Download - Understanding Simulation
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:
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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
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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
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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.’)
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‘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
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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
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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