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DOI 10.1007/s00221-012-3143-3

RESEARCH ARTICLE

Egocentric mental transformation of self: effects of spatial
relationship in mirror-image and anatomic imitations
Tamami Sudo • Tomomitsu Herai • Ken Mogi

Received: 5 September 2011 / Accepted: 6 June 2012
Ó Springer-Verlag 2012

Abstract Assessing the mental state of others by considering their perspective plays an important part in social
communication. Imitation based on visual information represents a typical case of the translation of sensory input into
action. Although humans are often successful in imitatingcomplex actions, the mechanisms that underlie successful
imitation are poorly understood. In earlier findings, it has
been suggested that understanding others’ minds throughimitation is realized in the course of the comparison between
the representations of the self and others, involving a transformation of the egocentric perspective to the allocentricone. There are two possible strategies of transformation
between the representation of the self and others. One possible scenario is that the imitator perceives and imitatesothers as if looking in a mirror (mirror-image imitation,
where, for example, the demonstrator’s right hand corresponds to the imitator’s left hand). Alternatively, the imitator
might estimate the demonstrator’s action using the anatomically congruent limb (anatomic imitation, where, forexample, the demonstrator’s right hand corresponds to theT. Sudo (&)
Graduate School of System Design and Management,
Keio University, Collaboration Complex, 4-1-1 Hiyoshi,
Kohoku-ku, Yokohama, Kanagawa 223-8526, Japane-mail: t-sudo@sdm.keio.ac.jp
T. HeraiInterdisciplinary Graduate School of Science and Engineering,Tokyo Institute of Technology, 4259 Nagatsuta-cho,
Midori-ku, Yokohama 226-8502, Japane-mail: herai@brn.dis.titech.ac.jp
K. Mogi
Sony Computer Science Laboratories, Inc., Takanawa
Muse Bldg., 3-14-13, Higashigotanda, Shinagawa-ku,
Tokyo 141-0022, Japane-mail: kenmogi@qualia-manifesto.com

imitator’s right hand). Here, we conducted a series ofexperiments in which the subjects imitated simple handactions such as pushing a button presented from several
different spatial orientations rotated at various angles. We
observed that the imitators changed their strategy of imitation (mirror-image or anatomic imitation) depending on thenature of spatial configurations. Behavioral data from thisstudy support the hypothesis that mirror-image and anatomic
imitations provide complementary systems for understanding the actions and intentions of others.
Keywords Anatomic imitation  Mental own-body
imagery  Mirror-image imitation  Perspective-taking

Introduction
Understanding the intentions of others and considering
their mental state by taking their perspectives play animportant part in social communication. Humans are successful in imitating many complex skills in daily life;
however, mechanisms that underlie successful imitation
remain to be elucidated. Imitation based on visual information represents a typical case for the translation of
sensory information into action. Action implies a goal andan agent; therefore, action recognition implies the recognition of a goal and the understanding of the agent’s
intentions. The discovery of mirror neurons has provided
an effective model for the basic mechanism underlying
perception–action coupling, which is involved in imitation
and action understanding (Gallese et al. 1996; Rizzolatti
et al. 1996). The mirror system allows a direct matching of
the representation of observed and executed actions, thus
providing a precursor mechanism for the human ability toimitate (Iacoboni et al. 1999; Rizzolatti et al. 2001).

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While there is the view that the human mirror neuron
system plays an important role in imitation, imitation itself
would basically consist of a sequence of cognitive processes that involve a spatial assessment of the object,importing kinetic information from the object, transforming the information from within and then replicating theaction by imitators themselves. The parietal association
area responsible for spatial image transformation is heavily
involved in the perception–action coupling of imitation(Wohlschläger et al. 2003), whereas studies support anessential role of the inferior frontal gyrus (IFG) in imitative
facility (Iacoboni et al. 1999; Molnar-Szakacs et al. 2005).
In earlier studies, imitation was suggested to be realized
during the comparison of the representations of the self andothers, involving a transformation of the egocentric perspective to the allocentric one (Meltzoff and Moore 1994).
During the transformation process from the representationof the action of others to the action of the self, there are twoalternative strategies that can be used for imitation (Fig. 1).
One possible scenario is that the imitator perceives andimitates others as if looking in a mirror, for example, thedemonstrator’s right hand corresponding to the imitator’sleft hand. Alternatively, the imitator may estimate thedemonstrator’s action using the anatomically congruent
limb, for example, the demonstrator’s right handAcorresponding to the imitator’s right hand. There is evidence from psychological studies that a preference formirror-image imitation over anatomic imitation is observedin both children and adults (Avikainen et al. 2003; Schofield 1976). Studies of goal directed imitation in children
showed that young children prefer to imitate the demonstrator’s action using the mirror-image translation process;however, older children and adults gradually learn to follow the anatomic imitation process (Bekkering et al. 2000;
Wohlschläger et al. 2003). These tendencies might berelated to the properties of the mirror neuron system
located in the frontal area (Koski et al. 2003), where thefunction of the mirror neuron system is more general than asimple ‘‘mirroring’’ of action.
On the basis of these findings, we conducted a series ofexperiments using the two different (mirror or anatomical)
imitation strategies. In daily situations, action observation
occurs in miscellaneous orientation angles; therefore, it isimportant to study the properties of the imitation system atvarious orientation angles. It is interesting to observe how
the two alternative (mirror-image or anatomic) imitation
strategies are employed at intermediate orientation angles.
In these experiments, the subjects were asked to imitatea series of simple hand actions, for example, pushing abutton presented from several different spatial orientations
rotated at various angles using mirror-image and anatomic
imitation. We analyze how successful imitations areaccomplished depending on the perspective and strategy.
Finally, we discuss the general relationship between therole of perspective-taking and the fundamental aspects ofsocial cognition, such as considering other’s mental statethrough processes for mental own-body imagery.

Methods
Subjects

B
Eight healthy subjects (3 females and 5 males) participatedin this study. The mean age of this group was 27 years(range, 24–30 years). All of the subjects provided informed
consent prior to their inclusion in this study. The subjects
were all right-handed (as determined by the Edinburgh
Handedness Inventory) and had normal or corrected-tonormal vision.
Fig. 1 Two possible processes of transformation between the representation of the self and others. a Mirror-image imitation: The
imitator perceives and imitates the other as if looking in a mirror, forexample, the demonstrator’s right hand corresponding to the imitator’s left hand. b Anatomic imitation: The imitator estimates thedemonstrator’s action using the anatomically congruent limb, forexample, the demonstrator’s right hand corresponding to the imitator’s right hand

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Procedure
The subject and the experimenter, performing as thedemonstrator, sat in front of a round table (1 m in diameter). They both had a box with 4 buttons arranged symmetrically in a line (Fig. 2a). The experimenter pushed
buttons with either their right or left index finger in a

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random order. The subjects were instructed to observe andimitate the experimenter’s hand movement as rapidly andaccurately as possible using either the mirror-image or
anatomical imitation strategies.
At the beginning of each session, the subjects were
instructed as to which kind of imitation they were required
to perform. The experimenter’s button press action was
repeated 24 times in each session. The inter-stimulusintervals were set at 5 s. The imitation sessions wereconducted in various spatial relationships with relativeorientation angles of 45, 90, 135 and 180° in the clockwise
and counterclockwise directions (Fig. 2b, c). The session
with the relative orientation angle set at 180° was considered to be the facing situation, and the session with a relative orientation angle of ±45° was considered to be theside-by-side situation. The remaining sessions with relativeorientation angles of ±90° and 135° were considered to beAB

the intermediate situations. The procedure was designed toinvestigate the nature of imitation as it gradually changes
depending on perspective and strategy, during imitative
trials in the intermediate orientations between the ‘‘facing’’and ‘‘side-by-side’’ conditions.
Each session consisted of 24 trials that were conducted forevery relative orientation angle and both kinds of imitation,
resulting in a total of 672 trials. 2 blocks of mirror-image
imitations and 2 blocks of anatomic imitations were conducted alternately. All sessions in each block were conductedin the clockwise and counterclockwise order starting fromthe adjacent position. To facilitate the subjects’ performance, a warm-up session was conducted until obvious
errors, for example, incorrect button pressings or the use of
the wrong hand, were eliminated (Fig. 3). The warm-up
session was conducted for an average of 4 trials per session.
The experimenter’s and the subject’s movements wererecorded by a digital video camera positioned approximately
1 m away from the table, which facilitated the examinationof whether there were any obvious errors. When there were
obvious errors, the session was started again. We measured
and analyzed the nature of subject’s responses in the imitation sessions. We recorded the response latency from thetime when the experimenter pressed a button until the subjectpressed the corresponding button.

ResultsC

The mean response latencies for all subjects in the facing
and side-by-side situations are shown in Fig. 4. In both ofthese visual perspectives, the analysis of response latencies
showed a significant effect for the imitation strategy used
(Fig. 4a). According to repeated-measures ANOVA of theimitation strategies, the subjects were significantly fasterwith the mirror-image imitation (522.5 ± 65.2 ms) thanA

Fig. 2 Material and experimental setup. a Subjects sat in front of abox with 4 buttons arranged symmetrically in a line on a round table.
b, c Spatial orientations in the mirror and anatomical imitation tasks

B

Fig. 3 Examples of correct responses in the tasks. a Mirror-image
imitation. b Anatomic imitation

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A

B

Fig. 5 Response latency during the 2 imitation strategies. Meanvalues of the response latency at all relative orientation angles (solidline anatomic imitation; dashed line mirror-image imitation)

Discussion

Fig. 4 Comparison of the facing with side-by-side situations. a Meanvalue of the response latency during the facing situation (180°) andside-by-side situation (±45°). b Effects of the subject’s relative
position during the side-by-side situation (right or left)

with the anatomic imitation (779.8 ± 219.4 ms) in thefacing situation (F (1,14) = 4.60, p = 0.01). On the contrary, subjects were significantly faster with the anatomic
imitation (489.6 ± 70.4 ms) than with the mirror-image
imitation (799.0 ± 196.8 ms) in the side-by-side situation(F (1,14) = 4.60, p \ 0.005). There was a significant effectof interaction between the positional relationship of thesubject and the experimenter and the imitation strategies(F (1, 28) = 4.20, p \ 0.001). Furthermore, examination of
the relationship exclusively within the side-by-side situation revealed no significant difference for position between
the subject and the experimenter during the anatomic imitation (F (1,14) = 4.60, p = 0.99) and the mirror-image
imitations (F (1,14) = 4.60, p = 0.64) (Fig. 4b). Tukey
post hoc tests confirmed these significant differences.
Linear regression analysis revealed strong correlations
between the absolute values of relative orientation angles
and response latencies. There was a negative correlation for
mirror-image imitations (r = 0.979 for the plus direction,and r = 0.979 for the minus direction) and a positive
correlation for anatomic imitations (r = 0.997 for the plus
direction, r = 0.995 for the minus direction) (Fig. 5).

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The present study described a behavioral experiment thatinvestigates the effects of perspective and strategy on
imitation. There is a spatial compatibility between theobserved and required action in the following two conditions: the mirror-image imitation in the facing situation andthe anatomical imitation in the side-by-side situation. In
these conditions, the spatial compatibility has made it
possible for the subjects to conduct the required actions
with faster reaction times. At various relative orientation
angles, the subjects may have implicitly performed amental transformation of their perspective either byimagining themselves in the demonstrator’s body position
or by imagining the demonstrator’s body as a reflection or
rotation of their own body. In the first case, mirror-image
imitation would demand a reflection symmetry, where thesubjects have to imagine themselves in the other’s body
position and to take their visuospatial perspective (thirdperson perspective), relating the action presented by thedemonstrator to the own-body image. Alternatively, ananatomic imitation would require a rotational symmetry,
where the subjects have to maintain their own visuospatial
perspective (first-person perspective) and superimpose theown-body image on the action presented by the demonstrator. The respective subsets of our data would reflect
these specific types of object mental rotation mechanism(Shepard and Metzler 1971).
Consistent with the results of a previous study (Jackson
et al. 2006), the reactions of the subjects during the mirrorimage imitation were significantly faster than during theanatomic imitation in the facing situation. In the side-byside situation, on the other hand, the mirror-image imitation took significantly longer. The effect of the angles ofrelative orientation revealed a pair of symmetrical aspects

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in the graph (Fig. 5), suggesting the existence of complementary systems between mirror-image and anatomic
imitations.
Verbal reports from the subjects after the sessions wereconsistent with the tendency for the two alternative imitation strategies revealed at intermediate angles. The subjects typically answered that the configuration was ‘‘almost
side-by-side’’ at 45 degrees, ‘‘more side-by-side than facing’’ at 90 degrees, and ‘‘more facing than side-by-side’’ at
135 degrees. These verbal reports reveal the cognitive
processes subserving the switching between alternative(mirror-image vs. anatomical imitation) strategies
depending on the angles.
The results reported here are consistent with the ‘generalist’ theory of imitation put forward in previous studies(Brass and Heyes 2005; Newman-Norlund et al. 2010; vanElk et al. 2011). The flexibility of the switching between
alternative imitation strategies, coupled with a robust
handling of the spatial configuration, is compatible with theidea that the observed behavior is a manifestation of ageneral learning and motor control mechanisms. The
switching of the hand of action is a general behavioral
requirement observed in many daily activities, rather than aspecial strategy specifically designed for imitation.
During imitation, subjects need to translate a complex
dynamic visual input pattern into motor commands for the
self-performed movement sequence. Previous studies
mainly dealt with imitative behavior in the facing situation(Avikainen et al. 2003; Jackson et al. 2006; Koski et al.
2003). These behavioral studies reported that the complex
translation process from visual inputs to motor commands
causes a delay in imitative behavior in the facing situation.
In comparison, our experimental sessions were conducted
for various spatial relationships with relative orientation
angles in addition to the facing situation that were notassessed by previous studies.
Our findings are closely related to the sense of theembodied self and the representation of others. The
embodiment of one’s own body is the foundation of thefirst-person perspective (Vogeley and Fink 2003; Grèzes
and Decety 2001) and subserves the cognitive processes
relating one’s body to those of others. The ‘‘own body’’ isconsidered to be involved in several phenomenologicalaspects of the self, for example, self-location, self-otherdistinction, and self-other interaction. Embodied selflocation may be somehow crucial for social cognitive
abilities. Several imaging studies have suggested that visuospatial perspective-taking requires spatial cognitive
abilities that rely on bodily processing, such as mental
body transformations and mental imagery with a disembodied self-location (Arzy et al. 2006; Blanke et al. 2005).
Since the discovery of mirror neurons in the ventral
premotor cortex (area F5) and parietal area PF of themonkey (Gallese et al. 1996; Rizzolatti et al. 1996), there
has been a growing debate as to whether they may be theneural basis for the ability to imitate. The perception andexecution of actions have been considered to possess acommon representational domain, operating with a mechanism to transform visual information directly into motor
acts (Bekkering et al. 2000). This conceptual idea wasconfirmed by brain imaging studies (Iacoboni et al. 1999;
Iacoboni et al. 2001; Nishitani and Hari 2000). Similar
results indicating that mirror neurons play a crucial role inimitation were obtained using repetitive transcranial
magnetic stimulation (rTMS) (Heiser et al. 2003). The
suggestion that the mirror neuron system overlaps with
the neural representations of observed and self-performed
actions has provided a physiological model for the basic
mechanism underlying perception–action coupling, whichis involved in imitation, action understanding, and reading
the intentions and mental states of others (Amodio andFrith 2006; Frith and Frith 2006; Gallese and Goldman
1998; Iacoboni et al. 2005; Uddin et al. 2007). The
activities of the mirror system may be significantly
affected by the relative orientations of the actor andobserver.
The properties of imitation process revealed in this study
provide clues to how we handle cognitive challenges whenfacing actors at various orientation angles. Recent investigations revealed that the mirror neuron system processes
the how, what, and why of other people’s actions. Ultimately, the robust handling of the reflection and rotation of
one’s own body, dealing with miscellaneous cognitive
challenges in complementary ways, would subserve a close
connection with the ‘‘how’’ and ‘‘what’’ aspects of imitations and mind reading.
Acknowledgments We thank Takumi Ueda for preparing theillustrations, Takayasu Sekine for helpful comments on an earlier
design of the experiment, and Takashi Maeno for discussions anduseful comments. This study was supported by a Grant-in-Aid for theJapan Society for the Promotion of Science Fellows.

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