Epistemology

Tihamér Margitay, Péter Hartl

2. Perception

Importance of perception

Perception has a great epistemological importance. Perception is one of the main sources of our knowledge. The process by means of we acquire information about the

world by using our five senses. Cognitive science examines perception by means of

scientific methods, and examines different questions (How are we able to recognize objects?)

Philosophers use different methods, and have different questions. They criticise the presupposed beliefs about perception.

Common sense view about the world

1. The perceived objects exist indepedently of perceivers.

Examples: We think that the Moon has been continously existed even if it wasn't being perceived by anybody.

2. The objects have properties, and they possess of these properties even when they are not being perceived.

The table has properties, it has mass, volume, shape, color, it is made of wood, etc. We usually think that the table has (some of) these properties indepedently from perceiver.

3. Perception is reliable. Perceptual knowledge is unproblematic: the world is like as we see it.

If we see the building E of BME, we think that there is E building, and E building is like as we see it.

The reliability of perception

We usually think that:

1. Our senses are reliable. We perceive the external world as it is.

2. Our most reliable beliefs about the external world are based on perception.

Example: We are looking out the window and we see that it is raining. We think that our perception represents the world correctly (like a mirror).

I know that it is raining, because I'm looking out the window and I see that it is raining.

In science: we make an experiment, we observe something, and we usually think that observations are reliable and unproblematic sourses of our scientific knowledge.

The line on the right side appears to be shorter, than the line on the left.

But actually they have exactly the same length.

We can see triangles, but actually there are no triangles.

A appears to be a darker color than B...

Actually, they have exactly the same color

The reliability of perception

Epistemological problems of perception:

How can we know that perception is reliable?

There are possible errors. Perceptual illusions and hallucinations.

Normative question:

How can we distinguish the veridical perceptions from the non-veridical ones?

There are cases when our sensory experience appears to be real, but in fact it isn't.

Questions

1. How can we know that our perception is reliable?

2. How can we distinguish the veridical experience from non-veridical experience?

3. What are the immediate objects of perception?

4. What is the relation between our perception and the „real object”? What does it mean our perception „represent” the world?

5. What properties of objects are „real”, and what properties are depend on the perceiver and/or the circumstances of perception?

Different philosophical theories of perception offer different answers to these questions.

Realism

Realism in the theory of perception: the objects we perceive are able to and commonly do exist, and retain some at least of their properties even when they are unperceived.

The existence of the object and the properties of object are independent from the perception.

Questions: What is the relation between the object itself and the perceiver?

What kind of properties retain their existence when the object is unperceived?

Direct realism

We are directly aware of the perceived (external) things.

What is given in the experience is the perceived object itself.

When we look at a table, we can see the table, and we are directly aware of the table itself.

There is no intermediary object in process of perception.

The physical world is directly presented for us, without perceiving any intermediary object.

The (direct) realist claims that: the objects retain some at least of their properties even if they are unperceived.

Direct realism

We see a table, and it looks angled. The direct realist thinks that:

1. the table is angled, indepently from any perceiver.

2. when we look at the table, we perceive directly the table itself, there is no intermediary object of perception.

Direct realism - summary

Direct realism is the view that the immediate (direct) objects of perception are external objects, qualities, facts, or events.

It should not be confused with the more naive view that the world is exactly as we perceive it to be.

We can misperceive the world. The direct realist does not deny that there are perceptual illusions.

When we do perceive something, the immediate and direct object of perception is in the external world, not the mind.

There are problems with direct realism.

Perceptual illusions

The pencil in the water looks bent.

Of course the pencil is actually straight.

But if we directly perceive the things how can be perceptual errors?

P1. The pencil is not bent.

P2. What we see is bent.

Therefore: C: What we see is not the pencil.

Argument from illusion (hallucinaton)

One of the strongest argument against direct realism.

Illusion: the object appears to us in a different way, but the object actually exists.

Hallucination: the object does not exist in the external world.

Veridical case: It seems to me there is a mouse on the floor. The mouse actually exists, and I see a real mouse.

And I'm scared.

Hallucination: It seems to me there is a mouse on the floor. But the mouse does not exist. I just hallucinated it.

And I'm scared.

The argument based on comparsion of two cases of perception. It says the veridical case and hallucination are indistinguisable for the perceiver.

Argument form illusion (hallucination)

1: In a hallucination the immediate object of perception is a mental object.

In hallucination there is something present to consciousness.

When I have an auditory hallucination, I wrongly think that I'm hearing a sound, but in some sense I've experienced something.

There is something in my sensory field.

Of course there is nothing in front of me, because I'm hallucinating.

Therefore the object of my sensation cannot be the real, external object, when I hallucinate. The hallucinated object exists only in „my head”.

Argument form illusion (hallucination)

2: The hallucination and the veridical experience are phenomologically indistinguishable from each other.

At the time when we have a hallucinatory experience, we are unable to distinguish the hallucinatory from the veridical experience.

When we hallucinating we are unable to know that we are hallucinating.

There are good empirical evidences for that.

Of course, there will be difference in the way that experiences are caused.

Argument form illusion (hallucination)

3: If the hallucinatory and non-hallucinatory experience may be indistinguishable, then their immediate objects must be entities of the same kind.

It's possible to have an identitical veridical and hallucinatory experience.

If in hallucination I directly perceive a mental object, and I would have exactly the same experience when I would have a veridical experience, then even in non-hallucinotary cases the immediate object of perception is a mental object (sense-datum).

Argument from illusion (hallucination)

P1: In a hallucination the immediate object of perception is a mental object (sene-datum).

P2: A hallucinatory experience may be indistinguishable from non-hallucinatory experience.

P3: If immediate object of perception in a hallucination is a mental object, and a hallucinatory experience may be indistinguishable from non-hallucinatory experience, then even in a non-hallucinatory experience the immediate object of perception is a mental object.

C: In non-hallucinatory expericence the immediate object of perception is a mental object (sense-datum).

Indirect realismThe argument from illusion is a good argument against the

direct realist view. (i. e. we perceive directly the physical object itself)

C: In non-hallucinatory expericence the immediate object of perception is a mental object (sense-datum).

C supports the indirect realist view about perception.

Indirect realism: We perceive physical objects in virtue of mental objects.

We immediatly perceive mental objects, we don't perceive immediately the physical objects

We do not (and cannot) perceive the external world as it really is. Instead we know only our ideas and interpretations of the way the world is.

Direct vs. indirect realism

Indirect (representative) realism

Indirect realist's analogous conception of perception: mirror, image on television screen.

There are intermediary objects of perception, between the object and the perceiver.

We are directly aware of mental images, not the real physical thing itself.

These mental „images” have many names: impression, idea, sense-data.

Indirect realism as a form of realism

Realism: The external, physical object exists independly from perceiver. The object retains some at least of its properties even when it is unpercieved.

An indirect realist believes our ideas of the world are derived from a real external world (unlike idealists).

Another arguments for indirect realism

Time-lag argument:

1. When we perceive an object (such as a star), it is possible that the object has ceased to exist by the time we perceive it.

The object of perception is not present to us at the moment of perception.

Therefore what we percieve that cannot be the object (star) itself.

We perceive an intermediary, mental object (idea).

2. Perception of an object must be indirect in all other cases, because there is always a time-lag even if only very short.

Though the object does exist, the state of object which is presented to us is not in existence at the moment of perception. (it is a past state of object)

Therefore the object itself cannot be the content of awareness.

Another arguments for indirect realism

Argument based on neuropsychology

Perception involves a succession of causal events such as the reflection of photons, bleaching of retinal pigments, and complex brain processes.

There are many states and processes in the brain intermediate between the external object and perception.

(Consider: There is a reverse picture of the external objects on the retina, and then our brain reverse it.)

It can only be perceived indirectly by means of the stimuluses on our retinal surface.

Indirect realism and neuropyshology

Sense-Datum theory

A form of indirect realism is sense-datum theory.

What is given in experience is not public physical objects, but sense-data.

Sense-data: element of experience, private, non-physical entities.

First person point of view: „It seems to me it is blue.”

They actually possess the various sensory qualities that a person experiences.

Epistemological problem with indirect realism

Problem of scepticism

If we are aware of sense-data, how can we have knowledge about external, physical objects?

If we cannot perceive immedietly the external physical object, we cannot compare it with our sense datas (mental representation).

How can we know that sense datum resembles to physical objects?

There is a „gap” between our mental representations and the real physical obejcts.

From the indirect realist point of view we cannot be sure that we have reliable knowledge about external objects. We can have knowledge only about our sense datas?

Phenomenalism

Phenomenalism is motivated by eliminating the sceptical problem of indirect realism.

We have certain knowledge about our sensations, and that's all. Phenomenalist denies the reality of physical world.

Phenomenalism is not a realist view.

The only reality is that we actually perceive or which can be perceived.

The objects of the world are really collection of experiences (or possible experiences).

Phenomenalism

Explanation of perception:

„My car is in the garage” = Whenever I open the door and I look into the garage, I would see my car.

Phenomenalists accept that „something” do exist when nobody perceive it, but it's not clear what is it.

John Stuart Mill: the „permanent possibility of perception” exists indepedenly from perception.

But: this kind of account of perception has problems.

Problems of phenomenalism

Explanation of perception:

„I see the wall.”

Realist's explanation: There was the wall all the time. This fact explains why do you see the wall.

Phenomenalist: There is something continously there, but it is not a physical object, but the permanent possibility of experience.

Explaning perception by means of a conditional: If certain conditions occur you would seem the wall.

Problem: But how can we know that this conditional is true?

? Appealing to past regularities of experience

Explanation of dispositional properties

The objects have dispositional properties (the knife is sharp, the glass is fragile, etc.).

The object behaves in a certain way or has certain effects, in certain circumstances.

But why? Why the glass is fragile? Why the knife is sharp?

Phenomenalist is not able to give a good explanation. She can only appeal to the regularity of past experience.

Realist has an explanation: the molecules of the object have a certain arrangement.

Qualities of the objects

We explain fragility by appealing molecular structure of the object.

The property of the glass (it is fragile) can be derived from its molecular structure.

Of course the molecules cannot be fragile, or not fragile either.

Quesiton: What properties are „real”, objective? How can we know what are the „real” qualities of the objects?

Given the various circumstances of perception: what properties of the perceived object are indepedent from perception?

Has the object color, taste or smell even if it is not perceived?

Distinction between two types of qualities

Argument for distinction between primary and secondary qualities:

When we explain our perception we don't need to suppose that these qualities are indepedent properties of the object.

Contemporary science explains why are we see colors. We appeal only to microscopical, pyhsical, chemical processes, but not colors.

Our explanation of an object looking green based on only relation between properties of object, brain, and conditions of perception.

Therefore: Scientific evidence shows us there are no such things in the „real”, physical world as color, taste, or heat (warm or cold). We have no reason to think that the „real” grass is green, which color is still remain even grass is unperceived.

Primary and secondary qualities

Locke's distinction:

primary qualities: mass, shape, size, molecular structure, electric charge, etc.

The primary qualities are real properties of the object. It has these properties indepedenly from perceiver.

Basis of the secondary qualities.

secondary qualities: color, taste, smell, heat.

The perceived object does not possess the secondary qualties indepedently from perception.

Color, taste, smell, heat: are properties of our way of being aware of external world, rather than indepedent property of the pyhsical world itself.

Primary and secondary qualities

Primary qualities: physical properties of the object, properties objects have that are independent of any observer, such as solidity, extension, motion, number and figure.

They exist in the thing itself, can be determined with certainty, and do not rely on subjective judgments.

Secondary qualities: properties that produce sensations in observers, such as colour, taste, smell, and sound. They can be described as the effects what things have on the perceiver.

Perceptions about secondary qualities does not provide objective knowledge about things.

Primary qualities are measurable aspects of physical reality. Secondary qualities are „subjective”.

Problems with this distinction

From scientific point of view:

Our representations of so-called primary qualities are produced by very similar brain processes to perceiving of the so called secondary qualities.

We see that the blackboard is longer than the table. But this experience is depend on certain circumstances (light, etc.) too.

Perceiving shape, size, mass can be considered as at least „subjective” as perceiving color or taste.

Causal theory of perception

How can we know that our perception „represents” properly the physical object?

How can we distinguish vivid hallucinations from real experiences?

Possible answer: Perceive an object is to be in a state that has some appropriate causal relationship to it.

There is an (immediate) causal relation between the real object (BME E building) and my experience. I percieve BME E building because BME E building is really there.

When I hallucinate or when I see an projected image there is no appropriate causal relationship between me and the object.

Causal relation is relation between my perceptions and the pyshical world, this relation cannot be directly perceived.