Manipulation of physical 3-D and virtual 2-D stimuli: comparing digit placement and fixation position.

The visuomotor processes involved in grasping a 2-D target are known to be fundamentally different than those involved in grasping a 3-D object, and this has led to concerns regarding the generalizability of 2-D grasping research. This study directly compared participants' fixation positions and digit placement during interaction with either physical square objects or 2-D virtual versions of these objects. Participants were instructed to either simply grasp the stimulus or grasp and slide it to another location. Participants' digit placement and fixation positions did not significantly differ as a function of stimulus type when grasping in the center of the display. However, gaze and grasp positions shifted toward the near side of non-central virtual stimuli, while consistently remaining close to the horizontal midline of the physical stimulus. Participants placed their digits at less stable locations when grasping the virtual stimulus in comparison to the physical stimulus on the right side of the display, but this difference disappeared when grasping in the center and on the left. Similar outward shifts in digit placement and lowered fixations were observed when sliding both stimulus types, suggesting participants incorporated similar adjustments in grasp selection in anticipation of manipulation in both Physical and Virtual stimulus conditions. These results suggest that while fixation position and grasp point selection differed between stimulus type as a function of stimulus position, certain eye-hand coordinated behaviours were maintained when grasping both physical and virtual stimuli.