Perception, the Brain,
and Consciousness
Minds and Machines
Our Eyes as a
Window to the World
The Myth of ‘Perfect’ Perception
• The myth of perception is that as long as:
–
–
–
–
–
–
Our eyes are functioning properly
We’re not wearing rose-colored glasses
We’re not drugged
We’re not subjected to some visual illusion
We’re not in the Matrix
… (other exceptional/rare situations)
• … we perceive the world exactly as it is.
• Wrong!
Our Senses are Limited
• Our eyes only perceive a very small part of
the electromagnetic spectrum; we don’t see
infrared, ultraviolet, X-Rays, Gamma-Rays,
Micro-waves, Radio-Waves, etc.
• Similar for our other senses.
• OK, but what we do perceive, is still exactly
as it is, right?
• Wrong!
The Checker Board Shadow
Illusion
A
B
The Checker Board Shadow
Illusion
A
B
Which Perception is ‘Correct’?
• But is it wrong to perceive A to be darker
than B?
• If it is a chess board, then A really is darker
than B in some real physical sense, even if
the raw stimulus happens to be the same.
• And that’s just it: perception is an
interpretation of the raw sensory stimuli.
• Perception = f(sensory stimuli)
Perception as an
Inversion Problem
• We can look at perception as an inversion
problem: our mind/brain has to figure out what is
going on in the world ‘out there’, given the raw
incoming sensory stimuli.
• But this inversion problem is inherently
underspecified: that is, at all times, an infinite
number of scenarios can produce the incoming
sensory stimuli we get.
• Hence, we have to make a guess, i.e. perception is
inherently inferential (and non-deductively so!)
The Blind Spot
X
X
Color Contrast
A
B
Devils, Angels, Aliens, Jesus, Mary,
and … Illinois!
Mary
Jesus
Jesus Pan
Local
Jesus
Perception and Concepts
• We see faces in lots of things because faces
are important in our lives.
• Indeed, our interpretation of incoming
stimuli is in terms of concepts: faces,
people, trees, tables, chairs, etc.
• Concepts are useful ways to think about the
world ... but are they ‘real’?
• (if a tree falls in a forest …)
The Necker Cube
E
A
F
B
G
C
H
D
Expectations, Fears, and Wishes
• What we perceive is effected by:
– Our expectations
• Corridor Experiment
– Our fears
• Monsters under the bed
• Person in the shadow
– Our wishes
• N-Rays, St. Nick
– And probably many other states of mind
Summary:
Perception is Constructive!
• At all times, how we perceive things is a
construction of our mind (brain).
• Perception = f(raw sensory input, attention,
beliefs, expectations, …)
• A very complex function!
• It is estimated that about a third of our brain
is dedicated to visual processing alone!
Why Perception
Doesn’t Feel Constructive
• Two big reasons:
– We are, under normal circumstances, getting a
lot ‘right’
• I rarely get contradicted in my constructions of
reality and how I subsequently act on that
– We consistently perceive the world in the same
way (we’re stuck in Plato’s cave)
• But what if things go wrong?
– Video discusses interesting cases of brain
damage revealing pretty strange perceptions
Some Philosophical Questions
• Is the ‘self’ a mere perception?
• So what are things really like?
– How is knowledge and science possible?
• How do I know what it is that you perceive?
– Do you have any conscious perceptions?
– Do animals and machines have any conscious
perceptions?
Perception of ‘Self’
• We don’t just perceive the outside world.
• We also perceive things about our self
– Interoception (hunger, pain)
– Proprioception (balance, body posture)
• But again, what we perceive about our self
is a construction of our self
– Video: Phantom Limb Syndrome
– Video: God Syndrome
• Is the self a mere construct?
What is the World like?
?
How do you Perceive the World?
?
Invertoids
?
Weirdoids
?
How is Science Possible?
‘Publicly Observable’ Things
!
16 ‘green trees’
F= m*a
…
Blindsight
I can’t see it, but I think there is a tree
Blindsight and
Animal Consciousness
• Blindsight is often explained by pointing to the
fact that there are two neural pathways from our
eyes to our visual processing centers in (the back
of!) our brain: one evolutionary old pathway
(through the brain stem), and one new (through
the thalamus)
– If the new pathway has suffered damage, but the old
pathway is still intact, we can process visual
information without being conscious of it
• Does this mean that animals without the new
pathway do not have conscious experiences?
Blindsight, Consciousness, and
Philosophical Zombies
• If we can process visual information
unconsciously, why do we have any
conscious visual experiences at all?
• What is the purpose of consciousness??
• Why are we conscious at all???
– Why aren’t we all (philosophical!) zombies?
• Why does certain brain activity ‘lead to’
conscious experiences, and other not????
• What the hell is consciousness?????
Zombies
I see a tree!
Materialist Theories of
Consciousness
• Consciousness is:
– quantum collapses in microtubules internal to neurons (Penrose,
Hameroff)
– thalamically modulated patterns of cortical activation (Llinas)
– left hemisphere based interpretative processes (Gazzaniga)
– emotive somatosensory hemostatic processes based in the frontallimbic nexus (Damasio)
– synchronous neural oscillations at 40-70Hz (Crick, Koch)
– spatiotemporal patterns in electro-magnetic field produced by brain
(McFadden, Pockett)
– global workspace of cognitive activity (Baars)
– integrated information (Tononi)
Consciousness and New Dualism
• Philosophers like Thomas Nagel (in “What is it
like to be a bat?”) and David Chalmers (in “The
Puzzle of Conscious Experience”) claim that while
the quantitative aspects of consciousness (such as
awareness) can be described and studied
objectively, the qualitative, phenomenal aspects of
consciousness (qualia) can not.
• So, if by ‘physical’ we mean anything that can be
described and studied by physics (or any other
scientific discipline) physicalism is false.
The Subjective Nature of
Consciousness
• ‘ … [A]n organism has conscious mental states if
and only if there is something that it is like to be
that organism – something it is like for the
organism. We may call this the subjective
character of experience. It is not captured by any
of the familiar, recently devised reductive analyses
of the mental, for all of them are logically
compatible with its absence. It is not analyzable in
terms of any explanatory system of functional
states, or intentional states, since these could be
ascribed to robots or automata that behaved like
people though they experienced nothing’ (Nagel)
The Easy Problem of
Consciousness
• ‘The easy problems of consciousness include the
following: How can a human subject discriminate
sensory stimuli and react to them appropriately?
How does the brain integrate information from
many different sources and use this information to
control behavior? How is it that subjects can
verbalize their internal states? Although all these
questions are associated with consciousness, they
all concern the objective mechanisms of the
[mind]. Consequently, we have every reason to
expect that continued work in [cognitive science]
will answer them’ (Chalmers)
The Hard Problem of
Consciousness
• ‘The hard problem, in contrast, is the question of
how physical processes in the brain give rise to
subjective experience. This puzzle involves the
inner aspects of thought and perception: the way
things feel for the subject. When we see, for
example, we experience visual sensations, such as
that of vivid blue. Or think of the ineffable sound
of a distant oboe, the agony of an intense pain, the
sparkle of happiness or the meditative quality of a
moment lost in thought.’ (Chalmers)
Why Neuroscience Fails to
Explain Consciousness
• ‘Consider the hypothesis put forward by [Crick
and Koch]. They suggest that consciousness may
arise from certain oscillations in the cerebral
cortex, which become synchronized as neurons
fire 40 times per second. … The hypothesis could
conceivably eludicate one of the easy problems
about how information is integrated in the brain.
But why should synchronized oscillations give rise
to a visual experience, no matter how much
integration is taking place? This question involves
the hard problem, about which the theory has
nothing to offer.’ (Chalmers)
Why Fancy Physics Fails to
Explain Consciousness
• ‘Some have suggested that to solve the hard
problem, we need to bring in new tools of physical
explanation: nonlinear dynamics, say, or new
discoveries in neuroscience, or quantum
mechanics. But these ideas suffer from exactly the
same difficulty. … The trouble is that physical
theories are best suited to explaining why systems
have a certain physical structure and how they
perform various functions. … But consciousness
is a different sort of problem entirely, as it goes
beyond the explanation of structure and function.’
(Chalmers)
The Zombie Paradox
I am conscious, so I am not a zombie, but it is
conceivable that others are!