Self-awareness and action
Sarah-Jayne Blakemore?and Chris Frithy
In this review we discuss how we are aware that actions are
self-generated. We review behavioural data that suggest that a
prediction of the sensory consequences of movement might be
used to label actions and their consequences as self-generated.
We also describe recent functional neuroimaging experiments
and studies of neurological and psychiatric patients, which
suggest that the parietal cortex plays a crucial role in the
awareness of action.
?Institute of Cognitive Neuroscience, University College London,
17 Queen Square, London WC1N 3AR, UK
yCorrespondence: Wellcome Department of Imaging Neuroscience,
Institute of Neurology, University College London, 12 Queen Square,
London WC1N 3BG, UK
Current Opinion in Neurobiology 2003, 13:219–224
This review comes from a themed issue on
Edited by Brian Wandell and Anthony Movshon
0959-4388/03/$ – see front matter
? 2003 Elsevier Science Ltd. All rights reserved.
functional magnetic resonance imaging
position emission tomography
‘She raised one hand and flexed its fingers and won-
dered, as she had sometimes before, how this thing,
this machine for gripping, this fleshy spider on the end
of her arm, came to be hers, entirely at her command.
Or did it have some little life of its own? She bent her
finger and straightened it. The mystery was in the
instance before it moved, the dividing moment
between not moving and moving, when her intention
took effect. It was like a wave breaking. If she could
only find herself at the crest, she thought, she might
find the secret of herself, that part of her that was
really in charge. She brought her forefinger closer to
her face and stared at it, urging it to move. It remained
still because she was pretending, she was not entirely
serious, and because willing it to move, or being about
to move it, was not the same as actually moving it. And
when she did crook it finally, the action seemed to
start in the finger itself, not in some part of her mind.
When did it know to move, when did she know to
Ian McEwan, Atonement
In this review, we discuss studies on action and awareness
in the context of a well-established framework of motor
control. This framework proposes that our actions and
interactions with objects are represented in the form of
internal models . The crucial component of the for-
ward model, a type of internal model, is the predicted
sensory consequence(s) of movement, which can be
compared with the actual sensory consequence(s) of
movement and used to optimise motor control [1,2,
Davidson and Wolpert, this issue]. Here, we suggest that
of our awareness of action.
What aspects of action are we aware of?
Being aware of initiating and controlling actions is a major
component of conscious experience, but many aspects of
action occur without our awareness. Evidence that sensa-
tions associated with actual movements are unavailable to
awareness comes from a study in which the sensory
consequences of movement were made to deviate from
a subject’s expectations . In this study, the subject’s
task was to draw a straight line on a computer screen.
Subjects could not see their arm or hand and were given
false feedback on the screen about the trajectory of their
arm movement. Thus, they had to make considerable
However, verbal reports indicated that subjects were
unaware that they were making deviant movements –
they claimed to have made straight movements. These
results suggest that we are aware of the movements we
is some evidence to suggest that the exact threshold
above which the discrepancy between the intended
and actual movement becomes available to awareness
depends to some extent on the task at hand [4?,5]. When
and the sensory (visual) consequences, subjects seem to
become aware that the movement is not their own when
or by 150 ms temporally [4?]. If subjects are not asked to
discrepancy, even when the sensory (tactile) conse-
quences of their movements are delayed by 300 ms .
In his studies of motor consciousness, Libet investigated
the time at which awareness emerges during the genera-
tion of an action. Libet  asked healthy volunteers to
estimate retrospectively the time at which they initiated a
finger movement (the time at which their finger started to
move; the ‘M’ judgement). The volunteers consistently
anticipated the actual starting time of the movement by
50–80 ms. Recently, Haggard and Magno  carried out a
Current Opinion in Neurobiology 2003, 13:219–224
series of experiments that were based on the Libet
paradigm. They showed that the perceived time of move-
ment onset is slightly delayed (by about 75 ms) if the
motor cortex is stimulated using transcranial magnetic
stimulation (TMS), whereas this stimulation causes a far
greater delay (of around 200 ms) in the initiation of the
actual movement . These observations support the
idea that our awareness of initiating a movement is not
because such signals are not available until after the limb
has started moving. Instead our awareness appears to be
linked, at least in part, to a signal that precedes the
movement. One signal that is available before a move-
ment is initiated is the prediction of the sensory con-
sequences of the movement. Perhaps one signal that we
are aware of when making a movement is this prediction,
rather than the movement itself. Sensory feedback from
the movement would also be important to check the
movement was completed as planned.
Action in the imagination
Sensory prediction might underlie the ability to prepare
and imagine movements. It is well established that ima-
gining a movement and preparing to move activate a
a movement [8–10,11?,12??]. Healthy subjects can con-
fuse actions performed in the imagination and in reality
when they are asked to recall such actions twoweeks later
[13?]. A recent functional magnetic resonance imaging
(fMRI) study scanned subjects while they executed
movements or imagined making the same movements.
A direct comparison between brain activity during ima-
gined and executed movements revealed that imagining
movements activates the left posterior and inferior par-
ietal lobe to a greater extent than executing the same
movement . Subjects show a speed-accuracy trade off
for imaginary as well as real movements, but this effect is
lost in the imaginary movements of patients with parietal
lesions [15,16?]. Taken together, these data suggest that
the parietal lobe plays an important role in the generation
are necessary for motor imagery. The same lack of speed-
accuracy trade off is seen in imagined movements made
by schizophrenic patients with delusions of control [17?].
This is in line with the proposal that delusions of control
are associated with a faulty internal representation of
Awareness of intentions
Are we aware of our intentions to move? In a second task,
Libet asked volunteers to indicate the time at which they
became aware of having the ‘urge’ to make a movement
(that is, of their will or intention to move; the ‘W’
judgement; ). Subjects’ W judgements consistently
precede the production of the movement by about
300 ms. Interestingly, this is well after the onset of the
readiness potential, the negative potential arising from
movement by one second or more. On the basis of these
results, Libet concluded that, ‘‘The brain... decides to
initiate... or prepares to initiate the act at a time before
there is any reportable subjective awareness that such a
decision has taken place’’ .
Using a similar paradigm, Haggard and Eimer  asked
subjects to indicate the time at which ‘‘they first began to
prepare the movement’’ and related this to various com-
ponents of the readiness potential. In this study, subjects
moved either their left or their right index finger. The
onset of the lateralised readiness potential (occurring at
around 500 ms before the movement), rather than earlier
components of the readiness potential (starting more than
1 s before the movement), co-varied with the perceived
time at which preparation of the movement began. This
suggests that the awareness of preparing to move is
associated with the exact specification of the movement
(which finger will be moved) rather than some more
abstract representation of action, such as the goal of
A sense of agency
An important aspect of awareness of action is our sense of
agency; the feeling that we cause movements and their
consequences. In a recent study, Haggard and co-workers
[21??] investigated the consequences of a sensory event
being causally linked to a subject’s action. Subjects made
a key-press, which on some trials was followed 250 ms
later by an auditory tone. The subject’s task was to judge
the time at which they were aware of pressing a key or the
time at which they were aware of hearing a tone. When
their key-press caused a tone, subjects judged the timing
of their key-press as occurring about 15 ms later and the
tone as occurring 46 ms earlier than if the two events
occurred alone. This ‘temporal attraction’ seems to
depend on the perceived causal relationship between an
action and its sensory consequence(s). In a second experi-
ment, a varying delay (250, 450, or 650 ms) was introduced
between the key-press and the tone. Thefurther apart the
the tone to the key-press was diminished. Furthermore,
the temporal attraction between the perception of actions
and their sensory consequences did not occur when an
involuntary movement (caused by stimulating the motor
cortex using TMS) was followed 250 ms later by a tone, or
when subjects judged the timing of two causally related
external sensory events. The temporal attraction between
self-generated actions and their sensory consequences
binds together these events, and enhances our experience
If an explicit goal is suggested just prior to the action that
achieves that goal, then the action will be perceived as
intended. Wegner and Wheatley  have shown that
this can lead to errors in the perception of intention. A
Current Opinion in Neurobiology 2003, 13:219–224www.current-opinion.com
naive subject and a confederate simultaneously used a
single mouse to control the position of a pointer on a
screen. If the attention of the subject was drawn to an
object on the screen and the pointer stopped near that
object shortly afterwards, then the subject frequently
believed that s/he had intentionally moved towards the
object. In reality, his/her arm had been moved passively
by the confederate. As long as the action did not conflict
with some explicitly suggested goal then the action was
perceived as intended.
How do we recognise our own actions?
A clever paradigm that has been used to investigate self-
movement recognition involves subjects viewing the
can be manipulated so that the ownership of the hand is
that is either their own or the experimenter’s performing
movements that are either congruent or incongruent with
the subject’s own hand movements. Using this paradigm,
Daprati and co-workers  showed that normal subjects
confuse their own hand movements with those of the
experimenter about 30% of the time when the move-
ments are similar. Thus, even in an ambiguous situation
in which the experimenter’s hand makes the same move-
ments as the subject’s hand, the subject is able to recog-
nise their own hand movements 70% of the time, and
recognition is better for the dominant hand than the non-
dominant hand [24?].
A recent series of experiments by Knoblich, Prinz and co-
workers [25?,26?] has shown that subjects are adept at
recognising their own actions when they are played back
to them. In one study, subjects drew various characters,
and their movement patterns were recorded. A week later
they were presented with films of a moving dot, which
represented either their own pre-recorded movements or
the movements of someone else drawing the same char-
acter. Subjects were easily able to recognise which move-
ments were their own. Velocity seemed to be the crucial
component — self-movement recognition was not possi-
ble when the moving dot that represented their move-
ment was made to move at constant velocity while all
other factors remained the same as during the original
We are easily able to distinguish our own movements
from those of other people. How is this achieved, given
the overlapping neural system that is involved in the
part of the motor system is activated both when we
execute an action and when we observe a similar action
being executed [27–30,31?,32??,33]. If my brain ‘mirrors’
observed actions, how do I know that it is someone else,
and not me, who is moving when I observe an action?
Accumulating evidence indicates that the parietal cortex
plays a role in the distinction between self-produced
parietal cortex is activated when subjects mentally simu-
late actions from someone else’s perspective but not from
their own (Figure 1; [34?]). This region is also activated
when subjects observe their own actions being imitated
by someone else, but not when they imitate someone
else’s action [35?], and when subjects attend to someone
else’s actions rather than their own [36?,37]. It seems that
theinferiorparietalcortexisinvolved inclassifying move-
ments as external as well as in representing imagined
Confusing our own actions with other
The observation that patients with left parietal lobe
damage, with and without apraxia, are more likely to
confuse their hand movements with those of another
agent supports the idea that the parietal lobe is involved
in producing a sense of agency . Conversely, a recent
case study demonstrated that a patient with neglect and
somatoparaphrenic delusions caused by a right thalamic-
temporo-parietal lesion tended to deny that his left hand
was his own .
Certain psychiatric symptoms are characterised by an
inability to distinguish self- and externally produced
actions. Many patients with schizophrenia describe ‘pas-
sivity’ experiences in which actions, speech and thoughts
are controlled by some external agent rather than by their
own will. The experience of alien control could arise from
a lack of awareness of the predicted limb position [18,19].
Under normal circumstances, the awareness of initiating a
movement must depend on the predicted limb position,
because awareness of initiating a movement precedes the
actual movement and any feedback about actual limb
position (; see above). Patients with delusions of con-
trol are aware of their goal, of their intention to move and
of their movement having occurred, but they are not
to the problem of imagining movements, which we have
already discussed [17?].
Several studies have shown that patients that have delu-
sions of control confuse self-produced and externally
generated actions. Using the paradigm in which subjects
see feedback of their own hand movement or that of the
experimenter’s hand making similar movements, Daprati
and co-workers  found that schizophrenic patients
that have delusions of control are more likely than control
subjects to confuse their hand with that of the experi-
menter. Such people are less able to detect a discrepancy
between their movement and its consequences than
schizophrenic patients that do not have delusions of
control or control subjects. They become aware that a
movement is not their own when their movement and its
sensory (visual) consequences are discrepant spatially by
30 degrees or temporally by 300 ms, compared with 15
Self-awareness and action Blakemore and Frith 221
Current Opinion in Neurobiology 2003, 13:219–224
degrees and 150 ms, respectively, for control subjects
[4?]. One explanation for this is that the schizophrenic
patients that have delusions of control only have pro-
prioceptive and visual feedback to rely on for recogni-
tion, whereas control subjects are additionally able to
compare the sensory prediction with sensory feedback
from the movement.
Because a movement is predicted, its sensory conse-
quences can be perceptually attenuated relative to exter-
nal sensations . There is evidence that the confusion
between self and others in subjects with delusions of
control is a consequence of an abnormal sensory predic-
tion . Patients with delusions of control do not show
this perceptual attenuation of self-produced sensory sti-
mulation . The normal perceptual attenuation of the
sensory consequences of movement is accompanied by,
and might be attributable to, a reduction in activity in the
parietal operculum (secondary somatosensory cortex) and
the anterior cingulate cortex during self-produced tactile
stimulation compared with external tactile stimulation
. If delusions of control are associated with an impair-
ment in sensory prediction, we would expect to see no
attentuation of the activity in sensory regions. This was
precisely the result of a study in which schizophrenics
with and without delusions of control were scanned in
position emission tomography (PET) while they per-
formed a movement task (Figure 1; ). The presence
of delusions of control was associated with over-activity in
the right inferior parietal cortex. Moreover, activity in this
region returned to normal levels when the schizophrenics
were in remission. Over-activity of the inferior parietal
cortex might reflect a heightened response to the sensory
consequences of movements the schizophrenic patients
made during the scan, contributing to the feeling that
movements are externally controlled.
0 2040 60 –20–40–60–80 –100
Current Opinion in Neurobiology
Farrer & Frith 
Attribution of agency
Spence et al. 
Delusions of control
Blakemore et al. 
delusions of control
Weiller et al. 
Schematic diagram showing the lateral surface of a brain. Arrows indicate regions of parietal cortex that were activated by; the attribution of movement
to an external source for visually guided movements [34?], delusions of control in schizophrenia , hypnotically induced delusions of control
in the healthy brain  and passive movements .
Current Opinion in Neurobiology 2003, 13:219–224 www.current-opinion.com
This result was supported by a recent study that inves-
tigated brain activity associated with delusions of control
self-generated movement to an external source in healthy
individuals. PET was employed to investigate the neural
correlates of active movements correctly attributed to the
self, compared with identical active movements misat-
tributed to an external source. Active movements attrib-
uted to an external source resulted in higher activations in
the parietal cortex and cerebellum than identical active
movements correctly attributed to the self. The brain
activations associated with the misattribution of active
movements resembled brain activity associated with pas-
sive movements (Figure 1; ). Together with the
results of Spence et al. , these results suggest that
of the cerebellar-parietal network.
We have briefly reviewed recent evidence that suggests
that many aspects of action occur without awareness. We
have argued that one aspect of an action that might be
available to awareness is the prediction of the sensory
consequences of that action. This prediction might
underlie the ability to distinguish between self-produced
and externally generated actions, a process that appears to
involve theparietal cortex.Thisbrainregion has also been
implicated in psychotic symptoms, in which patients
confuse their own actions with externally produced
actions. Future studies using new paradigms are needed
to elucidate the hypothesis that the forward model pre-
diction contributes to the awareness of action. In particu-
lar, the study of motor awareness in patients with poor
sensorimotor prediction might be fruitful in this context.
C Frith and S-J Blakemore gratefully acknowledge the support of the
Wellcome Trust UK. S-J Blakemore is supported by a Wellcome Trust
International Research Fellowship. Extract from ATONEMENT by Ian
McEwan. Copyright ? 2001 Ian McEwan. Published by Jonathan Cape, and
NanTalese/Doubleday. Used by permission of The Random House Group
Limited, and Alfred A Knopf, Canada.
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