Yann Coello

Movement control in golf putting

The purpose of the study was to understand how force is controlled for impact movements such as golf putting. Expert players (10) and control subjects (10) executed a putt as accurately as possible, in order to reach a target distance of 1, 2, 3, or 4 m. Movements of the club were recorded at 200 Hz via a SELSPOT system. Overall, the results showed that, in order to increase club velocity at the moment of contact with the ball with increasing distance of the target, subjects increased the downswing (DS) amplitude maintaining DS movement time constant. The change in force required to reach the different distances seemed to rely on an adjustment of the magnitude of the motor command within the same time period. Furthermore, our results showed that the movement of putting consists primarily in specifying the amplitude of the Backswing (BS) as a function of the distance of the target. This gives rise to a motor impulse originating the force-time function required for an adequate DS movement.

Embodiment, spatial categorisation and action

Despite the subjective experience of a continuous and coherent external world, we will argue that the perception and categorisation of visual space is constrained by the spatial resolution of the sensory systems but also and above all, by the pre-reflective representations of the body in action. Recent empirical data in cognitive neurosciences will be presented that suggest that multidimensional categorisation of perceptual space depends on body representations at both an experiential and a functional level. Results will also be resumed that show that representations of the body in action are pre-reflective in nature as only some aspects of the pre-reflective states can be consciously experienced. Finally, a neuro-cognitive model based on the integration of afferent and efferent information will be described, which suggests that action simulation and associated predicted sensory consequences may represent the underlying principle that enables pre-reflective representations of the body for space categorisation and selection for action.

Subjective Visual Vertical in Pitch and Roll in Right Hemispheric Stroke

Background and Purpose— Patients with right hemispheric stroke usually present an anticlockwise deviation of the subjective visual vertical (SVV) in the frontal (roll) plane. However, the occurrence of a similar disorder in the sagittal (pitch) plane has never been assessed. We investigated the subjective visual vertical in both planes in those patients. Methods— Eight patients, 4 with spatial neglect (N+) and 4 without neglect (N−), were compared with 4 healthy participants (C). They sat facing a luminous bar adjustable in rotation, either in the roll or in the pitch plane, and had to orient it in a vertical position, in the dark. Results— Compared with N− (−0.1°) and C (+1.1°) groups, N+ patients presented with a significant backward deviation (−4.5°) of the SVV in pitch. In accordance with other studies, they also showed a significant anticlockwise deviation (−8.8°) of the SVV in roll, as compared with N− (−1.9°) and C (+0.4°) subjects. This was associated with an opposite trunk deviation in both planes. Conclusions— While confirming the anticlockwise deviation already reported in the frontal plane, we showed for the first time to our knowledge a backward deviation of the SVV in neglect patients, which has to be put in relation with their balance disorders.

The visual vertical in the pusher syndrome: influence of hemispace and body position.

AbstractThe subjective visual vertical (SVV) was investigated in right brain–damaged (RBD) patients with pusher syndrome (PS) which is thought to stem from an erroneous perception of body orientation. The participants, sitting or lying, had to align a luminous rod with gravity. The task was performed in darkness with the rod centred to the body, or placed in the left (neglected) or in the right hemispace. The error, negligible in the control group (+0.3°; n = 6) and mild in the nonneglect non–pusher patients (–1.8°; n = 6), was clearly clockwise in the pusher neglect patients (N+P+; +7.2°; n = 4), but anticlockwise in the non–pusher neglect patients (–6.6°; n = 6). In both neglect groups, error was greater when the rod was in the left space. In N+P+ patients, the performance was strongly affected by posture (lying: +5.2°; sitting: +9.2°). Intra–individual variability was also much greater in this group. This study confirms the contralesional deviation of SVV in RBD patients without PS and suggests the presence of an opposite bias in RBD patients affected by PS.

Effect of Structuring the Workspace on Cognitive and Sensorimotor Distance Estimation: No Dissociation between Perception and Action

Independent processing of visual information for perception and action is supported by studies about visual illusions, which showed that context information influences overt judgment but not reaching attempts. The objection was raised, however, that these two types of performance are not directly comparable, since they generally focus on different properties of the visual input. The goal of the present study was to quantify the influence of context information (in the form of a textured background) on the cognitive and sensorimotor processing of egocentric distance. We found that the subjective area comprising reachable objects (probed with a cognitive task) decreased, whereas the amplitude of reaching movement (probed with a sensorimotor task) increased in the presence of the textured background with both binocular and monocular viewing. Directional motor performance was not affected by the experimental conditions, but there was a tendency for the kinematic parameters to mimic trajectory variations. The similar but opposite effects of the textured background in the cognitive and sensorimotor tasks suggested that in both tasks the visual targets were perceived as closer when they were presented in a sparse environment. A common explanation for the opposite effects was confirmed by the percentage of background influence, which was highly correlated in the two tasks. We conclude that visual processing for perception and action cannot be dissociated from context influence, since it does not differ when the tasks entail the processing of similar spatial characteristics.

Perceiving What Is Reachable Depends on Motor Representations: Evidence from a Transcranial Magnetic Stimulation Study

Background Visually determining what is reachable in peripersonal space requires information about the egocentric location of objects but also information about the possibilities of action with the body, which are context dependent. The aim of the present study was to test the role of motor representations in the visual perception of peripersonal space. Methodology Seven healthy participants underwent a TMS study while performing a right-left decision (control) task or perceptually judging whether a visual target was reachable or not with their right hand. An actual grasping movement task was also included. Single pulse TMS was delivered 80% of the trials on the left motor and premotor cortex and on a control site (the temporo-occipital area), at 90% of the resting motor threshold and at different SOA conditions (50ms, 100ms, 200ms or 300ms). Principal Findings Results showed a facilitation effect of the TMS on reaction times in all tasks, whatever the site stimulated and until 200ms after stimulus presentation. However, the facilitation effect was on average 34ms lower when stimulating the motor cortex in the perceptual judgement task, especially for stimuli located at the boundary of peripersonal space. Conclusion This study provides the first evidence that brain motor area participate in the visual determination of what is reachable. We discuss how motor representations may feed the perceptual system with information about possible interactions with nearby objects and thus may contribute to the perception of the boundary of peripersonal space.

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.

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.

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.

Embodied perception of reachable space: how do we manage threatening objects?

This study aimed at determining whether the size of reachable space is affected by the level of danger of some everyday manipulable objects. Two possibilities are examined: Dangerous objects affect the size of reachable space because of long-term semantic knowledge of their potential hurtful value or the on-line relation between objects’ dangerous attributes and the body. The experimental paradigm combined the danger value (dangerous/not dangerous) and the orientation of objects (e.g. pointing away from/towards the perceiver). Reachability judgments measured the size of peripersonal space, and perception of objects’ danger was estimated through questionnaires. Results revealed that, whatever the estimated level of objects’ danger, the extent of peripersonal space was reduced when the threatening part of dangerous objects was oriented towards participants, not when oriented away. This suggests that the characteristics of the here and now body-objects interaction are crucial in affecting the boundary of peripersonal space.