AbstractGrasping requires that an individual process absolute visual information for optimal hand/target interactions. For example, the visuomotor system demonstrates peak grip aperture (PGA) scaling for targets that differ by as little as 0.5 mm – a resolution far greater than the visuoperceptual system. In the present work, participants grasped adjacent to a target (i.e., pantomime-grasp) to determine whether actions requiring decoupled stimulus-response spatial relations rely on the same visual information as their naturalistic counterparts. For each trial a target and an adjacent non-target was presented, and participants grasped or pantomime-grasped the target. Importantly, target and non-targets differed in size by 0.5 mm, and prior to or after the grasp, or pantomime-grasp, participants' reported whether the target was larger than the non-target (i.e., perceptual judgment). Experiment 1 employed rectangular bars as target stimuli, whereas Experiment 2 employed circular annuli. Experiment 1 showed that PGAs for grasps and pantomime-grasps scaled to target size and surprisingly participants provided accurate perceptual judgments of target size. Experiment 2 PGAs for grasps – but not pantomime-grasps – scaled to target size and in both tasks participants did not provide accurate perceptual judgements. Accordingly, results demonstrate that the perceptual system's resolution is shape-dependent (Experiment 1), and that grasps, and pantomime-grasps, are mediated via distinct visual information (Experiment 2).
Acknowledgments: Supported by NSERC.