Non-obstructing 3D depth cues influence reach-to-grasp kinematics

It has been demonstrated that both visual feedback and the presence of certain types of non-target objects in the workspace can affect kinematic measures and the trajectory path of the moving hand during reach-to-grasp movements. Yet no study to date has examined the possible effect of providing non-obstructing three-dimensional (3D) depth cues within the workspace and with consistent retinal inputs and whether or not these alter manual prehension movements. Participants performed a series of reach-to-grasp movements in both open- (without visual feedback) and closed-loop (with visual feedback) conditions in the presence of one of three possible 3D depth cues. Here, it is reported that preventing online visual feedback (or not) and the presence of a particular depth cue had a profound effect on kinematic measures for both the reaching and grasping components of manual prehension—despite the fact that the 3D depth cues did not act as a physical obstruction at any point. The depth cues modulated the trajectory of the reaching hand when the target block was located on the left side of the workspace but not on the right. These results are discussed in relation to previous reports and implications for brain–computer interface decoding algorithms are provided