The effect of varying the visual context on trajectory planning

1. 5 cm Direct Visual Feedback (DVF) Indirect Visual Feedback (IVF) Conclusion (1) Under direct vision, 3D pointing movements evidenced a curvature that increased as a function of target eccentricity. when similar movements are executed in a indirect visual feedback condition (video-controlled pointing movements), trajectories tended to be straight whatever the direction of the movement, suggesting a control of hand displacement in extrinsic coordinates, as movements performed in a two-dimensional space. This variation of hand path, depending on the direct or indirect feedback condition, suggests that perceptual constraints may dominate biomechanical constraints. Individual performance in the evaluation of the starting position Mean angular direction of the movement evaluation 45° 0° In the 45° condition both starting position and movement direction are judged according to visual signals. 45° 0° The effect of varying the visual context on trajectory planning and perceptual awareness of one’s own performance 1 Psychology and Neurocognition Laboratory (CNRS UMR-5105), Grenoble, France Richard Palluel-Germain1, Frederic Boy1, Jean-Pierre Orliaguet1, Y. Coello2 2 URECA, Université Lille3, 59653 Villeneuve d'Ascq, France. The effect of varying the visual context on trajectory planning In order to define the nature of the variables used by the motor system to plan goal directed movements, a large set of behavioral studies examined trajectories carried out by the hand in a reaching movement. Concerning 3 dimensional (3D) movements it has been shown that the shape of the trajectory, carried out by the hand, was curve and depended on movement direction (e.g., Atkenson & Hollerbach, 1995; Desmuget et al., 1997; Osu et al., 1997). This suggests that 3D movements are planned in intrinsic space in which the control parameter is the position of each of the joints contributing to the movement. The goal of the present study is to show that the visual constraints generated in situations of remote visual control could affect trajectory planning. More precisely, we hypothesize that 3D movements executed with a 2D visual feedback are planned to be straight in extrinsic space. Method Results 10 particpants were asked to perform 3D pointing movements toward dots (19 mm circles) located at 20°, 40°, 60° and 80° to the right with respect to the sagital axis and at 20 cm from the starting position. Each subject performed pointing movements in an Indirectand in aDirect Visual Feedback condition (respectively, IVF and DVF conditions). In the IVF condition direct vision of the workspace was precluded. A video camera recorded arm displacements (1:1 spatial relationship) and transmitted continuously and in real time movement images on a video screen located 0.50 cm from the head. In the DVF condition subjects directly viewed a similar arrangement of the workspace. In each condition ten pointing movements were performed toward each target A path curvature index (PCI) was calculted. A significant interaction was observed between visual feedback and target eccentricty: Path curvature was influenced by targets eccentricity only in the DVF condition and trajectories are straighter in the IVF Condition. The effect of varying the visual context on perceptual awareness of one’s own performance The goal 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 motor response carried out under a remote visual feedback. Visual bias is expected to be more influential when evaluating the spatial aspect of the workspace than when evaluating the dynamical components of the response. Method and results I Sensorimotor adaptation II Evaluation Tasks Participants had to perform 20 three-dimensional pointings to a target disposed on the table in two conditions of presentation of the visual feedback: • Once subjects were adapted to the visual bias : • In the Spatial Evaluation task (SE), subjects were asked to point to the initial hand location and to trace on the table the direction of the movement they carried out (i.e. Evaluating Where the movement was performed). • In theMovement Reproduction (MR) task, after being rapidly replaced on the starting position, they were asked to reach for the target in a single movement (i.e. Evaluating Howthe movement was performed) In the 0° condition(control)the visual hand-to-target gap was aligned with the actual gap In the 45° conditionthe camera was rotated by 45° clockwise so that the hand and the target appeared on the screen as displaced in opposite direction 0° 45° Spatial Evaluation task Condition 45° Condition 0° In the 1st trials of the 45° condition motor performance is influenced by the biased visual feedback. But, after 20 trials, motor performance isadaptedto the visual-kinesthetic discordance (straight trajectories) 45° 0° Conclusion (2) Movement reproduction We found dissociation in the influence of visual information in two non-visual evaluations of previous sensorimotor performance. We propose that when judging one’s own motor performance, intrinsic (proprioception and efferent-copy related signals) or extrinsic (visual) signals are electively processed depending upon the dimension of the movement that is evaluated (spatial or dynamical aspects). Perceiving one’s own motor production relies on separate sensory integration processes that depend on the dimension of action that is judged, suggesting a dissociation between perceptual and motor awareness. Ipsilat. Arm:Similar pattern of error in both 45° & 0° conditions (4.7 deg & 0.28 deg respectively). Production of unbiased estimates (i.e. close to the veridical direction). Contral. Arm: Different pattern of error for 45° (-26.8 deg) with respect to the 0° condition (3.85 deg) References Boy, F., Palluel-Germain, R., Orliaguet, J.P., Coello, Y.(2005). Dissociation between "where" and "how" judgements of one's own motor performance in a video-controlled reaching task., Neuroscience Letters, 386. Palluel-Germain, R., Boy, F., Orliaguet, J.P., Coello, Y. (2004). Visual and motor constraints on trajectory plannig in pointing movements. Neuroscience Letters, 372.