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\title {Philosophical Psychology \\ 05: What Is the Mark That Distinguishes Actions?}

\maketitle

# 05: What Is the Mark That Distinguishes Actions?

\def \ititle {05: What Is the Mark That Distinguishes Actions?}
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Q1

Donald Davidson asks, ‘What is the mark that distinguishes ... actions?’ Are scientific discoveries relevant to answering this question?

Q2

What is the mark that distinguishes actions?

Q3

How are non-accidental matches between intentions and motor representations possible?

\section{Philosophical Methods}

\section{Philosophical Methods}
Philosophical methods include informal observation, guesswork (‘intuition’), imagination (including for ‘thought experiments’), reasoning and argument, & theoretical elegance.

philosophical
methods

informal observation,

guesswork (‘intuition’),

imagination (including for ‘thought experiments’),

reasoning and argument,

& pursuit of theoretical elegance

First, think about the methods philosophers use. Am I missing any?
Next, think about how philosophers construct theories of action ...
Here’s Ayesha and she’s about to act, which involves some kind of processes occurring in her imnd.
Ben want’s to predict Ayesha’s action, perhaps so he can coordinate his actions around hers. He is therefore having a think about what Ayesha might be up to.
Implicit in Ben’s thinking is a model of actions.
And along comes the philosopher and attempts to guess what is going on in Ben’s mind when he is thinking about Ayesha. The philosopher asks, in effect, What model of actions is implicit in Ben’s thinking?
And this, essentially, is the raw material for philosophical theories of actions.
Focus on Ben for a moment.
What mundane purposes does thinking about actions serve? Prediction and coordination; ethical (assigning responsibility, blame; living together); normative (he wants himself and others to live it out as much as to describe how things are; there may also be something about ‘understanding’ here). So it’s not all about accuracy; in fact, of these, only prediction and coordination even potentially requires that his model of actions is accurate.

Functions of Ben’s model of minds and actions:

• ethical
• normative
• predictive
Second, consider Ben’s concern with making predictions.

--- speed vs accuracy

Whenever you are making predictions about anything at all, you face a \textbf{trade-off between accuracy and speed}. Making more accurate predictions requires considering more information and integrating it in a more complex model of minds and actions. By contrast, making faster predictions requires narrowing the information you consider and using a less complex model of minds and actions. Since Ben often has to make predictions fast enough to actually coordinate his actions with Ayesha’s, and since making predictions consumes scarce cognitive resources, Ben is usually needs to trade accuracy for speed.
So Ben’s model of minds and actions is not built for accuracy.

speed vs accuracy

Since this is an important point for me, let me repeat: any broadly inferrential process must make a trade-off between speed and accuracy.

Henmon (1911, table 2)

speed vs accuracy:
Here you see the results of an old experiment by Henmon who had subjects judge which of two only very slightly different lines was longer. He noted that ‘under each category of judgment the wrong judgments are in general shorter’.

‘the wrong judgments are in general shorter’

This experiment doesn’t provide evidence for a speed-accuracy trade off and wasn’t designed to (speed was not experimentally manipulated). But it’s interesting that the idea of a speed-accuracy trade-off goes back such a long way.
Henmon p. 195: ‘A continuation of this investigation (1) where the time of exposure of stimuli was limited, (2) where the time of judgment was voluntarily shortened or prolonged, (3) and with varying differences in stimuli, should give significant results. footnote: The writer had planned such an investigation, but a change of work has necessitated its indefinite postponement; hence the publication of these preliminary results.’
\textbf{The value of having two systems which process inputs from a single domain arises from this trade-off.} Having multiple systems enables complementary trade-offs to be made. So it is not obvious that there could not be two systems both of which can predict the trajectories of moving objects.
Focus on Ben for a moment.
What mundane purposes does thinking about actions serve? Prediction and coordination; ethical (assigning responsibility, blame; living together); normative (he wants himself and others to live it out as much as to describe how things are; there may also be something about ‘understanding’ here). So it’s not all about accuracy; in fact, of these, only prediction and coordination even potentially requires that his model of actions is accurate.

Functions of Ben’s model of minds and actions:

• ethical
• normative
• predictive

--- speed vs accuracy

So this is the model of minds and actions on which many philosophical theories are based ... they are cast as attempts to characterise this model.

Relying on philosophers to characterise actions
would be like
relying on Aristotelians to characterise physical objects.

In the case of physical objects, I suppose few people seriously think there is much we can understand without appeal to physics.
As Newton stressed, contemporary philosophical methods are not well suited to the task. Contemporary philosophical methods are of limited use in making discoveries about the world.

Godfrey-Smith contrasts models with theories,
and suggests that philosophers are often
best seen as constructing models rather than theories.

Q1

Donald Davidson asks, ‘What is the mark that distinguishes ... actions?’ Are scientific discoveries relevant to answering this question?

Q2

What is the mark that distinguishes actions?

Q3

How are non-accidental matches between intentions and motor representations possible?

So I was asking whether scientific discoveries are relevant ot answering Davidson’s question, ‘What is the mark that distinguishes ... actions?’
My conclusion is that PHILOSOPHICAL THEORIES ARE NOT LIKELY TO BE RELEVANT to answering the question. Because philosophical methods are of limited use in making discoveries about the world.
Ultimately, the scientific discoveries are our only hope.
So why would philosophers think about Davidson’s question at all? One thing philosophical methods are ideally suited to is identifying limits on scientific theories and asking questions. Not knowing things is what philosophers are best at.
This brings me to my next question ...

\section{Intentions and Goals}

\section{Intentions and Goals}
What is the relation between a purposive action and the outcome or outcomes to which it is directed? One way of answering this question appeals to intentions. On any standard view, an intention represents an outcome, causes an action, and does so in a way that would normally facilitate the outcome’s occurrence.
Which events are actions? In philosophy, answering this question would typically answered by appeal to intention or practical reasoning.
Let me suggest one reason why this view seems tempting ...
You tilt the bottle thereby pouring prosecco all over Zac's trousers. You might say, the goal of my actions was not to soak Zac's trousers but to fill his glass.

What is the relation between a purposive action and the outcome or outcomes to which it is directed?

As this illustrates, some actions involving are purposive in the sense that
among all their actual and possible consequences,
there are outcomes to which they are directed
In such cases we can say that the actions are clearly purposive.
Concerning any such actions, we can ask What is the relation between a purposive action and the outcome or outcomes to which it is directed?
The standard answer to this question involves intention.
An intention (1) specifies an outcome,
(2) coordinates the one or several activities which comprise the action;
and (3) coordinate these activities in a way that would normally facilitate the outcome’s occurrence.
What binds particular component actions together into larger purposive actions? It is the fact that these actions are all parts of plans involving a single intention. What singles out an actual or possible outcome as one to which the component actions are collectively directed? It is the fact that this outcome is represented by the intention.
So the intention is what binds component actions together into purposive actions and links the action taken as a whole to the outcomes to which they are directed.
Which events are actions? In philosophy, answering this question would typically answered by appeal to intention or practical reasoning.
Such views tend to be neutral on how the attitudes and processes ultimately connect to bodily movements; that is considered to be merely an implementation detail ...
They are neutral in this sense: the views do not depend in any way on facts about that distinguish one kind of body from another, or on facts about how the body’s movements are ultimately controlled ...
In cognitive science ... little to say about actions whose purposes involve things the motor system doesn’t care about---your motor system doesn’t care whether the plane you are stepping is headed for Milan or for Rome, but this sort of difference can affect whether your actions succeed or fail.

\section{Motor Representation}

\section{Motor Representation}
Motor representations are involved in performing and preparing actions. Not all representations represent patterns of joint displacements and bodily configurations: some represent outcomes such as the grasping of an object, which may be done in different ways in different contexts.
Markers of motor representation \begin{enumerate} \item are unaffected by variations in kinematic features but not goals \citep[e.g.][]{cattaneo:2010_state-dependent,umilta:2008pliers,cattaneo:2009_representation,rochat:2010_responses} \item are affected by variations in goals but not kinematic features \citep[e.g.][]{Fogassi:2005nf,bonini:2010_ventral,cattaneo:2007_impairment,Umilta:2001zr,villiger:2010_activity,koch:2010_resonance} \end{enumerate} So: \begin{enumerate}[resume] \item carry information about goals (from 1,2) \end{enumerate} Also \begin{enumerate}[resume] \item Information about outcomes guides planning-like processes \citep[consider][]{grafton:2007_evidence,jeannerod:1998nbo,wolpert:1995internal, miall:1996_forward,arbib:1985_coordinated,mason:2001_hand,santello:2002_patterns}. \end{enumerate}

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’ \citep[p.~294]{cohen:2004_wherea}.

‘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 \citealp{kawato:1999_internal}). This anticipatory control of grasp, like several other features of action performance (\citealp[see][chapter 1]{rosenbaum:2010_human} 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, \emph{motor representation} is a label for such representations.% \footnote{% Much more to be said about what motor representations are; for instance, see \citet{butterfill:2012_intention} for the view that motor representations can be distinguished by representational format. }]
‘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’ \citep[p.~294]{cohen:2004_wherea}.
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 \citealp{rizzolatti_functional_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.
Since this is important, let me pause for a moment. To say that something is an outcome is not to say very much: merely that it is a possible or actual state of affairs which is brought about in some way by an action.
What I mean is that motor representations represent the sort of outcomes that are plausibly thought of as goals of actions, things such as transporting and breaking an egg, or flipping a switch.
This kind of outcomes are quite different from both patterns of joint displacement and bodily movements and also from end states.
In my terms, a goal is merely outcome. Contrast goals with goal-states, which are mental or functional states which specify goals. A motor representation is a goal-state; the goal is the thing it represents.
Motor schema are just motor representations which specify incomplete outcomes. [Of course schema are incomplete, so do not specify outcomes but outcome types.]
Motor schema are ‘internal models or stored representations that represent generic knowledge about a certain pattern of action and are implicated in the production and control of action’ \citep{mylopoulos:2016_intentions}.
‘Motor schemas are more abstract and stable representations of actions than motor representations.’
‘They are internal models or stored representations that represent generic knowledge about a certain pattern of action and are implicated in the production and control of action. For instance, in the influential Motor Schema Theory proposed by Richard Schmidt (1975, 2003), a motor schema involves a generalized motor program, together with corre- sponding ‘recall’ and ‘recognition’ schemas. The generalized motor program is thought to contain an abstract representation defining the general form or pattern of an action, that is the organization and structure common to a set of motor acts (e.g., invariant features pertaining to the order of events, their spatial configuration, their relative timing and the relative force with which they are produced). This generalized motor program has parameters that control it. In order to determine how an action should be performed on a given occasion, parameter values adapted to the situation must be specified. Thus, a motor schema also includes a rule or system of rules describing the relationships between initial conditions, parameter values and outcomes and allowing us to perform the action over a large range of conditions (the ‘recall schema’ in Schmidt’s terminology). Finally, the motor schema also includes a rule or system of rules describing the relationships between initial conditions, exteroceptive and propri- oceptive sensory feedback during an action, and action outcome (a recognition sche- ma), allowing agents to know when they have made an error – i.e., the action does not have the sensory consequences it is expected to have – and to correct for it.’
Are motor schemas an alterantive to motor representations? Tempting to think that where they talk about motor schema, we think of motor representations that represent outcomes that are relatively distal from action (e.g. are affector-neutral).
This would explain why they contrast motor schema with motor programmes. We use ‘motor representation’ to include both.
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 ...

Aside: The Double Life of Motor Representations

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 will be a focus of interest in a later session. For now it’s just a handy fact that simplifies testing.

‘word listening produces a phoneme specific activation of speech motor centres’ \citep{Fadiga:2002kl}

‘Phonemes that require in production a strong activation of tongue muscles, automatically produce, when heard, an activation of the listener's motor centres controlling tongue muscles.’ \citep{Fadiga:2002kl}

‘Phonemes that require in production a strong activation of tongue muscles, automatically produce, when heard, an activation of the listener’s motor centres controlling tongue muscles.’

How did they reach these conclusions?

birra / berro (pseudo-word) / baffo

Inovlves tongue
No tongue required
Given TMS to motor cortex tp amplify activity. Prediction: MEP in tongue muscle stronger for ‘rr’ than ‘ff’.

Fadiga et al 2002, figure 2

[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 \citealp{rizzolatti:1988_functional,Rizzolatti:2001ug}; 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.

\section{Motor Representations Ground the Directedness of Actions to Goals}

\section{Motor Representations Ground the Directedness of Actions to Goals}
Some motor representations represent action outcomes, play a role in generating actions, and do this in a way that normally facilitates the occurrence of the outcomes represented. Like intentions, motor representations ground the directedness of actions to outcomes which are thereby goals of the actions.
You tilt the bottle thereby pouring prosecco all over Zac's trousers. You might say, the goal of my actions was not to soak Zac's trousers but to fill his glass.

What is the relation between a purposive action and the outcome or outcomes to which it is directed?

As this illustrates, some actions involving are purposive in the sense that
But is intention the only thing that can link actions to outcomes? I will suggest that motor representations can likewise perform this role.
Now as Elisabeth Pacherie has argued (and I’ve had a go at arguing this in joint work with Corrado Sinigaglia recently too), motor representations are relevantly similar to intentions. Of course motor representations differ from intentions in some important ways (as Pacherie also notes). But they are similar in the respects that matter for explaining the purposiveness of action. (1) Like intentions, some motor representations represent outcomes (and not merely patters of joint displacement, say). (2) Like intentions, some motor representations play a role in coordinating multiple more component activities by virtue of their role as elements in hierarchically structured plans. (3) And, like intentions, some motor representations coordinate these activities in a way that would normally facilitate the outcome’s occurrence. The claim is not that \emph{all} purposive actions are linked to outcomes by motor representations, just that some are. In some cases, the purposiveness of an action is grounded in a motor representation of an outcome; in other cases it is grounded in an intention. And of course in many cases it may be that both intention and motor representation are involved.
I started by observing that there are two quite different approaches to answering the question, Which events are actions? What does the ground I’ve so far tell us about this?
I don’t think it tells us much yet (there’s much more to come).
First, both stories are stories about purposive actions. So they don’t have clearly demarcated domains.
Second, it may make it tempting to think that motor representations are just a kind of intention, and so to take the radical view that there are not really two distinct stories here at all.

intention = motor representation? No!

Q1

Donald Davidson asks, ‘What is the mark that distinguishes ... actions?’ Are scientific discoveries relevant to answering this question?

Q2

What is the mark that distinguishes actions?

Q3

How are non-accidental matches between intentions and motor representations possible?

In conclusion, here are my questions.
The answer to the first question is that, ultimately, scientific discoveries are our only hope. And in fully answering the second question, we will have to appeal to both motor representation and a state that is like intention.

appendix

## Motor Representations Aren’t Intentions

\section{Motor Representations Aren’t Intentions}

\section{Motor Representations Aren’t Intentions}
Explains why motor representations aren’t intentions.
As background we first need a generic distinction between content and format. Imagine you are in an unfamiliar city and are trying to get to the central station. A stranger offers you two routes. Each route could be represented by a distinct line on a paper map. The difference between the two lines is a difference in content.
Each of the routes could alternatively have been represented by a distinct series of instructions written on the same piece of paper; these cartographic and propositional representations differ in format. The format of a representation constrains its possible contents. For example, a representation with a cartographic format cannot represent what is represented by sentences such as There could not be a mountain whose summit is inaccessible.'\footnote{ Note that the distinction between content and format is orthogonal to issues about representational medium. The maps in our illustration may be paper map or electronic maps, and the instructions may be spoken, signed or written. This difference is one of medium.} The distinction between content and format is necessary because, as our illustration shows, each can be varied independently of the other.
Format matters because only where two representations have the same format can they be straightforwardly inferentially integrated.
To illustrate, let’s stay with representations of routes. Suppose you are given some verbal instructions describing a route. You are then shown a representation of a route on a map and asked whether this is the same route that was verbally described. You are not allowed to find out by following the routes or by imagining following them. Special cases aside, answering the question will involve a process of translation because two distinct representational formats are involved, propositional and cartographic. It is not be enough that you could follow either representation of the route. You will also need to be able to translate from at least one representational format into at least one other format.
How in general can we identify or distinguish representational formats? Because representational formats are typically associated with characteristic performance profiles, it is sometimes possible to infer similarities and differences in representational format from similarities and differences in the processes in which representations feature.
To illustrate, suppose that you have a route representation and I want to work out whether it this representation has a cartographic or propositional format. One way to do this might be to test your performance on different tasks. If the representation is propositional you are likely to be relatively fast at identifying key landmarks but relatively slow at translating the route into a sequence of compass directions; but the converse will be true if your representation is cartographic.
The same principle---distinguishing and identifying formats by measuring characteristic processing profile---works for mental representations too.
To illustrate, compare imagining seeing an object moving with actually seeing it move. For this comparison we need to distinguish two ways of imagining seeing. There is a way of imagining seeing which phenomenologically is something like seeing except that it does not necessarily involve being receptive to stimuli. This way of imagining seeing, sometimes called sensory imagining', is commonly distinguished from cognitive ways of imagining seeing which might for example involve thinking about seeing. It is this way of imagining seeing an object move that we wish to compare with actually seeing an object move.
Imagining seeing an object move and actually seeing an object move have similarities in characteristic performance profile (\citealp{kosslyn:1978_measuring}; \citealp[p.\ 99ff]{kosslyn:1994_image}; \citealp{kosslyn:1978_visual})
Imagining seeing an object move and actually seeing an object move have similarities in characteristic performance profile. For instance, whether an object can be seen all at once depends on its size and distance from the perceiver; strikingly, when subjects imagine seeing an object, whether they can imagine seeing it all at once depends in the same way on size and distance (\citealp{kosslyn:1978_measuring}; \citealp[p.\ 99ff]{kosslyn:1994_image}).
Also, how long it takes to imagine looking over an object depends on the object's subjective size in the same way that how long it would take to actually look over that object would depend on its subjective size \citep{kosslyn:1978_visual}.
The similarities in characteristic performance profile and the particular patterns of interference are good (if non-decisive) reasons to conjecture that imagining seeing and actually seeing involve representations with a common format.
The way imagining performing an action unfolds in time is similar in some respects to the way actually performing an action of the same type would unfold \citep{decety:1989_timing, decety:1996_imagined, Jeannerod:1994oz, parsons:1994_temporal, frak:2001_orientation}
One way of imagining action is phenomenologically something like acting except that such imaginings are not necessarily responsive to the features of actual objects and do not necessarily result in bodily movements.
There is evidence that the way imagining performing an action unfolds in time is similar in some respects to the way actually performing an action of the same type would unfold.
For instance, how long it takes to imagine moving an object is closely related to how long it would take to actually move that object \citep{decety:1989_timing, decety:1996_imagined, Jeannerod:1994oz}.
In addition, for actions such as grasping the handle of a cup, manipulating the target object in ways that would make the action harder (such as orienting the cup's handle to make it less convenient for you to grasp) make a corresponding difference to the effort involved in imagining performing the action \citep{parsons:1994_temporal, frak:2001_orientation}.
Contrast imagining rotating a ball with imagining seeing a ball rotate.
As is implied by what we’ve already said, these have quite different characteristic performance profiles.
How quickly the former can be done is a function of how long it would take the agent to rotate the ball, whereas how quickly the latter can be done depends on how rapidly the ball can rotate and still be perceived as rotating.
Further, in some cases rotating a ball clockwise is easier than rotating it anti-clockwise, and so is imagining a ball rotate. By contrast, the effort involved in actually seeing or imagining seeing a ball rotate does not similarly differ depending on direction.
Judging the laterality of a hand vs of a letter. For ordinary subjects, the tasks differ: they are less accurate when the hand's position is biomechanically awkward. But \citet{Fiori:2012fk} show that the tasks do not so differ for subjects suffering Amyotrophic Lateral Sclerosis (ALS), which impairs motor representation \citep{parsons:1998_cerebrally}.
It may be objected that performance differences such as these can be explained without appealing to a difference in format. After all, rotating a ball involves an action whereas a ball rotating does not; consequently, imagining the former may be thought to differ from imagining the latter with respect to the contents of the representations involved. Supposing that there are differences in content here and in other cases, could these fully explain differences in performance profile? To see why not, consider two tasks involving mental rotation. Judging the laterality of a rotated letter is thought to involve phenomenologically vision-like imagination \citep{jordan:2001_cortical}, whereas judging the laterality of a rotated hand is thought to involve phenomenologically action-like imagination \citep{parsons:1987_imagined, gentilucci:1998_right}. Ordinary subjects who are asked to judge the laterality of a hand rotated to various degrees are less accurate when the hand's position is biomechanically awkward. By contrast, no such effect occurs for comparable tasks involving letters rather than hands. How could this difference in performance in imagining hands and letters be explained? Consider the claim that the difference in performance can be fully explained by a difference in the content of the representations involved. Initially this might seem plausible because one task involves hands whereas the other involves letters. However, there are subjects who can perform both tasks but whose performance is not different for hands and letters \citep{Fiori:2012fk}. These are subjects suffering Amyotrophic Lateral Sclerosis (ALS), which impairs motor representation \citep{parsons:1998_cerebrally}. Since ALS and ordinary subjects encounter the same stimuli and perform the same tasks, there seems to be no reason (other than our hypothesis about a difference in format) to suppose that the two groups' performance involves representations with different contents. So if the hand-letter difference in performance were entirely explained by a difference in content, we would expect ALS and ordinary subjects to exhibit the same difference in performance. But this is not the case. This is an obstacle to supposing that the hand-letter difference in performance in ordinary subjects could be explained by appeal to content.
So far we have been arguing that motor and visual representations differ in format. Why suppose that motor representations also differ in format from intentions? Contrast two ways of imagining taking a shot in basketball, one involving the phenomenologically action-like kind of imagination and the other involving a cognitive kind of imagination. The contrast we require is roughly between the way a former player might imagine this and the way that someone who has only ever read about basketball might imagine it. As we have seen, the way phenomenologically action-like imagination unfolds in time and the amount of effort it involves will depend on bio-mechanical, dynamical and postural constraints, among others. These constraints are closely related to those which govern actually performing such actions \citep{Jeannerod:2001yb}, and some can be altered by acquiring or losing motor expertise. By contrast no such constraints would be expected always to apply where a cognitive kind of imagination is involved. In line with the general strategy of inferring differences in format from differences in characteristic performance profile, we conclude that motor representations differ in format from those involved in cognitive kinds of imagination, which are plausibly propositional.
\begin{enumerate} \item Only representations with a common format can be inferentially integrated. \item Any two intentions can be inferentially integrated in practical reasoning. \item My intention that I visit the ZiF is a propositional attitude. \end{enumerate} Therefore: \begin{enumerate}[resume] \item All intentions are propositional attitudes \end{enumerate} But: \begin{enumerate}[resume] \item No motor representations are propositional attitudes. \end{enumerate} So: \begin{enumerate}[resume] \item No motor representations are intentions. \end{enumerate}

Only representations with a common format can be inferentially integrated.

Any two intentions can be inferentially integrated in practical reasoning.

My intention that I visit the ZiF is a propositional attitude.

Therefore:

No motor representations are propositional attitudes.

All intentions are propositional attitudes

No motor representations are intentions.