Perception

Seeing is believing

What we know

• We know that we inhabit a world of material objects (trees, books, plates, people, etc.)

• We know this mostly through our senses (vision, hearing, touch, smell, taste)

• Knowledge obtained through the senses is called perception.

Perception and Belief

• Perception causes belief (or “judgment”) • E.g. when you see a glove, you don’t just see a

brown blob. You see it as a glove. You see that there is a brown glove in the drawer.

• Thus perception involves concepts, or categories, such as glove, brown, spatial relations, etc. It’s not “raw data”.

• Perception causes belief in a proposition.

Knowledge goes beyond perception

• We know about things we do not perceive. E.g. the past, the future (?), electrons, physical

forces, universal laws, mathematical truths, moral truths, etc.

Perception is fallible • There are optical illusions, such as a stick half

submerged in water appearing bent. This raises the threat of scepticism. Do we really know anything?

Scepticism • Scepticism means doubt, or suspending

judgment, keeping an open mind.

• A sceptic demands evidence for a claim before believing it.

• Scepticism is good, unless perhaps it threatens to destroy all of our (supposed) knowledge!

Is Perception direct? Or an inference?

• An “inference” is forming a belief on the basis of old beliefs, by means of logical reasoning, math calculations, etc.

• E.g. you may see a chair next to the kitchen counter, the cookie jar on the counter open, and cookie crumbs on the floor nearby. You infer that your toddler has gotten into the cookies again.

Is Perception direct? Or an inference?

• So we commonly distinguish between what is actually seen, and what is inferred (from what is seen).

• But perhaps even what we actually see is also an inference? (An unconscious one, carried out by mechanisms we’re unaware of.)

Is Perception direct? Or an inference?

• When we see something, we are aware of it. There is a certain “object”, the glove, or the pencil, etc. that is present in our consciousness.

• Is the physical glove itself present in our consciousness? Or are we aware of some “construction” of our own minds, which has been inferred from the raw data (optic nerve signals)?

• How big is the man?

3D images

With “3D glasses” on, we see a 3D chair here. Why?

Wiggle stereoscopy

Wiggle stereoscopy

3D vision

• When our eyes are provided with slightly different images, showing the same objects from slightly different perspectives, we become aware of 3D objects that don’t really exist. Why?

3D vision

These optical illusions are generally taken by philosophers to show that perception is inference.

Our brains analyse the signals from the optic nerves,

and try to figure out what could be “out there” that would cause such signals. The brain “draws” its best guess, in our conscious awareness. That’s what we see.

Hollow face

What do you see?

• Images (a) and (b) are identical, except that (b) has been turned upside down.

The visual field • The “visual field” is the spatial array of visual

sensation. • It consists of 3D objects, which are coloured, in a 3D

space.

• The visual field seems to be a logical construction, based on the optic nerve signals. It requires very complex calculations, performed in real time. (Fortunately we are not aware of these!)

• In the case of the 3D chair, the brain constructs the chair that best explains the data it’s getting.

What do we see? Ideas?

• The “objects” within the visual field are not (ordinary) physical objects. They are known as (sensory) ideas. (Or percepts by psychologists.)

• When we see a tree, for example, there is a tree-idea in our visual field.

What do we see?

• Do we see

(a) the tree, or (b) the tree-idea, or (c) the light coming from the tree?

• Let’s not use language in a confusing way. 1. We see the tree. 2. We are aware of our own ideas (we don’t

see ideas) 3. The light causes our brain to construct the

idea. (We don’t see light -- light is actually invisible).

• The ‘veil of perception’. (Though there is no homunculus.)

“Direct Realism”

• This is the “naïve” view that we are directly aware of external objects (e.g. trees) so that perception involves no ideas obtained by inference.

“…when we see something, the very thing we see is there, before our eyes, available for inspection…” (Landesman, p. 21)

Representative Realism

• This is what most philosophers (e.g. Locke) believe.

• Perception involves the construction (or inference) of ideas which represent external objects.

Anti-realism

• Anti-realism says that we have knowledge only of our own ideas, not external objects.

• External objects either do not exist, or are likely very different from how we perceive them. (Who can say?)

(Who can get outside his own mind to see the “things in themselves”?)

Ideas are different from objects: 1. Ideas are fuzzy

• E.g. the speckled hen. If we see a speckled hen from a distance, then the idea of it is just vaguely speckled, whereas the real hen has individual speckles in particular places.

2. Ideas can be inaccurate

Some ideas are based on comparison

• Put one hand into hot water, the other into cold water, for a few minutes.

• Then take them out and put both hands into lukewarm water.

• How does the warm water feel? (N.B. the temperature feeling of the water is also an idea.)

• It feels hot and cold: Hot to the hand that was in the cold water, and cold to the hand that was in the warm water.

• The sensations of “hotness” and “coldness” of the water seem to exist in the perceiver, in this case, rather than in the water.

• What is going on in the water, that causes us to have a sensation of warm or cold?

How do the colours of A and B compare?

The colours are the same, but the ideas are different!

Do ideas represent the world?

• The relation of representation is very familiar to us. • For example, a map represents a territory, i.e. a

portion of the earth’s surface.

Is this accurate and complete?

• Accurate: Does every feature of the map correspond to something in reality?

Pretty much, in this case. But note that some features of the

map (e.g. road colours, widths) aren’t literal.

• Complete: Does every feature of reality

correspond to something on the map? Heck no! No houses, trees, sidewalk slabs…

• Completeness is too lofty a goal for representation. (Even if a complete map were possible, it would be hard to read.)

• A maximal representation is one that cannot be added to. Maps are not maximal either.

(The present mathematical model of the hydrogen atom may well be maximal. Is it also complete?)

Non-literal aspects

• Aspects of the map that are literal: – Shapes – Most relative sizes

• Aspects of the maps that are not literal: – Absolute size – Most colours – Contour lines, labels, road widths, etc.

• Derek Zoolander on literal representation

Do ideas have non-literal aspects?

• Perceptual ideas (of material objects) are solid (i.e. filled in, no gaps), coloured, have geometrical form, and size.

• Contemporary physics describes material objects in terms of shape and (relative) size, but says that objects are mostly empty space.

• Also, physics seems to have no place for colour!

MRI scan of a brain

• Are those colours real?

Does a pin have pain in it?

Is ‘red’ light actually red?