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The Motor Theory of Goal Tracking

Fogassi et al 2005, figure 5

The Double Life of Motor Representation

What follows rests on three background assumptions about the control of action. First, I follow \citet{jeannerod_motor_2006} and others in rejecting the view that all motor representations specify only bodily configurations, joint displacements and end states. Instead some motor representations specify outcomes to which actions are directed, such as the grasping of a particular handle or the transporting of a given object.
Second, some motor processes involve computing means from ends and generating sensory expectations concerning the effects of actions \citep[e.g.][]{Wolpert:2003mg}.
Third, multiple means--ends computations can occur simultaneously, or at least rapidly enough for action preparation to involve selection on the basis of multiple means-ends computations \citep[e.g.][]{wolpert_internal_1998}.
It is now a familiar, if still interestingly controversial idea, that motor representation leads a DOUBLE LIFE. For it is involved not only in coordinating the performance of small-scale purposive actions like reaching, grasping, placing and transporting but also in action observation.
We know this in large thanks to the discovery of mirror neurons and their consequences.
‘(A) Congruence between the visual and the motor response of a mirror neuron. Unit 169 has a stronger discharge during grasping to eat than during grasping to place, both when the action is executed and when it is observed. Conventions as in Fig. 1. (B) Population-averaged responses during motor and visual tasks (12).’
Suppose you are reaching for, grasping, transporting and then placing a pen. Performing even relatively simple action sequences like this involves satisfying many constraints that cannot normally be satisfied by explicit practical reasoning, especially if performance is to be rapid and fluent. Rather, such performances require motor representations. These representations are paradigmatically involved in preparing, executing and monitoring actions.% \footnote{% See \citet{wolpert:1995internal, miall:1996_forward, jeannerod:1998nbo, zhang:2007_planning}. Note that motor representations sometimes occur in an agent who has prepared an action and is required (as it turns out) not to perform it: although she has prevented herself from acting, motor representations specifying the action persist, perhaps because they are necessary for monitoring whether prevention has succeeded \citep{bonini:2014_ventral}. } But they also live a double life. Motor representations concerning a particular type of action are involved not only in performing an action of that type but also sometimes in observing one. That is, if you were to observe Ayesha reach for, grasp, transport and then place a pen, motor representations would occur in you much like those that would also occur in you if it were you---not Ayesha---who was doing this.
Converging evidence for this assertion comes from a variety of methods and measures; but I won’t mention any of that here.

What are those motor representations doing here?

So we have to ask, What are those motor representations doing here? And when you do ask that you find that, in adults, they appear to be facilitating your abilities to track the goals of observed actions. This is inspiration for the Motor Theory of Goal Tracking ...

Motor Theory of Goal Tracking (including Speech Perception)

mTgt is an alternative to the Simple View. The idea is that pure goal-tracking involves motor processes rather than thinking and reasoning about goals.
But how could motor processes enable goal tracking?

Sinigalia & Butterfill 2015, figure 1

Goal-tracking is acting in reverse. -- in action observation, possible outcomes of observed actions are represented -- these representations trigger planning as if performing actions directed to the outcomes -- such planning generates predictions -- a triggering representation is weakened if its predictions fail The result is that the only only outcomes to which the observed action is a means are represented strongly.
There is evidence that a motor representation of an outcome can cause a determination of which movements are likely to be performed to achieve that outcome \citep[see, for instance,][]{kilner:2004_motor, urgesi:2010_simulating}. Further, the processes involved in determining how observed actions are likely to unfold given their outcomes are closely related, or identical, to processes involved in performing actions. This is known in part thanks to studies of how observing actions can facilitate performing actions congruent with those observed, and can interfere with performing incongruent actions \citep{ brass:2000_compatibility, craighero:2002_hand, kilner:2003_interference, costantini:2012_does}. Planning-like processes in action observation have also been demonstrated by measuring observers' predictive gaze. If you were to observe just the early phases of a grasping movement, your eyes might jump to its likely target, ignoring nearby objects \citep{ambrosini:2011_grasping}. These proactive eye movements resemble those you would typically make if you were acting yourself \citep{Flanagan:2003lm}. Importantly, the occurrence of such proactive eye movements in action observation depends on your representing the outcome of an action motorically; even temporary interference in the observer's motor abilities will interfere with the eye movements \citep{Costantini:2012fk}. These proactive eye movements also depend on planning-like processes; requiring the observer to perform actions incongruent with those she is observing can eliminate proactive eye movements \citep{Costantini:2012uq}. This, then, is further evidence for planning-like motor processes in action observation.
So observers represent outcomes motorically and these representations trigger planning-like processes which generate expectations about how the observed actions will unfold and their sensory consequences. Now the mere occurrence of these processes is not sufficient to explain why, in action observation, an outcome represented motorically is likely to be an outcome to which the observed action is directed.
To take a tiny step further, we conjecture that, in action observation, \textbf{motor representations of outcomes are weakened to the extent that the expectations they generate are unmet} \citep[compare][]{Fogassi:2005nf}. A motor representation of an outcome to which an observed action is not directed is likely to generate incorrect expectations about how this action will unfold, and failures of these expectations to be met will weaken the representation. This is what ensures that there is a correspondence between outcomes represented motorically in observing actions and the goals of those actions.

Pure goal-tracking could,
in principle,
be implemented motorically.

‘proactive gaze’ and ‘explicit judgement’ are variables whose values represent whether there is a proactive gaze or explicit judgement, and what is it to or about. Likewise, ‘motor process’ is a variable whose values represent ...
The lines depict how the variables are causally related. I’ve used thick and thin lines informally, to indicate weaker and stronger influences.
The dual-process theory of goal-tracking makes perfect sense of development. It says that what we observe in six- and nine-month-olds is motor-based goal-tracking. Presumably the more flexible, reasoning-based goal-tracking processes emerge some time later in development.

Motor Conjecture

In 9-month-olds,

all pure goal-tracking is explained by the Motor Theory;


‘we believe that the three proposed mechanisms of goal attribution [...] complement each other’

Csibra & Gergely, 2007 p. 74


Infants can track goals from nine months of age (or earlier).


In infants (and adults),
goal-tracking is limited by their abilities to act.

The ‘Teleological Stance’
~ The goals of an action are those outcomes which the means is a best available way of bringing about.

Csibra & Gergely


1. This means, m, has been adopted (observation)

2. G is an outcome such that: m is a best available* way of bringing G about

3. ∴ G is a goal of the observed action

Important that mTgt is not an alternative to the Teleological Stance but to it plus the claim about reasoning.
Simple View and mTgt do not differ on the relation between means and goals that is to be computed in pure goal-tracking. The Simple View and mTgt differ only on what processes is responsible for identifying which outcome or outcomes the observed means is a best available way of achieving.

‘simulation is clearly a natural and effective way to find the most efficient action towards a goal state.’

Csibra & Gergely, 2007 p. 72

The Simple View Motor Conjecture
What is the function to be computed? [Teleological Stance] [Teleological Stance]
How is this function computed? By reasoning from beliefs. By using motor processes ‘in reverse’.
Why is goal-tracking limited by action ability? ??? Because both rely on motor processes.
There’s just one small problem. It’s not quite true to say that infants goal-tracking is limited by action ability. Some of it is, but some of it isn’t ...