PERCEPTION

Why an issue?

• Sensory perception a key source of our beliefs about the world.

• Empiricism – senses the basis of knowledge.

Key questions• What is the relationship between me (the subject) and

the world?

• What is the relationship between appearance and reality?

• When I perceive something, what is it that I am aware of?

• How are misperceptions and illusions to be explained?

• What happens when an object is not being perceived? What can we know of it?

The common sense approach to the questions…

• One’s awareness or perception is directly of the object.

• The object exists independently of us.

• The object is the cause of my perceptual experience.

• When unperceived the object retains (at least some of) its properties.

The challenge of illusions

PARIS IN THE

THE SPRING

The challenge to direct realism

• The Time-Lag Argument.

• There is a time lag between my perception of an object and the object actually having the properties I perceive it to possess

• Well-known objection to direct realism but one that is easily answered. It trades on a confusion between two senses of immediate.

• Immediate #1: without delay

• Immediate #2: direct, without anything coming between.

A bigger worry… Misperception and Illusion

• a round coin can appear elliptical from certain angles, a straight stick bent when in water, parallel lines convergent as they move into the distance, a non-existent limb can feel painful to an amputee

• The basic problem is how to explain why an apparently direct relationship with the world can give rise to such errors.

• Also – think about how we can explain the phenomenal sameness of really seeing a small green man and having an hallucination of a small green man.

Physics and perceptual experience

• Physics tells us how the world really is.

• Yet we do not experience the world as it is described in our best physical theory, even though according to direct realism it is with the world as such that I have direct contact.

• Furthermore, at least some of the properties an object has seem to depend upon the perspective of the observer

The appeal to representative realism…• Faced by the challenges to direct realism,

particularly the view that the realist struggles to explain the obvious fact that we do suffer misperceptions and illusions.

• The realist can suggest that our direct awareness is of inner, mental objects representing the thing out there in the world.

• That is, we preserve realism by introducing sense data.

Hmm…

• Let’s try to picture the claim…

What the hell are sense-data?• If I see a dagger or hallucinate one, it looks the same. There is a

dagger-shaped object in my visual field.

• This object is called a (visual) sense-datum. A visual sense-datum is a two-dimensional object with a certain shape and coloured a certain way.

• My current visual experience is mosaic of such objects – of sense-data. As I look at the white disc before me, there is a white circular sense-datum as part of my visual experience. As I tilt the disc, it is replaced by a white elliptical sense-datum.

• Notice therefore that there is a distinction between the three-dimensional object in the world that remains the same and the two-dimensional sense-data that exist only so long as my visual experience does not change.

Why believe in sense-data?• The Primary/Secondary Quality Distinction.

Objects don’t really have colours or tastes, according to science. They are features of my ideas or sense-data.

• Perceptual relativity. There is a distinction between an object and its appearance: the circular disc may appear elliptical. We need to account for the fact that there is a circular thing in my visual experience.

• They explain misperception: the stick is not really bent but the stick-sense-datum is.

• They explain hallucination: in normal perception, a real dagger causes a dagger-sense-datum in my visual experience.

• They explain how we can ‘see’ stars that may now be dead: the star’s light emitted millions of years ago causes a star-sense-datum when it reaches me.

• They fit in with modern physics: nothing is really coloured – colours are the properties of sense-data caused by the interaction of objects, light, my eyes and my brain.