Abstract and Figures

The discovery of mirror neurons in monkeys, and the finding of motor activity during action observation in humans are generally regarded to support motor theories of action understanding. These theories take motor resonance to be essential in the understanding of observed actions and the inference of action goals. However, the notions of "resonance," "action understanding," and "action goal" appear to be used ambiguously in the literature. A survey of the literature on mirror neurons and motor resonance yields two different interpretations of the term "resonance," three different interpretations of action understanding, and again three different interpretations of what the goal of an action is. This entails that, unless it is specified what interpretation is used, the meaning of any statement about the relation between these concepts can differ to a great extent. By discussing an experiment we will show that more precise definitions and use of the concepts will allow for better assessments of motor theories of action understanding and hence a more fruitful scientific debate. Lastly, we will provide an example of how the discussed experimental setup could be adapted to test other interpretations of the concepts.
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Understanding motor resonance
Sebo Uithol a , Iris van Rooij a , Harold Bekkering a & Pim Haselager a
a Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen,
Nijmegen, The Netherlands
Version of record first published: 04 Mar 2011.
To cite this article: Sebo Uithol , Iris van Rooij , Harold Bekkering & Pim Haselager (2011): Understanding motor resonance,
Social Neuroscience, 6:4, 388-397
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SOCIAL NEUROSCIENCE, 2011, 6 (4), 388–397
Understanding motor resonance
Sebo Uithol, Iris van Rooij, Harold Bekkering, and Pim Haselager
Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, Nijmegen, The
Netherlands
The discovery of mirror neurons in monkeys, and the finding of motor activity during action observation in humans
are generally regarded to support motor theories of action understanding. These theories take motor resonance to
be essential in the understanding of observed actions and the inference of action goals. However, the notions of
“resonance,” “action understanding,” and “action goal” appear to be used ambiguously in the literature. A survey of
the literature on mirror neurons and motor resonance yields two different interpretations of the term “resonance,
three different interpretations of action understanding, and again three different interpretations of what the goal
of an action is. This entails that, unless it is specified what interpretation is used, the meaning of any statement
about the relation between these concepts can differ to a great extent. By discussing an experiment we will show
that more precise definitions and use of the concepts will allow for better assessments of motor theories of action
understanding and hence a more fruitful scientific debate. Lastly, we will provide an example of how the discussed
experimental setup could be adapted to test other interpretations of the concepts.
Keywords: Mirror neurons; Motor resonance; Action understanding; Goals.
The discovery of mirror neurons in macaque monkeys
(Di Pellegrino, Fadiga, Fogassi, Gallese, & Rizzolatti,
1992; Gallese, Fadiga, Fogassi, & Rizzolatti, 1996;
Rizzolatti, Fadiga, Gallese, & Fogassi, 1996) has
generally been greeted as support for the idea that
motor areas play an essential role in understanding
observed actions and the inference of the pursued
goals of these actions, as these neurons fire upon
both observing and executing actions, leading to the
idea that the observer simulates the observed action
(Gallese & Goldman, 1998). This suggestion was fur-
ther backed up by the finding that the human motor
system becomes activated during action observation
(Buccino et al., 2001; Buccino, Binkofski, & Riggio,
2004; Fadiga, Craighero, & Olivier, 2005; Rizzolatti
& Craighero, 2004). Due to the supposedly direct
and non-inferential character of this process, this phe-
nomenon is often referred to as “motor resonance.”
Correspondence should be addressed to: S. Uithol, Donders Institute for Brain, Cognition and Behaviour, Spinoza Building, B01.03, PO
Box 9104, 6500 HE Nijmegen, Netherlands. E-mail: Uithol@donders.ru.nl
The present study was supported by a Donders internal graduation grant to the second and last authors, and the EU-Project Joint Action
Science and Technology (IST-FP6-003747) grant and an NWO-VICI grant to the last author. The authors wish to thank Janny Stapel for
commenting on an earlier draft of this paper.
Ever since the discovery of mirror neurons, many
fascinating findings have been reported. However, the
explanatory power of mirror neurons regarding action
understanding has fallen out of step with the contin-
uing stream of experiments and accompanying find-
ings. Theories on the mirror-neuron system (MNS)
and motor resonance have recently received criti-
cism (Dinstein, Thomas, Behrmann, & Heeger, 2008;
Hickok, 2009; Jacob, 2008). The general purport of
this criticism is that mirror neurons cannot account
for certain experimental findings (Hickok, 2009; Saxe,
2005a, 2009), or that the generalization from monkey
data to the human MNS is not warranted (Dinstein
et al., 2008; Lingnau, Gesierich, & Caramazza, 2009).
Theoretical concerns about the limitation of action
understanding by means of direct-matching have also
been raised (Csibra, 2007; Jacob & Jeannerod, 2005;
Uithol, van Rooij, Bekkering, & Haselager, in press).
© 2011 Psychology Press, an imprint of the Taylor & Francis Group, an Informa business
www.psypress.com/socialneuroscience DOI: 10.1080/17470919.2011.559129
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UNDERSTANDING MOTOR RESONANCE 389
It is not the purpose of this paper to review the
extensive body of research on mirror neurons and to
argue for a specific framework in which the experi-
mental findings are best explained. To a large extent,
we will remain neutral on these matters. Instead, we
will show that the ongoing discussion of the function
of motor resonance often makes use of imprecise ter-
minology. Due to the use of ambiguous concepts on
both sides, the discussion between proponents and crit-
ics of motor resonance-based theories of action under-
standing advances only with great difficulty. By means
of a careful analysis of the concepts of “motor reso-
nance,” “action understanding,” and “action goals,” we
aim to clarify the troubled debate on motor theories
of action understanding and the role mirror neurons
play.
The notion “motor resonance” appears to be used
ambiguously in the literature on the MNS. At least two
fundamentally different interpretations of the notion of
resonance are used in neurocognitive explanations of
the MNS, which we will call intrapersonal and inter-
personal resonance. Each interpretation has different
elements taking part in the resonance process. Next we
will show that three qualitatively different interpreta-
tions can be found of what the goal of an action is:
the goal as a more abstract action, the goal as a gras-
pable object, and the goal as a desired world state.
We will discuss these three interpretations. Finally,
we will show that the notion of action understanding
can describe three different cognitive functions, which
we will label action recognition,goal recognition, and
action anticipation. An overview of the different inter-
pretations and our terminology is shown in Table 1.
The interpretations will be discussed in detail below.
It is important to note that none of these interpreta-
tions is in itself right or wrong, or better than another
one. As long as it is specified what is precisely meant
by a notion, any of the interpretations is valid and
could fulfill a role in theories on action understanding.
A consequence of this variability in interpretations
is that the exact meaning of any claim about motor
resonance, action goals, and action understanding that
does not specify which of the interpretations of these
notions is used can vary to a great extent. A care-
ful analysis of these claims allows better interpretation
of theories about underlying neurocognitive matching
mechanisms of action observation and action execu-
tion, and can help guide the design of future experi-
ments. We will discuss an existing experiment from the
literature, Umiltà et al.’s (2001) mirror-neuron paper,
as a case study and illustrate how the experimental data
and the interpretation of them have diverged as a result
of the above-mentioned indeterminacy of terminology.
As an indication of the empirical applicability of the
distinctions we propose, we will finish by presenting a
concrete suggestion of how this study could be adapted
so that other interpretations of the concepts presented
in Table 1 can be tested.
RESONANCE
In the literature on the MNS, the notion of resonance
is used to describe the activation of the motor sys-
tem during action observation. The notion is adopted
from physics and is used to describe the phenomenon
that one (part of a) system oscillates at the same fre-
quency and in the same phase as another (part of
TABLE 1
The possible interpretations of resonance, action goal, and action understanding, as found in the literature
Notion Interpretation Explanation Example
Resonance Intrapersonal Resonance between visual and
motor areas
Visual representation of grip type
is propagated to motor areas
Interpersonal Resonance between observer and
executor of action
Both observer and executer have
representation of grasp action
in motor areas
Action goal Action Action of higher abstraction than
observed action
Drinking
Object Object at which the action is
directed
Cup
World state Desired world state that can be
achieved by action
A full cup of coffee
Action understanding Action recognition Recognition of observed action Recognize action as grasping
Goal recognition Recognition of goal of an action Recognize grasping action as
serving drinking
Action anticipation Generation of response to
observed action
Prepare grasping action when
offered a cup.
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390 UITHOL ET AL.
the) system. In the neurocognitive domain, it is not
claimed that the motor system is literally resonating
in the sense that premotor neurons are firing in the
same frequency and phase as neurons in other areas
(we will come to the question of what areas soon).
These claims should thus not be read as claims about
neural synchrony (Damasio, 1989; Ward, 2003) or
neural oscillation (Fries, 2005). Instead, a more liberal
sense of the notion is usually adopted. Rizzolatti et al.
(2001, p. 661) write, “We understand actions when we
map the visual representation of the observed action
onto our motor representation of the same action.”
Elsewhere (Rizzolatti & Craighero, 2004, p. 172), it is
explained: “The proposed mechanism is rather simple.
Each time an individual sees an action done by another
individual, neurons that represent that action are acti-
vated in the observer’s premotor cortex.... the motor
‘resonance’ translates the visual experience into an
internal ‘personal knowledge.”’ This process is often
characterized as a form of simulation, in which the
observer simulates the observed motor act in order
to understand it (Decety & Grezes, 2006; Gallese &
Goldman, 1998).
When we examine the literature on mirror neu-
rons and action understanding, two different meanings
or interpretations of the notion can be discovered,
each having different elements participate in the res-
onance process. We will call these two interpretations
intrapersonal resonance and interpersonal resonance.
In the intrapersonal interpretation of resonance, it
is claimed that the motor system of the observer of an
action resonates with her own perceptual system, so
both brain areas taking part in the resonance process
lie within the same person. Examples of this kind of
use can be found in, for example, Rizzolatti, Fogassi,
and Gallese (2001), Rizzolatti and Craighero (2004),
and Buccino et al. (2004).
The idea is that the observation of an event leads
to a representation in the perceptual system of the
observer. This perceptual representation is thereupon
propagated to the motor system. When the perceived
event is an action and a matching motor representation
is available, the motor system resonates like a tuning
fork that starts to resonate when a note of the right
pitch is played nearby (Jacob, 2009; Saxe, 2005b). As
the resonance of the tuning fork provides information
about the pitch of the note played, the resonance of the
motor system provides information about the action
that is perceived. This is possible, according to the
theory, because the resonance is specific for different
actions. For example, at the observation of a certain
grasping action, such as a precision grip, a motor rep-
resentation corresponding with that specific grasping
action is activated in the motor system. The observer
“recognizes” the activity in her motor system as being
a representation of the specific grasping action, and
she thereby recognizes the observed precision grip
action. As the coupling of a perceptual representa-
tion to a motor representation happens unmediated by
higher cognitive processes, this theory is also known as
the direct-matching hypothesis (Iacoboni et al., 1999;
Rizzolatti et al., 2001; Rizzolatti & Sinigaglia, 2010).
Figure 1 depicts the causal chain from a motor
plan in the executor to an action representation in the
observer, and the place where intrapersonal resonance
occurs.1
The strongest evidence for this theory comes from
single-cell recordings in macaque monkeys. Neurons
in the inferior premotor areas were shown to fire selec-
tively for different actions and action means, such
as precision and power grips, both performed and
observed (Di Pellegrino et al., 1992; Gallese et al.,
1996; Rizzolatti et al., 1996). This has led to the con-
clusion that these areas are involved in the recognition
(and understanding) of actions. These monkey data
were backed up by imaging data that showed that
the human motor system is activated differently upon
observations of different actions (Buccino et al., 2001,
2004; Fadiga et al., 2005; Rizzolatti & Craighero,
2004).
This theory can elegantly account for the finding
that mirror neurons do not fire when the observed
event is not an action (Gallese et al., 1996), or when
the action is carried out by a non-biological effec-
tor (e.g., a robot arm) (Kilner, Friston, & Frith, 2007;
Tai, Scherfler, Brooks, Sawamoto, & Castiello, 2004).
Resonance occurs when a matching motor represen-
tation is available, so when the perceived event is
not an action or an action that is carried out by a
non-biological effector, there is no matching motor
representation and the motor system remains silent.2
In a second interpretation, the notion of resonance
is used to denote functional correspondence between
the states in the motor system of the observer and that
of the executor of an action. This view is present in
the work of, for instance, Decety and Grezes (2006),
de Vignemond and Haggard (2008), Fadiga et al.
1It is still debated whether the final action representation—provided
that such a representation exists— resides in motor areas (as embod-
ied approaches to cognition argue) or whether there are disembodied
representations of actions. Here we choose not to take a side in this
debate.
2There are experiments, such as those of Fogassi et al. (2005) and
Umiltà et al. (2008), that show mirror-neuron response to tool-based
actions, but this was only after extensive training with tools. A pos-
sible explanation is that, through training with tools, the monkey
creates a motor representation of these actions.
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UNDERSTANDING MOTOR RESONANCE 391
Figure 1. The causal path from action plan in the executor to action representation in the observer and the location of intrapersonal resonance.
Figure 2. The causal path from action plan in the executor to action representation in the observer as presumed in motor theories of action
understanding, and the two parts of the system that take part in interpersonal resonance.
(2005), Gallese (2001), Jacob (2008), and Wilson and
Knoblich (2005). As the two systems taking part in
the resonance process are situated in two different per-
sons, we will call this form of resonance interpersonal
resonance.
In the interpersonal interpretation of resonance, the
notion is used in an even more metaphorical sense.
It is assumed that there is a semantic or functional
resemblance between the motor representation in the
observer of an action and the motor representation of
the executor of the action (e.g., both motor systems
represent a grasping action at the same time). In a
sense, the observer and the executor of an action share
a representation (de Vignemont & Haggard, 2008). It
is therefore stated that the observer’s motor system
resonates with that of the executor (Gallese, 2001;
Gallese & Goldman, 1998; Goldman, 2009; Jacob,
2008; Wilson & Knoblich, 2005) or, in shorter form,
that the observer resonates with the executor (Fadiga
et al., 2005). Figure 2 shows the presumed causal
sequence from an action plan in the executor to a
representation of that action in the observer. The two
elements that take part in the interpersonal resonance
are marked with an arrow.
Resonance in the interpersonal meaning is a higher-
level description of the result of various processes from
a motor representation in the executor to an activated
motor system in the observer. It describes a resem-
blance between the two motor systems, and it can be
established without making claims about the underly-
ing mechanism. This is evident from Figure 2: The
resonance process covers multiple causal steps that can
be accomplished by various underlying mechanisms.
This interpretation of resonance is not committed
to specific mechanisms bringing about these steps.
Usually, a form of intrapersonal resonance is presumed
to establish interpersonal resonance, but this is not nec-
essarily the only option: An inferential process could
also result in interpersonal resonance.
SETTING GOALS
It is often claimed that motor resonance allows the
recognition of not only the action as such, but also of
the goal that is served by the action (Iacoboni et al.,
2005; Rizzolatti et al., 2001; Rizzolatti & Sinigaglia,
2010). Yet, like the notion of motor resonance, the
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392 UITHOL ET AL.
notion of goal allows for various interpretations. A
survey of the literature on mirror neurons yields three
qualitatively different interpretations of the goal of an
action.
First, the goal of an action is often interpreted as
another, less specific action that is abstracted from exe-
cution specifics. For example, Gallese et al. (1996)
classify mirror neurons as broadly congruent when
the neurons appear to be activated by the goal of the
observed action, regardless of how it was achieved.
An example of such a goal could be “grasping,” and
grasping with a precision grip, grasping with a full-
hand grip, and grasping with the mouth all serve the
goal of grasping. The goal-as-an-action interpretation
is also present in the work of Ferrari, Rozzi, & Fogassi
(2005), Fogassi et al. (2005), and Iacoboni (2005), and
it predominates in the early papers on mirror neurons
(Gallese et al., 1996; Rizzolatti et al., 1996).
The fact that the goal of an action is itself another
action is potentially problematic, as nearly every
action itself can be said to serve a new, higher goal.
To illustrate, the action “grasping a cup,” can serve
the goal, “drinking.” Thus conceived, drinking is an
action goal. “Drinking,” however, can also be consid-
ered an action, having “quenching thirst” or “engaging
in social activity” as a goal. Quenching thirst serves
the goal “maintaining homeostasis,” which serves the
goal “survival,” and so on. There thus exists a con-
tinuum from concrete, readily observable events (the
use of a precision grip) to highly abstract events
(survival).3Although individual preferences may be
possible, there seems to be no a priori level at which
actions are located and a level at which action goals
are located.
Umiltà et al. (2008) provide a clear example of
goals and actions lying on the same continuum.
Macaque monkeys were trained to use normal and
reverse pliers to grasp objects. The researchers found
that the same motor neurons that under normal con-
ditions fire when an object is grasped, also fire when
the object is grasped with reversed pliers, which means
that the hand needs to be opened to grasp the object.
This suggests that these motor neurons respond to the
act of grasping (an action higher in the continuum)
3Besides actions and action goals, two more related notions can be
found in the literature. An “action means” is a particular way of per-
forming an action. Action means also lie on the same continuum as
actions and goals, and can therefore, upon different interpretations,
also be actions themselves. The notion “movement” is often used to
denote a movement that does not serve a goal —see, for instance,
Gallese and Goldman (1998) or Hommel (2003). Action thus con-
ceived is a subclass of movements; that is, those movements that
serve a goal.
and not the motor act of closing the hand (an action
lower in the continuum). Although not discussed in
the paper, it is not difficult to see how the grasping
with pliers serves actions of even higher abstraction,
such as eating. Fogassi and his colleagues, for instance,
found different responses in mirror neurons, depending
on whether the grasping action was part of an eat-
ing action or a placing action (Fogassi et al., 2005).
In all, because interpretations on all levels are possi-
ble, a clear indication of the level at which the analysis
takes place can be helpful in interpreting the findings
correctly.
A second interpretation of the goal of an action is a
target object. It is this interpretation that has given us
the term “goal-directed action,” meaning a transitive
or object-directed action.4This interpretation can be
found in, for instance, Umiltà et al. (2001, p. 161), who
state that “mirror neurons have to infer and represent
the occluded specific action in addition to the inferred
object, which is the goal of the action.”5This interpre-
tation of goals is also often present in the early mirror-
neuron papers (Gallese et al., 1996; Rizzolatti et al.,
1996), but also later (Hamilton & Grafton, 2006).
Similar to this is the interpretation of a goal as a point
in space, such as a cross on the desk (Wohlschläger
& Bekkering, 2002) or the end location of an action
(Bekkering, Wohlschläger, & Gattis, 2000). At other
places, the goal as an object is contrasted with the goal
as a location (Hamilton & Grafton, 2006).
A third interpretation of goal is a desired state of the
world. A possible state could be “a full cup of coffee”
and several actions—picking up the coffee pot, trans-
ferring it to the cup, tilting the coffee pot, etc.—are
needed in succession to reach that state. This inter-
pretation can be found in, for example, Csibra and
Gergeley (2007), Grafton and Hamilton (2007), or
Sebanz, Bekkering, and Knoblich (2006).
These interpretations do not necessarily exclude
each other. For example, “taking possession of an
object” seems to have aspects of all three interpre-
tations. First, taking possession can be viewed as an
4As we said in footnote 3, the difference between a movement and
an action is often taken to be that the latter serves a goal and the
former does not. This would entail that every action serves a goal,
making the term “goal-directed action” a pleonasm for other inter-
pretations of “goal”, as non-goal-directed actions cannot exist—just
non-goal-directed movements.
5This statement illustrates how terminology can cause confusion.
Apart from the personal/subpersonal violation, the claim that “mir-
ror neurons infer” also departs from the initial claims that mirror
neurons engage in direct reflection and no inferential processes are
needed. See Uithol et al. (submitted) for a more detailed discus-
sion on direct reflection versus inferential processing with respect
to mirror neurons.
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UNDERSTANDING MOTOR RESONANCE 393
action that can be executed in different ways (grasping,
ordering, buying). Second and obviously, this action
is directed toward an object. Third, taking possession
of an object can be viewed as reaching a world state
in which a certain object is in my possession (in my
hands, my mouth, my stomach). In general, the dif-
ference between the interpretation of goal as another
action and goal as a desired world state seems to be a
matter of emphasis. Sometimes one of the interpreta-
tions is more natural or evident; sometimes the other.
For example, when one or two persons are carrying a
table out of the room (Sebanz et al., 2006), it is gener-
ally not the action that one is interested in; it is a state
of the world in which the table is located outside the
room. In other cases, such as eating and drinking, it is
not so much the world state that a person is interested
in, but the action itself: The person enjoys the action
of eating or drinking. Of course eating serves a pur-
pose and is a mechanism by which a species acquires
necessary nutrients. So in a way one could say that
having the food in one’s stomach is a desired world
state albeit often an unconscious one, but this seems a
rather awkward way of phrasing a goal.
Notwithstanding the possible overlap, the differ-
ences can be crucial. The meaning of the claim that
mirror neurons respond selectively to goals can differ
to a great extent in the three different interpretations
of “goal.” For example, recognizing that an action
is directed toward a cup and recognizing that this
cup-grasping contributes to getting a clean table are
two quite different capacities that require different
experiments for testing the nature of motor activation.
As a consequence, experimental results that support
a certain neuroscientific hypothesis (e.g., about neu-
ral mechanisms underlying goal understanding) under
one interpretation of goal understanding do not auto-
matically support that same hypothesis under other
interpretations of goal understanding. Fogassi et al.’s
(2005) study on parietal mirror neurons provides a
clear example of an experimental setup where precise
terminology is crucial. The researchers found mirror
neurons in the monkey’s inferior parietal lobule that
responded selectively for different intentions underly-
ing the same actions. Monkeys were trained to grasp
a piece of food and either place it in a container on
their shoulder or eat it. Some neurons responded dif-
ferently for these two intentions. Importantly, in some
neurons, this difference in firing was preserved when
the monkeys observed the experimenters perform the
same actions. Because Fogassi and his colleagues use
the unambiguous notions “object” and “intention” to
denote the different interpretations of goal (although
the latter is sometimes also referred to as “goal”),
there is no confusion or conflation of the notion “goal”
here. However, if Fogassi and his colleagues had used
the notion “goal” in both the meaning of object and
intention—as can be found elsewhere in literature, as
shown above—then the finding that the recognition of
an object can cause the recognition of the intention of
the actor would result in a circular statement about goal
recognition causing goal recognition.
Hamilton and Grafton (2007) provide an illustration
of all three uses of this notion. In their introduction,
they discuss goals as being a desired world state (e.g.,
getting refreshment), and they refer to goal-dependent
mirror neuron firing in the meaning of a more abstract
action, while their experiments are based on the object
interpretation of goals. The authors themselves seem to
be aware of the differences in interpretation when they
write, “It is also important to note that the goals we
have studied were defined by the identity of the object
taken by the actor, contrasting between a ‘take wine
bottle’ goal and a ‘take dumbbell goal.’ It remains to
be seen if the same parietal regions encode other types
of goal, for example manipulating the same object in
different ways.” Yet, the discussion of these other inter-
pretations in the introduction, and the fact that the
authors do not further specify their interpretation of
goal throughout the paper could easily entice other
researchers into applying the results to the other inter-
pretations as well. In the section entitled “Diverging
concepts,” we will discuss a case in which, upon sys-
tematic conceptual analysis, the original experimental
setup no longer matches subsequent interpretations by
other authors.
UNDERSTANDING ACTION
What is meant by “action understanding” differs from
paper to paper. The difficulty with the notion is that
it consists of two elements, action and understanding,
and the meaning of these elements is interdependent
and open to different interpretations. To start with
actions: We have seen that action means, actions, and
action goals can be placed on a continuum from spe-
cific, readily observable events (e.g., the use of a
precision grip) to highly abstract events (maintaining
homeostasis), and there seems to be no a priori way to
make a clear-cut and objective contrast between action
means, actions, and action goals.
Despite the lack of a priori considerations for con-
trasting actions with goals in this interpretation of
goals, it seems that the capacity to understand grip
types differs to such an extent from the capacity to
understand homeostasis that differentiation is neces-
sary. With the mirror-neuron literature in mind, we will
limit the use of the notion “action” to movements that
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394 UITHOL ET AL.
exist in the here and now and that serve a goal, such
as grasps. We use the label “goals” for more abstract
actions than the observed one, in the sense that they
either are nonvisible (like maintaining homeostasis or
keeping to one’s diet) or involve future actions (grasp-
ing in order to clean up the table; cleaning up the table
might be a visible action, but it is not yet observed at
the time of picking up a cup).
The fact that actions can be found along a
broad continuum of increasing abstraction has con-
sequences for the interpretation of “understanding.”
Understanding can mean recognition (i.e., a form of
classification: “That’s a precision grip”), but also rec-
ognizing the goal that is served by an action (“That’s
grasping to eat”). However, as we have just seen, what
is considered to be an action and what is the goal of an
action, are liable to interpretation. This makes the dif-
ference between recognizing an action and recognizing
the goal of an action also a matter of interpretation.
To stick with the drinking example, when “grasping
a cup” is interpreted as an action, the goal of the
action can be “to drink.” So the action can be recog-
nized (“that’s grasping”), or its goal can be recognized
(“that’s drinking”). When, however, we see drinking as
an action, and quenching thirst as the goal of an action,
then “that’s drinking” is a matter of action recognition,
and “that’s quenching thirst” is understanding the goal
of the action.
Many authors seem to pitch their interpretation of
action understanding somewhere along this contin-
uum, but very few delimit or make their interpretation
explicit. This makes it difficult to assess the exact
claims that are made. For example, Rizzolatti and
Craighero (2004, p. 172) state, “This automatically
induced, motor representation of the observed action
corresponds to that which is spontaneously generated
during active action and whose outcome is known
to the acting individual” (our italics). Without spec-
ification, this “outcome” can mean anything from a
precision grip to maintaining homeostasis. However,
the claim that the MNS detects grip types is quite dif-
ferent from (and more modest than) the claim that the
MNS is capable of detecting long-term goals or inten-
tions. The two claims presume different capacities of
the system and demand different tests to verify them.
Beside recognizing the action and recognizing the
goal an action serves, a third interpretation is that
understanding an action is “knowing how to respond
appropriately to an observed action” (Gallese et al.,
1996; Rizzolatti et al., 2001). For example, Rizzolatti
et al. (2001, p. 661) write: “By action understand-
ing, we mean the capacity to achieve the internal
description of an action and to use it to organize appro-
priate future behavior” (our italics). So in addition to
“the capacity to achieve the internal description of an
action,” which is in line with the first interpretation,
this definition adds that it should be used to generate
an appropriate response.
Again, the different interpretations of action under-
standing refer to capacities that can differ to a large
extent, so we will have to disentangle them. We will
use the term “action recognition” when we mean the
classification of an action and the ability to differen-
tiate it from other actions. By “goal recognition,” we
mean classification of the goal of an action. This goal
can be an action more abstract than the movement that
takes place in the here and now, as discussed above,
or another interpretation of goal, as discussed in the
previous paragraph. Knowing how to respond appro-
priately to an action we will call “action response.”
Table 1 presents an overview of these different inter-
pretations.
To illustrate the empirical relevance of our concep-
tual discussion and terminological distinctions, we will
analyze a well-known mirror-neuron study by Umiltà
et al. (2001) that produced fascinating results. We will
show that a univocal interpretation of the experimen-
tal data is troubled by the use of indefinite terms.
As a result, their data is often interpreted as sup-
porting mirror neurons involvement in forms of goal
understanding, while, in our terminology, only action
recognition is demonstrated.
DIVERGING CONCEPTS
Umiltà and her colleagues (2001) had monkeys watch
grasping actions with the object to be grasped occluded
from the monkey’s sight. By means of single-cell
recordings, they showed that the monkey’s mirror neu-
rons that normally respond to the observation of a
certain action also respond when the final, crucial part
of that action was hidden. This shows that the build-
up to the action (e.g., the opening of the hand and
the reaching toward an object) is enough to trigger
the mirror-neuron response, and that observation of the
actual action (the grasping of an object) is not neces-
sary. The authors conclude that these findings support
the idea that the goal of an action can be recognized,
even when the monkey is provided with an incom-
plete perception of an action, provided that the monkey
knew that there was an object behind the occluder.
They subsequently conclude that their findings “fur-
ther corroborate the previously suggested hypothesis
that the mirror neurons’ matching mechanism could
underpin action understanding” (p. 161); a conclusion
that is subsequently adopted by others (e.g., Ferrari
et al., 2005; Rizzolatti & Sinigaglia, 2010).
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UNDERSTANDING MOTOR RESONANCE 395
However, interpretation of these findings is not
straightforward. We have shown that three different
interpretations of both the notions “action understand-
ing” and “action goal” circulate (let alone the range
of abstraction on which actions and goals can be
formulated). Umiltà and colleagues showed that cer-
tain mirror neurons that fire upon observing a certain
action also fire when the final part of the action was
occluded. As the neuron exclusively fires upon view-
ing actions of this type, this is a form of what we
would call action recognition: the recognition and clas-
sification of an action. Their interpretation of “goal”
is that of “object,” as becomes clear in phrases like
“the inferred object, which is the goal of the action”
(p. 161).
So, when we rephrase their findings in our sys-
tematic terminology (see Table 1), this experiment
shows that the recognition of an action depends on
knowledge of the presence of a graspable object.
This suggests that the monkey understands that the
observed movement is grasping only when it knows
that it is directed toward an object. This finding is in
line with early mirror-neuron studies (e.g., Gallese et
al., 1996; Rizzolatti et al., 1996) that also found that
mirror neurons did not respond to mimed actions (i.e.,
actions not directed toward an object). These stud-
ies show that mirroring in order to recognize actions
involves more than mirroring the kinematic features,
as these features in mimed actions are identical to
object-directed actions but do not evoke mirror-neuron
response.
However, the findings of this experiment cannot be
used to draw conclusions regarding goal understand-
ing, that is, inferring the goal that is served by a certain
action from observation of that action alone, as the data
show that the presence of a goal in the object sense is
a prerequisite for the recognition of the action.
So the tenability of the claim that these find-
ings “further corroborate the previously suggested
hypothesis that the mirror neurons’ matching mech-
anism could underpin action understanding” depends
on what is meant by both the “previously suggested
hypothesis” and “action understanding.” Regarding
the first, support for the direct-matching hypothesis
(Rizzolatti et al., 2001) is problematic. This hypothe-
sis states that the visual representation of the observed
action (i.e., the kinematic features of the movement)
is mapped onto the motor representation of the same
action, and when a matching motor representation
exists, resonance occurs and the action is recog-
nized. According to this hypothesis, action recognition
thereby enables goal inference, as the observer of the
action knows, from his own experience, which goal is
(usually) served by the recognized action.
When we try to explain Umiltà et al.’s data within
the framework of the direct-matching hypothesis, we
seem to run into some circularity: Goal recognition is
a prerequisite for action recognition, yet, according to
the direct-matching hypothesis, action recognition is a
prerequisite for goal inference.
In their 2010 paper, Rizzolatti and Sinigaglia have
reformulated the direct-matching hypothesis. In this
formulation, action mirroring is rendered as a dual-
route process, with one route directly matching move-
ments and the other mapping the goal of the observed
motor act onto the observer’s own motor repertoire.
When these routes are genuinely parallel, action recog-
nition no longer is a prerequisite for goal recognition,
but these two processes take place simultaneously and
independently.
However, support for this revised direct-matching
hypothesis is also problematic, and now what is meant
by action understanding becomes crucial. When action
understanding is taken to mean action recognition,
then these data can only provide support for half
the reformulated hypothesis. Umiltà et al. found neu-
rons that respond selectively to different actions, and
this can only support the already well-established part
of the revised direct-matching hypothesis: the direct
matching of actions. No evidence is provided for the
second route: the direct matching of goals.
When action understanding is taken to mean goal
recognition, the findings cannot support the direct-
matching hypothesis, as only action recognition is
established, and according to the revised formulation
of the hypothesis, action recognition does not under-
pin goal recognition, but goal recognition takes place
independently along a different route.
In all, these findings seem more in line with com-
peting hypotheses, such as Csibra’s (2007) or Jacob’s
(2008), that state that action understanding is modu-
lated by non-mirroring processes, such as processing
of the presence of an object.
Based on proper distinctions of terms, as done in
Table 1, we have been able to reveal difficulties in
the interpretation of data in the literature. We have
given an example of how our conceptual work can
help analyze existing data, allowing for a more pre-
cise match between empirical results and conceptual
interpretations. Next we will show that this conceptual
analysis can also help guide the design of new exper-
iments in such a way that conceptual confusion can
be prevented. As an illustration of one such possible
experiment, we will discuss how Umiltà et al.’s (2001)
experiment can be modified in a way to test a different
interpretation of the concepts in Table 1.
Let us interpret “action understanding” as “goal
recognition,” and let us stick to the interpretation of
Downloaded by [Radboud Universiteit Nijmegen] at 12:31 01 January 2013
396 UITHOL ET AL.
goal as object. In that case, “goal recognition” means
“recognizing what object an action is directed at.” One
way to test mirror neurons’ contribution to goal recog-
nition in this sense is to identify mirror neurons that
fire differently upon grasping actions toward different
objects. This could be done by placing two objects
instead of one behind the occluder, each demand-
ing a different grip type (say, an apple and a peanut,
demanding a full hand grip and a precision grip respec-
tively). When the monkey knows that only one of the
objects is placed behind the occluder, and this object is
approached with the wrong grip type, mirror neurons
that fire for that grip type should remain silent, as this
action cannot have the object behind the occluder as
its goal. For example, the monkey knows that there is
only an apple, but observes a grasping action with pre-
cision grip toward the occluder, When mirror neurons
that respond only to actions performed with a precision
grip remain silent (as they should when they fire selec-
tively for different objects and there is no appropriate
object behind the occluder), it could be considered fur-
ther evidence that mirror neurons’ firing characteristics
are dependent on the object that an action is directed
at. Failure to demonstrate the ability of mirror neurons
to “recognize” the wrong grip for the object behind
the occluder could be considered evidence against the
idea that mirror neurons contribute to goal recognition
when the goal is interpreted as the target object of an
action.
In all, different interpretations of the concepts used
in theories on action understanding demand different
experimental setups. We have given an example of
how Umiltà et al.’s (2001) experiment can be modified
in such ways that other interpretation of the concept
of action understanding could be tested. Other inter-
pretations of action understanding and goal will each
require a different setup tuned specifically to the con-
ceptualization and hypothesis that one intends to test.
CONCLUSION
The exact meaning of any statement involving action
understanding, goal recognition, and motor resonance
can vary to a great extent, depending on the interpreta-
tion of the concepts used. In the cognitive neuroscience
literature, it is often not explicated which of the multi-
tude of possible interpretations are used. As a result,
different sets of experimental data can be taken in
mutual support of neuroscientific hypotheses, even
though interpretations might diverge in ways that make
the result in fact incompatible.
By means of a careful conceptual analysis,
we aimed to disentangle the different possible
interpretations of “action understanding”, “action
goals,” and “motor resonance.” The fine-grained dis-
tinctions we have proposed, exemplified in Table 1,
allow better interpretations of experimental data and
more adequate design of experiments. We have shown
that our proposed systematic labeling scheme is empir-
ically relevant in interpreting research data, by show-
ing how the use of the scheme leads to a reinterpre-
tation of existing experimental results in the cognitive
neuroscience literature. Moreover, we have illustrated
how our scheme can guide the design of experimental
setups aimed to test different interpretations of action
understanding.
The systematic use of well-defined concepts is an
important aspect of the constructive and fruitful analy-
sis of experimental data. In this paper, we performed
a conceptual analysis to arrive at more precise and
unequivocal definitions of the terms “action under-
standing,” “action goal,” and “motor resonance,” terms
that are central to the cognitive neuroscientific study
of action and perception. We hope to have shown that
the types of conceptual analyses that we performed
in this paper are not mere theoretical exercises, but
a constructive contribution to the empirical cognitive
neuroscience.
Original manuscript received 2 September 2010
Revised manuscript accepted 24 January 2011
First published online 4 March 2011
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... According to Rizzolatti 56 , MR is the key to successful social interaction. The concept of MR has been widely investigated, with the purpose of unravelling the conditions under which it emerges, and the factors that may influence its occurrence 57 . Current evidence suggests that MR is not an all-or-nothing phenomenon. ...
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... This effect has been explained as a reactivation of past perceptual and motor experiences occurring during memory retrieval and language comprehension. This implies a sort of simulation; the term "motor resonance" has been borrowed from the mirror neuron theory, but it can result in being more ambiguous than "simulation" (Uithol et al., 2011). ...
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Pierre Jacob (2008) raises several problems for the alleged link between mirroring and mindreading. This response argues that the best mirroring-mindreading thesis would claim that mirror processes cause, rather than constitute, selected acts of mindreading. Second, the best current evidence for mirror-based mindreading is not found in the motoric domain but in the domains of emotion and sensation, where the evidence (ignored by Jacob) is substantial. Finally, simulation theory should distinguish low-level simulation (mirroring) and high-level simulation (involving pretense or imagination). Jacob implies that bi-level simulationism creates an unbridgeable ‘gap’ in intention reading, but this is not a compelling challenge.