Response: No need to match: a comment on Bach, Nicholson, and Hudson's “Affordance-Matching Hypothesis”

We are grateful for Uithol and Maranesi's (2014) insightful comments on our article " The affordance-matching hypothesis: How objects guide action understanding and prediction " (Bach et al., 2014). There, we argued that action understanding is not well-accounted for by process in which observed actions are simply matched, based on kinematic information, to an action in one's motor repertoire. Instead, we proposed that action understanding draws heavily on object information. Humans represent objects in terms of both (1) the goals that can be achieved with them (function knowledge), and (2) the specific motor behaviors required to achieve these goals (manipulation knowledge). This knowledge can make a major contribution to action observation, allowing observers not only to infer the goals someone wants to achieve with an object (via function knowledge) but also to predict the actions that this person would need to carry out to achieve these goals (via manipulation knowledge). A key question in such a view is what derives the affordances—the known manipulations—of objects handled by other people. As Uithol and Maranesi rightly point out, and as we conclude in our article, canonical neurons are an unlikely candidate. While canonical neurons indeed seem to encode actions one can perform with an object (grasping, tearing), their firing is restricted to the peripersonal space, coding for actions the monkey could do itself. A much better candidate are the mirror-canonical neurons discovered by Bonini et al. (2014), which fulfill a similar role in the peripersonal space of other people. They fire both when the monkey sees an object, and when seeing someone else perform an appropriate action on the object. The Bonini et al. (2014) study was published shortly before our article, and we were only able to discuss it briefly in our paper. Yet, the response properties of these neurons match the predictions of affordance matching perfectly, and we are grateful to Uithol and Maranesi for further highlighting them. They nicely complement the wealth of behavioral evidence that reveal that observers extract object affordances for other people, even outside their own peripersonal space (for a review, see Creem-Regehr et al., 2013), and that mental simulation of hand-object interactions shows similarly lateralized motor activity as when actually performing such manipulations (e.g., when Borghi and Scorolli, 2009; Marino et al., 2012). Next to highlighting this supportive evidence, Uithol and Maranesi provide two challenges for the affordance-matching hypothesis. First, we had argued that mirror …