Biomedical subjects

Y Coello

Publications and source records attributed to Y Coello.

10 recordsLinked to original sources

PubMed2006

Where is the "straight ahead" in spatial neglect?

We investigated the subjective straight-ahead (SSA) projection of body-midline parts (head and trunk) in patients with neglect and patients with nonneglect, using a method disentangling lateral shift and lateral tilt components of the bias. Patients with neglect showed a similar counterclockwise SSA tilt for each body part and an ipsilesional lateral shift, more severe for the trunk than for the head. Thus, neglect results in a tilt of the body midline representation.

Adult↗

PubMed2006

Influence of visual constraints in the trajectory formation of grasping movements.

The main objective of the present study is to show that the visual context can influence the trajectory formation of grasping movements. We asked participants to reach and grasp a cylinder disposed at three different positions: -20 degrees , 0 degrees and 20 degrees of eccentricity with respect to the midsagittal axis. Grasping movements were performed in a direct and in an indirect visual feedback condition (i.e., controlled through a vertical video display). Results revealed that for grasping movements directed toward objects located at -20 degrees and 0 degrees , path curvatures of the wrist, the thumb and the index finger were significantly straighter in the indirect visual feedback condition. However, no significant difference concerning hand path curvature was observed when the movement was directed toward the object located at 20 degrees . This suggests that grasping movements controlled through a remote visual feedback tend to be planned in extrinsic space and that the effect of the visual context on movement planning appears to be not isotropic over the workspace.

Adolescent↗

PubMed2005

Dissociation between "where" and "how" judgements of one's own motor performance in a video-controlled reaching task.

The aim of the present study is to show that the sensorimotor system makes a differential use of visual and internal (proprioception and efferent copy) signals when evaluating either the spatial or the dynamical components of our own motor response carried out under a remote visual feedback. Subjects were required to monitor target-directed pointings from the images furnished by a video camera overhanging the workspace. By rotating the camera, the orientation of the movement perceived on the screen was either changed by 45 degrees (visual bias) or maintained in conformity with the actual trajectory (0 degrees ). In either condition, after completing twenty pointings, participants had to evaluate their visuomotor performance in two non visual testing: They were both asked to reach the target in a single movement (evaluation of "how to reach the target"), and to evaluate the mapping of the spatial layout where they acted (evaluations of "where the starting position was and, what movement direction was"). Results revealed that though motor performance in the 45 degrees conditions was adapted to the visuomotor conflict, participants' evaluation of the spatial aspect of the performance was affected by the biased visual information. A different pattern was revealed for the evaluation of "how" the target was reached which was not affected by the visual bias. Thus, it is suggested that segregated processing of visual and kinesthetic information occurs depending upon the dimension of the performance that is judged. Visual information prevails when identifying the spatial context of a motor act whereas proprioception and/or efferent copy related signals are privileged when evaluating the dynamical component of the response.

Adaptation, Physiological↗

PubMed2004

Visual and motor constraints on trajectory planning in pointing movements.

The aim of the present study was to show that planning and controlling the trajectory of a pointing movement is influenced not solely by physical constraints but also by visual constraints. Subjects were required to point towards different targets located at 20 degrees , 40 degrees , 60 degrees and 80 degrees of eccentricity. Movements were either constrained (i.e. two-dimensional movements) or unconstrained (i.e. three-dimensional movements). Furthermore, movements were carried out either under a direct or a remote visual control (use of a video system). Results revealed that trajectories of constrained movements were nearly straight whatever the eccentricity of the target and the type of visual control. A different pattern was revealed for unconstrained movements. Indeed, under direct vision the trajectory curvature increased as the eccentricity augmented, whereas under indirect vision, trajectories remained nearly straight whatever the eccentricity of the target. Thus, movements controlled through a remote visual feedback appear to be planned in extrinsic space as constrained movements.

Adolescent↗

PubMed2004

Position coding in a video-controlled pointing task with a rotated visual display: evidence for individual differences in visuo-proprioceptive interaction.

In video-controlled tasks, visuomotor performance is generally initially poor with rotated visual display, but improves through trial-by-trial learning. We hypothesise that the inaccurate processing of the visual hand-to-target vector mainly results from the persistent influence of non-visual information relating to arm posture. To test this hypothesis, arm-related proprioceptive and visual information were independently manipulated in a video-controlled pointing task. Analysis of movement vectors revealed that the target was located according to the visual hand but its proprioceptive orientation (Allelocentric(1) system of reference, N = 10), or according to the proprioceptive hand location and orientation (Egocentric system of reference, N = 8). The prevalence of one system of reference correlated with the accuracy of proprioceptive signals informing about arm posture. One obstacle in mastering video-controlled task results thus from the persistent influence of proprioceptive information in the spatial coding of visual goals for action, which however differs across individuals.

Adolescent↗

PubMed2003

Vision for spatial perception and vision for action: a dissociation between the left-right and near-far dimensions.

Neuropsychological and psychophysical studies have suggested that two distinct visual sub-systems are responsible for perception and action. One of the main psychophysical arguments for this is based on visual illusion such as the Induced Roelofs Effect (IRE), where the location of a visual target presented with an off-centre frame is misperceived when evaluated verbally, but not with a reaching response. This dissociated effect suggests the existence of two independent representations of visual space devoted, respectively, to categorisation and to egocentric localisation of reachable objects. These "cognitive" and "sensorimotor" representations have been assumed to be produced through specific anatomical pathways stemming from the primary visual cortex (respectively, the ventral and dorsal streams). To account for the dissociation found with the IRE, it has been suggested that only the cognitive system is sensitive to contextual information. However this view has been challenged by recent psychophysical studies demonstrating the influence of environmental cues on distance perception and the guiding of movement. In the present study, the IRE is re-evaluated but the near-far and right-left dimensions were dissociated. In agreement with previous findings, our results showed that the IRE in the right-left dimension gives rise to a perceptual misperception of target position with no effect on motor performance. Conversely, when the IRE was induced in the near-far dimension a misperception of the target position affected both perceptual and motor responses. This dissociation indicates that the spatial constraints of the task, and not only the nature of the response, interfere with sensitivity to contextual information leading to visual illusions. It is thus likely that the action system (imputed to the dorsal stream) can be sensitive to contextual information, at least when depth processing is emphasised.

Adult↗

PubMed2003

Visuokinesthetic realignment in a video-controlled reaching task.

The authors investigated the accuracy of horizontal pointing movements toward a visual target viewed on a vertical video monitor; the view included a directional distortion between perceptual and action spaces. Although accurate coding of the movement vector in a relative (visual) system of coordinates has been found to occur when there is a prismatic perturbation, provided that the hand and the target are continuously visible, such accurate performance has never been reported for video-controlled situations with larger deviations. To evaluate whether visual relative coding is task specific or depends on the magnitude of the induced misalignment, the authors manipulated the intensity of directional perturbation (10 degrees or 40 degrees) in a video-controlled task. Whatever the directional bias, participants (N = 40) were initially inaccurate but adapted quickly within a few trial rehearsals, with a concomitant recalibration of segmental proprioception. In contrast with prism studies, relative coding of the hand-to-target vector seemed not to be operative in video-controlled situations, suggesting that target location is specified in an egocentric system of reference that includes hand-related proprioceptive signals, despite the presence of a (consciously) detected misalignment between visual and kinesthetic systems.

Adolescent↗

PubMed2000

Pointing movement visually controlled through a video display: adaptation to scale change.

This study concerns the adaptation of motor system when the production of movement was visually controlled through a video display. The subjects had to perform a pointing movement in two visual-feedback conditions: they could see the displacement of their hand or only the final location of the hand on the videoscreen. By changing the zoom of the camera, the amplitude of the movement perceived on the screen was increased, decreased or held equal to the actual movement. Results showed that the movement adapted quickly to the apparent distance changes. In the full visual-feedback condition, the adaptation was smaller in magnitude than in the partial visual-feedback condition. Even though the actual movement was always the same, the subjects thought they carried out different movements. Therefore, the subjects did not use kinematic information provided by the kinaesthetic system but essentially visual information furnished by the video-screen. Taken together, these results show that adaptation to scale changes does not allow the achievement of the perception of a single working space but seems rather specific to each scale.

Adaptation, Physiological↗

PubMed1997

Effect of size and frame of visual field on the accuracy of an aiming movement.

The aim of this study was to analyse the effects of manipulating the size and contour of the visual field on the accuracy of an aiming task. Subjects were required to perform pointing movements without seeing their moving hand. The target was displayed in either a wide structured visual field (control condition), a narrow visual field with orthogonal frame, or a narrow visual field with circular frame. The visual information surrounding the target was always provided prior to movement onset, but during the execution of the movement on only half of the trials. Overall, the results showed that undershooting was a common performance characteristic in all of the conditions. In comparison to the control performance, an increase of the degree of undershoot was found when the target was displayed inside a narrower visual field. An additional radial error was found when the contour of the visual scene was circular, but only when the visual context was available during the movement. The same pattern of results was observed for variable error. However, angular errors were not found to vary over the different conditions. Overall, the findings suggested that the visual context contributed to the assessment of the target locations, and the subsequent motor programming. Furthermore, visual information aided the on-line control of the unseen hand, but the extent of this was dependent on the size and shape of the frame denoting the visual scene. Finally, in the absence of any unexpected perturbation, the en-route amendment of the arm trajectory, based on visual information processing, seemed to be more related to distance than azimuth control.

Adult↗

PubMed1996

Pointing movement in an artificial perturbing inertial field: a prospective paradigm for motor control study.

The present experiment focused on spatial accuracy and kinematics of fast pointing movements submitted to a multi-directional inertial perturbation. Pointing movements were performed without direct visual control, on a rotating armchair adding centrifugal and Coriolis forces to the natural displacement of the arm. The simultaneous action of these two forces induced a perturbation of the arm displacement both in amplitude and direction. Results showed that these two parameters were adjusted differently according to their own temporal constraint. Movement amplitude was adjusted on-line from the very first trial through the amendment of the whole acceleration pattern. Conversely, adjustment to directional perturbation was progressively achieved through several movement rehearsals. This correction appeared to be primarily due to a modification of the initial orientation of the arm trajectory, based seemingly on kinaesthetic knowledge from previous performances. The amendment of spatial parameters during motor response in the perturbing environment was discussed with an emphasis on the involvement of the cerebellum in reaching movement and the learning process.

Adult↗