Development of Embodied Sense of Self Scale (ESSS): Exploring Everyday Experiences Induced by Anomalous Self-Representation

Abstract

The scientific exploration of the self has progressed, with much attention focused on the Embodied Sense of Self (ESS). Empirical studies have suggested the mechanisms for self-representation. On the other hand, less attention has been paid to the subjectivity itself of the self. With reference to previous studies, the current study collected items that reflect the ESS and statistically extracted three factors for it: Ownership, Agency, and Narrative. The developed questionnaire [Embodied Sense of Self Scale (ESSS)] showed good enough validity and reliability for practical use. Furthermore, ESSS discriminated schizophrenia, a disorder of the ESS, from controls. We discuss the factorial structure of ESS and the relationship among factors on the basis of the current results.

Full text

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ORIGINAL RESEARCH
published: 05 July 2016
doi: 10.3389/fpsyg.2016.01005
Edited by:
Isabella Pasqualini,
EPFL, Switzerland
Reviewed by:
Cor Baerveldt,
University of Alberta, Canada
Pelham Carter,
Birmingham City University, UK
*Correspondence:
Tomohisa Asai
asai.tomohisa@lab.ntt.co.jp
Specialty section:
This article was submitted to
Cognitive Science,
a section of the journal
Frontiers in Psychology
Received: 01 December 2015
Accepted: 20 June 2016
Published: 05 July 2016
Citation:
Asai T, Kanayama N, Imaizumi S,
Koyama S and Kaganoi S (2016)
Development of Embodied Sense
of Self Scale (ESSS): Exploring
Everyday Experiences Induced by
Anomalous Self-Representation.
Front. Psychol. 7:1005.
doi: 10.3389/fpsyg.2016.01005
Development of Embodied Sense of
Self Scale (ESSS): Exploring
Everyday Experiences Induced by
Anomalous Self-Representation
Tomohisa Asai1*, Noriaki Kanayama2, Shu Imaizumi1,3, Shinichi Koyama3and
Seiji Kaganoi4
1Nippon Telegraph and Telephone Communication Science Laboratories, Human Information Science Laboratory,
Kanagawa, Japan, 2Department of Psychiatry and Neurosciences, Institute of Biomedical and Health Sciences, Hiroshima
University, Hiroshima, Japan, 3Graduate School of Engineering, Chiba University, Chiba, Japan, 4Department of
Rehabilitation, Geisei Hospital, Kochi, Japan
The scientific exploration of the self has progressed, with much attention focused on the
Embodied Sense of Self (ESS). Empirical studies have suggested the mechanisms for
self-representation. On the other hand, less attention has been paid to the subjectivity
itself of the self. With reference to previous studies, the current study collected items that
reflect the ESS and statistically extracted three factors for it: Ownership,Agency, and
Narrative. The developed questionnaire [Embodied Sense of Self Scale (ESSS)] showed
good enough validity and reliability for practical use. Furthermore, ESSS discriminated
schizophrenia, a disorder of the ESS, from controls. We discuss the factorial structure
of ESS and the relationship among factors on the basis of the current results.
Keywords: sense of self, embodiment, agency, ownership, narrative
INTRODUCTION
One of the distinctive scientific interests in this decade has been characterized by studies of the self.
Recent psychological and neuroscience studies have focused on examining the self-representation
in the brain. This trend started with revisiting our sense of body and action (Gallagher, 2000;
Jeannerod, 2007;Blanke et al., 2015). Since these senses can be examined empirically, how the
subjective feeling of “my own body” or “my own action” is elicited has been revealed in behavioral,
neural, and computational approaches (Miall and Wolpert, 1996;Wolpert, 1997;Blakemore et al.,
2002;Frith, 2005;Tsakiris et al., 2007;Blanke et al., 2015) and also applied to induce virtual
presence and immersion in Cyberpsychology in tandem with recent technological progress (see
for review, Slater et al., 2008;Blanke et al., 2015). The sense of body (e.g., “this is my own hand”)
needs multimodal sensory integration (Kilteni et al., 2015), while the sense of action (e.g., “I myself
am moving the hand”) derives from matching motor predictions with actual feedback or outcomes
(David et al., 2008). These subjective feelings of the self, which are grounded within our own body
or sensorimotor system (Weiss et al., 2014), might be called as the Embodied Sense of Self (ESS).
Though this progress based on empirical or objective measures has revealed mechanisms for
ESS, its subjectivity itself has been treated as secondary. As a result, the phenomenological aspects
of the ESS have not yet been fully examined (e.g., Longo et al., 2008;Haggard and Chambon,
2012): this study, entitled as “What is embodiment?”, specifically focused on the phenomenological
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sensations in the rubber hand illusion (RHI; Botvinick and
Cohen, 1998; see also Discussion). A difficulty in exploring the
subjective ESS is that we are not always aware of the feeling
of self (i.e., pre-reflective self, Gallagher, 2000;Legrand, 2007;
Praetorius, 2009;Trehub, 2009) because the brain automatically
regulates many functions including body and action unless
an operational error is detected (Nielsen, 1963;Fourneret and
Jeannerod, 1998;Knoblich and Kircher, 2004;Tajadura-Jimenez
et al., 2012;Asai, 2015b). Therefore, a possible approach for
the awareness for the self would be to focus on those errors,
namely, everyday experiences that might be caused by an
abnormal ESS (e.g., Sivertsen and Normann, 2015). That was
how the current study explored the factorial structure of the
ESS, and as a result, and more importantly, the current study
developed a questionnaire that reflects on that factorial structure.
The questionnaire could be a useful tool for measuring an
anomalous ESS, especially for patients with mental illnesses, such
as schizophrenia. Similar approaches based on subjective reports
for the sense of self have already been reported (e.g., Jones et al.,
2008;DaSilveira et al., 2015). For example, prototype scales for
the sense of action (i.e., “sense of agency”, see below) have been
developed (Asai et al., 2009b;Polito et al., 2013). Parnas et al.
(2005a,b) have suggested a checklist for an abnormal sense of
body and action (i.e., “minimal self”, see below). With reference
to these previous studies, the current study aimed to develop a
scale for a more comprehensive ESS and examine its factorial
structure.
What factors can we assume contribute to the ESS? First of all,
as noted above, the sense of body, the physical boundary between
the self and the environment, is fundamental for the ESS. Once
we have a body, we can move it (Asai, 2015a). The body enables
us to act as an agent in the world. Gallagher (2000) has theorized
this online sensory level of self as the minimal self, a self devoid of
temporal extension, wherein the “sense of ownership” means the
feeling of owning my own body and, therefore, the experiencing
of sensations on it (Gallagher, 2000;Tsakiris, 2010), while the
“sense of agency” means the feeling of causing my own action
(Haggard and Chambon, 2012). This concept has been extended
by empirical evidence so that the sense of ownership includes not
only my own body but external tools (Iriki et al., 1996;Maravita
and Iriki, 2004), and the sense of agency also includes the sense of
self-attribution of an action’s outcome (i.e., sensory event) in the
external world (Haggard, 2005;Sato and Yasuda, 2005). In this
sense, “I” seems to be the recursive feeling both as a “physical
existence” that can be owned and as an “intentional agent” that
can affect the world.
The minimal self, however, might be imperfect for self-
representation. Gallagher (2000) also referred to the narrative
self, the self with temporal extension and continuity across time
(White, 2015). Right after we have a sensory experience, it
goes past. As the sensory experiences that construct minimal
self accumulate across time as memory (i.e., autobiographical
source memory, Sugimori et al., 2012;Sugimori and Asai, 2015),
what we have done and what we have experienced construct a
narrative for the self (Habermas and Kober, 2015). This temporal
extension of selfness might generally be referred to as identity
or personality (Ramachandran, 1998;Damasio, 1999;Habermas
and Kober, 2015) so that we can imagine what we will do in the
future and simulate how we will behave in a certain situation
on the basis of past experiences. At this stage, the self finally
achieves a uniqueness (i.e., identity) that includes behavioral
traits and prospective decision making patterns (e.g., prospective
agency, Chambon and Haggard, 2012;Chambon et al., 2015).
In this sense, the narrative self simply includes autobiographical
memory and identity (Gallagher, 2000). The self, not a simple
substance (e.g., minimal self) but something that is maintained
by mental experience (e.g., personal identity), is not an already
existing entity that produces the narrative. Instead, it is the
“product of the narrative itself” (Di Francesco, 2008).
According to these discussions, the ESS seems to include
the minimal self and narrative self: the former further contains
the sense of ownership and agency, while the latter contains
autobiographical memory and identity. Though the relationship
between minimal and narrative self is still unclear (Gallagher,
2000), these two domains might construct a unified self-
representation in terms of embodiment (Damasio, 1999). The
mental experience involving the minimal and even narrative
self is not simply cognitive, but also emotional and embodied
(Gallagher, 2004), where we refer to ourselves as an identical or
narrative entity through our own online sensory experiences in
body and action and also through its memorized experiences
(see also Discussion). Ramachandran (1998) also suggested
similar essential factors for self-representation: embodied
self (=ownership), executive self (=agency), mnemonic self
(=autobiographical memory), and unified self (=identity). The
current study refers to these potential factors as ownership,
agency, continuity, and uniformity. We first collected items in
accordance with these factors with reference to previous studies
and then developed a questionnaire for the ESS with a statistical
procedure to confirm its validity and reliability by administering
five successive surveys (the total number of participants were
1167). Specifically, Survey A explored the factorial structure of
ESS: the potential factors including ownership and agency for
minimal self as well as continuity and uniformity for narrative
self were hypothesized to comprise the ESS. Survey B confirmed
the validity of the developed questionnaire [the Embodied
Sense of Self Scale (ESSS)] by examining correlations with other
to-be-correlated scales, including the schizotypal personality
scale. Survey C further examined the relationship between
the ESSS and potentially related scales, including self-esteem,
and self-efficacy questionnaires. Survey D confirmed the
reliability of the ESSS in terms of temporal consistency. Survey
E examined differences in the ESSS among schizophrenics and
amputees. We discuss the factorial structure of the ESS on the
basis of that developed ESSS questionnaire and the statistical
results.
MATERIALS AND METHODS
The questionnaires used in the current study, including our newly
developed one here, were in Japanese for Japanese participants.
We used Japanese versions of the existing questionnaires shown
below. All of them have been reported to have good validity and
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reliability. The items in the newly developed one are expressed in
English here with back-translation.
Item Collection
With reference to previous studies, we collected and created
120 potential items that reflect the ESS (Supplementary Material
S1). These studies include the following questionnaire studies:
the schizotypal experience scales (linked with ESS; Launay and
Slade, 1981;Claridge and Broks, 1984;Bentall et al., 1989;Raine,
1991;Mason et al., 1995;Waters et al., 2003;Cyhlarova and
Claridge, 2005;Sugimori et al., 2009), depersonalization scales
(linked with ownership; Putnam, 1997;Sierra and Berrios, 2000),
and agency or minimal self scales (Parnas et al., 2005b ;Asai et al.,
2009b). We also considered many other empirical, theoretical,
and phenomenological studies to prepare for potential new items
(e.g., Cahill, 1996;Iriki et al., 1996;Daprati et al., 1997;Botvinick
and Cohen, 1998;Blakemore et al., 2000;Frith et al., 2000a;Peled
et al., 2000;Fourneret et al., 2001;Franck et al., 2001;Platek
and Gallup, 2002;Wegner, 2003;Blanke, 2004;Knoblich and
Kircher, 2004;Maravita and Iriki, 2004;Sato and Yasuda, 2005;
Asai and Tanno, 2007, 2008, 2013;Jones and Fernyhough, 2007;
Asai et al., 2008, 2009a, 2011;David et al., 2008;Longo et al.,
2008;Johns et al., 2010;Newport et al., 2010;Hauser et al., 2011;
Hommes et al., 2011;Sugimori et al., 2011a,b, 2012;Sugimori
and Asai, 2015). Ownership was assumed to include items like
“Sometimes it feels like my body is jerky like a robot.” Agency
might include “I sometimes bump into things or people when I
am out walking.” Continuity might include “I cannot remember
what I did during that period because my memory was fuzzy.”
Uniformity might include “Sometimes I feel that I no longer know
my own personality.” A tense and an expression for items were
unified so that a higher score on a five-point Likert scale means a
more anomalous ESS. This 120-item temporal scale is called the
Embodied Sense of Self Scale temporal (ESSSt). The instruction
was “Please indicate the extent to which the following statements
generally apply to you by circling the corresponding number
(1–5) next to the statement. (i) Strongly disagree, (ii) Disagree
somewhat, (iii) Neither disagree nor agree, (iv) Agree somewhat,
and (v) Strongly agree”.
Participants and Procedure
Survey A
Japanese university students (N=718, male =364, average
age =19.7, SD =2.60) participated in this survey during
psychology classes where the 120-item ESSSt was conducted so
that the items would be selected with a statistical procedure.
Then we explored the factorial structure. At this stage, we finally
developed a 25-item ESSS that was used in the following surveys
(see the “Results” Section for details).
Survey B
A community sample was recruited individually (N=106,
male =72, average age =30.7, and SD =6.67). They
answered some other questionnaires for confirming criterion-
related validity as well as the ESSS. The prototype agency
scale [Sense of Agency Scale (SOAS); Asai et al., 2009b] and
multidimensional schizotypy scale [Oxford–Liverpool Inventory
of Feelings and Experiences (O-LIFE); Mason et al., 1995]
were used for convergent validity, while the empathy scale
[Interpersonal Reactivity Index (IRI); Davis, 1980, 1983] was used
for divergent validity. It was necessary to discriminate between
the sense of self (targeted by the current scale) and the sense
of others (e.g., empathy) since they might somehow be related
to each other (Miall, 2003;Sinigaglia and Rizzolatti, 2011). The
IRI, one of the commonly used scales for empathy, might simply
correlate with the ESSS in a weak manner, but we expected that
this superficial correlation would diminish after controlling for
other potentially mediating variables like schizotypy (e.g., Asai
et al., 2011).
Survey C
We asked a marketing company to conduct a web survey
in order to collect an area-independent community sample
(N=153, male =74, average age =26.0, and SD =2.74).
They answered the self-esteem scale [Rosenberg Self Esteem Scale
(RSES); Rosenberg, 1965] and self-efficacy scale (Generalized
Self Efficacy Scale, GSES, Sherer et al., 1982) as well as the
ESSS for confirming criterion-related validity again from a
more explorative perspective. Self-esteem and self-efficacy have
a concept similar to (but not totally the same as) the ESS. We,
therefore, hypothesized a weak significant correlation between
the ESSS and RSES or GSES (convergent validity).
Survey D
The web survey was conducted again for the same sample who
answered in Survey C after approximately a month interval
(N=132, male =62, average age =25.7, and SD =3.31). In
order to confirm re-test reliability, they answered the ESSS again.
Survey E
The final survey was to confirm validity of the ESSS in terms
of a clinical perspective. Schizophrenic patients (N=15,
male =9, average age =60.9, and SD =6.45, average year of
hospitalization =10.7, average medication =657.8 CP-mg) and
upper limb amputees (N=11, male =11, average age =67.1,
and SD =12.1, average of years since amputation =43.3) as well
as age-matched healthy controls (N=32, male =25, average
age =66.3, and SD =8.00) answered the ESSS. The schizophrenic
patients, none of whom had a history of cerebrovascular diseases,
were diagnosed as chronic schizophrenics on the basis of DSM-
V (American Psychiatric Association, 2013) and were clinically
stable at the time of the survey. There was no statistical difference
in age among three groups [F(2,55) =2.42, p=0.10]. We
hypothesized that people with schizophrenia have an anomalous
ESS (enhanced score in the ESSS), indicating convergent
validity, compared with healthy controls and even amputees,
indicating divergent validity. This is because schizophrenia might
be a disorder of the self, characterized by a disturbed self-
representation in the brain (Frith et al., 2000b;Cermolacce et al.,
2007;Jeannerod, 2009). Such a disturbed self-representation
has not been suggested for amputees since they have no self-
related mental symptoms like hallucinations or delusions, though
both schizophrenics and amputees claim an anomalous feeling
or inconvenience in their bodily sensations and motor abilities
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(Walker, 1994;Meier, 2001;Putzhammer and Klein, 2006;
Mayer et al., 2008;Gallese and Ferri, 2014;Imaizumi et al.,
2014).
Ethical Treatment
The procedure and policy in treating personal information in the
current surveys were approved by the local ethics committees of
each responsible institution (Chiba University, Geisei Hospital,
and NTT Communication Laboratories).
RESULTS
The data obtained in the current surveys were analyzed by SPSS
17.0j as follows.
Item Selection and Factor Analysis
(Survey A)
The 120-item ESSSt was answered by 718 university students.
First of all, 40 items were excluded because their distributions
were skewed, with their average scores ±1SD out of the scoring
range (1–5), indicating ceiling or floor effects. At this stage,
the extreme items like “I sometimes feel as if my body doesn’t
actually exist.”, “Sometimes I feel like I am in a dream state
where I hallucinate and have weird experiences.” or “When I
am really tired, I get motion sickness when I am walking.”
were dropped. Though these items might be a direct expression
of an anomalous ESS, statistically speaking, these experiences
are so rare in the general population on a daily basis that
they should not be included in the following analysis. The first
explorative factor analysis was conducted for the remaining 80
items. Because the assumed factors were thought to be correlated
with each other, promax rotation with maximum likelihood
method was applied. Since there were four assumed factors
(ownership, agency, continuity, and uniformity), the four factor
model was applied (the number of factors was fixed at four).
However, the potential items for continuity and uniformity were
not separable for each factor, while the items for ownership and
agency were. Therefore, the items for continuity and uniformity
were assumed again to be loaded to one factor: Narrative.
At this stage, items with smaller loads in the above factor
analysis (<0.3), items that had loads to multiple factors, and
items for specific people (e.g., regarding driving, cellphones, or
PC) were removed (for example, “It sometimes seems like the
cellphone in my pocket or bag is vibrating.” is not applicable
for non-cellphone users). After that, the second confirmative
factor analysis with a three-factor model (ownership, agency,
and narrative) was conducted for the remaining 40 items,
which revealed three interpretable factors as we hypothesized.
After items with smaller loads in this factor analysis (<0.3)
and items that had loads to multiple factors were removed
again, the final factor analysis reconfirmed the three factors
of the 25-item ESSS (eigenvalues were 5.46, 2.00, 1.51, 1.09,
and 1.03 for factor 1, 2, 3, 4, and 5, respectively; Table 1).
Though the item “I think I am more ticklish than other people.”
had a smaller load (0.30) than the others (>0.35), the fact
that this item was included in Agency should be important in
terms of the factorial validity of the ESSS. Therefore, this item
was not removed (see below for the interpretation of Agency
factor).
The first factor, Ownership, includes nine items like
“Sometimes the clothes I am wearing feel heavy.”, “Sometimes I
become aware that my body has become chilled.” and “When I
am doing something, it seems like I am observing myself from a
distance.” This factor reflects the sense of ownership over one’s
own body and property (e.g., external operational tools), and
further on the sense of the existence or reality of ourselves. The
recent updated understanding of ownership is included in these
items, where ownership is not only for our own body and its
counterpart but for even selfness, whose disorder could cause
depersonalization (Putnam, 1997) (see also the “Discussion”
Section).
The second factor, Narrative, includes eight items like “My
personality changes depending on the setting and the situation.”,
“No matter how hard I concentrate, unrelated thoughts intrude
upon my thinking.”, and “It seems like the person I was in the
past and the person I am today are completely different.” This
factor reflects the continuity (i.e., temporal extension through
autobiographical memory) and uniformity (i.e., uniqueness
known as identity, personality, and behavioral traits) of the
self. Though these two aspects of the “narrative self ” had been
assumed to have their own factor, statistical results indicated they
contributed to just one factor simultaneously. Compared with the
first and the third factor shown below, there is still much to be
clarified about the narrative self (Gallagher, 2000) (see the results
of “Survey C” and “Discussion”).
The third factor, Agency, includes eight items like “I tend
to drop things when I carry things around.”, “It is difficult to
grope around for something without being able to see it.”, and
“Sometimes I forget what I was going to say.” This factor reflects
the sense of controllability of a target, including our own body,
and the intentionality of our own action. In particular, though
the item “I think I am more ticklish than other people.” might
be superficially unrelated to agency, self-ticklishness (i.e., sensory
attenuation, Blakemore et al., 1998) is thought to be an implicit
measure for agency according to the computational theory of
motor control (Wolpert, 1997). Therefore, the fact that not the
factor Ownership, that is related to bodily sensation, but the factor
Agency included this item supports the factorial validity of the
ESSS.
The descriptive statistics of the current surveys (Surveys A–D)
are summarized in Table 2. Since there was no statistical gender
difference in the ESSS total score in Survey A, the following
analysis excluded gender difference.
Confirmation of Reliability (Survey A):
Internal Consistency
In order to confirm the internal consistency of the 25-item ESSS,
αcoefficients were calculated for the total score and each factor
score among the 718 university students sample. The results
indicate sufficient values for practical usage of the ESSS: α=0.84
for total, 0.74 for Ownership, 0.75 for Narrative, and 0.71 for
Agency.
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TABLE 1 | The items and the factorial structure of ESSS.
Item Ownership Narrative Agency Communality
1 Sometimes the clothes I am wearing feel heavy 0.652 −0.073 0.035 0.390
2 Sometimes it feels like my body is jerky like a robot 0.637 −0.082 0.053 0.374
3 Thoughts that come to mind seem to be someone else’s 0.529 0.116 −0.006 0.365
4 I am strangely bothered by the way clothing rubs against my skin 0.430 −0.063 0.137 0.214
5 When out walking, I rarely notice my reflection in mirrors or shop windows 0.429 −0.047 −0.116 0.141
6 Sometimes I become aware that my body has become chilled 0.423 0.090 0.024 0.245
7 Sometimes my existence seems to lack a sense of reality 0.404 0.294 −0.127 0.330
8 Sometimes I sense that my body is very light 0.387 −0.109 0.038 0.120
9 When I am doing something, it seems like I am observing myself from a distance 0.367 0.187 −0.010 0.248
10 Sometimes I feel that I no longer know my own personality 0.025 0.665 −0.025 0.446
11 My personality changes depending on the setting and the situation −0.043 0.599 −0.109 0.279
12 No matter how hard I concentrate, unrelated thoughts intrude upon my thinking −0.159 0.555 0.179 0.337
13 When a song gets stuck in my head, it is really hard to turn it off −0.059 0.541 0.070 0.298
14 It seems like the person I was in the past and the person I am today are completely different 0.126 0.449 −0.020 0.275
15 I feel like sometimes people misunderstand my personality 0.160 0.427 −0.099 0.245
16 I cannot remember what I did during that period because my memory was fuzzy 0.089 0.397 0.111 0.273
17 I sometime recall things that make me smile to myself −0.141 0.379 0.140 0.157
18 I lose things without even being aware they are lost −0.020 −0.041 0.633 0.368
19 I tend to drop things when I carry things around 0.147 −0.051 0.628 0.452
20 I sometimes bump into things or people when I am out walking 0.035 0.102 0.534 0.372
21 I have been told that my voice is too loud −0.089 −0.094 0.491 0.186
22 Something may attach itself to me without me realizing it −0.004 0.062 0.439 0.223
23 It is difficult to grope around for something without being able to see it 0.013 0.048 0.368 0.160
24 Sometimes I forget what I was going to say −0.043 0.184 0.367 0.218
25 I think I am more ticklish than other people 0.063 −0.006 0.303 0.109
Inter-correlation among factors (after rotation) 1 2 3
– 0.605 0.402
– 0.512
–
These items in English were back-translated from the original Japanese items that were used in the current study.
Confirmation of Validity (Survey B):
Convergent and Divergent Validity
Survey B examined the relationship between the ESSS and
other existing scales among 106-member community sample.
For the convergent validity, the correlations between the ESSS
and O-LIFE (schizotypy) /SOAS (sense of agency) in their total
scores were positively significant (rs >0.67) (see Table 3 for
correlations among sub-scores of scales). On the other hand, the
correlation between ESSS and IRI (empathy) was also significant
(r=0.46), but the effect size was smaller than the above values,
indicating the divergent validity. In particular, from the sub-score
results (Table 3), we see that the ESSS was significantly correlated
with two factors of the IRI: Fantasy and Distress. Since these
two factors have been suggested to correlate with schizotypal
personality (Asai et al., 2011), the correlation between the ESSS
and IRI might be a spurious correlation, mediating schizotypy.
Indeed, when the schizotypy score (total O-LIFE) was partialled
out (i.e., partial correlation), the above-mentioned significant
correlation between the ESSS and IRI mostly disappeared, while
the correlation between the ESSS and SOAS remained significant
(Table 4). This indicates that the ESS, the awareness for the self,
is independent from empathy, the awareness of others. These
results, in summary, suggested the criterion-related (convergent
and divergent) validity of the ESSS.
Confirmation of Validity (Survey C): In
Relation with Similar Concepts
Survey C examined the relationship with similar concepts for
the self among the 153-member community sample. The well-
accepted concept of self-efficacy means self-evaluation of the
ability to perform necessary behaviors according to the situation
(Sherer et al., 1982). The concept of self-esteem means self-
respect and therefore high evaluation (Rosenberg, 1965). These
scores should be modulated by the ESSS since the ESS was
developed to comprehend not only the sensory level of self
(minimal self) but identity and personality (narrative self) so
that self-efficacy and self-esteem should be more related to
Narrative than Ownership or Agency. Results indicated that
is the case, where the negative correlations were observed
between the total ESSS and GSES (self-efficacy)/RSES (self-
esteem) (r= −0.28 and −0.30, respectively). Since these
relationships were not so strong, the ESSS and GSES/RSES are not
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TABLE 2 | Descriptive statistics of the current study.
Survey (N) Average (SD) Minimum–Maximum
ESSS Survey A (718) 73.7 (13.8) 33–118
Ownership 20.3 (6.23) 9–43
Narrative 28.1 (5.68) 8–40
Agency 25.1 (5.70) 8–40
O-LIFE Survey B (106) 40.5 (11.7) 14–70
Positive 6.97 (5.41) 0–24
Negative 13.3 (1.89) 9–17
Disorganized 12.3 (5.14) 0–24
Impulsive 8.07 (3.69) 1–22
SOAS Survey B (106) 40.1 (5.99) 26–57
Mental 14.8 (3.56) 8–25
Bodily 15.6 (3.01) 6–23
Social 9.60 (1.94) 5–14
IRI Survey B (106) 92.3 (10.7) 50–116
Perspective 24.3 (5.25) 9–35
Fantasy 23.1 (5.11) 7–35
Concern 24.6 (3.94) 14–33
Distress 20.3 (5.42) 7–31
RSES Survey C (153) 29.6 (6.53) 12–46
GSES Survey C (153) 10.3 (4.96) 0–22
ESSS, Embodied Sense of Self Scale; O-LIFE, The Oxford Schizotypal Personality
Scale; SOAS, Sense of Agency Scale; IRI, Interpersonal Reactivity Index; RSES,
Rosenberg Self Esteem Scale; GSES, Generalized Self Efficacy Scale.
Please see references for the meaning of sub-scores in each existing questionnaire.
sharing totally the same concepts but rather an anomalous ESS
might entail weaker self-esteem and self-efficacy because these
two concepts showed the strongest correlation with Narrative
(Table 5). Narrative self means the temporal extension of minimal
self. An anomalous narrative self, that includes identity or
personality, would decrease our positive self-evaluation (self-
respect or self-esteem), where we recognize ourselves as a
less unified and inconsistent representation of the self. These
contrasting results indicate factorial validity in terms of factor
interpretation.
Confirmation of Reliability (Survey D):
Re-test Reliability
Survey D examined the re-test reliability of ESSS among the
same 132 participants in Survey C. The interclass correlation
coefficients between the two surveys with a month interval
showed high enough values for practical use: rICC =0.82 for total,
0.84 for Ownership, 0.81 for Narrative, and 0.78 for Agency.
Confirmation of Validity (Survey E):
Clinical Validity
One application of the ESSS is to simply evaluate people with an
anomalous ESS and the effect of rehabilitation and intervention
in a more objective way. For that purpose, we examined the
clinical validity of the ESSS, whether the ESSS could differentiate
people with anomalous self-representation like schizophrenia.
Fifteen schizophrenic patients, 11 amputees, and 32 healthy
controls answered the ESSS. Figure 1 shows the group difference
in the ESSS score. A two-way ANOVA with sub-scores (i.e.,
factors) as the within-subject independent variable, groups as
the between-subject independent variable, and averaged score
per item as the dependent variable revealed that the interaction
was not significant [F(4, 110) =0.50, p>0.70] but the
main effect of groups [F(2, 55) =11.82, p=0.00] as well as
the main effect of factors [F(2, 4) =17.23, p=0.00] were
significant. Regarding the difference among groups, a post-hoc
multiple comparison using Ryan’s method (the most powerful in
statistical power among the commonly used multiple comparison
methods, Kirk, 1995) revealed significant differences between
schizophrenics and amputees/controls (ps <0.05). Regarding
the difference among factors, Ryan’s method revealed the
difference between Ownership and Narrative/Agency (ps <0.05).
TABLE 3 | Pearson’s inter-correlation matrix among scales.
O-LIFE Positive Negative Disorganized Impulsive SOAS Mental Bodily Social IRI Perspective Fantasy Concern Distress
ESSS 0.69∗∗ 0.61∗∗ 0.04 0.64∗∗ 0.36∗∗ 0.81∗∗ 0.70∗∗ 0.67∗∗ 0.18 0.46∗∗ 0.18 0.33∗∗ 0.09 0.35∗∗
Ownership 0.57∗∗ 0.61∗∗ 0.04 0.50∗∗ 0.19∗0.64∗∗ 0.54∗∗ 0.52∗∗ 0.17 0.32∗∗ 0.13 0.23∗∗ 0.06 0.24∗
Narrative 0.72∗∗ 0.60∗∗ 0.65∗∗ 0.06 0.49∗∗ 0.77∗∗ 0.64∗∗ 0.65∗∗ 0.18 0.32∗∗ 0.13 0.23∗∗ 0.06 0.24∗
Agency 0.45∗∗ 0.33∗∗ –0.02 0.49∗∗ 0.23∗0.66∗∗ 0.61∗∗ 0.53∗∗ 0.10 0.43∗∗ 0.18 0.16 0.12 0.43∗∗
∗∗p<0.01, ∗p<0.05.
ESSS, Embodied Sense of Self Scale; O-LIFE, The Oxford Schizotypal Personality Scale; SOAS, Sense of Agency Scale; IRI, Interpersonal Reactivity Index.
TABLE 4 | Partial-correlation controlling O-LIFE total score.
SOAS Mental Bodily Social IRI Perspective Fantasy Concern Distress
ESSS 0.65∗∗ 0.57∗∗ 0.42∗∗ 0.05 0.24∗0.13 0.03 0.07 0.23∗
Ownership 0.42∗∗ 0.37∗∗ 0.25∗∗ 0.07 0.09 0.07 –0.04 0.02 0.10
Narrative 0.56∗∗ 0.48∗∗ 0.38∗∗ 0.05 0.20∗0.11 0.20∗0.02 0.07
Agency 0.54∗∗ 0.50∗∗ 0.36∗∗ 0.00 0.29∗0.13 –0.05 0.10 0.35∗∗
∗∗p<0.01, ∗p<0.05.
ESSS, Embodied Sense of Self Scale; O-LIFE, The Oxford Schizotypal Personality Scale; SOAS, Sense of Agency Scale; IRI, Interpersonal Reactivity Index.
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TABLE 5 | Inter-correlation among Embodied Sense of Self, Self-Esteem,
and Self-Efficacy.
RSES GSES
ESSS –0.28∗∗ –0.30∗∗
Ownership –0.24∗∗ –19∗
Narrative –0.36∗∗ –0.37∗∗
Agency –0.17∗–0.24∗
∗∗p<0.01, ∗p<0.05.
ESSS, Embodied Sense of Self Scale; RSES, Rosenberg Self Esteem Scale; GSES,
Generalized Self Efficacy Scale.
FIGURE 1 | The difference in Embodied Sense of Self Scale (ESSS)
among clinical groups. Controls =age-matched healthy controls (N=32),
Amputees =upper-limb amputees (N=11), Schizophrenics =chronic
schizophrenia patients (N=15), and Error bars = ±1SE.
Even when a one-way ANOVA with groups as the between-
subject independent variable was repeated for each factor, the
statistical results were the same: there was a significant difference
between schizophrenics and amputees/controls, regardless of
factors (ps <0.05). These results indicate that the ESSS
selectively predicted anomalous self-representation in people
with schizophrenia, suggesting its predictive and clinical validity.
DISCUSSION
The current study focused on the concept of the ESS, which
has attracted researchers in various fields, and revealed its
factorial structure. With reference to previous studies, we first
collected 120 potential items. Through statistical processes, we
finally developed a 25-item ESSS with three factors: Ownership,
Narrative, and Agency. These extracted factors match our
hypothesis wherein the notions of Gallagher, Ramachandran
and Damasio were considered (Ramachandran, 1998;Damasio,
1999;Gallagher, 2000). As a scale for practical use, the ESSS’s
validity and reliability were confirmed from multiple perspectives
(criterion-related validity, factorial validity, clinical validity,
internal consistency, and re-test reliability). In what follows, we
discuss each factor in detail.
Ownership
When it comes to the sense of self, the mechanism for the sense
of ownership over our own body has been intensively examined
recently. One reason for this is the outstanding and handy
phenomenon known as the rubber hand illusion (RHI; Botvinick
and Cohen, 1998). The RHI indicates that we would feel an
illusory sense of ownership over a fake hand after observing
simultaneous brush stroking both on our own hand and a fake
hand for a short period, suggesting multi-modal (especially,
vision, and somatosensation) integration contributes to our
sense of body-ownership (Kilteni et al., 2015). Furthermore,
even the out-of-body experience might be caused by electrical
stimulation of a specific brain area (i.e., temporal–parietal
junction) that is responsible for such multi-modal integration
(Blanke, 2004). These studies have suggested that multi-modal
integration “constructs” our sense of ownership over our body.
Therefore, we can predict that when that integration fails for
any reason, that sense for body might also be disturbed. That is
the case in schizophrenia. People with schizophrenia or higher
schizotypal personality even in the general population have been
reported to be more susceptible to RHI (Peled et al., 2000;Asai
et al., 2011). This might be because they have a weaker sense of
ownership over their own body due to a disturbed multi-modal
integration. Indeed in the current study, the Ownership score
was positively correlated to the schizotypy score, especially to
positive symptomatology (Table 3). This is consistent with the
notion that a positive symptom is a result of the disorder of self-
representation (Frith, 2005;Cermolacce et al., 2007) (see also
Embodied Sense of Self below).
The concept of the sense of ownership has been extended
recently. Some might refer to a special term of the sense
of “body”-ownership, which means ownership over our own
body. However, our body might be just an operational tool for
brain, like other external tools, though our body has a hard-
wired connection with the brain (“body-as-subject” or “body-
as-object”, Sivertsen and Normann, 2015). Operable objects can
be attributed to ourselves as our own body (Maravita and Iriki,
2004), in the service of “distributed cognition” for tool use
(Baber et al., 2014). Further, we can have an extended sense
of ownership over the existence or reality of ourselves. Some
people with depersonalization, who have a disorder in integration
of perception, motor, memory, and hence identity and who
then have no reality for themselves, lose this extended sense
of ownership as well as the sense of body-ownership (Putnam,
1997;Sierra and Berrios, 2000). The current study collected items
for Ownership in line with these discussions. As a result, in
addition to our body, the sense of existence or reality as well as
our thoughts and tools (i.e., cloths) are included in this factor,
suggesting the extended concept of Ownership, where ownership
over the body is expanding its target to include higher cognition.
There might be some mechanisms for achieving the sense
of ownership, depending on its target. As mentioned above,
the sense of body-ownership is derived from multi-modal
integration (visuo-somatosensary passive integration). In order
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to expand its target, there should be an additional function,
since we cannot get a somatosensation from external objects
unless an illusory situation like the RHI is applied. One
possible mechanism for extended ownership is controllability
of the target (e.g., tool embodiment, Maravita and Iriki, 2004).
The controllability is closely related to Agency (Haggard and
Chambon, 2012, discussed below), where we can learn how
to manipulate objects and get a sense of controllability. The
sense of agency or controllability would entail the sense of
ownership over that object in turn (Asai, 2015a). Since we
feel ownership even over external objects, which have no
somatosensation, by manipulating them (active integration
between motor predication and sensory feedback), this is referred
to as the “override” of ownership by agency (Tsakiris et al.,
2006). In other words, we feel ownership too when agency is
elicited. Next, we will see that Agency has a close relationship with
Ownership.
Agency
The relationship between agency and (body-) ownership is
complicated as mentioned above, since they might have a
cross-referred relationship (Tajadura-Jimenez et al., 2012;Asai,
2015a,b;Serino et al., 2015). They are sometimes regarded as
a set (e.g., minimal self; Hur et al., 2014), while they can be
dissociated conceptually (Gallagher, 2000), phenomenologically
(Longo et al., 2008) and in brain activity (Tsakiris et al., 2010).
The simple theoretical difference between them is whether our
own motor system is involved. The sense of ownership is elicited
even when others raise our hand (“the raised hand is my own
hand”) while the sense of agency is elicited only when we
ourselves raise our hand (“I am raising my hand”). Though
agency and ownership are caused simultaneously in voluntary
actions (so they are confusing and difficult to distinguish
even empirically), Agency, unlike Ownership, needs our own
action and intention that precedes that action. Indeed, in the
current study, they were statistically extracted separately as
independent factors. When it is difficult to manipulate our
own body, agency over body is lost. When it is difficult to
manipulate external tools, agency over that tool is lost. In that
situation, we might not be aware of the intention for that
action and more seriously entail a failure of the desired action
(Table 1), that people with schizophrenia exhibit (e.g., Walker,
1994).
Agency has been examined in tandem with schizophrenia
historically. Though now we can regard schizophrenia as
a disorder of the ESS, not solely as one of Agency, since
some studies have also indicated a disorder in Ownership or
Narrative, the concept of Agency started with schizophrenia.
Many studies have examined their reported agency during
motor tasks including hand action, speech production,
or cursor manipulation (e.g., Daprati et al., 1997;Franck
et al., 2001;Johns et al., 2010). Though the results are not
always consistent, a meta-analytic study concluded that
patients with schizophrenia have a disturbed agency (“self-
recognition” in action, Waters et al., 2012). In the current
study, Agency was positively correlated with schizotypal
scores. Furthermore, even when the schizotypy score was
controlled, Agency was still correlated with the agency
scale (SOAS). This suggests that anomalous agency is not
a schizotypal experience itself. Rather, we have a function
of agency, independent of schizotypal experiences, and
an expression of its disturbance would be schizotypal
symptomatology.
The mechanism for agency is thought to be related to our
motor control system. Since we have learned the controllability
of our own body from birth, we have achieved the input-output
coordination where we can predict how the body moves when
the motor command is given. The sense of agency is the feeling
that evaluates how successfully such an intentional action is
executed. Therefore, not only for our body but for external
tools whose controllability we can learn, we feel agency. Also
as a result in that situation, we feel ownership over the tools
as mentioned above. In this way, agency and ownership have a
complicated but necessary interaction so that they construct a
sensory level of self-representation (i.e., minimal self). Further
studies should still examine how they interact while sometimes
overriding each other, and how they construct the minimal self
during a short temporal scale (Imaizumi and Asai, 2015;White,
2015).
Narrative
Narrative self, with its being achieved over a long temporal
scale (i.e., years), has received less attention than minimal
self (but White, 2015). Though Gallagher (2000) suggested a
further necessity to examine this aspect of self, the sense of
continuity and uniformity would be potential keywords for this.
Specifically, autobiographical source memory and prospective
decision making for action in terms of self-representation
have already been examined recently. Through these studies,
we should reveal in the future how the sensory self (i.e.,
minimal self) at a specific moment, for example, “I am doing
this action”, would be retained in our memory, “I did that
action”, and would determine the next action, “I will do that
action”.
Theoretically, the narrative self is a temporal extension
(i.e., continuity and uniformity) of the minimal self, indicating
that Narrative might be a crystallized self-representation
including Ownership and Agency. In this sense, the narrative
self is also embodied, where we refer to ourselves as identical
entity through memorized experiences based on body and
action. Though schizophrenic symptomatology has been
suggested to be linked with Ownership (e.g., RHI), Agency
(e.g., action recognition) and Narrative (e.g., source memory)
(see also Section “Embodied Sense of Self” below), schizotypy
scores showed stronger correlation with Narrative than
Ownership/Agency in the current study (Table 3). Narrative
also showed the strongest correlation with self-evaluation
(meta self-representation) like self-esteem and self-efficacy
(Table 5). In line with the theory, these results might indicate
that narrative self, including continuity and uniformity, is a
higher or integrated function for self-representation based on
the minimal self.
In that case, the question here is how the minimal self
develops the narrative self, with achieving temporal extension
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Asai et al. Development of Embodied Sense of Self Scale
(Damasio, 1999;Gallagher, 2000). A possible mechanism is “self-
labeling” of sensory information. The minimal self basically
depends on online sensory information, where each sensation
is distinguished between its being self-related or not. For
example, the brain specifically responds to this self-related
information, such as our own name, face, or objects like a
favorite cup (Legrand and Ruby, 2009;Miyakoshi et al., 2010)
where this visual or auditory information is given a self-
label, that is derived from the sense of ownership. On the
other hand, we can’t tickle ourselves (Blakemore et al., 1998)
because self-originated sensory input (i.e., sensory feedback)
is suppressed (Miall and Wolpert, 1996). This helps us to
save our attention resource or prevent desensitization (Poulet
and Hedwig, 2002). We can say that that sensory feedback is
given a self-label that is derived from the sense of agency. The
narrative self might utilize self-labels on sensory information,
not the sensory information itself (c.f., Miyakoshi et al., 2008;
Quiroga et al., 2008;Habermas and Kober, 2015). For example,
when we can “hit” our own action in a recognition task
of source memory (i.e., when we correctly judge “this is
what I did”), we feel more agency for that action in the
learning phase (i.e., during action execution). This indicates
an important contribution of the online minimal self to the
narrative self, where self-labels are used. Though the current
study extracted three (semi-) independent factors—Ownership,
Narrative and Agency—in terms of the Embodied Sense of
Self, they should interact with each other (cross-reference,
compensation, overriding, etc.), as we can see among previous
studies. Further study should examine the relationship among
those factors in order to reveal the hierarchic structure of unified
self-representation.
Embodied Sense of Self
The current study suggested that the ESS consists of the
above-mentioned three factors, focusing on the everyday
experiences that an anomalous ESS would entail. Survey E
indicates that people with schizophrenia have more such
experiences on a daily basis, aside from their acute symptoms
themselves, regardless of factors (Figure 1). This finding is
consistent with previous studies where an anomalous ownership,
agency, or narrative self have been reported for schizophrenia
empirically (e.g., Daprati et al., 1997;Peled et al., 2000;
Wang et al., 2011;Shakeel and Docherty, 2012). Though
schizophrenic symptomatology, especially positive symptoms,
had initially been regarded as a disorder in agency, now we
should regard it as a disorder of the ESS, where each factor
interacts in a complicated manner but finally constructs a
unified representation of the self. That factorial relationship,
however, is still unclear. Untying that complexity would also
help us understand the psychopathology of schizophrenia
and other mental disorders in the future. A larger sample
would be necessary for that purpose. This simple and
easy evaluation tool will be especially useful for clinical
studies.
The scientific interest in the self is not new. Researchers
have been exploring the origin of the self for decades, but
that question still remains the ultimate mystery. The new
challenge for this old but new question is the embodiment
approach (Niedenthal et al., 2005). As brain imaging techniques
progress, we might have gotten the idea in the “brain era”
that processing for everything, including the self, is embedded
within our brain (c.f., “brain in a vat”, Hilary, 1982). The
embodiment approach (e.g., Damasio, 1999, 2001;Bargh et al.,
2001;Pfeifer et al., 2007;Taylor et al., 2009;Blanke et al.,
2015;Caspar et al., 2015), however, considers that the brain
is just for the body and action. This view has attracted many
researchers because a measurable index is the essential factor
for the self; that is, body and action themselves are the self,
not just a proxy. When we tackle the self-specific brain activity,
methodological limitations (i.e., s/n ratio, spatial resolution,
etc.) are also problematic (Legrand and Ruby, 2009). In this
sense, we first have to explore the structure of the subjectivity
of the self in terms of embodiment so that we would know
how each factor for the self is represented in our brain in the
future. We still don’t know yet whether this approach takes
us higher, but we hope this new tool for measuring the ESS
(Supplemental Material S2) will contribute to finally coming to
a conclusion.
AUTHOR CONTRIBUTIONS
TA, NK designed the study. TA, NK, SI, SK, and SK performed
the surveys. TA analyzed the results and wrote the manuscript.
All authors approved the final version of the manuscript.
SUPPLEMENTARY MATERIAL
The Supplementary Material for this article can be found
online at: http://journal.frontiersin.org/article/10.3389/fpsyg.
2016.01005
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