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Motor Representation

some
motor representations (/schema) represent ???outcomes = goals

‘a given motor act may change both as a function of what motor act will follow it—a sign of planning—and as a function of what motor act preceded it—a sign of memory’ (Cohen & Rosenbaum, 2004, p. 294).

‘a given motor act may change ... as a function of what motor act will follow it—a sign of planning’

Cohen & Rosenbaum 2004, p. 294

Let me go back and start with some almost uncontroversial facts about motor representations and their action-coordinating role.
Why postulate motor representations at all? [Dependence of present actions on future actions is one reason for doing so.]
Suppose you are a cook who needs to take an egg from its box, crack it and put it (except for the shell) into a bowl ready for beating into a carbonara sauce. Even for such mundane, routine actions, the constraints on adequate performance can vary significantly depending on subtle variations in context. For example, the position of a hot pan may require altering the trajectory along which the egg is transported, or time pressures may mean that the action must be performed unusually swiftly on this occasion. Further, many of the constraints on performance involve relations between actions occurring at different times. To illustrate, how tightly you need to grip the egg now depends, among other things, on the forces to which you will subject the egg in lifting it later. It turns out that people reliably grip objects such as eggs just tightly enough across a range of conditions in which the optimal tightness of grip varies. This indicates (along with much other evidence) that information about the cook’s anticipated future hand and arm movements appropriately influences how tightly she initially grips the egg (compare Kawato, 1999). This anticipatory control of grasp, like several other features of action performance (Rosenbaum, 2010, p. see][chapter 1 for more examples), is not plausibly a consequence of mindless physiology, nor of intention and practical reasoning. This is one reason for postulating motor representations, which characteristically play a role in coordinating sequences of very small scale actions such as grasping an egg in order to lift it.
[The scale of an actual action can be defined in terms of means-end relations. Given two actions which are related as means to ends by the processes and representations involved in their performance, the first is smaller in scale than the second just if the first is a means to the second. Generalising, we associate the scale of an actual action with the depth of the hierarchy of outcomes that are related to it by the transitive closure of the means-ends relation. Then, generalising further, a repeatable action (something that different agents might do independently on several occasions) is associated with a scale characteristic of the things people do when they perform that action. Given that actions such as cooking a meal or painting a house count as small-scale actions, actions such as grasping an egg or dipping a brush into a can of paint are very-small scale. Note that we do not stipulate a tight link between the very small scale and the motoric. In some cases intentions may play a role in coordinating sequences of very small scale purposive actions, and in some cases motor representations may concern actions which are not very small scale. The claim we wish to consider is only that, often enough, explaining the coordination of sequences of very small scale actions appears to involve representations but not, or not only, intentions. To a first approximation, _motor representation_ is a label for such representations.]
‘a given motor act may change both as a function of what motor act will follow it—a sign of planning—and as a function of what motor act preceded it—a sign of memory’ (Cohen & Rosenbaum, 2004, p. 294).
What do motor representations represent? An initially attractive, conservative view would be that they represent bodily configurations and joint displacements, or perhaps sequences of these, only.
However there is now a significant body of evidence that some motor representations do not specify particular sequences of bodily configurations and joint displacements, but rather represent outcomes such as the grasping of an egg or the pressing of a switch. These are outcomes which might, on different occasions, involve very different bodily configurations and joint displacements (see Rizzolatti & Sinigaglia, 2010 for a selective review).
Such outcomes are abstract relative to bodily configurations and joint displacements in that there are many different ways of achieving them.
A goal represented motorically triggers a process which, via computations of things like end states, starting states and smoothness, eventually results in joint displacements; and when things go well, these joint displacements together with the resulting bodily configurations bring about, or constitute, the occurrence of the goal.
But of course this is a simplification. Motor representations can trigger processes which result in further goals being represented, as for example when a motor representation of the transporting of an object triggers representations of reaching, grasping, placing and releasing.
The processes linking motor representations are planning like in two respects: (i) means-end ...
... and (ii) relational constraints

How do we know that outcomes are represented motorically?

But how do we know that motor representations carry information about such outcomes? I’m glad you asked, let me explain ...

background

The Double Life of Motor Representation

Rizzolatti and Sinigaglia, 2006 figure 1.1

‘The posterior section of the frontal lobe contains the motor areas,’ (p. 4) Now you know as much about the brain as I do.
Mention primary and supplementary motor areas : we use the term ‘motor’ loosely (compare ‘visual’, which also has narrower and broader uses in neuroscience).

Fogassi et al 2005, figure 5

Same thing seen another way ...
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.
If you were to observe someone phi-ing, then motor representations would occur in you much like those that would occur in you if it were you, not her, who was phi-ing.
This is not our focus, it’s just a handy fact that simplifies testing.
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).’ .notes: :t 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. //- .slide //- +blur('.fogassi img, .source', '5px') //- p.em-above glossary: TMS .notes. Converging evidence for this assertion comes from a variety of methods and measures; but I won’t mention alll of that here. Except one TMS experiment ...

D'Ausilio et al (2009, figure 1)

For a quick illustration of how we know about the double life of motor representation, consider this experiment ....
‘Double TMS pulses were applied just prior to stimuli presentation to selectively prime the cortical activity specifically in the lip (LipM1) or tongue (TongueM1) area’ (D’Ausilio et al., 2009, p. 381)
‘We hypothesized that focal stimulation would facilitate the perception of the concordant phonemes ([d] and [t] with TMS to TongueM1), but that there would be inhibition of perception of the discordant items ([b] and [p] in this case). Behavioral effects were measured via reaction times (RTs) and error rates.’ (D’Ausilio et al., 2009, p. 382)

D'Ausilio et al (2009, figure 2)

[end of aside on the double life of motor representation]

background

The Double Life of Motor Representation

[end of aside on the double life of motor representation]

How do we know that outcomes are represented motorically?

first illustration: same kinematics, different goal

glossary: MEP

Villiger et al, 2010 figure 1AB

TMS to measure MEP
They also had an occluded end version ...

Villiger et al, 2010 figure 2

Incidentally, ‘the observed direction of the modulation was not consistent with previous TMS literature. Specifically, MEP amplitudes were significantly lower in the Object-Present than in the Object-Absent conditions (Fig. 2), suggesting that there was an inhibitory effect of object manipulation on the activity of M1 during action observation.’

first illustration: same kinematics, different goal

second illustration: different kinematics, same goal

Umiltà et al, 2008 figure 1

Umiltà et al, 2008 : single cell recordings in monkeys
MEPs (TMS amplified) in humans

Cattaneo et al, 2010 figure 1

TMS MEP, humans.
Shown video, then a static picture. Is this the same goal as you saw in the video? Press one of two keys. ‘They were explicitly told to ignore the effector and make a judgment on the type of act only.’

Cattaneo et al, 2010 figure 3

Key finding: TMS to both ventral premotor cortex (PMv) and left supramarginal gyrus (SMG) increases RTs regardless of whether it’s the same effector or a different effector. (You can’t see same/different effector in this figure.)
KEY: superior temporal sulcus (STS), and a parietofrontal system consisting of the intraparietal sulcus (IPS) and inferior parietal lobule (IPL) plus the ventral premotor cortex (PMv) and caudal part of inferior frontal gyrus (IFG). In some instances also, the superior parietal lobule (SPL)

Cattaneo et al, 2010 figure 4

By contrast, TMS to superior temporal sulcus (STS) increased RT only for judgements where the video effector was the same as the photo effector.

Markers of motor representation ...

The experiments providing such evidence typically involve a marker of motor representation, such as a pattern of neuronal firings, a motor evoked potential or a behavioural performance profile, which, in controlled settings, allows sameness or difference of motor representation to be distinguished. Such markers can be exploited to show that the sameness and difference of motor representation is linked to the sameness and difference of an outcome such as the grasping of a particular object. (Pioneering uses of this method include G. Rizzolatti et al., 1988; Giacomo Rizzolatti, Fogassi, & Gallese, 2001; it has since been developed in many ways: see, for example, \citet{hamilton:2008_action, cattaneo:2009_representation, cattaneo:2010_state-dependent, rochat:2010_responses, bonini:2010_ventral, koch:2010_resonance}.)

1. are unaffected by variations in kinematic features but not goals

2. are affected by variations in goals but not kinematic features

So: 3. carry information about goals (from 1,2)

Also

4. Information about outcomes guides planning-like processes ...

To illustrate, consider a sequence of actions which might be involved in shoplifting an apple: you have to secure the apple, transport it, and position it in your pocket. Each of these outcomes can be represented motorically.
Motor processes are planning-like in that they involve computing means from ends. Thus a representation of an end like securing it [the apple] can trigger a process that results in the representation of outcomes that are means to this end.
Motor processes are also planning-like in that which means are selected in preparing an action that will occur early in the sequence may affect needs that will arise only later in a later part of the actions. For instance, how the apple is grasped at an early point in the sequence may be determined in part by what would be a more comfortable way for the other hand to grasp it later.
So motor representations of outcomes guide planning-like processes. This is why I think it’s not just that they carry information about outcomes like grasping an apple, but that they also represent such outcomes.

Markers of motor representation ...

1. are unaffected by variations in kinematic features but not goals

2. are affected by variations in goals but not kinematic features

So:

3. carry information about goals (from 1,2)

Also

4. Information about outcomes guides planning-like processes.

some
motor representations (/schema) represent outcomes

‘a given motor act may change ... as a function of what motor act will follow it—a sign of planning’

Cohen & Rosenbaum 2004, p. 294

In conclusion, two ideas about the control of action. First, I follow Jeannerod (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 (Wolpert, Doya, & Kawato, 2003, p. e.g.][).