Reaching During Virtual Rotation: Context Specific Compensations for Expected Coriolis Forces

Abstract

Subjects who are in an enclosed chamber rotating at constant velocity feel physically stationary but make errors when pointing to targets. Reaching paths and endpoints are deviated in the direction of the transient inertial Coriolis forces generated by their arm movements. By contrast, reaching movements made during natural, voluntary torso rotation seem to be accurate, and subjects are unaware of the Coriolis forces generated by their movements. This pattern suggests that the motor plan for reaching movements uses a representation of body motion to prepare compensations for impending self-generated accelerative loads on the arm. If so, stationary subjects who are experiencing illusory self-rotation should make reaching errors when pointing to a target. These errors should be in the direction opposite the Coriolis accelerations their arm movements would generate if they were actually rotating. To determine whether such compensations exist, we had subjects in four experiments make visually open-loop reaches to targets while they were experiencing compelling illusory self-rotation and displacement induced by rotation of a complex, natural visual scene. The paths and endpoints of their initial reaching movements were significantly displaced leftward during counterclockwise illusory rotary displacement and rightward during clockwise illusory self-displacement. Subjects reached in a curvilinear path to the wrong place. These reaching errors were opposite in direction to the Coriolis forces that would have been generated by their arm movements during actual torso rotation. The magnitude of path curvature and endpoint errors increased as the speed of illusory self-rotation increased. In successive reaches, movement paths became straighter and endpoints more accurate despite the absence of visual error feedback or tactile feedback about target location. When subjects were again presented a stationary scene, their initial reaches were indistinguishable from pre-exposure baseline, indicating a total absence of aftereffects. These experiments demonstrate that the nervous system automatically compensates in a context-specific fashion for the Coriolis forces associated with reaching movements.

The Influence of Passive Haptic Feedback and Difference Interaction Metaphors on Presence and Task Performance

“…Some movements, such as those made to reach a virtual object or to wave to virtual avatars, might suggest that participants actually believe that they are within the VE. Hence, postural movements seem to be an interesting indicator of presence, as reported by other authors (Cohn, DiZio, & Lackner, 2000;Held & Durlach, 1993;Prothero, Parker, Furness, & Wells, 1995;Sheridan, 1992;Slater, Usoh, & Steed, 1995). Nichols, Haldane, and Wilson (2000) visually classified participants' reactions to a startling event and found that the results of this measurement correlated positively with the reported sense of presence.…”

“…The studies have attempted to measure behaviors such as reactions with an avatar (Bailenson et al, 2001;Bailenson et al, 2008), in order to measure social presence; movements to avoid a danger such as a virtual cliff (Slater, Usoh, & Steed, 1995); or induced movements or vection (Cohn et al, 2000) as a consequence of virtual scenes in movement. Following the approach of objectively estimating presence, we propose a procedure based on measuring reactions to events originated within the VE.…”

Reaching Within a Dynamic Virtual Environment

“…During most active motions the individual and the external world are moving at the same time. While there is ample evidence that dynamic visual inputs affect motor behavior, (e.g., disrupting upper extremity movement trajectory and endpoint [5] and increasing postural instability [6,7]), the weighting of such visual information and the exact role that visual motion plays in human motor control is not well understood. In recent years, virtual reality technology has emerged as a powerful tool to study motor control in healthy subjects and in patients with stroke or labyrinthine deficiency [8][9][10] because it enables us to manipulate the visual world.…”

Adaptation to a Space-variant Visuomotor Delay can Cause Neglect-like Effects on Drawing Symmetry

“…In adaptation studies, the internal representation is typically evaluated from the movements of participants following visual or force perturbations. Throughout the adaptation, the participants modify the kinematics and dynamics of their movements to reduce task-related errors and to maximize task success (Krakauer et al, 2000, Cohn et al, 2000, Simani et al, 2007, Shadmehr and Mussa-Ivaldi, 1994. A common way to assess the adaptation and the construction of an internal model is by examining aftereffects when the perturbation is unexpectedly removed.…”