Allocentric visual cues influence online limb adjustments.

The present investigation sought to examine the nature of the visual information supporting online movement corrections. Participants were instructed to maintain gaze on the veridical endpoint of a neutral Müller-Lyer (ML) configuration in advance and during reaches performed with and without continuous limb vision. At movement onset, the stimulus array remained either the same (i.e., the neutral ML figure) or was perturbed to a fins-in or fins-out ML configuration. We reasoned that our illusion-based paradigm would provide a novel basis to examine the nature of the visual information supporting online movement corrections without the intrusion of putative biased ocular/manual motor interactions. Early reaching kinematics were refractory to the illusion-based perturbation; however, later kinematics were influenced in a direction consistent with the well-documented perceptual effects of the ML illusion. This illusory bias was present irrespective of the presence or absence of limb vision and the corollary extent reaches were controlled online. These results counter the view that metrical visual information specified in an egocentric frame of reference supports online movement corrections (e.g., Glover, 2004). Instead, the present results suggest online movement control is subserved by visual input specified via interacting egocentric and allocentric reference frames.