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Abstract
Single cell recordings in monkeys provide strong evidence for an important role of the motor system in action understanding. This evidence is backed up by data from studies of the (human) mirror neuron system using neuroimaging or TMS techniques, and behavioral experiments. Although the data acquired from single cell recordings are generally considered to be robust, several debates have shown that the interpretation of these data is far from straightforward. We will show that research based on single-cell recordings allows for unlimited content attribution to mirror neurons. We will argue that a theoretical analysis of the mirroring process, combined with behavioral and brain studies, can provide the necessary limitations. A complexity analysis of the type of processing attributed to the mirror neuron system can help formulate restrictions on what mirroring is and what cognitive functions could, in principle, be explained by a mirror mechanism. We argue that processing at higher levels of abstraction needs assistance of non-mirroring processes to such an extent that subsuming the processes needed to infer goals from actions under the label ‘mirroring’ is not warranted.
Notes
Notes
[1] Technically, a consequence of this inability to measure individual neurons in humans is that mirror neurons have not yet been unequivocally established in humans. There is indirect evidence of mirror neurons in humans based on repetition suppression (Kilner, Neal, Weiskopf, Friston, & Frith, Citation2009; Mukamel, Ekstrom, Kaplan, Iacoboni, & Fried, Citation2010), but this result is not unequivocal (Chong, Cunnington, Williams, Kanwisher, & Mattingley, Citation2008; Lingnau, Gesierich, & Caramazza, Citation2009).
[2] This contrast is also denoted with the terms ‘intention in action’ and ‘prior intention’ (Searle, Citation1983).
[3] The activity of the mirror neuron system is often described as a form of resonance. This resonance is claimed to be either interpersonal, i.e., between parts of the premotor system of the observer and of the executor; or intrapersonal, i.e., between a visual and a motor representation in the observer. See for an elaboration on this distinction (Uithol, van Rooij, Bekkering, & Haselager, forthcoming).
[4] Strictly speaking, this statement reflects a category mistake in the sense that “we” can use mirror neurons. One may wonder what the “we” consists of if neurons are not part of it. However, we do not want to elaborate on this along the lines of Bennett and Hacker (2003). Rather, we see this statement (and many similar others) as a “rough and ready” type of description that could be formulated more appropriately (e.g., by speaking of mirror neurons that implement our “capacity to…”) when the occasion requires it.
[5] Evidently, real world situations can vary in many more than just 35 features, but to make our case we do not need to assume any more such features.
[6] These limitations, however, are as such not enough to provide a solid and undisputable bound for content attribution to the firing of individual mirror neurons. That would require a deep understanding of the functioning of the MNS at the neuronal level, as well as taking an ontological position on the nature of representation, which would be beyond the scope of this article.
[7] Umiltà et al. (2008) found motor neurons that fired selectively for pinching with pliers, irrespective of whether the pinching was achieved with normal or reverse pliers (so irrespective of whether the hand had to close or open in order to pinch). While we agree that this is indeed an abstraction from the basic kinematics of a motor act, it is still a relatively basic act, remote from, say, Iacoboni et al.'s, “intention to clean the table.” Moreover, the same reserve as presented in the discussion of Fogassi et al's results is relevant here: from the data we cannot conclude whether the firing is indicative or constitutive of goal understanding. In addition, as this study analyzed motor neurons, not mirror neurons, the relation to a mirroring process in goal recognition is not elucidated.