manual tracking, frequency and coherence analysis were performed on finger and eye movements while they simultaneously tracked a visual target moving in intermittently visible sinusoidal patterns. 2. Two different frequencies of common or linked oscillation were found. The first, at 2-3 Hz, was dependent on visual feedback of target and finger tracking positions. The second, at around 10 Hz, still occurred when both target and finger positions were largely obscured, indicating that this common oscillation was generated internally by the motor system independent of visual feedback. Both 3 and 10 Hz oscillation frequencies were also shared by the right and left fingers if subjects used these together to track a visual target. 3. The linking of the 10 Hz range oscillations between the eyes and finger was task specific; it never occurred when eye and finger movements were made simultaneously and independently, but only when they moved simultaneously and followed the target together. However, although specific for tracking by the eyes and fingers together, the linking behaviour did not appear to be a prerequisite for such tracking, since significant coherence in the 10 Hz range was only present in a proportion of trials where these combined movements were made. 4. The experiments show that common oscillations may modulate anatomically very distinct structures, indicating that single central oscillations may have a widespread distribution in the central nervous system. The task-specific manifestation of the common oscillation in the eye and finger suggests that such mechanisms may have a functional role in hand-eye co-ordination.

Adult↗

PubMed1990

Errors in force estimation can be explained by tendon organ desensitization.

Here we report observations on the sense of muscle tension in human subjects and compare them with responses of tendon organs in cat hindlimb muscles. Human subjects learned under visual guidance to estimate a 4% maximum voluntary contraction (m.v.c.) of elbow flexors of one arm. When they were able to reproduce this force reliably without visual feedback, they repeated the estimation immediately after a 5 second m.v.c. or a 5 second period of relaxation. In a second experiment the 4% m.v.c. was generated under visual control with one arm, and matched with the other, test arm, without visual feedback. The matching task was then repeated after test arm conditioning. In both experiments subjects reported an accurate match using significantly more than the reference force ("overmatched") after an m.v.c. The overmatching was greatest during the first 5 second period following the conditioning contraction, and during the subsequent 20 seconds it gradually declined to near reference levels. The size of the matching error was directly proportional to the duration of the conditioning contraction. In the first experiment extension of the arm immediately following conditioning increased the error, in the second it slightly decreased it, although tension continued to be overmatched. In a series of experiments on the soleus muscle of anaesthetised cats responses of tendon organs to 10% of maximum contraction were seen to drop sharply when preceded by a conditioning maximum contraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1998

Closely spaced, fast dynamic movements in disparity vergence.

Conflicting theories exist describing how symmetrical vergence responses, the inward or outward turning of the eyes, are mediated. Classical theories describe vergence control as mediated by visual feedback. Extensive experimental evidence indicates that two distinct control components comprise the vergence response, and a recent theory supports the concept that one of these components is not visually guided. Occasionally, saccadic eye movements will respond to a single step stimulus with two closely spaced saccades, a behavior that is indicative of its switching control structure. If a portion of the vergence response is controlled in a manner analogous to saccades, then occasional double fast dynamic components might be expected. During this study, eye movements were recorded in response to symmetrical vergence stimuli of 2, 4, 6, 8, and 10 degrees steps. The left and right eye movements were subtracted to yield a net vergence response, and only convergent responses were investigated. Double fast dynamic components associated with high-velocity movements were observed in all four subjects studied. In double high-velocity component responses, the average peak velocity of both fast dynamic movements was always considerably less than the average peak velocity found when the response to the same stimulus was made with only a single component. Response amplitudes of single and double movements showed that if the primary component of a double response did not reach >/=80% of the stimulus amplitude, a secondary component would be generated to aid the movement. Plots of peak velocity as a function of response amplitude for both double and single movements followed the main sequence for vergence eye movements demonstrating that the first-order dynamic characteristics of all high-velocity components were the same. The time at which maximum velocity occurred (relative to stimulus onset) was also the same for both single component responses and the first component of double responses. The similarity in dynamics and timing implies that the high-velocity components were processed by the same controller mechanism. The existence of double high-velocity movements is indicative of an internal, switching mechanism similar to that found in saccades and is difficult to explain with theories that rely on visual feedback control alone.

Calibration↗

PubMed2001

Delayed grasping of a Müller-Lyer figure.

Grasping movements are more sensitive to the Müller-Lyer (ML) illusion when the response is made after a brief period of visual occlusion. It is unclear whether this effect is due to (1) the elimination of on-line visual feedback, or (2) reliance on a stored perceptual representation of the target for movement planning. Here participants grasped objects from within two forms of a ML figure in four visual conditions (full vision, open-loop, brief delay, and 2-s delay) and estimated object size in the full-vision condition. Peak grasping aperture was influenced by the ML figure in the full-vision condition, although to a much smaller extent than was true for manual size estimation. The effect of the ML figure on peak grasping aperture was substantially increased in the open-loop and delay conditions, which did not differ from one another. These findings highlight the importance of on-line visual feedback for the resistance of grasping to the ML illusion and also call to attention the relevance of task factors such as target previewing, the visuomotor relevance of illusion-inducing elements, and participant strategies.

Adult↗

PubMed1998

Comparison of a functional obstacle course with an index of clinical gait and balance and postural sway.

BACKGROUND: Older adults commonly experience falls because of balance and mobility problems. Better assessment methods are needed to understand and correct balance and mobility disorders. METHODS: We used a low technology, functional obstacle course (FOC) to measure balance and mobility in 352 community-dwelling elderly participants. To establish concurrent validity of the FOC, we compared performance on the FOC with two established measures of balance and mobility: performance on the Tinetti Index (TI) and postural sway area measured on a force platform. RESULTS: Bivariate correlation analyses revealed significant inverse correlations between FOC completion time, the TI balance and gait subscores, and the TI total score (r = -.73 to -.78). The FOC quality scores and TI balance and subscores gait and TI total scores (r = .76 to .82) were significantly positively correlated. FOC time had significant, but small, positive correlations with sway area with eyes open (r = .18) and closed (r = .17) and nonsignificant correlation with sway area with visual feedback. FOC quality also had significant, but smaller, inverse correlations with sway area with eyes open (r = -.024) and closed (r = -.015), and nonsignificant correlation with sway area with visual feedback. Regression analysis showed that TI gait and balance measures accounted for most of the variance found in FOC performance. CONCLUSIONS: Our findings support the position that the FOC and the TI measure dynamic balance, whereas postural sway measures a different aspect of balance. Advantages of the FOC include the evaluation of environmentally influenced falls and balance problems.

Accidental Falls↗

PubMed2004

Control of reaching movements in children and young adults with myelomeningocele.

The aim of the present study was to analyze the ability to programme and execute reaching movements in individuals with myelomeningocele (MMC) and in a control group. Thirty-one participants (18 males, 13 females; mean age 12 years 11 months, SD 2 years 7 months, range 9 to 19 years) with MMC and 31 participants (matched for age and sex) without disabilities were investigated. Reaching was performed with and without visual feedback toward three targets displayed on a computer screen and data were collected using a digitizing tablet linked to a computer. The kinematics of reaching were analyzed and analysis of variance was used for statistical analysis. Results showed that both groups were able to programme reaching movements under both visual conditions. Although the execution of reaching was poor in the MMC group compared with the control individuals, as indicated by larger end-point errors (p=0.002), less straight movements (p=0.018), and shorter deceleration phases (p=0.004), movement time was not prolonged in the MMC group. Those with shunt treatment (n=21) had more difficulties when visual feedback was provided. Those with symptoms of early brainstem dysfunction (n=5) had shorter deceleration phases under both visual conditions.

Adolescent↗

PubMed2001

Characteristics of somatosensory feedback in postural control during standing.

In the present study, the function of the somatosensory feedback system in postural control was investigated. For the sake of simplicity, the present study considered only balancing in the anteroposterior direction using the ankle strategy, in which the ankle moment is mainly used to maintain balance. To suppress the vestibular and visual feedback paths, a subject stood on a force-measuring platform with a fixed back support. Because the subject's body was immovable under these conditions, the subject controlled a computer model that simulated the subject's load at the ankles. Information about the sway angle of the model was fed through the somatosensory feedback path. Frequency response functions of the ankle moment in response to the sway angle were calculated. The experimental results suggest that the human somatosensory feedback system has derivative characteristics and, consequently, can maintain an upright posture by itself. The results were compared with those of previous studies on vestibular and visual feedback systems. The comparison reveals that subject-to-subject variance in the somatosensory system is significantly smaller than that in the other systems. This may indicate that the somatosensory feedback is the most automatic of the systems and plays a dominant role when a subject maintains an upright posture using the ankle strategy.

Adult↗

PubMed2000

Visual and haptic feedback in the control of force.

The ability to control index finger and elbow flexion forces was measured while subjects used either haptic feedback or both haptic and visual feedback to control the forces exerted. Over a 120-s time period subjects were able to control the finger forces ranging from 2 to 6 N to within 1 N using only haptic feedback, and elbow flexion forces to within 4.5 N over a force range of 10-30 N. At the same force amplitude there was no significant difference between the two muscle groups in the precision or accuracy with which the force could be controlled, suggesting that there is not a proximal to distal gradient in force control as has been found for the control of limb movement and position.

Adult↗

PubMed2002

Adaptation to changes in vertical display gain during handwriting in Parkinson's disease patients, elderly and young controls.

Parkinson's disease (PD) patients, matched elderly controls, and normal young subjects were tested using a visuo-motor adaptation paradigm in which the gain of the vertical component of the visual feedback of handwriting was manipulated in real-time. Handwriting was performed on a digitizer tablet and displayed in real-time on a computer screen in front of the participant. Vision of the hand and pen was occluded. Feedback could be normal (pre- and post-exposure conditions), smaller, or larger than the actual handwriting (exposure conditions). All groups showed a gradual adaptation that compensated for the distorted visual feedback during the exposure conditions. Moreover, all the groups showed significant after-effects during the post-exposure conditions suggesting that all the participants learned to compensate for the novel display gains. Taken together, these data suggest that the mechanisms for visuo-motor adaptation to changes in vertical display gain during handwriting are robust to aging and early stage of PD. These results may have implications for the treatment of micrographia in Parkinsonism.

Adaptation, Psychological↗

PubMed1996

Visual cues and the handwriting of older adults: a kinematic analysis.

Kinematic techniques determined the nature of any age-related changes in the fluency of handwriting movements and also the extent to which any changes can be related to a differential utilization of visual feedback. To quantitatively document the kinematics of handwriting movements, 24 young and 24 older adults were compared by having them write simple cursive letter ls 4 times on a graphics tablet, under 4 different visual conditions (no vision, non inking pen, inking pen, and lined paper). Pen tip position was sampled at 200 Hz, from which kinematic indexes of movement efficiency and consistency were derived. Quantitative differences in movement trajectories were found in the older adults, who produced less efficient movements with a concomitant increased utilization of external visual cues. Older adults made a differential use of visual feedback to modify movement trajectories, rather than to control the effects of neural noise. Handwriting movements of older adults resembled only to a limited extent those of patients with Parkinson's disease.

Adult↗

PubMed2004

Independent component analysis of dynamic brain responses during visuomotor adaptation.

To investigate the spatial and temporal changes in electro-cortical brain activity and hand kinematics during the acquisition of an internal model of a novel screen-cursor transformation, we employed single-trial infomax independent component analysis (ICA), spectral estimation, and kinematics methods. Participants performed center-out drawing movements under normal and rotated visual feedback of pen movements displayed on a computer screen. Clustering of task-related and adaptation-related independent components identified a selective recruitment of brain activation/deactivation foci associated with the exposure to the distorted visual feedback, including networks associated with frontal-, central-, and lateral-posterior alpha rhythms, and frontal-central error-related negativity potential associated with transient theta and low beta rhythms locked to movement onset. Moreover, adaptation to the rotated reference frame was associated with a reduction in the imposed directional bias and decreases in movement path length and movement time by late-exposure trials, as well as after-effects after removal of the visual distortion. The underlying spatiotemporal pattern of activations is consistent with recruitment of frontal-parietal, sensory-motor, and anterior cingulate cortical areas during visuomotor adaptation.

Adaptation, Physiological↗

PubMed2005

Neural correlates of reach errors.

Reach errors may be broadly classified into errors arising from unpredictable changes in target location, called target errors, and errors arising from miscalibration of internal models (e.g., when prisms alter visual feedback or a force field alters limb dynamics), called execution errors. Execution errors may be caused by miscalibration of dynamics (e.g., when a force field alters limb dynamics) or by miscalibration of kinematics (e.g., when prisms alter visual feedback). Although all types of errors lead to similar on-line corrections, we found that the motor system showed strong trial-by-trial adaptation in response to random execution errors but not in response to random target errors. We used functional magnetic resonance imaging and a compatible robot to study brain regions involved in processing each kind of error. Both kinematic and dynamic execution errors activated regions along the central and the postcentral sulci and in lobules V, VI, and VIII of the cerebellum, making these areas possible sites of plastic changes in internal models for reaching. Only activity related to kinematic errors extended into parietal area 5. These results are inconsistent with the idea that kinematics and dynamics of reaching are computed in separate neural entities. In contrast, only target errors caused increased activity in the striatum and the posterior superior parietal lobule. The cerebellum and motor cortex were as strongly activated as with execution errors. These findings indicate a neural and behavioral dissociation between errors that lead to switching of behavioral goals and errors that lead to adaptation of internal models of limb dynamics and kinematics.

Adolescent↗

PubMed1985

Early stages in the acquisition of a bimanual motor skill.

Children and adults were trained and tested on a coordinated bimanual task that required them to rotate both hands either at the same or at different angular velocities in order to move the pen of an X-Y recorder along three angles of slant (45, 67 and 22 degrees), and to rotate both hands in the same clockwise direction rather than as mirror image movements. Initially both groups exhibited a tendency to rotate both hands at the same angular velocity even when the task required differential motor output from the two hands. With visual feedback, the tendency toward synchronization, such that both hands moved at the same angular velocity, was asymmetrically distributed, but under blindfolded conditions such asymmetries disappeared. Accuracy of performance increased with practice; and visual feedback enhanced accuracy of performance. The findings suggest that during early stages in the acquisition of a bimanual skill, unintended bilateral coactivation occurs at multiple levels of motor organization; mirror associated movements are only one simple subset of unintentional intermanual synergies.

Adult↗

PubMed1993

Adaptive coordination and alignment of eye and hand.

Under spatial misalignment of eye and hand induced by laterally displacing prisms (11.4 degrees in the rightward direction), subjects pointed 60 times (once every 3 s) at a visually implicit target (straight ahead of nose, Experiment 1) or a visually explicit target (an objectively straight-ahead target, Experiment 2). For different groups in each experiment, the hand became visible early in the sagittal pointing movement (early visual feedback). Adaptation to the optical misalignment during exposure (direct effects) was rapid, especially with early feedback; complete compensation for the misalignment was achieved within about 30 trials, and overcompensation occurred in later trials, especially with an explicit target. In contrast, adaptation measured with the misalignment removed and without visual feedback after blocks of 10 pointing trials (aftereffects) was slow to develop, especially with delayed feedback and an implicit target; at most, about 40% compensation for the misalignment occurred after 60 trials. This difference between direct effects and aftereffects is discussed in terms of separable adaptive mechanisms that are activated by different error signals. Adaptive coordination is activated by error feedback and involves centrally located, strategically flexible, short-latency processes to correct for sudden changes in operational precision that normally occur with short-term changes in coordination tasks. Adaptive alignment is activated automatically by spatial discordance between misaligned systems and involves distributed, long-latency processes to correct for slowly developing shifts in alignment among perceptual-motor components that normally occur with long-term drift. The sudden onset of misalignment in experimental situations activates both mechanisms in a complex and not always cooperative manner, which may produce overcompensatory behavior during exposure (i.e., direct effects) and which may limit long-term alignment (i.e., aftereffects).

Journal Article↗

PubMed2004

Practice-related modulations of force enslaving and cortical activity as revealed by EEG.

OBJECTIVE: To examine the role of practice in the modification of force enslaving and motor-related cortical potentials using finger force production tasks. This study follows-up previous studies in our laboratory using experienced piano players. METHODS: Two experiments were performed. In Expt. 1, 6 subjects participated in a pre and post EEG session separated by 12 practice sessions which were conducted 3 days a week for 4 weeks. With visual feedback regarding the accuracy of force output, subjects produced one of two force levels with either their ring or index finger. Experiment 2 followed a similar procedure to that of Expt. 1 with additional visual feedback to the degree of finger independency. Both behavioral (isometric force output) and EEG data preceding and accompanying force responses were measured. RESULTS: In Expt. 1 we found that forced enslaving increased along with improved accuracy following 4 weeks of practice. We found a reduction of motor potential (MP) amplitude for the index but not the ring finger following practice. Experiment 2 showed an increase in accuracy and reduction in force enslaving after practice with adequate feedback. The amplitude of MP for the index finger also decreased after practice as in Expt. 1. In contrast, the amplitude of MP for the ring finger increased after practice. CONCLUSIONS: The present study extends our earlier work with piano players and shows the role of practice in modifying behavioral and cortical measures. The concluding theme emergent from our studies is that individuated finger control is not hard-wired, but rather plastic and greatly influenced by deliberate practice. SIGNIFICANCE: This research supports the idea that experience and practice are associated with changes in behavioral and EEG correlates of task performance and have clinical implications in disorders such as stroke or dystonia. Practice-related procedures offer useful approaches to rehabilitation strategies.

Adult↗

PubMed2000

Influence of arm movements on saccades in humans.

When reaching for an object we usually look at it before we touch it with the hand. This often unconscious eye movement prior to the arm movement allows guiding of the final part of the hand trajectory by visual feedback. We examined the temporal and spatial coordination of this control system by psychophysical measurements of eye and arm movements of naive human subjects looking or looking and pointing as fast as possible to visual targets in physical and virtual-reality setups. The reaction times of saccades to a step-displaced target were reduced, and the number of corrective saccades decreased, when the subject had to produce a corresponding simultaneous hand movement to the same target. The saccadic reaction time was increased when saccade and hand movement went in opposite directions. In a double-step task the reaction time for the second saccade was longer than for the first. Co-use of the hand leads to an additional increase of saccadic reaction time. Taken together this study shows an improvement in initial saccades if they are accompanied by hand movements to the same target. This effect might ensure that the reach target is foveated early and accurately enough to support the visual feedback control of the hand near the target. Longer reaction times for the second saccade to double-step displaced targets might reflect a saccadic refractory time intensified by simultaneous arm movements. These results are discussed in the light of recent findings from our laboratory on saccade- and reach-related neurons in the superior colliculus of macaque monkeys.

Adult↗

PubMed2006

Impairment of online control of reaching movements with aging: a double-step study.

This study investigated the influence of aging on the online control of goal-directed arm movements through visual feedback of target position. Two groups of human adults, aged 28 and 56 years on average, reached with their unseen hand for targets that were unexpectedly displaced sideways at movement onset. Both stationary and displaced targets were continuously illuminated, briefly lit or not visible. When no visual information of target position was available, only an auditory signal indicated the location of the target. Results showed that when the target remained stationary, visual information enhanced movement accuracy for both age groups. When the target was displaced, visual information contributed to greater and earlier corrections for both groups. However, young adults corrected for more of the 21 degrees target displacement than older adults (95% versus 72%). Moreover, first adjustments of movement trajectory were triggered faster by young adults as compared to older adults (339 ms versus 538 ms after movement onset). Therefore, the present results highlight the impairment of older adults to monitor online movement trajectory through visual feedback processes. The detrimental effect of aging is evident when large adjustments of trajectory are necessary to reach the target.

Acoustic Stimulation↗

PubMed2003

Effects of Parkinson's disease on visuomotor adaptation.

Visuomotor adaptation to a kinematic distortion was investigated in Parkinson's disease (PD) patients and age-matched controls. Participants performed pointing movements in which the visual feedback of hand movement, displayed as a screen cursor, was normal (pre-exposure condition) or rotated by 90 degrees counterclockwise (exposure condition). Aftereffects were assessed in a post-exposure condition in which the visual feedback of hand movement was set back to normal. In pre- and early-exposure trials, both groups showed similar initial directional error (IDE) and movement straightness (RMSE, root mean square error), but the PD group showed reduced movement smoothness (normalized jerk, NJ) and primary submovement to total movement distance ratios (PTR). During late-exposure the PD subjects, compared with controls, showed larger IDE, RMSE, NJ, and smaller PTR scores. Moreover, PD patients showed smaller aftereffects than the controls during the post-exposure condition. Overall, the PD group showed both slower and reduced adaptation compared with the control group. These results are discussed in terms of reduced signal-to-noise ratio in feedback signals related to increased movement variability and/or disordered kinesthesia, deficits in movement initiation, impaired selection of initial movement direction, and deficits in internal model formation in PD patients. We conclude that Parkinson's disease impairs visuomotor adaptation.

Adaptation, Physiological↗