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!)

X X

The Blind Spot

Color ContrastA

B

Devils, Angels, Aliens, Jesus, Mary, and … Illinois!

Jesus PanLocal Jesus

Jesus

Mary

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

A

C D

G H

B

FE

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 frontal-

limbic 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!