AbstractGrasping a 2D object requires the processing of relative target features and functions distinct from the absolute visual information supporting the grasp of a 3D object (Holmes & Heath, 2013: Brain Cogn). Interestingly, the distinct visual cues mediating 2D and 3D grasping may â€“ in part â€“ reflect the fact that the former task does not entail the provision of terminal haptic feedback (Davarpanah Jazi et al. 2015: Neuropsychologia). As such, in the present study we investigated whether the provision of terminal haptic feedback influences the nature of the information supporting 2D grasping. In particular, participants grasped differently sized 3D objects and their 2D counterparts in conditions wherein terminal haptic feedback was present (i.e., 2DH+) or absent (i.e., 2DH-). More specifically, the 2DH+ condition provided terminal haptic feedback comparable to that associated with the grasping of a 3D object. Just noticeable difference scores (JNDs) computed at peak grip aperture in the 2DH- condition scaled to target size, whereas values for 3D and 2DH+ trials elicited a null scaling. In other words, grasping a 2D object adhered to the relative psychophysical principle of Weber's law, whereas the provision of terminal haptic feedback resulted in grasps that violated the law. Accordingly, we propose that terminal haptic feedback provides absolute size cues that supports veridical aperture shaping.
Acknowledgments: National Sciences and Engineering Research Council of Canada (NSERC)