Active visuomotor interactions with virtual objects on touchscreens adhere to Weber's law.

Recent findings suggest that the functional separation between vision-for-action and vision-for-perception does not generalize to situations in which two-dimensional (2D), virtual objects, are used as targets. For example, unlike grasping movements directed at real, three-dimensional (3D) objects, the trajectories of grasping movements directed at 2D objects adhere to the psychophysical principle of Weber's law, indicating relative and less efficient processing of their size. Such inefficiency could be attributed to the fact that everyday interactions with touchscreens do not usually entail grasping movements. It is possible, therefore, that more typical interactions with virtual objects, which involve active manipulation of their size or location on a touchscreen, could be performed efficiently and in an absolute manner, and would violate Weber's law. We examined this hypothesis in three experiments in which participants performed active interactions with virtual objects. In Experiment 1, participants made swiping gestures to move virtual objects across the touchscreen. In Experiment 2, participants touched the edges of virtual objects to enlarge their size. In Experiment 3, participants freely enlarged the size of virtual objects, without being required to touch their edges upon contact. In all experiments, the resolution of grip aperture decreased with the size of the target object, adhering to Weber's law. These results suggest that active interactions with 2D objects on touchscreens are not performed in a natural, absolute manner which characterize visuomotor control of real objects.