Ganel, Freud, Chajut, and Algom (2012) demonstrated that maximum grip apertures (MGAs) differ significantly when grasping perceptually identical objects. From this finding they concluded that the visual size information used by the motor system is more accurate than the visual size information available to the perceptual system. A direct comparison between the accuracy in the perception and the action system is, however, problematic, given that accuracy in the perceptual task is measured using a dichotomous variable, while accuracy in the visuomotor task is determined using a continuous variable. We addressed this problem by dichotomizing the visuomotor measures. Using this approach, our results show that size discrimination in grasping is in fact inferior to perceptual discrimination therefore contradicting the original suggestion put forward by Ganel and colleagues.
Bibliographical noteFunding: This work was supported by the DFG Priority Program SPP 1772 “Human performance under multiple cognitive task requirements: From basic mechanisms to optimized task scheduling” (DFG/SCHE 735/2-1) and also research funding from the following two projects: DFG/SCHE 735/3-1 und DFG/SCHE 735/4-1.
Acknowledgments: We want to thank Lara Werner and Regina Härtl for help in data acquisition.
- perception-action model
- Two Visual Streams Hypothesis
- object size
- Just Noticeable Difference