Understanding motor resonance

Abstract

The discovery of mirror neurons in monkeys, and the finding of motor activity during action observation in humans are generally regarded to support motor theories of action understanding. These theories take motor resonance to be essential in the understanding of observed actions and the inference of action goals. However, the notions of “resonance,” “action understanding,” and “action goal” appear to be used ambiguously in the literature. A survey of the literature on mirror neurons and motor resonance yields two different interpretations of the term “resonance,” three different interpretations of action understanding, and again three different interpretations of what the goal of an action is. This entails that, unless it is specified what interpretation is used, the meaning of any statement about the relation between these concepts can differ to a great extent. By discussing an experiment we will show that more precise definitions and use of the concepts will allow for better assessments of motor theories of action understanding and hence a more fruitful scientific debate. Lastly, we will provide an example of how the discussed experimental setup could be adapted to test other interpretations of the concepts.

Keywords:

• Mirror neurons
• Motor resonance
• Action understanding
• Goals

Acknowledgments

The present study was supported by a Donders internal graduation grant to the second and last authors, and the EU-Project Joint Action Science and Technology (IST-FP6-003747) grant and an NWO-VICI grant to the last author. The authors wish to thank Janny Stapel for commenting on an earlier draft of this paper.

Notes

¹ It is still debated whether the final action representation—provided that such a representation exists— resides in motor areas (as embodied approaches to cognition argue) or whether there are disembodied representations of actions. Here we choose not to take a side in this debate.

Figure 1. The causal path from action plan in the executor to action representation in the observer and the location of intrapersonal resonance.

² There are experiments, such as those of Fogassi et al. (2005) and Umiltà et al. (2008), that show mirror-neuron response to tool-based actions, but this was only after extensive training with tools. A possible explanation is that, through training with tools, the monkey creates a motor representation of these actions.

³ Besides actions and action goals, two more related notions can be found in the literature. An “action means” is a particular way of performing an action. Action means also lie on the same continuum as actions and goals, and can therefore, upon different interpretations, also be actions themselves. The notion “movement” is often used to denote a movement that does not serve a goal —see, for instance, Gallese and Goldman (1998) or Hommel (2003). Action thus conceived is a subclass of movements; that is, those movements that serve a goal.

⁴ As we said in footnote 3, the difference between a movement and an action is often taken to be that the latter serves a goal and the former does not. This would entail that every action serves a goal, making the term “goal-directed action” a pleonasm for other interpretations of “goal”, as non-goal-directed actions cannot exist—just non-goal-directed movements.

⁵ This statement illustrates how terminology can cause confusion. Apart from the personal/subpersonal violation, the claim that “mirror neurons infer” also departs from the initial claims that mirror neurons engage in direct reflection and no inferential processes are needed. See Uithol et al. (submitted) for a more detailed discussion on direct reflection versus inferential processing with respect to mirror neurons.