fpsyg-07-01272 August 25, 2016 Time: 14:45 # 1
REVIEW
published: 29 August 2016
doi: 10.3389/fpsyg.2016.01272
Edited by:
Morten Overgaard,
Aarhus University, Denmark
Reviewed by:
Felipe De Brigard,
Duke University, USA
Roy Salomon,
École Polytechnique Fédérale
de Lausanne, Switzerland
*Correspondence:
James W. Moore
j.moore@gold.ac.uk
Specialty section:
This article was submitted to
Consciousness Research,
a section of the journal
Frontiers in Psychology
Received: 11 May 2016
Accepted: 10 August 2016
Published: 29 August 2016
Citation:
Moore JW (2016) What Is the Sense
of Agency and Why Does it Matter?
Front. Psychol. 7:1272.
doi: 10.3389/fpsyg.2016.01272
What Is the Sense of Agency and
Why Does it Matter?
James W. Moore
*
Department of Psychology, Goldsmiths, University of London, London, UK
Sense of agency refers to the feeling of control over actions and their consequences.
In this article I summarize what we currently know about sense of agency; looking at
how it is measured and what theories there are to explain it. I then explore some of the
potential applications of this research, something that the sense of agency research field
has been slow to identify and implement. This is a pressing concern given the increasing
importance of ‘research impact.’
Keywords: consciousness, free will, responsibility, human-computer-interaction, legal, aging, schizophrenia,
OCD
INTRODUCTION
This article aims to serve two purposes. First, I wish to provide a general overview of research on
sense of agency. This is by no means exhaustive, and is instead intended to give the reader a broad
introduction to the topic. Second I wish to explore some areas in which this research may have
some kind of impact. Impact is becoming an increasingly important issue for research scientists.
According to the UK’s 2014 Research Excellence Framework, impact can be defined as research
having an “an effect on, change or benefit to the economy, society, culture, public policy or services,
health, the environment or quality of life, beyond academia.” Although many scientists are dubious
of this increased focus on impact, it is almost certainly here to stay, at least for the foreseeable
future. We all, therefore, would be well-served by being mindful of it in our own research. Some
research topics lend themselves to impact more than others. Sense of agency falls more into the
latter group; those working on this topic may struggle to articulate the relevance and potential
impact of what they do. This article is, in part, an attempt to address this issue.
WHAT IS THE SENSE OF AGENCY?
Background
When we make voluntary actions we tend not to feel as though they simply happen to us, instead
we feel as though we are in charge. The sense of agency refers to this feeling of being in the driving
seat when it comes to our actions.
Synofzik et al. (2008) draw an important distinction between the Feeling of agency (FOA) and
the Judgment of agency (JOA). FOA is a lower level non-conceptual feeling of being an agent; it
is the background buzz of control we feel for our voluntary actions when not explicitly thinking
about them. JOA, on the other hand is a higher-level conceptual judgment of agency, and arises
in situations where we make explicit attributions of agency to the self or other. The FOA is linked
to low-level sensorimotor processes, whilst the JOA to higher-level cognitive processes such as
background beliefs and contextual knowledge relating to the action. These two levels of agency
processing, although related, can be dissociated from one another. For example, an unexpected
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action outcome, which would signal non-agency at the FOA level,
can nevertheless be attributed to the self at the JOA level if beliefs
and contextual factors imply self-causation (for example, when
an unexpected action outcome happens when acting alone in a
room). This distinction between FOA and JOA also highlights
an important distinction between agency and causality. Whilst
the low-level FOA automatically registers agency or non-agency
by tracking sensorimotor contingencies, the higher-level JOA
deploys more general-purpose causal attribution processes that
are not specifically linked to the sensorimotor system (see
Gallagher, 2000, for a detailed discussion of this).
As with other aspects of conscious experience, the sense of
agency is not an infallible reproduction of objective reality. As
a consequence of this our experiences of agency can go awry.
This is quite common in gambling, where players often feel an
exaggerated sense of agency. An example of just such an illusion
of control was noted by Henslin in the 1960s (Henslin, 1967).
Henslin was a sociologist and spent a number of weeks observing
cab drivers in St. Louis in the USA. A popular past-time among
the cabbies was craps, a dice rolling gambling game. Henslin
joined in with these games and made an intriguing observation.
When these cab drivers came to roll the dice they altered their
behavior depending on the number they needed, throwing harder
for higher numbers and more gently for lower numbers. What is
striking about this kind of behavior is that the outcome of dice
rolling is objectively uncontrollable. Nevertheless these cabbies
clearly felt otherwise. This is an example of where the sense of
agency can be quite divorced from objective reality.
You might think that you are immune to such cognitive
foibles, but you would almost certainly be mistaken. I would
bet that most of us have fallen foul, at some point, of so-called
‘placebo buttons.’ These are buttons that we encounter every
day that we think do things, but actually do nothing (McRaney,
2013). Buttons at pedestrian crossings are a common example
of placebo-buttons. Most of these buttons are ineffective and
instead the changing of the traffic lights are linked to timers.
This was shown by a recent survey of pedestrian crossings in
New York (McRaney, 2013). Intriguingly, most of us fail to notice
the causal inefficacy of our button presses. Other examples of
placebo buttons include ‘close door’ buttons in lifts and even
thermostats in offices (many of which, apparently, do not work).
There are two reasons for flagging up the occasional lapses
in our sense of agency. The first is to show that the accuracy
of this experience is not a given. Instead, the brain appears to
actively construct the sense of agency, and because of this, our
experiences of agency can be quite divorced from the facts of
agency. The second reason is that these lapses reveal something
quite remarkable about our sense of agency: its impressive
flexibility. Beyond the examples I have given here, we see over and
over again that people come to experience control over outcomes
in many weird and wonderful situations. The voodoo doll is
another example; people taking part in this practice genuinely
believe that sticking a pin in an effigy of someone causes actual
physical harm in that person. At first blush this inference seems
irrational. However, examples like the voodoo doll actually hint
at the adaptability and flexibility of the agency processing system.
It is worth reminding ourselves that causal mechanisms are quite
opaque in a lot of modern technology (consider the simple act of
tapping on a keyboard and seeing a letter appear on the screen
in front of you – there are a lot of steps in this causal chain
that are hidden from you). Despite this causal opacity, we feel in
control of these interactions. So the flexibility that might make
us vulnerable to agency errors in things like placebo buttons
and voodoo dolls, can also allow our experience of agency to
extend into new domains and track the rapidly changing agentic
structure of our environment. Rather than our agency processing
system breaking down with the development of tools, which have
changed and extended our agentic capabilities, it has been flexible
and adaptable, allowing us to accommodate these changes.
Measures
The number of scientific investigations of sense of agency has
increased considerably over the past 20 years or so. This increase
is despite the fact that experiments on sense of agency face certain
methodological problems. A major one is that the sense of agency
is phenomenologically thin (Haggard, 2005). That is, when we
make actions we are typically only minimally aware of our agentic
experiences. This is quite unlike conscious experience in other
modalities, especially vision, where our experiences are typically
phenomenologically strong and stable. What this means is that
sense of agency can be difficult to measure. As a result of this,
experimenters have had to be quite inventive in order to develop
paradigms that capture this rather elusive experience.
You can generally group these paradigms into implicit
or explicit measures. Implicit measures assess a correlate
of voluntary action and infer something about the agentic
experience on the basis of this. In these paradigms no one is
ever asked, directly, about their agentic experience. Probably
the most widely used implicit measure of sense of agency is
intentional binding (for a review see Moore and Obhi, 2012).
This was developed by Haggard et al. (2002) and is based on
time perception. Haggard et al. (2002) found that when we
make a voluntary action, the perceived times of the action and
its effect are shifted toward each other. This change in time
perception is taken to be an implicit marker of sense of agency.
Other implicit measures of sense of agency include sensory
attenuation paradigms. It has been shown that the perceived
intensity of the sensory consequences of voluntary action is lower
than for passive movements (Blakemore et al., 1998, 1999). This
can explain why we are unable to tickle ourselves (Blakemore
et al., 1998). In these sensory attenuation paradigms, researchers
use changes in perceived intensity of sensory feedback to infer
something about the participant’s sense of agency.
Explicit measures, on the other hand, directly ask the
participant to report something about their agentic experience.
These measures are more intuitive but they can be vulnerable
to problems like demand effects. A number of these paradigms
require participants to make action recognition judgments.
Typically the participant makes an action, but does not directly
see that action. Instead they are shown some kind of feedback on
a screen. This feedback may depict the participant’s action or it
might depict the action of someone or something else (perhaps
an experimenter or a computer), and the participant is asked
whose movement it is. Importantly, the experimenter ensures
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that there is some uncertainty over the agent of the action being
displayed. An example of this kind of task was used by Farrer
et al. (2008). They had participants perform regular finger tapping
movements while wearing a glove. They could not directly see
these movements, and instead they were shown video feedback
of the movement on the screen. A delay was inserted between
the movement and the feedback presented to the participant.
The participants were not aware that the movement was always
their own, and instead were led to believe that the movement
was either their own or an experimenter performing the same
movement, and that this could switch at any time. The participant
simply had to indicate when they thought they were seeing
their own movement and when they thought they were seeing
the experimenter’s movement. Farrer et al. (2008) found that
participants experienced a bi-stable impression of agency in
this situation, with judgments of agency spontaneously flipping
between self and experimenter.
Other explicit measures also use visual feedback about
movements, but will not create this kind of self/other confusion.
Instead, the participant is required to make a judgment about the
feedback itself. An example of this kind of action monitoring task
can be seen in an experiment carried out by Synofzik et al. (2010).
In this experiment participants made pointing movements under
a screen, meaning that they could not directly see the movement.
On the screen participants were shown a visual marker (white
disk) that tracked the pointing movement. This marker was
rotated by varying degrees relative to the actual movement. The
participants had to indicate the direction in which the visual
feedback was rotated relative to the actual movement. This gave
the experimenters a measure of action awareness and, more
specifically, sensitivity to distortions in action-relevant feedback.
A final kind of explicit measure requires participants to report
on their feeling of agency for certain action outcomes that their
movements might have caused. A simple example of this would
involve a key press that causes an outcome after a variable delay.
Participants would then judge how much they felt their action
caused the outcome. A common finding is that such causal
judgments are stronger for shorter delays (e.g., Shanks et al., 1989;
Chambon et al., 2015). Interestingly, this kind of explicit measure
taps into a slightly different aspect of the agentic experience
compared with the other two kinds of explicit measure described
in this section. Action recognition/monitoring tasks focus more
on the action element, whereas, causal judgment tasks focus on
the outcome component. Although, both of these are central to
the agentic experience, this difference is often overlooked and not
very well-understood.
Theories
The two most influential theories of sense of agency have been the
‘Comparator Model’ developed by Frith et al. (2000) and Frith
(2005), the ‘Theory of apparent mental causation’ developed
by Wegner and Wheatley (1999) and Wegner (2002). The
comparator model takes as its starting point the motor control
system. We now know a great deal about the computational
processes underpinning the control of voluntary movement
(see Wolpert and Miall, 1996, for a review). According to the
comparator model, some of these processes also inform the sense
of agency. On this view, our actions start with intentions or goals,
which enables a representation to be formed of the desired state
of the motor system. Controllers within the motor control system
then use this information about the desired states to generate a
motor command. This motor command produces a movement,
which changes the state of the motor system, and generates
sensory feedback. On the basis of this information the new state
of the system can be estimated. This estimate is compared with
the desired state at a comparator. If there is a mismatch then an
updated motor command is issued. This process can continue
until the desired state is achieved (indicated by the absence of a
mismatch at the comparator).
The issue with a motor system operating only in this way
is that it is slow to respond to error. Because of this, the
organism is vulnerable. The solution, it would appear, is to have
an additional predictive component within the motor system,
and it is this that is thought to be particularly relevant to sense
of agency. This predictive component uses a copy of the motor
command that is issued (a so-called ‘efference copy’) to predict
the future state of the system. This includes predictions about
changes to the motor system as well as the sensory consequences
resulting from those changes. On the basis of these predictions, a
representation of the predicted state of the system can be formed,
and this representation can be compared both with the desired
state of the system and with the actual state of the system. The
former comparison is important for motor control, as it allows
the organism to rapidly adjust motor commands in advance
of incorrect actions being performed. The latter comparison
is thought to be important for sense of agency. According to
the comparator model, the output of the comparison between
predicted and actual states determines whether or not we feel a
sense of agency. If there is a match, then we feel a sense of agency;
if there is mismatch then we do not.
A number of studies support this idea that sense of agency is
closely tied to sensorimotor processes. For example, as predicted
by the comparator model, it has been shown that the perceived
intensity of self-produced tactile sensations is attenuated relative
to externally produced ones (Blakemore et al., 1998, 1999). It
has also been shown that sensorimotor prediction contributes
to intentional binding (Moore and Haggard, 2008). Finally,
mismatches between expected and actual sensory feedback
influence action recognition judgments (e.g., Daprati et al., 1997;
Franck et al., 2001).
The ‘Theory of apparent mental causation’ approaches sense
of agency from a quite different angle. Whereas the comparator
model places a heavy emphasis on the contribution of the
motor system to sense of agency, the theory of apparent
mental causation explicitly downplays this contribution. Indeed,
according to this theory, it is because we do not have conscious
access to the motor control system that our sense of agency
can, at times, be so misleading, as seen in phenomena like
voodoo dolls and placebo buttons. According the theory of
apparent mental causation when we make a voluntary action
there is an unconscious causal pathway that is responsible for the
action. This pathway corresponds to the workings of the motor
control system. There is also an unconscious causal pathway
that is responsible for the associated thoughts about actions (i.e.,
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intentions). In addition to these unconscious causal pathways,
there are certain events that we are conscious of, namely the
intention to act and the act itself. According to Wegner it is the
relationship between the thought and the action that determines
the sense of agency (or in Wegner’s term, the ‘experience of
conscious will’). If our intention to act happens before we act,
is consistent with the action, and is the only plausible cause of
the action, then we feel as though we have caused the action.
A fundamentally important feature of Wegner’s theory is the
additional claim that this feeling is illusory – the inference
that our intentions have caused our actions is erroneous (the
unconscious pathways are the real causes of our actions.
A number of studies support Wegner’s theory of apparent
mental causation. For example, it has been shown that priming
thoughts about an upcoming action fosters an illusory sense of
agency for that action (Wegner and Wheatley, 1999; Wegner
et al., 2004). It has also been shown that manipulating high-level
contextual information about an action (in the form of causal
beliefs) alters sense of agency, as measured by intentional binding
(Desantis et al., 2011).
These two theories, the comparator model and the theory of
apparent mental causation, offer competing accounts of sense
of agency. They differ in terms of the sources of information
thought to be most important for producing sense of agency. For
the comparator model, sensorimotor processes are key. For the
theory of apparent mental causation, the emphasis, at least in the
experimental work carried out to test it, has been on information
that is external to the motor system, such as environmental and
social cues (for a more extensive discussion, see Wegner and
Sparrow, 2004). The traditional assumption has been, therefore,
that these two views are mutually exclusive. However, this
assumption has challenged by a number of studies. For example,
using the intentional binding measure Moore and Haggard
(2008) showed that both internal sensorimotor prediction and
external action outcomes contributed to the sense of agency.
It was found that binding of the action to the tone outcome
was present when the probability of that outcome was high,
even when it did not occur. This suggests that if sensorimotor
prediction is sufficiently strong binding will occur. On the other
hand, it was found that when sensorimotor prediction was weak,
binding would occur but only when the key press actually caused
the tone outcome. This would suggest that the presence of
an external tone outcome retrospectively triggered the binding
effect.
Findings such as these led us to develop an alternative ‘cue
integration’ theory of sense of agency (Moore et al., 2009; Moore
and Fletcher, 2012). This helped us move beyond the debate over
whether sense of agency was based on sensorimotor information
(comparator model) or information external to the motor system
(theory of apparent mental causation). Instead, according to the
cue integration theory both views have merit, and in fact the sense
of agency is based on various different sources of information
(or agency cues). We have also suggested that the relative
influence of the different sources of information may be linked
to their reliability, with the more reliable source of information
dominating the agentic experience. We can see evidence of
this in Moore and Haggard’s (2008) study, described above,
where the influence of external action outcomes on intentional
binding increased when the reliability of sensorimotor prediction
decreased. We can also see evidence of this in patients with
schizophrenia. Using an agency attribution paradigm, Synofzik
et al. (2010) showed that agency judgments in people with
schizophrenia relied more strongly on visual feedback about an
action rather than on internal sensorimotor cues. This reliance
on external visual feedback is consistent with the cue integration
theory, as it has been shown that sensorimotor prediction is
unreliable in people with schizophrenia (a similar finding was
also obtained by Voss et al., 2010). Although, a more thorough
examination of this theory is needed, it does promise to help us
understand the processes underpinning sense of agency in health
and disease.
WHY DOES SENSE OF AGENCY
MATTER?
The previous section provides an overview of sense of agency
research and theory. However, from this overview it would not be
entirely clear why any of this matters, particularly from an impact
point of view. In the following section I want to address this. I
will look at the possible impact of sense of agency research in the
context of health and well-being, human-computer-interaction,
and the broader issues of free will and responsibility.
Health and Well-being
Schizophrenia and Other Disorders
Schizophrenia is the classic disorder of sense of agency and
has been the subject of more agency research than any other
disorder. The symptoms of schizophrenia are grouped into
two categories: ‘positive symptoms’ and ‘negative symptoms.’
Negative symptoms are defined by the absence of a normal
function (for example, ‘alogia’ or reduced speech). Positive
symptoms, on the other hand, are defined by the abnormal
presence of perceptions (hallucinations) or beliefs (delusions).
Abnormal experiences of agency fall within the positive symptom
category. Although these abnormal experiences can take many
forms, the most common are passivity symptoms (or delusions
of control). A patient with passivity symptoms will feel as though
his or her actions are not under their control. You can see this in
the following patient reported by Mellor (1970, p. 18): ‘It is my
hand and arm which move, and my fingers pick up the pen, but I
don’t control them. What they do is nothing to do with me.’
Research on patients with schizophrenia has confirmed that
these individuals have agency processing problems. In one
relatively early study by Daprati et al. (1997), healthy controls
and patients with schizophrenia made simple hand movements.
They did not directly see their own movements. Instead they
saw visual feedback of the movement on screen via a video link.
These movements were either (a) their own actual movements,
(b) the same movements made by an experimenter in another
room, or (c) the movement of that experimenter performing a
different movement. The participants and the experimenter were
wearing gloves to prevent any visual identity clues. After each
trial the participant simply had to say whether the movement
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on the screen was their own movement or the experimenter’s.
Compared with controls, patients – especially those experiencing
passivity symptoms – made more errors in attributing the action
to its correct source when the experimenter made the same
movements as them. In this situation of agentic uncertainty,
patients struggled to recognize their own movements.
These action recognition problems have since been confirmed
in a number of other studies. For example, Franck et al. (2001)
tested patients and healthy controls on an action recognition
task. In this experiment they made movements and again
only saw video feedback of the movement. In one condition
different levels of spatial distortion were introduced. In another
condition different time delays were introduced. After each trial
participants had to say whether the hand movements on the
screen matched their own. Healthy participants tended to say no
earlier in both conditions than patients who took much longer
to detect these mismatches. Again this suggests abnormal action
awareness in patients.
Where agency research on patients has been particularly
useful is in uncovering the information processing abnormalities
underpinning these disordered experiences of agency. Patients
with schizophrenia seem to have specific problems with
sensorimotor prediction, which, as we saw in the previous
section, is crucial for the sense of agency. One line of
evidence comes from studies on sensory attenuation. The neural
response to sensory feedback generated by a voluntary action
is attenuated – the brain cares less about the things it can
predict (Blakemore et al., 1999). This can explain our inability
to tickle ourselves: self-tickling is less effective because we can
predict the sensory consequences of our actions, resulting in
the sensory percept being attenuated. Interestingly, patients with
schizophrenia can tickle themselves (Blakemore et al., 2000). This
finding strongly suggests that patients struggle predicting the
sensory consequences of their actions.
Another line of evidence comes from research on intentional
binding. As we saw in the previous section, voluntary actions are
associated with a compression of the perceived interval between
the action and its effect: the perceived time of action is shifted
toward the effect, and the perceived time of the effect is shift
back toward the action. In a study on healthy adults, Moore and
Haggard (2008) showed that the action component of the binding
effect (the shift in perceived time of action toward the outcome) is
partly linked to prediction. When the outcome was probable, but
not always present, there was a shift in perceived time of action
even on those trials where the outcome did not occur. This was
not the case when the outcome was unpredictable. In follow-up
work by Voss et al. (2010), it was found that this predictive effect
was absent in patients with schizophrenia.
These problems with prediction can help us explain the
behavioral findings from individuals with schizophrenia that I
described above. For example, Franck et al. (2001) found that
patients struggled to detect temporal and spatial discrepancies
between their movements and the feedback of those movements.
If the patient struggles to predict where their hand should be
during movement, they will struggle to detect spatial distortions.
Furthermore, if the patient struggles to predict when their hand
should move, they will struggle to detect temporal delays.
More recently it has been suggested that problems with
prediction represent a core deficit in the disorder (Fletcher and
Frith, 2009). On this view predictive deficits can explain positive
symptoms more generally, not just passivity symptoms. Clearly
we need to find out more about the nature and origins of this
predictive deficit in individuals with schizophrenia, but it at
least offers us a starting point in the quest to understand and
ultimately treat the disorder. Developing interventions to remedy
these agency processing problems is one possible avenue for
impact.
Aberrant experiences of agency are not just confined to
patients with schizophrenia. Indeed, aberrant experiences of
agency can be seen in various disorders. Anosognosia for
hemiplegia is one such disorder, and is attracting growing
interest in the field. ‘Anosognosia’ comes from Greek words
nosos (meaning “disease”), and gnosis (meaning “knowledge”),
so patients with anosognosia are unaware of their disease or
impairment. There are many kinds of anosognias, but the most
relevant for us is anosognosia for hemiplegia. These are patients
who are paralyzed, usually following stroke, but who are unaware
of this impairment. The following description from Berti et al.
(2007) is of a patient with anosognosia for hemiplegia:
“CR presented severe and persistent anosognosia for her
left hemiplegia... She never spontaneously reported her motor
problems. When questioned about her left arm, she always
claimed that it could move without any problem. When asked
to actually perform movements, she attempted to perform the
action, and after a few seconds she appeared to be satisfied with
her performance” (p. 172).
From an agency point of view this disorder is intriguing. It
suggests that an individual can experience a sense of agency
for movements that they cannot make, and for which there
is compelling sensory evidence to confirm their paralysis.
Research carried out by Fotopoulou et al. (2008) shows that
patients do in fact discount sensory evidence in their agency
assessments. When instructed to make a movement, they will
claim to have moved despite contradictory visual feedback.
What this implies is that the experience of agency in these
individuals is strongly governed by pre-motor agency cues,
such as intentions and sensorimotor predictions. As with
the schizophrenia patients, we clearly we need to find out
more about the exact nature of this deficit, but it again
gives us a useful starting point for the development of
therapeutic interventions. For example, it might be useful to
try to find ways of increasing the weighting that anosognosia
for hemiplegia patients give to sensory feedback, either
through cognitive/behavioral interventions or through neural
interventions (e.g., pharmacological).
Beyond anosognosia for hemiplegia and schizophrenia there
are a number of other disorders that are beginning to attract
interest from agency researchers. In Obsessive Compulsive
Disorder, for example, it has been shown that patients have
deficits in sensorimotor prediction resulting in a reduction of
sensory suppression (Gentsch et al., 2012). This finding echoes
those from patients with schizophrenia described above. It has
also been shown that individuals with high obsessive-compulsive
tendencies tend to omit agency from spoken language, perhaps
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