Biomedical subjects

José L Contreras-Vidal

Publications and source records attributed to José L Contreras-Vidal.

9 recordsLinked to original sources

PubMed2006

Development of forward models for hand localization and movement control in 6- to 10-year-old children.

An active kinesthetic-to-visual matching task was performed by 15 children aged 5-10 years and five young adults. The task required the participants to locate the target visually while performing center-out drawing movements to the located visual targets in the absence of visual feedback of hand/pen motion. Movement time (MT), terminal end-point position error (EPE), and initial directional error (IDE) were measured. The general finding is that the end-point error variability, representing the joint localization probability distributions for proprioceptive localization of the hand and visual localization of the target, was largest for the youngest children, but did not differ from one another for the older age groups. The localization distributions, as characterized by principal component analysis, showed that both errors in extent and direction were significantly larger in the youngest children. These error distributions could not be accounted for by initial localization errors prior to movement onset in the children. It is likely that at least some portion of the increased movement variability seen during sensorimotor development in young children can be attributed not only to immature control mechanisms per se, but also to partial, not yet stable, forward representations for hand localization which are used for movement perception, planning, and control.

Age Factors↗

PubMed2006

Magnetoencephalographic artifact identification and automatic removal based on independent component analysis and categorization approaches.

Artifact signals from eye movements, heart beat and muscle activity contaminate magnetoencephalographic (MEG) signals generated from the neural activities inside the brain. Rejection of contaminated trials not only causes data loss, but can also significantly increase the experimental time or even prevent the analysis of highly contaminated or noisy data. We combined the use of independent component analysis (ICA) and clustering methods to isolate the artifacts from MEG signals. Threshold-based clustering analyses based on the topographic pattern, statistical aspects and power spectral patterns of independent components (ICs) successfully identified ICs related to certain types of artifacts. Unsupervised neural network based on the Adaptive Resonance Theory (ART) also categorized the artifact ICs, albeit with lower accuracy. Performance of the identification methods were evaluated with measurements of underestimation and overestimation of the target artifactual ICs. The combination of threshold-based clustering and ART-2 neural network categorization methods demonstrated the best identification performance. Comparison between contaminated and artifact-cleaned MEG signal waveforms showed the efficiency of the proposed methods of artifacts rejection. The analysis of the artifact components suggested the possibility of automatic artifact removal based on general templates.

Algorithms↗

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↗

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↗

PubMed2004

Dynamic estimation of hand position is abnormal in Parkinson's disease.

Parkinson's disease (PD) is widely viewed as a disorder of central motor control. However, recent studies suggest that disordered kinesthetic processing may also contribute to bradykinesia and hypometria in PD. To examine the hypothesis that abnormal kinesthesia in PD would result in impaired hand motion estimation used for motor control, we tested PD patients, elderly people, and young adults in an active, multi-joint kinesthetic-to-visual matching task. To minimize initial localization errors, visual information about the starting position was always available. The participants performed center-out drawing movements to visual targets in the absence of visual feedback of hand/pen motion at their preferred speed. Movement time (MT), end-point position error (EPE), and initial directional error (IDE) were measured. No detrimental effects of aging were observed; however, the PD group showed prolonged MTs and higher EPE scores as compared to the elderly and young groups. Principal component analysis of the end-point error distributions showed that the PD patients had larger variability in both the extent and direction axes. These results suggest that PD patients have abnormal proprioception and deficits in the central processing and integration of kinesthetic signals, resulting in the incorrect assembly of multiple sensorimotor inputs into a motor plan. It is hypothesized that altered kinesthesia in PD causes improper estimation of hand motion used for motor control due to the degraded maintenance of a dynamic internal hand representation.

Adult↗

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↗

PubMed2003

Adaptation to display rotation and display gain distortions during drawing.

The relationship between movement extent and movement direction coding mechanisms was investigated using a visuomotor adaptation paradigm. To determine if these mechanisms are either modular or interdependent, young healthy college students were tested while they performed a visually guided drawing task that incorporated varying combinations of movement distance and direction distortions. Analysis of participants' standardized movement duration, initial directional error, and movement length over the course of the adaptation process revealed a certain degree of interdependence between direction and extent coding mechanisms. Specifically, changes in final adaptation levels and after-effects depended on the order of introduction of the visual distortions. This interaction can be characterized as unidirectional, where alterations in rotational feedback interfere with subsequent adaptation to gain changes, whereas alterations in "display gain" do not significantly impede the adaptation to "display rotation". Moreover, simultaneous exposure to gain and rotational distortions resulted in better learning. The results argue against an independent coding of movement direction and extent during adaptation by the central nervous system.

Adaptation, Physiological↗

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↗

PubMedDate not supplied

Visuomotor adaptation in normal aging.

Visuomotor adaptation to a gradual or sudden screen cursor rotation was investigated in healthy young and elderly subjects. Both age groups were equally divided into two subgroups; one subgroup was exposed to 11.25 degrees step increments of visual feedback rotation, every 45 trials (up to a total of 90 degrees), whereas a second subgroup was subjected to 90 degrees rotation from the onset of exposure. Participants performed discrete, horizontal hand movements to virtual targets in four randomized directions. Targets appeared on a computer screen in front of them, and a board prevented vision of the hand at all times. Differential effects of aging on visuomotor adaptation were found, depending on the time course of the visual distortion. In both age groups, early exposure to the sudden visual feedback distortion resulted in typical spiral-like trajectories, which became straighter by late exposure. However, the final adaptation level was reduced in the aged group, although the aftereffects were similar. When subjects were exposed to the gradual distortion, no statistically significant differences in measures of adaptation with advancing age were found. In this case, both age groups appeared to adapt equally. However, after removal of the distortion, elderly subjects showed reduced aftereffects as compared with the young group. These findings suggest differential effects of aging on adaptation to gradual versus sudden visual feedback distortions, and may help to explain the conflicting results obtained in previous visuomotor adaptation studies.

Adaptation, Physiological↗