Understanding Simulation1

susan hurley

University of Bristol

Alvin Goldman and I are on the same side of the broad debate

between simulation theory and its rivals. I’ve learned a great deal

from his rich and thought-provoking book, and we agree about many

things. We are both simulation theorists who are attracted to the

economy of simulating as opposed to theorizing (178–80), yet allow a

role for theorizing within hybrid views of mindreading (43ff).2 We

both believe that mindreading should be explained in ways that draw

on philosophy, psychology and neuroscience and that are empirically

exposed rather than purely a priori (3–5, 9). There are some points

of outright disagreement, however, and some issues on which I am

not clear about Goldman’s position. This commentary presents an

opportunity to explore differences of approach within the simulation

theory tent.

My remarks are divided into four sections:

s Two Concepts of Simulation

s High-Level Versus Low-Level Simulation

s Mirroring, Control, and Simulation

s Self Versus Other: Egocentric Bias or Reality Bias?

1 This paper derives from a commentary by Susan Hurley in an ‘‘author meets crit-

ics’’ session on Alvin Goldman’s Simulating Minds (2006), at the Pacific APA 2007

meeting. At the request of the author, who died before completing work on this

paper, Mark Greenberg revised and edited the paper.2 Page numbers without further citation refer to Goldman 2006.

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Philosophy and Phenomenological ResearchVol. LXXVII No. 3, November 2008� 2008 International Phenomenological Society

1. Two Concepts of Simulation

In this section, I will distinguish two ways of understanding

simulation—in terms of resemblance and reuse. Although Goldman’s

official account of simulation relies on the notion of resemblance, I’ll

suggest that the notion of reuse may be implicit in his discussions as

well. I’ll argue that the understanding of simulation in terms of reuse is

the more fundamental one.

First, I’ll give an exposition of Goldman’s official resemblance

account of simulation. In the course of this discussion, I’ll point out

two other distinctions that are related to the reuse ⁄ resemblance

issue—a distinction between processes and outcomes of processes

and a distinction between resemblance within one person and across

persons. Second, I’ll examine Goldman’s ways of contrasting simula-

tion and theory, which suggest an alternative account of simulation

in terms of reuse. Finally, I’ll draw out the contrast between reuse

and resemblance explicitly, and suggest that reuse is the more fun-

damental idea and should provide the generic understanding of

simulation.

Goldman begins by noting some ideas associated with simulation

theory: of empathy, putting oneself in another’s place via pretend

states, using one’s own psychology to mimic other minds, projecting

from the first to the third person (17–20). He explains that a simulator

uses processes of the same kind as the target uses in order to read the

target’s mind: for example, uses decision-making mechanisms of the

kind the target would use in decision-making, rather than factual rea-

soning mechanisms applied to the target’s mental states, which the tar-

get would not use in decision-making (34). He proceeds to distil a

generic conception of simulation that involves copying and resem-

blance, which can be paraphrased as follows:

Process P is a simulation of process P’ if, by definition, P duplicates,replicates, or resembles P’ in significant respects, and in doing so fulf-

ils a purpose or function. (37)

Mental simulations are simulations of mental processes. Simulation

theories of mindreading hold that mindreading aims at simulation and

hence at resemblance, not that mindreading always succeeds in produc-

ing a resemblance (38). Note that the official generic conception of sim-

ulation applies to processes, not the states that are their outcomes.

In Goldman’s view of mental simulation, what and where are the

entities that resemble one another? Both questions have dual answers.

Officially, the resembling entities are processes, but Goldman also

often talks of resemblance between the outputs of those processes:

756 SUSAN HURLEY

mental states and their contents.3 I’ll refer to this as the process ⁄outcome duality in his discussions. For example, Goldman explains

that, according to simulation theory (‘ST’), mindreading aims at simu-

lation of, and hence at matching, the target’s mental states, although it

may not succeed; pretend states may correspond only minimally to

mental states of the target (38). ST’s aim is thus put in terms of match-

ing states rather than matching processes. And we are told that the cog-

nitive mechanisms that operate on pretend input states produce

roughly the same sorts of output states as genuine nonimagined coun-

terpart inputs produce (287; see also 283–286 on resemblance between

pretend and real mental states).

As Goldman recognizes (37), there is also an interpersonal ⁄ intraper-sonal duality in his discussions. Simulative mindreading aims at resem-

blance between the processes or states of the mindreader and the

target: interpersonal resemblance. But Goldman’s discussion also makes

substantial reference to intrapersonal resemblance, for example, between

experience of emotion and recognition of emotion by the same person.

In another example of intrapersonal resemblance, the visualizing pro-

cess is regarded as similar to the seeing process, and the content of

visualizing is regarded as resembling the content of seeing (38). (Again,

note how for visualizing, resemblance is applied both to processes and

to the contents of states that are the outputs of processes.) Goldman dis-

tinguishes sharing of representations across and within individuals, and

comments that sharing within individuals is the case that most interests

him, as when pretend states are approximate equivalents of genuine

first order states in the same person (211; see also 283–284).

So far, I have highlighted two dualities in Goldman’s discussions.

First, while the official generic conception of simulation is in terms of

resemblance between processes, there is also discussion of resemblance

between outputs of processes—mental states. Second, resemblance is

applied both within one person, as between pretend and real states, or

between emotion experience and emotion recognition, and also inter-

subjectively, between mindreader and target. Indeed, simulative mind-

reading appears to involve both applications of resemblance: the

successful mindreader uses the same processes in himself both to experi-

ence and to recognize emotion, and his emotional processes or states

are similar to those of his target. Or again, the successful mindreader

generates pretend states in himself that resemble real mental states of his

own, and that also resemble mental states of his target.

3 At one point, Goldman suggests that a single mental state is the minimal case of a

process (132). I address this suggestion below (see the last five paragraphs of this

section).

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The process ⁄outcome duality and the interpersonal ⁄ intrapersonalduality are found throughout the book and contribute to a sense of

ambiguity about the fundamental idea of simulation employed. I’ll now

suggest that there are in fact two different concepts of simulation in

play, which should be distinguished: reuse and resemblance. Both are in

play, for example, in the general idea of using one’s own mechanisms

on pretend states to mirror or mimic the minds of others, which Gold-

man regards as ‘[a] fundamental idea of ST’ (20). Ultimately, I’ll argue

that the fundamental generic concept of simulation is reuse, not resem-

blance.

The contrast between reuse and resemblance emerges from attention

to another contrast, that between simulating and theorizing. My claim

will be that reuse rather than resemblance is really the core idea that

distinguishes simulating from theorizing.

How does Goldman distinguishing simulating from theorizing? I’ll

begin to answer this question by explaining how he does not distinguish

them. He rejects the ideas that any body of information is a theory

(25) or that any appeal to information, information–processing, or

computation implies theorizing (34, 150, 175). While theorizing involves

applying laws and making inferences from them, Goldman does not

rely on a merely negative characterization of simulation as not involv-

ing laws in these ways (34). He aims for a positive characterization of

simulation.

ST typically invokes the use of mental processes by the mindreader,

while theorizing invokes factual reasoning or information about mental

processes (28–29, 40). This suggests that something like a use ⁄mention

distinction is fundamental to distinguishing simulating from theorizing

(see also 177, 181). In response to Daniel Dennett’s argument that

simulation collapses into theorizing since theorizing is needed to drive

simulation, Goldman draws the important distinction between theory-

driven and process-driven simulation (31–32). A computer may simulate

wind flow around a suspension bridge by applying the laws of a rele-

vant theory to derive a symbolic description or graphical representation

that is about the target. In doing so, it does not use or undergo the

same type of processes as its target undergoes, but rather represents the

target processes, using another mechanism. This is not simulation in

the sense that contrasts with theorizing; it is driven by theorizing

(35–36). By contrast, a simulating system may resemble a target by

using processes shared with the target; it needs no theory about such

processes in order to use them. Such process-driven simulating is what

contrasts with theorizing. For example, Goldman explains, ST holds

that normal people use the same mental equipment in mindreading

emotion that they use when experiencing emotion, whereas theory

758 SUSAN HURLEY

theory (TT) holds that mindreading emotion exploits information about

emotion (114). As evidence of simulation in low level mindreading,

Goldman cites, among other things, the associations between deficits

for experiencing and for recognizing specific emotions, and the co-

localization of neural activity in experiencing and recognizing specific

emotions (115–119, 122). This is evidence that processes that are used

for one purpose are being reused for another.

According to the reuse conception of simulation, what distinguishes

simulating from theorizing is that information about a process is gener-

ated by reusing that very process, as opposed to by theorizing about

the process. The primary application of simulation as reuse is intraper-

sonal: processes for experiencing emotion are reused for recognizing

emotion, processes for seeing are reused for visualizing. Reuse of pro-

cesses is distinct from resemblance between mental states, whether

interpersonal (between mindreader and target) or intrapersonal

(between real and pretend states in enactive imagination). Moreover, in

general, the same process need not produce similar states each time

it is used or reused, and similar states can be produced by different

processes.4

There are two centers of gravity in Goldman’s discussions of simula-

tion. The implicit reuse conception focuses on intrapersonal reuse

of processes (A), while the official resemblance conception focuses on

interpersonal resemblance of mental states that are the outputs of

processes (B).

Two conceptions of simulation Processes Outputs, mental states

Intrapersonal A. Reuse C.Interpersonal D. B. Resemblance

The reuse ⁄ resemblance distinction is blurred by the fact that we

may also appeal to intrapersonal resemblance between the outputs of

4 Editor’s note: It seems that a type ⁄ token distinction is playing an important role in

Hurley’s thinking here. Reuse of a process is reuse for a particular purpose of a

token process that is used for other purposes. By a process, Hurley evidently means

not a series of events, but a mechanism or capacity. A process in one person can be

of the same type as a process in another person, but cannot be the same token pro-

cess. By contrast, in the intrapersonal case, we can have either two token processes

of the same type or reuse of the same token process. The chart in the text below

does not have room for the distinction between intrapersonal resemblance and intra-

personal reuse. As Hurley says below (last paragraph of this section), her view is

that intrapersonal resemblance of processes—i.e., sameness of type—is not sufficient

for simulation. There are interesting questions about the identity conditions for a

token process (in Hurley’s sense of a mechanism or capacity).—MG

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processes (box C), as when Goldman claims that the content of visual-

izing resembles the content of seeing. And we may appeal to interper-

sonal sameness of processes (box D), as when Goldman supposes that

mental processes used for mindreading are of the same kind as those

that produce the mental states of the mindreader’s target. However,

these two ‘mixed’ cases are off-center for purposes of characterizing

simulation. Intrapersonal resemblance between a visual perceptual state

and a visualization (box C) would not count as process-driven simula-

tion unless visualization reused processes used by that same person for

seeing. Without reuse of process, visualization could be like computer

simulations of wind flow around a suspension bridge—the mechanism

could involve application of a theory of vision to produce a graphical

representation the content of which is similar to that of seeing. And

interpersonal similarity of processes between mindreader and target

(box D) does not make for process-driven simulation unless intraper-

sonal reuse of the mindreader’s own mental processes is driving mind-

reading. That is, simulation requires that interpersonal similarity

between mental processes of mindreader and target arise from intraper-

sonal reuse of the mindreader’s own mental processes, not in some

other way. If the mindreader’s emotion-recognition processes do not

reuse his own emotion-experiencing processes, they are not simulative,

even if the mindreader undergoes emotion-experiencing processes of the

same kind as his target’s.

I’ve just argued that the two off-center cases of simulation (boxes C

and D), which may seem to fall between the poles of reuse and resem-

blance, tacitly rely on simulation as reuse (box A). It is a small further

step to argue that cases of simulation involving interpersonal resem-

blance of states (box B) also tacitly rely on simulation as reuse (A).

Similar points apply here. Interpersonal similarity of states between

mindreading and target (box B) does not make for process-driven

simulation unless intrapersonal reuse of the mindreader’s own mental

processes is driving mindreading. The mindreader’s undergoing emo-

tion-experiencing states of the same kind as his target’s is not enough,

if his emotion-recognition processes do not reuse his emotion-experi-

encing processes. The central case for the resemblance account, involv-

ing interpersonal resemblance of states, thus also tacitly relies on

simulation as reuse.

My central point in this section has been that reuse rather than

resemblance is the core generic sense of process-driven simulation.

Reuse is critical to distinguishing simulating from theorizing. More-

over, resemblance, whether between processes or their output states,

whether intrapersonal or interpersonal, does not make for simulation

without the element of intrapersonal reuse of process. Arguably, this is

760 SUSAN HURLEY

implicit in Goldman’s own discussion, and his own concept of

simulation as opposed to theory is best characterized in terms of reuse

rather than resemblance.

2. High-Level Versus Low-Level Simulation

Goldman distinguishes higher and lower level simulative mindreading.

I do not have a clear view of this distinction, however, and would like

to explain my uncertainty and ask for clarification.

Goldman’s prototype of low level simulation involves mirroring of

emotions or intentions, while his prototype of high level simulation

involves the use of enactment imagination to produce pretend states

(147). How is each level characterized further?

Low level simulative mindreading is described as relatively simple,

primitive, automatic and largely unconscious (49, 113, 131–132). High

level simulative mindreading has one or more of the following features:

(a) it targets complex mental states such as propositional attitudes, (b)

aspects of it are subject to voluntary control, at least ‘potentially and

intermittently,’ and (c) it has ‘some degree of accessibility to conscious-

ness’ (132, 147). Controlled processes are supposed to be an ‘important

factor’ in enactment imagination (210).

In low level simulation, Goldman understands resemblance function-

ally or neurally rather than phenomenally. How should we understand

resemblance in high level simulation? Does it involve phenomenal or

personal level resemblance? Early on, Goldman contrasts enactment

imagination with supposition: when I suppose that I am elated, I

merely assume or hypothesize it, while enactive imagination of being

elated involves conjuring up ‘a state that feels, phenomenologically,

rather like a trace or tincture of elation’ (47). However, Goldman does

not want to rely on phenomenological resemblance to characterize high

level simulation, but regards functional and neural resemblance as

more promising (49, 150–151).

Moreover, much high level mindreading is unconscious, and can

include enactment imagination that is unconscious or automatic, as

well as conscious and voluntarily controlled (151, 161–162). While

Goldman’s high ⁄ low distinction overlaps with the distinction between

controlled and automatic processes, it doesn’t precisely match it (207).

What does the high ⁄ low distinction boil down to? Goldman’s dis-

tinction does not coincide with conscious vs. unconscious, or controlled

vs. automatic (as he indicates). High level processes can be unconscious

or automatic, while low level processes are only comparatively auto-

matic and ‘largely unconscious.’ These seem to be differences in degree

rather than in kind. I don’t understand the gist of the complex vs.

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simple or primitive distinction, if that is critical. Does this have any-

thing to do with a distinction between representations with and without

conceptual structure? It might be argued that higher levels of mind-

reading can build on lower levels (I argue this in Hurley 2007); but

Goldman does not make such a suggestion.

We have our two prototypes of enactive imagination and mirroring,

but I’m left very uncertain how they support a generalizable high ⁄ lowdistinction. Like Gallese, I think of mirroring in functional subperson-

al terms, and mirror systems as the neural implementation of func-

tional mirroring. Indeed, my initial response to Goldman’s high ⁄ lowdistinction was to regard it as a version of the personal ⁄ subpersonaldistinction. But it doesn’t take long to see that this reading isn’t right;

Goldman makes no explicit appeal to the personal ⁄ subpersonal dis-

tinction in characterizing high vs. low, nor does he invoke standard

criteria for personal vs. subpersonal levels. Personal vs. subpersonal

seems to cut across Goldman’s distinction: for example, experiencing

and understanding emotions are low level processes but can certainly

be described at the personal level.

For these reasons, I’ve found Goldman’s distinction elusive and

would welcome clarification.

3. Mirroring, Control, and Simulation

I’ll now focus on mirroring, which Goldman views as a form of low

level simulation, and its relationship to control. I’ve addressed this

relationship in detail elsewhere (Hurley 2007), and there seems to be

substantial disagreement between us here. After reviewing Goldman’s

account of mirroring, I’ll argue that one source of what I regard as

Goldman’s mistaken views on relations between mirroring and control

is his focus on mirroring for emotion recognition rather than for inten-

tion reading. It is mirroring of instrumental, i.e., goal-directed or

intentional, action rather than expressive action that reveals the funda-

mental relationship between control and mirroring. Whether this

extends to the case of expressive action is a further question, on which

the fundamental relationship does not depend. I’ll also argue that there

is a tension between Goldman’s views on this topic and his views on

relationships between ST and TT.

Goldman provides four models of low level simulation for emotion

recognition. Three of the models are broadly similar in postulating that

the mindreader’s seeing another’s facial expression of emotion leads to

his having a similar emotion. They differ only in the links (italicized)

between these. (I will not discuss Goldman’s other model, which he

calls ‘generate and test.’)

762 SUSAN HURLEY

‘Reverse simulation’ for emotion: Target other has emotion, whichleads to other’s facial expression, which leads to mindreader’s seeingother’s facial expression, which leads to mindreader’s similar facialexpression, which leads to mindreader’s similar emotion, the like of

which mindreader attributes to the target other. (125–127, 130)

Goldman calls this ‘reverse simulation,’ presumably because the way

the mindreader’s facial expression leads to his emotion reverses our

normal assumption that emotion leads to facial expression. General-

izing, reverse simulation would involve behavior leading to the men-

tal state that we normally regard as causing that behavior. What is

reversed is not the direction of simulation, but the assumed direction

of causation from mental state to behavior. There is some evidence

for this reversal in the case of facial expression (126, 130), though

Goldman regards such reversal as exceptional given ‘the standard

forward directionality of mental processes’ (125, 183–184; see also

45).

‘As if reverse simulation’ for emotion: Target other has emotion, whichleads to other’s facial expression, which leads to mindreader’s seeing

other’s facial expression, which leads to somatosensory activation sim-ilar to that which would occur if the mindreader were to have a simi-lar facial expression, which leads to the mindreader’s similar emotion,the like of which the mindreader attributes to the target other. (127,

131)

Goldman calls this ‘as if reverse simulation,’ since it bypasses an actual

similar facial expression in the mindreader and instead goes via

somatosensory representation of what it would feel like if the mind-

reader had that facial expression.

Mirroring for emotion: Target other has emotion, which leads toother’s facial expression, which leads to mindreader’s seeing other’sfacial expression, which leads to mindreader’s similar emotion, the like

of which the mindreader attributes to the target other. (127–129,131–132)

Here, the link between the mindreader’s seeing the other’s facial expres-

sion and his having a similar emotion is direct and unmediated. The

mindreader uses his own emotion to recognize the target’s emotion.

Goldman has evidence-based doubts about mediating links postu-

lated by the reverse simulation and as if reverse simulation models of

emotion recognition (129–131), but thinks a good case can be made for

the unmediated mirroring model, for mindreading of emotions, feelings,

and intentions (131–132, 140).

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More generally, mirroring involves a regular causal path from

another’s mental state to behavior by the other and from an observer’s

perception of that behavior directly to a similar mental state in the

observer (133). The striking aspect of mirroring is the second link,

between the observer’s perceiving another’s behavior and his having a

mental state similar to that which caused the other’s behavior. On a

resemblance account of simulation, mirroring is simulation because of

the interpersonal resemblance of mental states. On a reuse account,

mirroring is simulation because of the intrapersonal reuse, in perceiving

another’s behavior as action, of motor processes that tend to cause

behavior.

The intrapersonal reuse aspect of mirroring could arise in develop-

ment through Hebbian associations whereby cells that ‘fire together

wire together,’ as when one performs a hand movement and sees

one’s hand move. (Goldman attributes this point to Keysers and Per-

rett 2004, but a prior attribution is due to Heyes 2001; see also Heyes

2005; Hurley 2005, 2007). Note the associative bidirectionality implicit

in this account of mirroring: moving one’s hand regularly leads to

seeing one’s own hand movement. An association is thus formed

between neural processes that tend to cause movement and neural

processes that enable perception of such movement. As a result, see-

ing another’s similar hand movement can activate a neural process

that tends to cause one’s own hand movement (though such move-

ment may be inhibited).

This bidirectionality, between processes for perceiving behavior and

processes that tend to cause behavior, is an essential aspect of mirror-

ing. It should not be confused with the bidirectionality implied by

what Goldman calls ‘reverse simulation’ and rejects on the grounds

that psychological processes are unidirectional (except in the case of

emotional expressions). The difference is exactly this: the bidirection-

ality of mirroring is between processes for perceiving behavior and pro-

cesses that tend to cause behavior, while the bidirectionality of

‘reverse simulation’ is between (processes for) behavior itself and states

(or processes) that tend to cause behavior. Perceiving another’s behav-

ior as intentional may activate a similar intention, even if merely

moving in a certain way does not activate an intention to move in

that way. I suggest that Goldman’s usage of the term ‘reverse simula-

tion’ for simulation that moves from behavior to its cause is better

avoided, because it lends itself to confusion with the bidirectionality

inherent to mirroring (hence I keep this usage in scare quotes). More-

over, the very account of mirroring Goldman endorses in terms of

Hebbian associations (142–143) demonstrates that mental processes

764 SUSAN HURLEY

can be bidirectional, contrary to his general skepticism about this

possibility (45, 125–127, 183–184).5

Goldman focuses on mirroring in low level mindreading of emo-

tions, but also recognizes the application I and others have focused on,

namely, mirroring for intention reading (138–140), which relates

directly to the main focus of work on neural mirror systems. My

account, unlike Goldman’s, is firmly at the subpersonal level.

Here is how Goldman’s mirroring model would apply to intention

reading:

Mirroring for intention: Target other has intention, which leads toother’s goal-directed action, which leads to mindreader’s seeing other’sgoal-directed action, which leads to mindreader’s similar intention, the

like of which the mindreader attributes to the target other.

Goldman’s ‘reverse simulation’ and ‘as if reverse simulation’ models

are not particularly relevant to the issues that follow about mirroring

and control.6

Having reviewed Goldman’s conception of mirroring, we can now

address relations between mirroring and control. As Goldman explains,

Vittorio Gallese (2001) understands simulation (for intentions and emo-

tions, inter alia) in a widely used generic sense that he locates within

control theory. As I read Gallese, he understands mirroring as a form

of simulation in this sense. However, Goldman comments that this is

not clear to him, and says that ‘it is unclear how the control functional

5 My shared circuits model (Hurley 2005, 2007) uses the term reverse simulation to

mean something quite different, in the context of mirroring’s inherent bidirectionali-

ty: to refer to the use of associations to simulate processes that tend to cause behav-

ior given perception of behavior, as opposed to simulating the perceived effects

of behavior given processes that tend to cause behavior. In my usage the direction

of simulation is reversed: from simulation of effects given causes to simulation of

causes given effects. Of course, we should not quarrel over labelling. Nevertheless, I

do think that Goldman’s usage can be quite puzzling. For example, he says: ‘I know

of no theoretical analysis or experimental evidence that bears directly on simula-

tion’s role in retrodictive mental attribution’ (184). However, the term ‘retrodictive

mental attribution’ is naturally understood to include cases in which perception of

behavior activates processes that tend to cause similar behavior. And this, we have

seen, is inherent to mirroring, which Goldman regards as a ‘clear form’ of simula-

tion (144).6 Nevertheless, to be systematic: the other two models would have the same endpoints

but differ in postulating intermediate links between perception of other’s action and

mindreader’s intention: ‘Reverse simulation’ for intention would postulate (implausi-

bly) that observing the target’s behaviour leads to similar actual behaviour by the

mindreader, which leads to the mindreader’s similar intention. ‘As if reverse simula-

tion’ for intention would postulate that observing the target’s behaviour leads to

somatosensory activation similar to that which would occur if the mindreader were

to engage in similar behaviour, which leads to the mindreader’s similar intention.

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approach would actually apply to this case [interpersonal mirroring],

examined in detail’ (215). True, Gallese does not explain the relation-

ship between control and mirroring in detail. It was partly for this rea-

son that I developed the shared circuits model, which precisely does

spell out the relationship, in a way that builds on and is consistent with

Gallese’s views. Goldman does not consider my account of exactly

what puzzles him in Gallese’s views.

Here is a generic account of sensorimotor control, without the tech-

nical terminology of efference copy and forward models. Consider

how, when I move my hand, I usually see and feel it move. Movement

produces regular sensory effects or feedback; motor and sensory signals

thus form sensorimotor associations (recall: neurons that fire together

wire together). Perhaps my goal is to grasp a peanut, and this goal is

neurally represented as target sensory inputs associated with peanut

grasping. As my hand moves, sensory feedback may be compared neu-

rally with the sensory target, and error signals used to adjust motor

output until sensory feedback matches sensory target. This is basic

feedback control.

Control can be improved by neural simulations. These use already

established sensorimotor associations predictively: motor processes are

used not just to cause movement but reused to anticipate associated

sensory feedback. Predicted sensory feedback can now be used to

adjust motor output in order to match the sensory target. A control

process that uses predicted sensory feedback in this way can be faster

and smoother than one that waits for actual sensory feedback. Note

that such a process involves simulation in the sense of intrapersonal

reuse, which I argued is the core generic sense of process-driven simula-

tion. This is also Gallese’s sense of simulation when he links it to con-

trol. Note also that it is not essential to simulation in this sense that it

be used offline (cf. Goldman, 20); predictive simulation can be used

online to improve sensorimotor control during action.

Goldman attempts to apply ideas from control theory to his favored

kind of mirroring, in emotion recognition. He considers recognition of

disgust from a facial expression of disgust, and fails to find control

phenomena. He concludes that: ‘In short, it seems impossible to com-

bine Gallese’s control-theoretic definition of simulation with the inter-

personal, replicationist sense of simulation’ (216). However, this is too

swift. Goldman has considered only how control might relate to emo-

tion recognition based on observing facial expressions, not how control

might relate to intention reading based on observing instrumental

actions—though he thinks that there is also a good case for mirroring-

based mindreading for intentions. But, as noted above, instrumental

action and intention reading provide the natural context in which to

766 SUSAN HURLEY

find control phenomena, not expressive action and emotion reading.

Since facial expressions are primarily expressive rather than goal-direc-

ted or instrumental, the idea of monitoring sensory feedback in order

to obtain a match to a goal seems out of place here (actors and actres-

ses aside). So does the idea of predictively simulating sensory feedback

in order to improve instrumental control. By contrast, sensorimotor

control is relevant to instrumental action, such as moving your hand in

order to grasp a peanut.

Why then does Goldman consider expressions of emotion but not

instrumental action in assessing the relationship between control and

mirroring? True, he resists the idea that all mirroring phenomena are

motoric phenomena (211). But this doesn’t provide a reason for

neglecting the motor aspects of mirroring where they are relevant.

Motoric mirroring may be fundamental to relations between control

and mirroring even if not all mirroring is motoric.

Here is the way the shared circuits model links mirroring to simula-

tion in a control framework. Control involves simulation when motor

processes that tend to cause behavior are reused intrapersonally to

anticipate the sensory effects or feedback from such motor processes. As

I explained earlier, mirroring is simulation (on my view) because motor

processes that tend to cause behavior are reused intrapersonally to per-

ceive another’s behavior as action. What is the relationship between

anticipating sensory feedback from one’s own motor processes and per-

ceiving another’s similar behavior as action? Sensory input from one’s

own and another’s behavior of the same kind (consider hand move-

ments) can be similar enough for perspective-invariant neurons or neu-

ron-groups to respond to both, without distinguishing them. If so, then

the same sensorimotor associations can serve simulative functions in

control and in mirroring. They can be used in control to simulate the

sensory effects of motor processes and in mirroring to simulate the

motor processes that tend to cause similar sensory effects in observed

behavior. The sensorimotor association is bidirectional; this is the bidi-

rectionality between processes for perceiving behavior as action and

processes that tend to cause behavior, which I earlier explained is

inherent to mirroring. Mirroring reverses the direction of association

found in control: control simulates the sensory effects of given motor

causes, while mirroring simulates the motor causes of given sensory

effects. Both involve simulation in the core generic sense of intraper-

sonal reuse.

The interpersonal aspect of mirroring arises as an artefact of neural

failure to distinguish between the sensory effects of one’s own motor

processes (seeing your own hand movement) and sensory inputs from

similar observed behavior (seeing another’s similar hand movement).

SYMPOSIUM 767

Mirror neurons likewise display indifference to the distinction between

self and other. Of course, the interpersonal aspect of mirroring can

then be exapted for further, social cognitive functions. However, pro-

cess-driven simulation does not require an interpersonal aspect: predic-

tive simulation in control is not interpersonal. Nor is visualizing, which

Goldman regards as a form of process-driven simulation. When ST

appeals to simulation for mindreading, it endorses an engineering strat-

egy that has many other applications.

There is more to the shared circuits story than this. Part of the story

concerns chains of cause-effect links in control and their use in mirror-

ing to enable imitative learning of new ways of achieving goals and,

with the addition of monitored motor inhibition, to enable understand-

ing of the intentional structure of observed action. But I don’t want to

tell any more of this story here, but rather to underscore the puzzle-

ment I expressed above.

The subpersonal story I’ve told about the intimate relations between

control and mirroring applies to instrumental or goal-directed actions;

it is a story about the simulative processes that enable intention read-

ing. This is the natural context set by control theory, which concerns

ends and means, or the processes by which goals are achieved. It is also

the natural context set by a large body of work on mirroring of goal-

directed actions. When sensorimotor control is invoked as a framework

for mirroring, surely instrumental action and intention reading provide

the most relevant territory to explore, not expressive actions and emo-

tion reading.

As indicated, however, Goldman tries to explicate the link between

control and mirroring in the prima facie unpromising territory of

emotion reading, and neglects the relevant territory of intention

reading. So it isn’t surprising that he doesn’t succeed. How control and

mirroring are related outside the context of instrumental action and

intention reading is a further question. I don’t think it can be

addressed until one has understood their fundamental relationship in

instrumental action and also developed a view about how instrumental

and expressive actions are related. In my view, mirroring for expressive

action builds on the more fundamental, control-related mirroring for

instrumental action.7

So far in this section, I have reviewed Goldman’s views about mir-

roring. I have also explained how simulation in the sense of intra-

personal reuse is present in both control and in mirroring, the close

7 Gallese’s ‘shared manifold’ includes both emotion mirroring and intention mirror-

ing. But I see no reason to attribute to him the view that emotion reading rather

than intention mirroring reveals the fundamental relation between control and

mirroring.

768 SUSAN HURLEY

relationships between these, and the way the interpersonal aspect of

mirroring arises from intrapersonal control. And I have explained what

I regard as the source of Goldman’s misunderstanding of these rela-

tions. There’s one more issue I want to pursue in this section, concern-

ing Goldman’s suggestion that simulation in control theory is more like

computer simulation or theorizing in TT than like simulation in ST

(216–217).

Goldman begins his section on simulation and control theory by

asking whether simulation can be understood within a control theoretic

framework, as Gallese suggests (213, 215). Goldman recognizes in a

note that control theorist Daniel Wolpert has discussed simulation with

a focus on action, and that Gallese may have this material in mind.

Goldman then comments that ‘it doesn’t follow from this special appli-

cation that the general control-theoretic framework … should be under-

stood in replicational terms’ (221, my emphasis). And he concludes the

section by expressing doubt that ‘control theory can be grounded in sim-

ulation’ in the sense he associates with ST (217, my emphasis). Gold-

man thus seems to shift from considering whether simulation can be

explained in a control framework to considering whether control can

be explained in a simulation framework.

Goldman suggests that the sense of simulation relevant to control is

not the sense relevant to simulation for mindreading.8 He argues that

simulation for control is more like theorizing than simulating in the

sense relevant to ST (216–217). Recall that computer simulation, say of

wind flow around a suspension bridge, counts as theory-driven, not

process-driven. If neural predictive simulations or ‘models’ are compu-

tational, using representations or descriptions of their subject matter,

Goldman suggests they are theoretically based in the way that com-

puter simulations are, not simulations in the resemblance sense he uses

to characterize ST. He takes talk of containing or capturing ‘informa-

tion’ to support this suggestion.

I will conclude this section by arguing that this suggestion of Gold-

man’s is in tension with his own view of the relation between ST and the-

orizing. Earlier I argued that simulation as reuse is the generic sense of

process-driven simulation that emerges from the contrast between ST

and TT, not simulation as resemblance. So I take issue with Goldman’s

criterion for assessing whether simulation for control is more like com-

puter simulation or theorizing in TT than like simulating in ST. This dis-

agreement was built into my account above, of how the reuse sense of

simulation applies both in control processes and in mirroring processes.

8 But cf. 43, where he seems friendly to the suggestion that simulation for mindread-

ing is a control process.

SYMPOSIUM 769

I do not accept the suggestion that control processes or predictive simula-

tions are theory-driven. However, I propose to assess Goldman’s sugges-

tion on his own terms, without invoking the reuse rival to his

resemblance account of simulation. His suggestion is that simulation for

control depends on theorizing in a way that is incompatible with simula-

tion in ST. My claim is that this view is in tension with Goldman’s vari-

ous statements of the compatibility of theorizing and ST.

The compatibility of theorizing and ST takes two general forms in

Goldman’s discussions. First, an account of mindreading can be a

hybrid, in which the elements of simulation and theorizing cooperate

(44–45). I agree on this point. Goldman gives an example of a hybrid

account, although he does not regard this account as plausible (again, I

agree; 129, 132): the generate and test model of low level simulation

for emotion recognition (45, 124–125, 129).

Second, simulation and theory need not compete, because theorizing

might implement simulation (43).

… although there is a prima facie conflict between simulation and the-ory at the personal level, there is no conflict between them at differentlevels. There is nothing wrong in supposing that mindreading is exe-

cuted at the personal level by simulation, which is in turn imple-mented at the subpersonal level by an underlying theory. (33)

This suggests an analogy to the way connectionist networks might imple-

ment a classical symbolic architecture, although now computational the-

orizing would be doing the implementing. The differences between the

psychological activities of simulating and theorizing ‘should not be

obscured by fact that all brain operations are computational’ (34). ST is

not threatened if it is implemented by theorizing (43).

Simulation could be causally responsible for mindreading even if theo-rizing is also at work, because theorizing might simply implement sim-

ulation rather than replace it. Under the positive approach, simulationand theory are compatible. ST … need not fear or resist tacit theoriz-ing to preserve its integrity. (34)

Goldman in fact supports the hybrid rather than the implementation

view of ST ⁄TT compatibility (44), but nevertheless holds that the

implementation of simulation by theory would not threaten ST.

The tension that concerns me is now evident: if the implementation

of simulation by theory is compatible with ST, why should the imple-

mentation of simulation by neural control processes, interpreted as a

kind of theorizing, be incompatible with ST? Reliance on information

does not undercut ST in general: ‘The approach to ST adopted in this

770 SUSAN HURLEY

book does not try to keep information out of the processing picture’

(175; see also 150). Then why does control theory talk of predictive

simulations as capturing or containing information support the sugges-

tion that it is incompatible with the ST sense of simulation (216)?

Mirroring may emerge from Hebbian associations, but Goldman

doubts the latter is a form of theorizing; and even if it were, for mirror-

ing to be grounded in theorizing would not threaten its status as simu-

lation (143–144). Why then do neural control systems’ predictive

simulations, also grounded in Hebbian associations, count as theory-

driven (216–217)? And even if they did, why would the grounding of

predictive simulation in theorizing threaten its status as simulation, any

more than it would threaten the status of mirroring? On Goldman’s

own terms, his suggestion that simulation in control systems involves

theorizing in a way that is incompatible with ST does not hold up.

To recap this section: I’ve reviewed Goldman’s account of mirroring,

explained the close connection between mirroring and control, argued

that Goldman misses it because of his focus on emotional mirroring

and neglect of instrumental action and intention reading, and finally

criticized his suggestion that neural control processes are theory-driven

in a way incompatible with ST, on the grounds that it is internally in

tension with his claim that theory can implement simulation compati-

bly with ST.

4. Self Versus Other: Egocentric Bias or Reality Bias?

My fourth and final topic concerns the interpretation of evidence that

Goldman cites as displaying a self-bias. He takes this evidence to sup-

port an asymmetry between first person and third person mental attri-

bution and the priority of first person attribution. Simulative

mindreading in his view involves projection from the first to the third

person, which makes first person attribution prior to third person attri-

bution.9 I will suggest another interpretation of the evidence in terms

of reality-bias, which is consistent with a quite different view of rela-

tions between the first and third person. Which of these interpretations

is correct is an empirical matter, for further experiments to resolve.

Goldman views projection from the first to third person as one of

the general ideas behind ST (40; he recognizes that Gordon disagrees:

9 Goldman remarks that no simulation theorist claims that simulation is used to self-

ascribe current mental states (24). Perhaps no self-conceived simulation theorist. But

sensorimotor views of perception claim that implicit practical understanding of the

sensory consequences of movement are part of what it is to perceive, even if one

does not actually move. This could be regarded as a claim that predictive sensori-

motor simulations are involved in current perceptual experience (self-ascription

thereof is a further issue).

SYMPOSIUM 771

185–187). In projecting a pretend state of one’s own to someone else,

one’s other, real states need to be quarantined and inhibited, so that

they are not wrongly attributed to another. If such inhibition is weak

(as in young children) or the quarantine has some tendency to fail or

‘leak’ (as it does even in adults), the predicted result would be overpro-

jection of one’s own mental states to others (148, 164–165). Goldman

argues that such overprojection is indeed found in phenomena that

illustrate an egocentric bias, such as the curse of knowledge, whereby

knowers (both children and adults) tend to assume that others possess

the same knowledge as they themselves possess (41–42, 74–75, 165–

166). The curse of knowledge can operate even when one has been

informed that others are ignorant (169). Similar egocentric bias is

found for valuations, preferences, feelings (100, 166–168). Projection

and failure to inhibit the prepotent first person mental states explain

observed egocentric biases.

Goldman interprets the experimental evidence in terms of an egocen-

tric bias. I’d like to suggest that quite a bit of it is open to another

interpretation, in terms of a reality bias, which would not support pro-

jection from the first to the third person. In some of Goldman’s discus-

sions, both interpretations are in play (e.g. 74, 197–198). I think it is

worth distinguishing them explicitly. The egocentric bias interpretation

holds that self-attributed mental states are prepotent, and failure to

inhibit them explains the relevant experimental results. The reality bias

interpretation holds that reality (including evaluative reality) is prepo-

tent and failure to inhibit truth explains the relevant results. Of course,

reality bias refers to reality and truth as perceived. But to perceive (or

seem to perceive) something in the world one does not need to attribute

a first-person mental state to oneself (otherwise, animals incapable of

self-attribution of mental states would also be incapable of perception).

Consider how these interpretations would apply to results in false

belief tasks, for example. In an ordinary false belief task, it could be

argued, the participant must inhibit her self-attributed belief in order to

attribute a false belief to another. But, alternatively, it is not necessary

to postulate that the participant attributes any belief to herself. Rather,

the participant must inhibit the truth in order to attribute a falsehood

to the other.10

10 Editor’s note: There’s something confusing about Hurley’s talk of inhibiting reality,

since it seems clear that even if the participant does not attribute a belief to herself,

what must be inhibited is a belief. Hurley’s point is presumably that, if the reality

bias interpretation is correct, the participant does not view herself as inhibiting her

belief since she has not attributed a belief to herself and may not have a belief ⁄reality distinction. From the participant’s point of view, she is inhibiting the truth.

This is how I understand Hurley’s remark in the previous paragraph that ‘reality

bias refers to reality and truth as perceived.’—MG

772 SUSAN HURLEY

As Goldman explains, nonverbal false belief tasks come in low inhi-

bition and high inhibition variants (171). In the low inhibition variant,

a participant watches as a man (the hider) places an object in one of

two boxes, though the participant cannot see which. The participant

also sees a woman (the communicator) watching, and that the woman

can see which of the two boxes the object is placed into. The woman

then leaves, and while she is gone, the man swaps the boxes. The

woman returns and points to a box. The participant should infer that

this will be the wrong box, as she does not know that the boxes have

been swapped. So the participant should conclude that the object is in

the other box. This is a low inhibition task because the participant does

not know directly which box contains the object. In the high inhibition

task, all is the same except that the participant does see which box the

object is placed in by the hider. One lesion patient passed the low inhi-

bition task but failed the high inhibition task. Why? On one interpreta-

tion, the low inhibition task does not require inhibition of a prepotent

self-ascribed belief about where the object is, while the high inhibition

task does. But on the other interpretation, the high inhibition task does

not require inhibition of a self-ascribed belief, but rather requires inhi-

bition of a prepotent truth, while the low inhibition task does not.

Someone could display reality bias while lacking a self ⁄other distinctionin ascribing mental states.

Given that perception of reality does not require self-attribution of

belief, these experiments don’t distinguish between egocentric bias and

reality bias. Instead of having prepotent self-attributed beliefs and fail-

ing to inhibit them, some participants who fail these false belief tasks

may lack a distinction between self-attributed and other-attributed

mental states. Truth may be prepotent for them rather than the first

person; they may tend to reference reality rather than self. Other exper-

iments may distinguish these interpretations.

The reality bias interpretation is worth considering and testing.

Some versions of ST, such as those of Gallese, Gordon, and myself, do

not postulate the priority of first person attribution over third person.

For Gallese (2005), mirror systems provides primitive intersubjective

‘we’ information that is prior to self ⁄other distinctions both phylo-

genetically and ontogenetically, and is preserved in human adults and

supports automatic empathy. My account follows Gallese in this

respect; mirroring provides subpersonal information that does not dis-

tinguish the first and third person. This distinction arises only with the

capacity to inhibit mirrored action and to monitor that one is inhibit-

ing. Inhibition is not of a prior first person, but is part of what enables

the distinction between self-attribution and other-attribution to be

drawn, overlaid on prior ‘we’ information in which self and other are

SYMPOSIUM 773

not distinguished. It is not obvious that these versions of ST would

predict an egocentric bias, though they are compatible with a reality

bias.

5. Concluding Remarks

My comments have fallen into four parts. I’ve distinguished Goldman’s

resemblance account of simulation from a rival reuse account and

argued that the latter is the core generic conception. I’ve queried the

distinction between low level and high level simulation for mindread-

ing. I’ve criticized Goldman’s view of the relations among simulation,

mirroring, and control, and put forward a different view. And I’ve dis-

tinguished egocentric bias from reality bias. While I’ve disagreed on

many points with Goldman, this shouldn’t obscure the fact that we are

on the same side of the broad debate. I’ve found it very rewarding to

focus on his book in trying to articulate our differences.

References

Gallese, V. (2001) ‘The ‘shared manifold’ hypothesis: from mirror neu-

rons to empathy,’ Journal of Consciousness Studies 8: 33–50.

——. (2005), ‘‘Being like me:’ Self-other identity, mirror neurons and

empathy,’ in S. Hurley and N. Chater (eds.) (2005): vol. 1: 101–18.

Goldman, A. (2006) Simulating Minds: The Philosophy, Psychology,

and Neuroscience of Mindreading (Oxford: Oxford University

Press).

Heyes, C. (2001) ‘Causes and consequences of imitation,’ Trends in

Cognitive Sciences 5: 253–261.

——. (2005), ‘Imitation by association,’ in S. Hurley and N. Chater

(2005): vol. 1: 157–76.

Hurley, S. (2005) ‘The shared circuits model: How control, mirroring

and simulation can enable imitation and mindreading,’ in What Do

Mirror Neurons Mean? Interdisciplines Web Forum, http://www.in-

terdisciplines.org/mirror/papers/5.

——. (2007) ‘The shared circuits model: How control, mirroring and

simulation can enable imitation and mindreading,’ forthcoming in

Brain and Behavioral Sciences. Pre-print at http://www.bbsonline.

org/Preprints/Hurley-05252004/Referees/Hurley-05252004_preprint.

pdf.

Hurley, S. and Chater, N. (eds.) (2005), Perspectives on Imitation: From

Neuroscience to Social Science, 2 volumes (Cambridge, MA: MIT

Press).

Keysers, C. and Perrett, D. (2004), ‘Demystifying social cognition: a

Hebbian perspective,’ Trends in Cognitive Sciences, vol. 8, 501–507.

774 SUSAN HURLEY