Planning versus online control: dynamic illusion effects in grasping?

The planning/control model of action assumes that grasping is sensitive to the context of an object only in early stages of the movement (planning), but not in later stages (control). In consequence, the effects of context-induced illusions (such as the Ebbinghaus/Titchener illusion) should decrease during a grasping movement. Here, we tested this claim by reanalysing a large data set (N = 26) on grasping in the Ebbinghaus illusion. Contrary to the predictions of the planning/control model, we found that the effects of the illusion did not decrease over time. Instead, the illusion effects stayed remarkably constant.