On-line adjustments of grasping movements under visual, haptic and visuo-haptic guidance

Abstract

A sudden change of object properties during reach-to-grasp actions requires a fast update of the motor commands, which rely on the available sensory feedback during movement execution. While the role of visual feedback in on-line movement adjustments has been widely studied, far less is known about the contribution of other sensory systems. In particular, are the adjustments to haptically-sensed perturbations as fast as those found in vision? And, does the combined visuo-haptic information lead to even faster adjustments? In the present study, participants were asked to reach and grasp an object with their right hand while the object's size was occasionally perturbed during the movement. The availability of sensory feedback was modulated in three different conditions. In the visual condition, participants had full vision. In the haptic condition, the actions were under the guidance of haptic information from the left hand, while vision was prevented. In the visuo-haptic condition, participants had access to the combined visuo-haptic information. We found that haptic and visual conditions were similar in movement duration, but differed in terms of their kinematic properties. In the haptic condition, movements were faster in the initial phase, whereas in the visual condition, movements were faster in the final phase. Nevertheless, the grasp adjustment times to perturbations were similar (~200 ms). In the visuo-haptic condition, instead, the availability of both visual and haptic information reduced movement duration by ~80 ms and shortened the grasp adjustment time by ~50 ms. Our findings demonstrate that even though the available sensory information influences the action kine- matics, haptic input is as effective as the visual input to quickly perform on-line movement adjustments in response to a perturbation. Moreover, the combination of both inputs not only leads to faster movements, but it also speeds-up the reactions to sudden perturbations. Meeting abstract presented at VSS 2017