Conscious Thought as Simulation of Action and Perception

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Conscious Thought as Simulation of Action and
Perception
Germund Hesslow Toward a Science of
Consciousness Skövde 2001
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Problems of consciousness

• How does the inner world arise?

• What are mental objects?

• What is the function of the inner world?

• Can animals and robots have inner worlds?

Notice that the problems are phrased in terms of
the inner world rather than consciousness.
Although the inner world is a part of
consciousness, some would hold that the latter
also requires emotions, meanings, qualia etc.
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The simulation hypothesis
1) Simulation of behaviour We can simulate
behaviour by covert preparatory action. Thinking
of doing something is similar to actually doing
it. It is covert behaviour. 2) Simulation of
perception We can simulate perception by
reactivation of sensory cortex Imagining that one
is perceiving something is similar to actually
perceiving it and activates the same brain
structures. 3) Anticipation Simulation of
behaviour can elicit other perceptual activity.
This entails that simulation of behaviour can
elicit perceptual activity which resembles the
activity which probably would have occurred if
the the simulated actions had actually been
performed.
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David Hume (1711-76)
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Alexander Bain (1818-1903)
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B.F. Skinner (1904-1990)
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Simulation of behaviour covert, incipient
behaviour
The tendency of the idea of an action to produce
the fact, shows that the idea is already the fact
in a weaker form. Thinking is restrained speaking
or acting. (Bain, 1868 p 340) In speech we
have a series of actions fixed in trains by
association, and performable either actually or
mentally at pleasure the mental action being
nothing else than a sort of whisper, or approach
to a whisper, instead of the full-spoken
utterance. (Bain, 1868, p.347)
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Hierarchical organisation of action
Draw triangle
Get pen Get paper Draw
Draw horizontal line Draw sloping .
Contract m brachioradialis Contract ....
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Main signal flow
Global motor commands are generated rostrally in
the frontal lobes. The more caudal we go, the
more specific the commands until we reach the
pyramidal tract neurons of the primary motor
cortex. When simulating a movement, the early
rostral parts are reproduced but not the final
specific motor commands.
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Simulation of perceptionsensory reactivation
What is the manner of occupation of the brain
with a resuscitated feeling of resistance, a
smell or a sound? There is only one answer that
seems admissible. The renewed feeling occupies
the very same parts, and in the same manner, as
the original feeling, and no other parts, nor in
any other assignable manner. ( Bain, 1868, p.
338)
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Pain perception
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Phantom pain
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Seeing
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Imaging
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Perceptual simulation
A signal reaching the brain from the outside will
appear the same, to the brain, and will generate
the same reactions regardless of whether the
signal starts at a peripheral receptor or on the
way to the brain. A signal reaching the frontal
lobe from the visual cortex will appear the same,
to the frontal lobe, even if it was not triggered
by an external stimulus. When I press the key A
on my computer keyboard, the processor perceives
the key press. If the signal was being generated
somewhere else, but fed into the processor in the
same way, it would appear to the processor as if
I had pressed A. If the computer can react to
the internal stimulus, it has an inner world.
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MRI signal intensity in primary visual cortex
during external vs imagined stimulus
Le Bihan et al. PNAS 9011802-11805, 1993
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MRI activity with external and imagined stimulus
Tootell et al, TINS, 2 174-183, 1998
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Classical Pavlovian conditioning
Tone Air puff
Air puff
Tone Air puff
Tone
Tone Air puff
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Is the CS associated with the stimulus or with
the response?
P p b B
CS - R
T
P p b B
CS - S
T
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Sensory preconditioning
Experimental paradigm
Training Test
Stage 1 Light - Tone No
overt response
Stage 2 Tone - foot shock Tone
Flexion
Stage 3 Light Flexion
Mechanism is CS associated with S or with R?
T t f F
T t f F
L
L
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Anticipationaction-sensation associations
The succession designated as cause and effect,
are fixed in the mind by Contiguity. The simplest
activity is where our own activity is the cause.
We strike a blow, and there comes a noise and a
fracture. The voluntary energy put forth in the
act, becomes thenceforth associated with the
sound and the breakage. Hardly any bond of
association arrives sooner at maturity, than the
bond between our own actions and the sensible
effects that follow from them. (Bain, 1868, p.
427)
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Anticipation
Actions, and hence preparations for actions,
often have predictable consequences which
generate new predictable stimuli. We will assume
that an organism can learn such relations in the
form of associations such that the early
preparatory phase of an action can elicit the
perceptual activity in sensory cortex that will
probably result from the completed movement. Such
anticipation would enable the organism to avoid
potentially harmful consequences of an act before
it is performed. It follows that simulated
movements can also elicit perceptual activity.
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Predictable consequence
Anticipation of consequence
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Do we need cognitive maps?
Tolman Gleitman (1949) J Exp Psych 39 810-819.
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Simulation of behavioural chains
Given the ability to simulate actions and
perceptions and an anticipation mechanism, the
organism can simulate long chains of actions and
perceptions without any external input. This
simulated interaction with the external world
will inevitably appear as an inner world.
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Behavioural chain
Simulation of behavioural chain
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Conversation
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Talking to oneself
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Simulating conversation
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Strong points of the simulation hypothesis

• Ontological parsimony no representations, mental
  events
• No evolutionary leaps same structures underlying
  inner world as are used for perception and
  movement
• Explains absence of specific brain structure (see
  above)
• Explains relationship between cognitive and motor
  functions simulated movement will require same
  structures (premotor ctx, cerebellum and basal
  ganglia) as overt movement

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Problems of consciousness

• How does the inner world arise?

By simulation of behaviour and perception

• What are mental objects?

Source of image is not object but simulated
seeing

• What is the function of the inner world?

Inevitable consequence of simulation

• Can animals and robots have inner worlds?

Yes, if their brains can generate their own
input
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References A previous version of the simulation
hypothesis was presented in Hesslow G. (1994)
Will neuroscience explain consciousness? J Theor
Biol 17129-39. Many of the critical ideas can
be found in the behaviourist literature, for
instance Bain A (1855, 1868) The Senses and the
Intellect Skinner BF (1953) Science and Human
Behavior. Macmillan, New York Skinner BF (1974)
About Behaviorism. Knopf, New York Much of the
empirical evidence for covert behaviour cited in
the lecture can be found in Jeannerod M (1994)
The representing brain Neural correlates of
motor intention and imagery. Behav Brain Sci 17
187-245 Evidence for simulation of perception is
reviewed in Kosslyn SM (1994) Image and Brain
The Resolution of the Imagery Debate. MIT Press,
Cambridge Further details will be added to my
website shortly www.mphy.lu.se/avd/nf/hesslow