Our discussion of people, nonhuman animals, and robots shows you what consciousness is: the ability to feel events—to suffer the pains and enjoy the pleasures of life. Now let’s examine the psychological processes of consciousness in detail. We’ll begin with a classic theory of conscious experience called dualism. As you’ll see, dualism is intuitively appealing yet deeply flawed. Try to detect the flaws. Thinking critically about the drawbacks of dualism helps you to understand how the mind and brain do—and do not—work.

Dualism is a theory about the mind, the brain, and conscious experience. Dualism proposes that mind and body are two separate entities. The body is a physical, material object, whereas the mind is nonphysical—an immaterial “spirit.” According to dualism, the physical brain does not produce consciousness. Consciousness is a property of the nonphysical mind. The brain is merely the location at which the conscious mind and physical body interact.

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Dualism is an ancient belief. Buddhism, some philosophies in ancient Greece, and Christianity all posit a mind, or soul, that is distinct from the body and lives on after the body’s death.

In later Western philosophy, the most famous dualistic view was developed by Descartes, whose ideas we discussed earlier in this chapter. He proposed that the mind and body interact at a specific spot within the brain: the pineal gland (Figure 9.1). Why the pineal gland? His reasoning combined two ideas:

In Descartes’s dualism, the nonphysical mind views the images in the pineal gland, makes decisions, and directs the body’s actions by affecting mechanisms in the brain.

Today, scholars recognize that dualism is deeply flawed (e.g., Dennett, 1991). Two problems stand out: the mind–body problem and the homunculus problem.

THE MIND–BODY PROBLEM. Dualism claims that the mind influences the body. The mind perceives information in the brain and then directs the body’s action.

In saying this, dualism encounters the mind–body problem. The problem is that there is no way to explain how the mind influences the physical body without violating laws of science (Dennett, 1991). A basic principle of science is that only physical objects or forces (e.g., gravity or magnetism) can influence other physical objects. Since, according to dualism, the mind is nonphysical, it should be unable to influence the body.

THE HOMUNCULUS PROBLEM. The homunculus problem is a problem in scientific explanation (McMullen, 2001). It arises whenever a theory states that a structure in the mind or brain has conscious experiences. That structure is like a small conscious person-in-the-head: a homunculus. (Homunculus in Latin means “small human.”) Descartes’s theory worked like this. He said that the mind experiences information displayed in the brain. The mind thus was consciously aware of the information; it was a homunculus in the brain.

What’s the problem with a homunculus? If a theory claims that people are conscious because a structure in the brain is conscious, it does not solve the problem of consciousness. It merely introduces a new problem to be solved: Why is the structure in the brain conscious? The cartoon here illustrates the problem. If Descartes says that “the person whose brain is shown has consciousness thanks to the homunculus, who consciously experiences sights and sounds displayed in the brain,” then he has not explained why the homunculus has consciousness, and so has not provided an explanation of how consciousness occurs. Saying that “the homunculus has, in his brain, an even smaller homunculus” clearly does not offer any serious progress in explaining how consciousness works.

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A challenge for psychology, then, is to build a theory of consciousness that does not run into the mind–body or homunculus problems.

One theory that avoids the problems of dualism has been proposed by the philosopher Daniel Dennett and his colleagues (Dennett, 1991; Dennett & Kinsbourne, 1992; Schnieder, 2007). The theory has three main features.

The first feature involves the distinction between two potential activities of the mind: reproducing a stimulus in the environment, and detecting a stimulus in the environment. In Descartes’s theory, the brain reproduces stimuli; it essentially creates a picture of the world within the head. If a red arrow appears in front of someone’s eyes, the person’s brain reproduces the image (see Figure 9.1). Dennett realized, however, that to explain consciousness, you do not need to propose that the mind reproduces stimuli. Instead, it may primarily detect features of stimuli and, based on what it detects, make “educated guesses” about what is in the environment. If a red arrow is placed in front of you, different parts of your mind detect different features of this stimulus: its long shape, pointy top, color, orientation (pointing up), and so on. Once a few of these features are detected, you can infer—that is, make a good guess—that the stimulus is a red arrow, because a red arrow is just about the only thing that has all these features (long, pointy, etc.).

The second feature involves time. Dennett explains that different parts of the brain take different amounts of time to do their work. A brain mechanism that detects shape, for example, might work faster than one that detects color. This means there is no single place in the mind—no inner theatre—in which the world is reproduced at any one particular time. Instead, conscious experience is continually updated as different brain regions do their work (Dennett, 1991). Usually, this updating is so fast that you are not aware of it. But sometimes it unfolds slowly, and you can sense your brain at work. Look at Figure 9.2, which depicts a Necker Cube. After a second or two, your conscious experience changes, and then changes again; the cube periodically “flips” (sometimes the front appears to be in the lower right of the image, but sometimes it is in the upper left). There is no one fixed, static conscious experience of the image, as Descartes’s theory would have suggested.

Finally, in Dennett’s theory, there is no homunculus. No single part of the mind observes images and makes decisions. Rather, consciousness is based on the action of large numbers of psychological processes that occur simultaneously, in fractions of a second. These multiple processes each contribute to interpretations of what is happening outside the mind, that is, to conscious experience of the world.

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Dennett is not the only contemporary theorist to formulate a theory of consciousness. Others have proposed that consciousness consists of a “workspace” with connections to different regions of the mind that process information simultaneously. The connections enable the mind to combine information of different types (Dehaene & Naccache, 2001). Consciousness results from the overall pattern of connections, not from a single homunculus.

These contemporary theories have an interesting implication. They imply that when you shift levels of analysis from mind to brain, you should not expect to find any one brain structure that independently produces consciousness. Instead, Dennett’s theory—unlike Descartes’s—implies that large numbers of separate brain mechanisms will each play a role in constructing our conscious experiences. Let’s now look at consciousness from a biological point of view.

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