Sometimes there is reciprocity in social cognition. It is not just that one individual is targeting another with her abilities to track actions, perceptions or thoughts. Rather, each individual is targeting her social intelligence at the other so that each is simultaneously both the subject and the target of social intelligence. This kind of reciprocity is characteristic of joint attention and at least some kinds of joint action.

We can distinguish three sorts of question about reciprocity.

The first is epistemological. Are there facts about others' minds or actions we do know but would not be in a position to know if reciprocity were impossible for us? Let me put this another way. It is a familiar idea that observation and inference are two ways of knowing. We can know facts about others' thoughts and actions by observing them, and by drawing inferences. Does reciprocity merely provide additional opportunities to observe and additional premises for inference? Or could there be a further way of knowing, one that essentially involves reciprocity? This is an epistemological question about reciprocity.

The second question concerns the emergence, in development or evolution. Which if any forms of reciprocity play a role in explaining the emergence of sophisticated forms of mindreading and referential communication?

There is also a conceptual question about reciprocity ... The conceptual question is, What forms of reciprocity are there?

One familiar way of characterising reciprocity involves involve higher-order ascriptions.

The mindreader ascribes to her target beliefs (say) about the mindreader's own beliefs and other mental states.

And if her target reciprocates, she might escalate by ascribing to the target beliefs about her own beliefs about the target's beliefs about her beliefs. While this might be useful in some situations,

there are two limits. First, this model of reciprocity can only apply where mindreaders are capable of metarepresentation, and there may be forms of mindreading that do not involve metarepresentation (or so I have argued elsewhere). Second, on this model of reciprocity the basic intuition goes unsatisfied.

A radical alternative to the model of higher-order escalation involves the idea that there are psychological states with plural subjects. This is the idea that there is a single thought, intention or perception that is both mine and yours. This is a shared thought in the strongest sense: we share the thought in just the sense that sisters share a parent. This idea clearly captures an intuition about the meeting of minds, but perhaps unfortunately it's one familar to Star Trek fans in the form of the borg. The borg idea has been endorsed by John Campbell in research on joint attention and by Hans Bernard Schmid in research on joint action. I aim to be neutral about the borg---that is, about whether there really are psychological states with plural subjects. I think everyone will agree that the bare appeal to this idea doesn't enable us to answer the questions about epistemology and emergence, perhaps because it sheds no light on the mechanisms that make reciprocity possible.

My broad aim in what follows is to see whether I can identify a model of reciprocity that avoids both higher-order escalation and direct appeal to the borg idea of psychological states with plural subjects. Hopefully doing this will eventually put us in a position to answer the epistemological, ontogentic and philogenetic questions reciprocity.

Those who have thought about reciprocity have focussed on two main cases, joint attention and joint action. In both cases the challenge of providing a model of reciprocity without higher-order escalation arises, but I think the two cases quite separate treatment. Today my focus is joint action.

Let me start with a challenge about emergence.

There seems to be some consensus on the idea that joint action is particularly important.

But what is joint action?

The second contrast case shows that the difference can’t just be that the resulting actions have a common effect because merely parallel actions can have common effects too.

 

At this point it is natural to appeal to intention.

If we are performing actions of some type phi,

then perhaps for our doing this to be a joint action is just for us to be doing this

because we each intend that we, you and I, phi together.

Does the appeal to togetherness make this circular? Not as long as we understand 'together' only in the sense in which the three legs of a tripod support the flask \emph{together}.

So we have to understand the intention as concerning an event type that could be a joint action but might also involve merely parallel actions.

 

This certainly distinguishes the cases on your left from those on your right.

But we can see that the Simple Account is too simple as it stands by adapting an example from Gilbert and Bratman ...

Since in this case there is something which all the agents involved intend, it seems that our being involved in a joint action can't be a matter only of there being something such that we each intend that we do it together.

What’s wrong with Bratman's account is exemplified by Beatrice and Baldric. Their problem is that they don’t conceive of their actions as an exercise of shared agency. What we want is some way to capture the sense that agents engaged in shared agency conceive of their actions as exercises of shared agency, without of course going in a circle by appealing directly to shared agency here. At this point it’s tempting to appeal to romantic notions of sharing, or to introduce distinctive ingredients like special modes of thought, special ontological constructs or special kinds of reasoning. I want to suggest a way of capturing the agents’ perspective without any such distinctive ingredients.

And in doing this, I want to try a minimal approach. Instead of starting with a sophisticated notion of shared intention, we try to find a minimal starting point and add ingredients as needed.

I want to consider cases where the coordination required for actions to have a collective goal involves motor representations rather than conscious thought.

This would seem unlikely if one's motor representations concerned only one's own actions. But do they? There is at least one sense in which they do not. Outcomes are represented motorically not only in performing actions but sometimes in observing others acting \citep{Rizzolatti:1996eu,rizzolatti_functional_2010}.

This can happen not only when observing a single agent acting alone but even when observing several agents performing a joint action \citep{manera:2013_time}.

These motor representations trigger planning-like processes in observer much like those that would occur if she were actually acting \citep{Jeannerod:2001yb,Gangitano:2001ft,ambrosini:2012_tie}.

Further, the occurrence of motor representations and planning-like processes in action observation is no mere quirk: it can enable observers to predict others' movements and to identify outcomes to which their actions are directed, so that it is almost as if the observer were covertly making predictions by planning how someone in the target's situation should proceed \citep{Wolpert:2003mg,kilner:2007_predictive,Costantini:2012fk}.

So much for observation. What about joint action?

There is evidence for motor representations, in agents involved in a joint action, of outcomes to which the joint action (or some part of it) is or could be collectively directed. For instance there is evidence that, sometimes, a pianist playing a duet will represent not only her own and her partner's individual contributions but also the chord that she and her partner are supposed to produce together \citep{loehr:2013_monitoring}.% \footnote{ Further studies using both neurophysiological and behavioural measures indicate that in some joint actions there are motor representations of outcomes to which that joint action could be collectively directed \citep{Menoret:2013fk,tsai:2011_groop_effect}. }

We also know that these motor representations trigger planning-like motor processes ...

... and that these processes concern not only actions that will be performed by the agent in whom they occur, but also actions that will eventually be performed by others involved in the joint action. There is indeed evidence that such planning-like motor processes sometimes occur in joint action \citep{kourtis:2012_predictive, meyer:2011_joint}.

Further, for a variety of joint actions including passing an object, jumping together and playing a piano duet, motor representations concerning another’s actions can facilitate interpersonal coordination (\citealp[p.\ 9]{kourtis:2012_predictive}; \citealp{loehr:2011_temporal}; \citealp{novembre:2013_motor}; \citealp{vesper:2012_jumping}; \citealp{vesper:2013_our}).% \footnote{ There is also evidence that when agents are engaged in joint action, they sometimes take into account future actions to be performed by others when choosing how to act now, and do so in much the way they would if they were performing the whole action alone \citep{meyer:2013_higher-order}. }

If we considered only motoric aspects, it might almost seem as if each agent were planning to performing alone the whole of what is in fact a joint action. \textbf{But how could this provide for coordination of the agents' actions?}

A second difference between the joint action and the individual action is this.

In joint action there are planning-like motor processes in each agent concerning some actions which she will not eventually perform.

There must therefore be something that prevents part but not all of the planning-like motor process leading all the way to action.

Exactly how this selective prevention works is an open question.

We expect bodily and environmental constraints are often relevant.

There may also be differences in how others’ actions are processed motorically \citep[compare][]{novembre:2012_distinguishing}.

\footnote{\citep[p.\ 2901]{novembre:2012_distinguishing}: 'in the context of a joint action—the motor control system is particularly sensitive to the identity of the agent (self or other) of a represented action and that (social) contextual information is one means for achieving this distinction'}

And inhibition could be involved too \citep[compare][]{sebanz:2006_twin_peaks}.

My proposal, then, is this. Speaking motorically, sometimes agents are able to achieve coordination for joint action not by representing each others’ plans but by treating each other's actions and their own as if they were parts of a single action.

So perhaps joint action is not always only a matter of intention, knowledge or commitment: perhaps sometimes joint action constitutively involves motor representation.

So this is my account of joint action without mindreading. These conditions are sufficient for an event with two or more agents to be a joint action: (a) the actions which are part of this event have a collective goal; and (b) the coordination required for the collective goal is provided by an appropriate interagential structure of motor representation.

That, anyway, is why I think there can be joint action without mindreading, and why I think it matters that this is possible.

Sometimes interlocking intentions and knowledge states are not enough. Sometimes no amount of forming intentions about others’ intentions and acquiring knowledge of such intentions is sufficient, all by itself, for shared intention. In some cases, joint action requires changing perspective to conceive of your own and others’ actions almost as if they constituted a single action. Perhaps it is these kinds of joint action that matter for understanding the emergence of sophisticated forms of mindreading and referential communication.