Theories of perception
Aims of a
theory of
perception
A theory of perception aims to answer this basic question: what are the immediate objects of perception? When one has a perceptual experience
(e.g. seeing a table or smelling burnt toast) one is immediately or directly aware of something. The question that has concerned philosophers as
well as e.g. psychologists and cognitive scientists is what exactly it is we are perceiving in perceptual experience. We examine three ways of
answering this question. Direct realism maintains it is the object itself, which is in the mind-independent external world. Indirect realism agrees
there is an external world of physical objects. These cause in us internal mental objects (sense-data) of which we are directly aware. Idealism is an
anti-realist theory. There is no mind-independent physical world as we ordinarily think of it. Reality consists of minds and ideas. Objects are stable
bundles of ideas (sense-data) and it is these we are directly aware of.
In examining the issue of the nature of the direct objects of perception a theory must address the following.
What is the relationship between me (the subject) and the world? What causes my perceptual experiences?
How can one explain the relationship between appearance and reality? Is the world just as it appears?
How are non-veridical perceptual experiences to be explained? The problem posed by misperceptions, illusions and hallucinations.
What happens when an object is not being perceived? What can we know of it? What properties does it continue to possess?
Does realism lead to scepticism?
Some key terms
Perceptual experience.
Object of perception
External world
Mind
Mind-independent v mind-dependent
Realism –Direct/Indirect
Anti-realism - Idealism
Representative
Resemblance
Primary v. secondary property
Sense-data
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Position
Direct Realism
Dancy,
McDowell
Summary/For/Against
The immediate objects of perception are mind-independent objects and their properties. This can be articulated in a very naïve form the world is just as I experience it. Sensible properties are located in the objects. Something like this is the view of the unreflective ‘man
in the street’ and the much more reflective view of medieval theories of perception.
Most modern philosophers hold a version of scientific (common-sense) direct realism. The world is as it seems under normal conditions
for human observers: there are, outside of my mind, physical objects at least some of whose sensible properties are located in these
objects (c.f. primary properties).
Common-sense motivation: if I see a red tomato, surely there’s a tomato out there that is red.
But –
Argument from perceptual relativity: a red tomato looks grey in dark light but surely isn’t. We must distinguish how things look from how they
are. (Russell’s table)
Argument from illusion. A stick placed in a glass of water looks bent – but that doesn’t mean it is. We must distinguish how things look from how
they are.
Time-lag argument. There is a delay between an object having a certain set of properties and my perceiving it as such (e.g. stars). So, I cannot
see the world as it is.
Argument from science: science tells us the world is radically different from how it appears.
Argument from hallucination: any veridical experience is indistinguishable from a hallucination. So, what I experience doesn’t depend on
whether it is caused by the world or my mind. So, experience doesn’t depend on the world and so I can’t directly perceive the world, only directly
perceive the ‘common layer’ of experience common to hallucinations and veridical experience. This common layer is made out of sense-data or
ideas or impressions.
Responding –
Time-lag argument confuses two sense of ‘immediate’. It relies on the temporal sense (straight-away; simultaneous), but direct realism is using it in
the sense of unmediated.
Common-sense revisited. We distinguish between how things look and how things are. It doesn’t follow that if something looks a certain way that
there exists something (e.g. internal mental object/a set of sense-data) that is that way. A bent-stick appearance doesn’t mean there is something
bent I see. I see a straight stick that looks bent. Compare: I see a badger that looks like a skunk. It doesn’t follow that there is some skunk-like
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creature I ‘really’ see. I simply see a badger that looks like a skunk.
We can explain perception in terms of the causal connection between the object in the world and the brain states it causes. Perceiving is a
happening in one’s brain, a change from one state to another. Seeing something is thus not an awareness of an inner mental object caused by an
object.
How to explain errors? Well, perceptual states are (at least in part) representational states – belief states. To this extent, the direct realist faces the
more general problem of explaining why we from false beliefs. One suggestion is that in certain conditions an object brings about a brain state that
does not accurately represent the object bringing it about.
That leaves the problem of hallucination. Here, we can appeal to McDowell’s disjunctivism. Perceptual states are individuated by the object
causing them, not just by the internal appearance. A veridical perception of x is not the same perceptual state as an hallucination of x. So, the
problem of explaining the identity of the states does not get off the ground. [Link – externalism]
Indirect
Realism Representative
/ Indirect
Realism
Locke, Hume,
Descartes,
Russell
I experience sense-data or ideas (Locke) or impressions (Hume) direct. These are caused by mind-independent objects and the
collections of sense-data represent the world beyond, which I thus perceive indirectly.
Reflection on hallucinations and dreams: our experience is the same whether it is real or hallucinatory. What we see directly must be private,
mental objects – sense-data or ideas or images or impressions.
Science and the primary/secondary quality distinction: Objects possess intrinsically mind-independent primary properties of e.g. shape and
size, solidity, motion or rest, location, number. No matter how an object changes, it will possess such properties. These primary properties can be
measured and described in mathematical terms. They are the ultimate bsis for scientific investigation. which can be investigated by science
(physics). Secondary properties can be destroyed through e.g. the division of an object (Lockean examples). Such secondary properties as colour,
smell, taste are mind-dependent in as far the experiencing of something as e.g. red involves a particular kind of sensation or qualitative experience
for creatures like us. The redness of a tomato does not exist in the tomato but in me (as a property of a sense-datum). Science tells me the world
is made out of atoms. To say a tomato is red means (i) that the tomato is made out of atoms arranged in such a way that they reflect certain
wavelengths of light and (ii) the effect this has on normal human observers is the production of a certain sensation. The sensation of heat
produced by a fire is in me not the fire – the same fire can produce a pleasant warmth or a painful burning sensation depending on where I stand.
Realism. We know there’s a world out there because perceptions of an organised world occur against my will. I cannot decide what to perceive.
The existence of the external world is the best hypothesis of my perceptual experience. But, that does not mean it is just as I perceive it.
But –
Sense-data are strange. They are mental objects but where do they exist? Not in the world – if we can’t see a table ‘out there’ directly because we
might be hallucinating then we’ll have the same problem for sense-data out there. Not in the brain – go have a look. In a non-physical mind? But
such things are unpopular: we think the mind is the brain.
Scepticism and solipsism. I can’t know for certain if there is a real world out there – sense-data constitute a veil of perception. Perhaps there is no
world out there and everything that exists is a product of my mind (solipsism). Just because I experience an organised world against my will,
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doesn’t mean it’s out there. It could be a complex hallucination or the product of the Matrix. But these conclusions are surely absurd.
The Primary/Secondary Quality distinction. As Locke drew it, my idea of a table resembles the table as far as primary qualities go but not as
secondary qualities go. But my idea of solidity (primary quality) does not resemble what solidity is (as physics tells me). It makes no sense to say
anyway that my 2D impression of a table resembles the 3D shape of the table. Finally, you can only say X resembles Y when you can compare X
and Y. But we can’t compare ideas with reality – only ideas with ideas as we are trapped behind a veil of perception.
Anti-Realism –
I experience ideas (sense-data) directly and this is all there is. Everything is made out of ideas in the mind of God which I can share in.
Reality consists of minds and ideas.
Idealism
Berkeley
Empiricism. Knowledge begins with the senses. So, we must understand the external world in terms of how it appears. So, strictly philosophically
speaking, to talk of an object is primarily to talk of a complex of appearances ‘it’ can present. Our experience of an object is ultimately to have a set
of perceptual experiences of sensible qualities. These experiences (as a set of ideas) are mind-dependent. Experience only warrants the view that
an object is a collection of sensible properties. What can we say of a sensible property? That is an experience of a certain kind of idea. So, if
objects are collections of sensible qualities and those qualities are ideas, then an object is a collection of ideas. The only way we can make sense
of a thing existing is as something we can perceive in some way – that is, as a collection of ideas: esse est percipi.
Common-sense. We know of the world through our senses. So, what more can there be to talking about something than to talk about the way that
it appears to us?
The Primary/Secondary Quality distinction collapsed. The distinction Locke drew is hopeless. Try to conceive of a bare material object
independently of how it appears. You can’t. e.g. I can’t imagine something being solid without thinking of it shaded a certain way or producing a
sensation of resistance when I push it. The reasons for thinking that secondary properties are mind-dependent also apply to our perception of
primary properties.
The Master Argument. You can’t conceive of something unconceived.
But –
Idealism rests upon ideas as the immediate objections of perception. This is the crucial complaint. If we reject the 17th century view and take
ourselves to have direct knowledge of things around us, we undercut the basis for the Principles argument. We reject the view that we only know
sensory ideas, and so we reject the view that sensible objects and qualities can be nothing more than collections of those ideas. We claim we do
perceive the world. Our experience of a tomato is not the experience of an inner tomato sense-datum but an experience of a tomato. The idealist
(along with the representative realist) mistakes the process of (directly) seeing the object with there having to be some thing in my mind of which I
am directly aware.
The Master Argument Refuted. Berkeley confuses the impossibility of conceiving of (e.g.) a badger without conceiving it (i.e. you can’t think of
anything without thinking) and the possibility of conceiving of something unconceived (i.e. we can easily imagine a badger unseen by anyone).
Common-sense. It goes against common-sense to think that there is nothing beyond appearances. We easily conceive of ourselves as things in a
world of things that appear certain ways to us in certain conditions.
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God. It commits you to a God whose Creation is a set of ideas we partake in. Not everyone will want this.
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