The role of action semantics in action control: Comment on “Action semantics: A unifying conceptual framework for the selective use of multimodal and modality-specific object knowledge” by Michiel van Elk, Hein van Schie and Harold Bekkering

Abstract

In this issue, van Elk, van Schie and Bekkering [4] succeed in presenting a well-organized, highly structured, and impressively complete summary of the available research on how knowledge may affect action control. However, their theoretical efforts remain unconvincing for three reasons. First, even though the suggested framework is presented as a general “model” of how people acquire, store, and make use of action knowledge, the authors restrict their theoretical reasoning to unimanual reaching for/grasping of objects—a surprisingly small subset of possible actions. Other actions often do not fit into the authors’ schema: walking, talking, singing, gesturing, typing, looking, driving, dancing, playing music, doing sports, and reading do not refer to particular objects and/or have goals other than being directed towards particular spatial locations—and yet they all rely on “what” and “how” knowledge. This suggests that the “multimodal object representation” box of the model is too specific to apply to action in a broader sense; it should rather refer to all sorts of events that people can aim at, generate, and imply by means of voluntary actions—as suggested by the Theory of Event Codes [2]. Event representations may also refer to the action itself, such as with a ballet figure, suggesting that the “object representation” box might sometimes merely consist of representations of the sensory consequences the action is intended to produce. It thus makes little sense to distinguish between “multimodal object representations”, “proprioceptive consequences” (which, strangely enough, are distinguished from other sensory consequences), and “sensory consequences”—this may just be different examples of “event representations” [2]. Second, the remaining concepts of the framework are ill-defined: Distinguishing between functional and manipulation knowledge makes sense for object grasping but not for many other actions, including gesturing, dancing, and singing. Worse, the authors’ definition that the action-related knowledge comprises of all “the procedural or manipulation knowledge” that enables us to carry out meaningful actions renders the model tautological: if humans can carry