Perception

Adam Pautz

• Éditeur: Routledge
• Année: 2021
• ISBN:
  9781317676874
• Édition: 1
• Sujet: Philosophy
• Sous-sujet: Philosophy History & Theory

Perception is one of the most pervasive and puzzling problems in philosophy, generating a great deal of attention and controversy in philosophy of mind, psychology and metaphysics. If perceptual illusion and hallucination are possible, how can perception be what it intuitively seems to be, a direct and immediate access to reality? How can perception be both internally dependent and externally directed?

Perception is an outstanding introduction to this fundamental topic, covering both the perennial and recent work on the problem. Adam Pautz examines four of the most important theories of perception: the sense datum view; the internal physical state view; the representational view; and naïve realism, assessing each in turn. He also discusses the relationship between perception and the physical world and the issue of whether reality is as it appears.

Useful examples are included throughout the book to illustrate the puzzles of perception, including hallucinations, illusions, the laws of appearance, blindsight, and neuroscientific explanations of our experience of pain, smell and color. The book covers both traditional philosophical arguments and more recent empirical arguments deriving from research in psychophysics and neuroscience.

The addition of chapter summaries, suggestions for further reading and a glossary of terms make Perception essential reading for anyone studying the topic in detail, as well as for students of philosophy of mind, philosophy of psychology and metaphysics.

1

THE SENSE DATUM VIEW: EXPERIENCING VIRTUAL REALITY

When I see [or hallucinate] a tomato … I cannot doubt that there exists a red patch of a round and somewhat bulgy shape, standing out from a background of other colour-patches, and that this whole field of colour is directly present to my consciousness.

—H. H. Price (1932)

It becomes evident that the real table is not the same as what we immediately experience by sight or touch or hearing.

—Bertrand Russell (1912a)

When you see a sunset, you take it that the vivid colors you experience are really out there. In general, the character of your experience is inherited from the character of the world. This is called naïve realism. We value experience because we take it to reveal the world in this way.

The sense datum view of experience tells us that this is all wrong. Experience is not what it seems. It does not reveal the world at all. Experience is a rip-off, an elaborate hoax. The vivid colors of the sunset are not really out there. Sounds, smells, tastes, and so on, are also not out there in the world of physics. All that is out there are colorless particles and fields, or an evolving multidimensional wavefunction, or something equally alien. The life-like colored “objects” you experience are in fact mental images (“sense data”) constructed by the brain, and the space in which they reside is in fact a private mental arena. They are so life-like that you take them to be physical things (so you are duped into accepting naïve realism), but in fact they are quite different from physical things. Likewise sounds, smells, tastes, and so on, are only “in the mind”.

The 18th-century Scottish philosopher Thomas Reid remarked that “all philosophers, from Plato to Mr. Hume, agree in this, that we do not perceive external objects immediately, and that the immediate object of perception must be some image present to the mind” (1875: Essay 7). In the early 20th century, it was defended by two luminaries of “analytic” philosophy, G. E. Moore and Bertrand Russell. It was very popular until the 1950s. However, it has largely fallen out of favor and now has very few defenders.¹

Nevertheless, the sense datum view is important. First, there is a formidable case for the view. As we shall see, it provides a neat solution to a central puzzle about perceptual experience, the puzzle of how experiences present items in space but also depend on our internal sensory processing. Second, the problems with the sense datum view lead to the contemporary views we will discuss in the rest of the book.

Traditionally, the sense datum view is pitted against naïve realism. So in Section 1.1 we will begin with naïve realism. Then in Section 1.2 we will formulate the sense datum view. Finally, in Sections 1.3–1.10 we will look at arguments for and against the sense datum view.

1.1 Naïve realism: the window shade model

Suppose you view a ripe tomato on a table. Your experience has a distinctive phenomenological character. An experience of a lemon on the table would have a very different character. The central question in the philosophy of perception is the character question. What is it to have an experience with a certain character? What do differences in the character of experience consist in?

Naïve realists answer that for you to have the tomato-experience on this occasion is simply for you to experience the objective color and shape of the physical tomato itself. Experience involves a special mental relationship that “leaps the spatial gap” between you and the tomato. The character of your experience is simply constituted by your experiencing the bright redness of the tomato, its bulgy shape, and so on (see Figure 1.1).

Figure 1.1 Naïve realism. Thanks to Stuart McMillen (http://www.stuartmcmillen.com/) for the drawing.

More generally:

Naïve realism. At least in normal cases, differences in the character of your experiences are constituted by your experiencing different states (colors, shapes, spatial layouts, sounds, smells, etc.) of mind-independent objects.

Here I am using “objects” very broadly to include ordinary things like tomatoes, pure visibilia like the sky and rainbows, events like the movement of a bird in your peripheral vision, and whatever else you might experience.

Naïve realism is in the first instance an account of the character experience. But it also makes a big assumption about the character of the world. In particular, it presupposes realism about sensible properties, such as colors, audible properties, taste qualities, and smell qualities. It requires that, even before we evolved, the physical world was replete with all these sensible properties. Tomatoes were red, the sky was blue, the whistling wind made a high-pitched sound, sulfur had a bad smell, and so on. The so-called “qualia” were already in the world. In some versions, these sensible properties just are objective physical properties, even if they seem very different from physical properties: redness-as-we-see-it just is a way reflecting light, smells are just chemical properties, audible qualities are complex physical properties involving frequency and intensity, and so on.

You might wonder how naïve realism coheres with scientific thinking about experience. Many ancient thinkers, including Plato, Euclid, and Ptolemy, accepted the extromission theory of the physical process underlying seeing. They speculated that we experience the world by way of rays emanating from the eye (perhaps with infinite velocity). As Euclid said, “Rays [proceed] from the eye [and] those things are seen upon which the visual rays fall and those things are not seen upon which the visual rays do not fall” (Gross 1999). If the character of experience is constituted by what objects and states of affairs we see, via the rays emanating from the eye, then this is a form of naïve realism.

In the early part of the 17th-century scientific revolution, the work of Da Vinci and Kepler established the opposing “intromission model” that we now all accept. In fact, well before them, Alhazen (c. 965–c. 1040) had already mounted an empirical case for the intromission theory. It is now part of educated commonsense that objects reflect light into the eyes. (However, it is interesting to note in passing that, according to a recent study (Winer et al. 2002), 60% of college students still accept the extromission theory!)

Now you might think that the intromission model of the causal process underlying experience immediately refutes the naïve realists' account of the character of experience. As Bertrand Russell said, “The observer, when he seems to himself to be observing a stone, is really, if science is to be believed, observing the effects of the stone upon himself [and so] naïve realism is false” (1940: 15).

But naïve realists can resist this argument by accepting the window shade model of the role of the brain. For instance, go back to the example of viewing a tomato. Naïve realists can say that the long causal process from the object to the brain (the “inward-pointing arrow” in Figure 1.1) is what “opens the window shade” and enables you to experience the character of the object (the “outward-pointing arrow”). On this view, you do not experience the end result of the causal process that starts when light is reflected from the tomato and stimulates the receptors in your eyes, as Russell assumed. Rather, it is just a fact about the way perception works that you only experience the tomato that starts off the causal process. The brain processes play an enabling role: they enable you to experience the pre-existing color and shape of the tomato. They select what elements of the mind-independent world you get to experience.

You might wonder what naïve realists say about illusions and hallucinations. We will discuss that later. First we must understand the sense datum view.

1.2 The sense datum view: the brain as a virtual reality device

Since the sense datum view is strange, understanding it will take some time. That is the goal of this section; potential reasons to believe it will come later.

Briefly, sense datum theorists accept a “virtual reality model” of the role of the brain instead of the “window shade model”. The brain doesn't enable us to experience what it is already there; rather, it constructs a virtual model and it is this model that we experience.

The first thing to understand is that sense datum theorists differ from the naïve realists concerning what the world is like. We just saw that naïve realists accept realism about the sensible properties. The physical tomato on the table before you really is red. By contrast, sense datum theorists accept illusionism about sensible properties. In this, they follow a long tradition that started with the scientific revolution. Science shows that the tomato is nothing but a collection of extremely small, colorless particles, which reflect some other colorless particles into our eyes (Newton called them “corpuscles”). So the tomato may have the spatial property round. But it lacks the sensible property red. Similarly, a tree falling in a forest with no one around to hear it doesn't make a sound with pitch, loudness, or timbre. High mean molecular kinetic energy in a body of water can cause you to feel pain, but the pain is not in the water. As Galileo famously wrote:

I think that tastes, odors, colors, etc., only exist in consciousness; so that if the animal were removed, every such quality would be abolished and annihilated.

(Galileo 1623/1957)

But if, contrary to naïve realists, the tomato is not red, why does it so vividly seem to you as if a round and red object is there? The appearance of color needs to be accounted for.

We can approach the answer offered by sense datum theorists using a modern analogy. Consider a “virtual reality” (or “augmented reality”) headset that displays highly detailed images on a screen right before your eyes. Suppose it is wintertime and everything outside is white and grey. So you decide to program your headset so that it creates vibrantly colorful and detailed images in real time of the things in front of you. If you pick up a white and round snowball, a reddish and round image appears on the display that you see within the headset. If you wore the headset long enough and walked around, then you would be “fooled”: the colored images would appear to be in three dimensions and you would mistake them for real objects. It would be an immersive experience.

On the sense datum view, you already occupy a similar virtual reality scenario. Your own brain is an elaborate virtual reality device. For instance, return to your experience of “a tomato on a table”. On the sense datum view, even though you take all the colored items in your field of vision to be physical and public (a tomato, a table, your arms, etc.), they are in fact all parts of a super-realistic, ostensibly three-dimensional, non-physical “image” constructed by your brain. This image is akin to a super-realistic, elaborate hologram. On the traditional sense datum view, it is not to be found anywhere in physical space; it is neither located in the physical space before you nor in the physical space occupied by your brain. Instead, the entire spatial arena in your field of vision is in fact a non-physical, private space that is newly created by your brain whenever you open your eyes. The non-physical parts of this image – the red and round part, the table-shaped part – are called “visual sense data”. Sense data exist no less than physical objects – they are just very different from physical objects. You instinctively take these visual sense data to be the facing surfaces of physical objects (Russell 1912a: 24), but that is not what they are. It is all a big fake.

If you find the sense datum view impossible to believe, suppose you cross your eyes. Then everything in your visual field will “move” and “become double”. Then you can get the sense that it is all an image constructed by your brain, an image that you can move around by screwing up your eyes.

Likewise, if a friend comes in the room at looks at the tomato, she is really experiencing a distinct, ostensibly three-dimensional image in the different mental arena created by her brain.

Now we can see how sense datum theorists answer the question: if the physical tomato is not red – and indeed the entire physical world is colorless and alien – why does it so vividly seem to you (and your friend as well) as if a round and red object is there? The answer is that the physical tomato reflects light into your eyes, setting up a cascade of neural processing. This neural processing somehow conjures up a new little world: an ostensibly three-dimensional mental realm containing a red and round sense datum and other colored sense data.² It is this temporary and private world of sense data that you experience. So appearance corresponds to reality; but it is a mental reality constructed by your brain.

While the sense datum differs from the physical tomato i...

Table des matières

• Cover
• Half Title
• Series Page
• Title Page
• Copyright Page
• Dedication
• Contents
• Preface and acknowledgements
• Introduction: What is the puzzle of perception?
• 1 The sense datum view: Experiencing virtual reality
• 2 The internal physical state view: Experiences as inner modifications
• 3 The representational view: Experiencing as representing
• 4 How does experience represent the world?
• 5 The return to naïve realism: Experience as openness to the world
• 6 Conclusion
• Glossary
• References
• Index