Some Thoughts on the Cognitive Neuroscience
of Primitive Self-Consciousness: Reply to Gallese
In The Paradox of Self-Consciousness I had relatively little to say about the neural dimension of primitive self-consciousness. The discussion there was largely conducted at the so-called personal level of explanation (Dennett 1969, Bermúdez 2000a, Bermúdez and Elton 2000) – the level of explanation at which we find both folk psychology and scientific psychology. But any personal-level account of self-consciousness is constrained by the facts at the various different subpersonal levels of explanation (Bermúdez 2000b). In the book I stressed the importance of what I termed the Acquisition Constraint (that no satisfactory philosophical account of a cognitive capacity can make it mysterious how that capacity could emerge in the normal course of development). Clearly, there is a parallel Implementation Constraint, to the effect that no satisfactory account of a cognitive capacity can make it mysterious how that capacity could be neurobiologically implemented. Current knowledge is too limited to make anything more than a very tentative assessment of the possible neural bases of primitive self-consciousness, but I am very grateful to Vittorio Gallese for pointing me in the direction of current neuroscientific research showing that my account of primitive self-consciousness is in several significant respects compatible with what is currently known about the neuroscience of perception and action. In these brief comments I make explicit how the research to which he has drawn attention meshes with my account of primitive self-consciousness.
information in vision
In Chapter 5 of The Paradox of Self-Consciousness I followed J. J. Gibson's (1979) ecological approach
to vision in stressing the proprioceptive dimensions of visual experience.
The optic array contains information about the self as well as information
about the environment. I characterised this as one of the two most
primitive form of self-consciousness – both ontogenetically and
phylogenetically. Visual proprioception is present at birth and
appears early on in evolution.
One of the planks of Gibson's
theory of self-perception is the notion of an affordance – the idea
that objects and surfaces in the environment have properties allowing
different animals to act and react in different ways and that those
properties are directly and immediately perceived in the environment
as higher-order invariants. The perception of affordances is a form
of self-perception. It is the pick-up of environmental information
about one’s own possibilities for action and reaction. The central
claim here is that affordances are themselves part of the content
of what is perceived. The animal does not work out his own possibilities
for action by analysing what he sees. He just sees what he can and
cannot do in a particular environment.
How might the Gibsonian view
be confirmed or disconfirmed at the neural level? We can compare
two different pictures of the relation between perception and action.
On the first, more traditional picture, perception and action are
insulated from each other by the mechanisms of "central processing".
Put crudely, sensory input feeds into the central decision-making
processes that integrate sensory information with other sources
of information and determine a plan of action. This planned action
is then implemented by the various motor systems. An influential
version of this conception of the relation between perception and
action is to be found in Fodor's The
Modularity of Mind (Fodor 1983), where both sensory
input is fed into the central belief system by encapsulated modules
that are domain-specific, fast and have shallow outputs. On this
view, perhaps the dominant view within the cognitive sciences, bare
sensory input is only transformed into meaningful perception when
the central belief system is brought to bear. The environment is
perceived from a point of view or perspective only in the minimal
sense that the perceived environment is represented on a subject-centred
frame of reference. The self features in the content of visual perception
only as a geometrical point – as the origin of the field of view.
On the second picture of the
relation between perception and action, in contrast, the environment
is not merely represented on a subject-centred frame of reference.
It is represented as an environment within which the perceiver can
act. The perceived environment is meaningful to the perceiver long
before the central processes of belief fixation become involved
– if indeed they do become involved. The content of perception is
such that it can feed directly into behaviour. Gibson's theory of
ecological perception adopts this second picture of the relation
between perception and action. Versions of this second picture have
also been canvassed by philosophers from very different traditions
(Dreyfus 1992, Hurley 1998).
The conception of primitive self-consciousness that I put forward in The Paradox of Self-Consciousness will meet the Implementation Constraint only if something like the second picture of the relation between perception and action receives corraboration at the neural level – if it turned out that the processing correlative with the environment becoming meaningful to the perceiver qua agent takes place at a relatively "early" stage in the perceptuo-motor system. It is interesting that much recent research carried out by various people (including Vittorio Gallese and his co-workers) seems strongly to suggest that this is in fact the case (for reviews see Jeannerod 1997, Rizzolati, Fogassi and Gallese 2000). I will comment here on two particular sets of results.
It is well known that there
exist many different representations of space at the neural level
(Wilson 2000), although from a phenomenological point of
view the spatiality of the environment is of course perceived as
a single and unified manifold. Space is represented egocentrically
in many different ways, with a range of frames of reference centred
on different body-parts. There are also many different allocentric
coordinate systems nested within each other. The mere fact that
perceptual experience is coded on egocentric frames of reference
is not itself evidence for the second picture of the relation between
perception and action. It is hard to see how the spatiality of perception
could be anything other than egocentric (except perhaps in the case
of God). But there is a particular type of egocentric frame of reference
whose existence does point strongly in favour of the second picture.
This is what has come to be known as peri-personal
space (Rizzolati, Fadiga, Fogassi
and Gallese 1997).
Experiments on the monkey ventral premotor cortex (area F4) have revealed the existence of neurons responsive to both visual and tactile stimuli (particularly those associated with movements of the head or arm). The visual and tactile receptive fields of these neurons (that is, the areas in objective space within which they detect stimuli in the relevant modality) are very closely linked. Visual stimuli can detected only in the area immediately around the skin surface (e.g. where tactile stimuli are detected). Moreover, the visual receptive fields move only when the body moves. They are not sensitive to changes in the direction of gaze that are unaccompanied by changes in posture. As Gallese suggests in his review, it seems likely that peri-personal space is a motor space, circumscribed by the range of efficacy of the various body-parts. The coding of objects's location in peri-personal space in the pre-motor cortex, and consequently at a relatively early stage in perceptuo-motor processing, seems strongly to support the second picture of the relation between perception and action.
Further support for the second
conception of perception and action comes from single neuron studies
of area F5 in the monkey premotor cortex. The firing of neurons
in F5 is correlated with distinct types of motor act. Studies have
show that groups of F5 neurons exist sensitive to the following
types of motor act:
• grasping with the hand
The grasping neurons are themselves
subdivided into three classes according to the grip type that they
involve. Small objects are grasped with the precision grip, in which
the thumb is opposed to the index finger. Medium-sized objects are
grasped with the thumb opposed to the other fingers (finger prehension)
and large objects using whole hand
prehension in which the fingers are
opposed to the palm.
Among these F5 neurons correlated with particular types of action, some respond only when the action in question is performed (the F5 motor neurons). Others (the F5 visuo-motor neurons) also respond to visual stimuli. These visuo-motor neurons discharge when an object is perceived, according to the type of grasp that would be most appropriate for that object. Experiments by Murata et al. (1997) show that this neuronal activity occurs even if no movement is performed, and they strongly suggest it occurs even when the monkey has no intention of grasping the object (by showing that the neurons fire even when the monkey is performing tasks in which grasping is not involved). The conclusion that seems to be imposed by the existence of these neurons in the pre-motor cortex is again that objects seem to be perceived in terms of the potential for action that they offer the perceiver. Again, self-specifying information (in the form of information about hand shape and size relative to the presented object) appears to be coded at an early stage in the process of perceptuo-motor transformation.
and passive movement: The role of proprioception and spatial representation
In his review of my book Gallese
expresses concern with my emphasis on Gibsonian accounts of perception.
He notes that Gibson's ecological theory of perception does not
lay enough stress on the distinction between active and passive
movement, suggesting that both types of movement function for Gibson
as "just a tool to capture the higher-order invariant features
which are prespecified in the afferent stimulation". In contrast,
the position that emerges from the neuroscientific work he discusses
and that he correctly identifies as being at the core of my account
of primitive self-consciousness is one in which agency is a key component.
This point is well taken (although
it is unclear how the notion of an affordance can be completely
understood in terms of passive movement). Gibson's theory of visual
perception is rather one-sided and it would be unwise either to
have it as the sole element in an account of self-consciousness
or to follow Gibson in some of his more extreme pronouncements.
In The Paradox of Self-Consciousness I tried to bring out how the self-specifying information
in vision is complemented by self-specifying information in somatic
proprioception, as well as by the awareness of spatial location
implicated in navigation (what I called a point of view). These
two further dimensions of primitive self-consciousness are closely
linked with agential motor activity. The mechanisms of proprioceptive
information are designed to operate in conjunction with the mechanisms
of efference copy (or corollary discharge) to provide feedback on
active movement and to distinguish active movement from passive
movement. In so doing they underwrite a form of self-awareness qua agent.
The point is even clearer for the form of self-awareness implicated in possession of what I termed a nonconceptual point of view. The basic idea here is that, since representing a particular space requires representing one's own location relative to it, the representation of space is a form of self-awareness. Since self-consciousness is essentially a contrastive notion, the richness of this form of self-awareness is a function of the complexity and richness of the representation of the environment within which the subject is located. I discussed the interplay between spatial representation and self-consciousness in terms of three central cognitive/navigational capacities:
• The capacity to think
about different routes to the same place
Of these only the first strictly implies agency and active movement, but it is clear that the second and third will only emerge in the context of active movement within the environment
self-awareness as an agent
The contrastive nature of
self-consciousness comes to the fore in psychological self-awareness,
that is, awareness of oneself as a bearer of psychological as well
as physical properties. In considering psychological self-awareness
I proposed what I termed the Symmetry Thesis:
Symmetry Thesis A subject's psychological self-awareness is constitutively
linked to his awareness of other minds
The rationale for the Symmetry
Thesis is that a subject's recognition that he is distinct from
the environment in virtue of being a psychological subject is dependent
upon his ability to identify himself as a psychological subject
within a contrast space of other psychological subjects. This self-identification
as a psychological subject takes place relative to a set of categories
which collectively define the core of the concept of a psychological
subject. Consequently there are some psychological categories which
a subject cannot apply to himself without also being able to apply
them to other psychological subjects. These psychological categories
are the categories which form the core of the notion of a psychological
I analysed the notion of a psychological subject in terms of three components – being an agent, being a perceiver and being a subject of reactive attitudes. The Symmetry Thesis entails that self-awareness relative to each of these three categories will be relative to awareness of other subjects falling under each of those categories. In The Paradox of Self-Consciousness I explored the relation between psychological self-awareness and awareness of other subjects in infancy. The neuroscientific research to which Gallese draws attention is also highly relevant. It suggests that this personal-level interdependence has subpersonal correlates.
neurons in F5 and the Symmetry Thesis
In addition to the canonical
neurons in F5 that have already been discussed in 1.2 there is a
second group of neurons sensitive to visual stimuli in F5. These
are the so-called mirror neurons. Whereas the canonical neurons
discharge in response to visually presented stimuli as a function
of the type of action appropriate to the perceived object, the mirror
neurons discharge in response to perceived actions. The surprising
feature is that they discharge not only in response to actions performed
by the subject, but also to actions performed by other individuals.
Like the canonical neurons, the mirror neurons classify actions
The existence of mirror neurons clearly shows that in the premotor cortex there is a level of coding actions that does not differentiate between those that are self-initiated and those that are other-initiated. It provides corroboration for the Symmetry Thesis in the following sense. The Symmetry Thesis implies that it is not possible to be aware of oneself as an agent without being aware of other individuals as agents. The functioning of the mirror neurons shows that the mechanisms for coding one's own actions serve equally as mechanism for coding the actions of others.
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