title: Visual guidance of arm reaching: online adjustments of movement direction are impaired by amplitude control.
abstract: Most reaching arm movements have amplitude and direction constraints. Here we investigated the interdependence of these movement parameters in terms of visual control. To do so, we asked human adults to look and reach toward targets such that, in a first experiment, both movement amplitude and direction had to be controlled. Randomly, hand visual feedback was shifted near arm movement onset to influence movement direction, movement amplitude or both. Because the visual shifts occurred during ocular saccades, they were not consciously perceived. The rapid reaching movements (mean duration = 334 ms) were slightly influenced by the visual shifts (approximately 15% and 8% of visual adjustment for movement direction and amplitude, respectively). Moreover, directional adjustments varied according to amplitude adjustments (and vice-versa). We thus examined, in a second experiment, the effect of relaxing the requirement to control movement amplitude. Asking participants to control only movement direction led to substantial directional adjustments (49%) based on shifted hand visual feedback. Overall, these findings indicate that the control of movement amplitude constrains the online adjustments of movement direction and that the mechanisms controlling movement amplitude and direction are not independent.
authors.affiliation: Institut des Sciences du Mouvement, Aix-Marseille University & CNRS, Marseille, France. fabrice.sarlegna@gmail.com
authors.forename: Fabrice R
authors.initials: FR
authors.lastname: Sarlegna
authors.forename: Jean
authors.initials: J
authors.lastname: Blouin
mesh_terms: D000328:Adult; D006225:Hand / Q000502:physiology*; D006801:Humans; D016014:Linear Models; D008297:Male; D009039:Motion Perception / Q000502:physiology*; D009068:Movement / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods; D011597:Psychomotor Performance / Q000502:physiology*; D012438:Saccades / Q000502:physiology*