title: Fitts' law is not continuous in reciprocal aiming.
abstract: It takes longer to accomplish difficult tasks than easy ones. In the context of motor behaviour, Fitts' famous law states that the time needed to successfully execute an aiming movement increases linearly with task difficulty. While Fitts' explicit formulation has met criticism, the relation between task difficulty and movement time is invariantly portrayed as continuous. Here, we demonstrate that Fitts' law is discontinuous in reciprocal aiming owing to a transition in operative motor control mechanisms with increasing task difficulty. In particular, rhythmic movements are implemented in easy tasks and discrete movements in difficult ones. How movement time increases with task difficulty differs in both movement types. It appears, therefore, that the human nervous system abruptly engages a different control mechanism when task difficulty increases.
authors.affiliation: UMR 6233 Institut des Sciences du Mouvement E.J. Marey, CNRS and Université de la Méditerranée, 163 Avenue de Luminy, CP910, 13288 Marseille, France. raoul.huys@univmed.fr
authors.forename: Raoul
authors.initials: R
authors.lastname: Huys
authors.forename: Laure
authors.initials: L
authors.lastname: Fernandez
authors.forename: Reinoud J
authors.initials: RJ
authors.lastname: Bootsma
authors.forename: Viktor K
authors.initials: VK
authors.lastname: Jirsa
mesh_terms: D006801:Humans; D011597:Psychomotor Performance / Q000502:physiology*