Could Motor Representations Ground Collective Goals?

Motor representations can ground collective goals in this sense: in some cases, two or more actions involving multiple agents have a collective goal in virtue of the actions being appropriately related to an interagential structure of motor representations. Or so the discoveries presented in this section suggest.

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This section considers the conjecture that some motor representations specify collective goals.^[1]

Why suppose that the conjecture is true?

Various predictions of the conjecture have recently been tested and confirmed (Sacheli, Arcangeli, Carioti, Butterfill, & Berlingeri, 2022; Sacheli, Arcangeli, & Paulesu, 2018; della Gatta et al., 2017; Clarke et al., 2019). As this evidence is still quite limited, we cannot yet be very confident that the conjecture is true. There is also a larger body of evidence that indirectly motivates it, some of which is introduced in the video.

If true, what could the conjecture explain?

Any account of joint action should answer the question,

In virtue of what could two or more agents’ actions have a collective goal?

In some cases, it is probably the agents’ shared intention in virtue of which their actions have a collective goal (whatever exactly shared intention turns out to be.)

But if the conjecture is true, there are cases in which it is in virtue of an interagential structure of motor representations that actions have a collective goal (whatever exactly shared intention turns out to be.)

What is this interagential structure of motor representations?

First, there must be an outcome to which the actions are, or could be, collectively directed, and in each agent there must be a motor representation of this outcome.

Second, these motor representations must trigger planning-like processes which result in plan-like hierarchies of motor representations in each agent.

Third, the plan-like hierarchy in each agent must involve motor representations concerning not only actions she will eventually perform but also actions another will eventually perform.

Fourth, the plan-like hierarchies of motor representations in the agents must non-accidentally match.

When all four conditions are met, the result is an interagential structure of motor representations.

Because the existence of this interagential structure would provide for the coordination of the agents’ actions around the outcome represented motorically, it ensures that sufficient conditions are met for the existence of a collective goal of their actions. (The sufficient conditions featured in the section on Collective Goals.)

Note that this does not imply that there are any cases of joint action which do not involve shared intention. The challenge to the philosophical accounts (e.g. Bratman on Shared Intentional Action) is not that they fail to give necessary conditions. It is that there are basic questions about joint action which cannot be fully answered without going beyond philosophical frameworks to consider scientific discoveries.

Appendix: More Detail

Does the interagential structure of motor representations identified above really provide for coordination?

How could it do so?

To fully understand this, we need two things. An understanding of bimanual coordination in ordinary, individual action. And the notion of parallel planning.

Bimanual Coordination in Ordinary, Individual Action

Consider what is involved when, in acting alone, you move a mug from one place to another, passing it between your hands half-way. In this action there is a need to coordinate the exchange between your two hands. If your action is fluid, you may proactively prepare to release the mug from your left hand moments in advance of the mug’s being secured by your right hand (compare Diedrichsen, Verstynen, Hon, Lehman, & Ivry, 2003). How is such tight coordination achieved? A full answer cannot be given by appeal to physiology alone (Jackson, German, & Peacock, 2002; Piedimonte et al., 2015). Instead, part of the answer involves the fact that there is a motor representation for the whole action which triggers planning-like motor processes, so that the motor representations and processes concerning the actions involving each hand are not entirely independent of each other (compare Kelso, Southard, & Goodman, 1979 and Rosenbaum, 2010, pp. 244--8). Such planning-like processes result in motor representations concerning different parts of the action which can be hierarchically arranged by the means-ends relation and ensure that relational constraints on components of the action are satisfied. So when you move a mug from one place to another, passing it between your hands half-way, and when this action and its components are represented motorically in a plan-like hierarchy, it is this plan-like hierarchy which ensures the movements of one hand constrain and are constrained by the movements of the other hand.

This is how motor representations of outcomes can coordinate the actions of an individual agent using two hands.

Now switch from an individual agent performing a bimanual action to two agents acting together.

Motor representation can play a similar role when two agents act together. To see how, we need the notion of parallel planning.

Parallel Planning

When we considered Bratman on Shared Intentional Action, we followed him in focussing on interconnected planning. This is planning in which facts about your plans feature in mine and conversely:

‘each agent does not just intend that the group perform the […] joint action. Rather, each agent intends as well that the group perform this joint action in accordance with subplans (of the intentions in favor of the joint action) that mesh.’ (Bratman, 1992, p. 332)

On Bratman’s view,

‘shared intentional agency consists, at bottom, in interconnected planning agency of the participants.’ (Bratman, 2011).

Our planning is _parallel_ just if you and I are each planning actions that I will eventually perform and actions that you will eventually perform, where the resulting plans non-accidentally match.

For parallel planning to be possible without irrationality, it can involve only agent-neutral representations and processes. It must also result in intentions that are open-ended with respect to who will act.

It may be controversial whether parallel planning involving practical reasoning and intentions is actually at all possible without irrationality. But our concern is different: we know that some motor processes are planning-like in that they involve computing means from representations of ends and in that they involve satisfying relational constraints on actions happening at different times. Perhaps there is something like parallel planning that involves not practical reasoning and intentions but motor processes and representations?

But is there any evidence that parallel planning involving motor representations ever occurs? Planning concerning another's actions sometimes occurs not only in observing her act but also in exercising collective agency with her (Kourtis, Sebanz, & Knoblich, 2013; Meyer, Hunnius, Elk, Ede, & Bekkering, 2011). Such planning can inform planning for your own actions, and even planning that involves meeting constraints on relations between your actions and hers (Vesper, Wel, Knoblich, & Sebanz, 2013; Novembre, Ticini, Schutz-Bosbach, & Keller, 2014; Loehr & Palmer, 2011; Meyer, Wel, & Hunnius, 2013).^[2]

How the Interagential Structure Coordinates

So how does the interagential structure of motor representations identified above provide for coordination of two agents’ actions?

The plan-like structure of motor representations in you concerns not only actions you will perform but also actions I will perform. This ensures that your actions are constrained by your plan for my actions. But because your plan-like structure matches my plan-like structure, this means that your actions are, in effect, constrained by my plan for my actions. And conversely.

So the interagential structure of motor representations identified above provides for the coordination of our actions in something like the way that motor representations coordinate the bimanual actions of an individual agent.^[3]

Appendix: Further Sources

There are lots of additional sources in the references section of a guide to psychological research on coordination in joint action written for philosophers (Butterfill, 2017).

As you can see from the video, quite a bit has happened since that guide was written. The new research mostly confirms and extends the earlier research.

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