Phantoms in the Brain: Probing the Mysteries of the Human Mind (41 page)

"red." Since you can imagine this more complex cascade happening without conscious awareness, doesn't it follow that consciousness is irrelevant to the whole scheme? After all, God (or natural selection) could have created an unconscious being that does and says all the things you do, even though "it" is not conscious.

This argument sounds reasonable but in fact it is based on the fallacy that because you can imagine something to be logically possible, therefore it is actually possible. But consider the same argument applied to a problem in physics. We can all imagine something traveling faster than the speed of light. But as Einstein tells us, this

"commonsense" view is wrong. Simply being able to imagine that something is logically possible does not guarantee its possibility in the real world, even in principle. Likewise, even though you can imagine an unconscious zombie doing everything you can do, there may be some deep natural cause that prevents the existence of such a being! Notice that this argument does not prove that consciousness must have a causal role; it simply proves that you cannot use statements that begin, "After all, I can imagine" to draw conclusions about any natural phenomenon.

I would like to try a somewhat different approach to understanding qualia, which I will introduce by asking you to play some games with your eyes. First, recall the discussion in Chapter 5 concerning the so−called blind spot—the place where your optic nerve exits the back of your eyeball. Again, if you close your right eye, fix your gaze on the black spot in Figure 5.2 and slowly move the page toward or away from your eye, you will see that the hatched disk disappears. It has fallen into your natural blind spot. Now close your right eye again, hold up the index finger of your right hand and aim your left eye's blind spot at the middle of your ex−

Figure 12.1
A field of yellow doughnuts (shown in white here). Shut your right eye and look at the small white
dot near the middle of the illustration with your left eye. When the page is about six to nine inches from your
160

face, one of the doughnuts will fall exactly around your left eye's blind spot. Since the black hole in the center
of the doughnut is slightly smaller than your blind spot, it should disappear and the blind spot then is "filled
in" with yellow (white) qualia from the ring so that you see a yellow disk rather than a ring. Notice that the
disk "pops out" conspicuously against the background of rings. Paradoxically, you have made a target more
conspicuous by virtue of your blind spot. If the illusion doesn't work, try using an enlarged photocopy and
shifting the white dot horizontally.

tended finger. The middle of the finger
should
disappear, just as the hatched disk does, and yet it doesn't; it looks continuous. In other words, the qualia are such that you do not merely
deduce
intellectually that the finger is continuous—"After all, my blind spot is there"—you literally
seethe.
"missing piece" of your finger.

Psychologists call this phenomenon "filling in," a useful if somewhat misleading phrase that simply means that you see something in a region of space where nothing exists.

This phenomenon can be demonstrated even more dramatically if you look at Figure 12.1. Again, with your right eye shut look at the small white dot on the right with your left eye and gradually move the book toward you until one of the "doughnuts" falls on your blind spot. Since the inner diameter of the doughnut—the small black disk—is slightly

smaller than your blind spot, it should disappear and the white ring should encompass the blind spot. Say the doughnut (the ring) is yellow. What you will see if your vision is normal is a complete yellow homogeneous disk, which will indicate that your brain "filled in" your blind spot with yellow qualia (or white in Figure 12.1). I emphasize this because some people have argued that we all simply ignore the blind spot and don't notice what's going on, meaning that there really is no filling in. But this can't be right. If you show someone several rings, one of which is concentric with the blind spot, that concentric one will look like a homogeneous disk and will actually "pop out" perceptually against a background of rings. How can something you are ignoring pop out at you? This means that the blind spot does have qualia associated with it and, moreover, that the qualia can provide actual "sensory support." In other words, you don't merely deduce that the center of the doughnut is yellow; you literally
see
it as yellow.7

Now consider a related example. Suppose I put one finger crosswise in front of another finger (as in a plus sign) and look at the two fingers. Of course, I see the finger in the back as being continuous. I know it's continuous. I sort of see it as continuous. But if you asked me whether I
literally see
the missing piece of finger, I would say no—for all I know, someone could have actually sliced two pieces of finger and put them on either side of the finger in front to fool me. I cannot be certain that I really see that missing part.

Compare these two cases, which are similar in that the brain supplies the missing information both times.

What's the difference? What does it matter to you, the conscious person, that the yellow doughnut now has qualia in the middle and that the occluded part of your finger does not? The difference is that
you cannot
change your mind
about the yellow in the middle of the doughnut. You can't think, "Maybe it's yellow, but maybe it's pink, or maybe it's blue." No, it's shouting at you, "I am yellow," with an explicit representation of yellowness in its center. In other words, the filled−in yellow is not revocable, not changeable by you.

In the case of the occluded finger, however, you can think, "There's a high probability that there is a finger there, but some malicious scientist could have pasted two half fingers on either side of it." This scenario is highly improbable, but not inconceivable.

In other words, I can choose to assume that there might be something else behind the occluding finger, but I cannot do so with the filled−in yellow of the blind spot. Thus the crucial difference between a qualialaden perception and one that doesn't have qualia is that the qualia−laden 161

perception is irrevocable by higher brain centers and is therefore "tamper−resistant," whereas the one that lacks qualia is flexible; you can choose any one of a number of different "pretend" inputs using your imagination. Once a qualia−laden perception has been created, you're stuck with it. (A good example of this is the dalmatian dog in Figure 12.2. Initially, as you look, it's all fragments. Then suddenly everything clicks and you see the dog. Loosely speaking, you've now got the dog qualia. The next time you see it, there's no way you can avoid seeing the dog. Indeed, we have recently shown that neurons in the brain have permanently altered their connections once you have seen the dog. )8

These examples demonstrate an important feature of qualia—it must be irrevocable. But although this feature is necessary, it's not sufficient to explain the presence of qualia. Why? Well, imagine that you are in a coma and I shine a light into your eye. If the coma is not too deep, your pupil will constrict, even though you will have no subjective awareness of any qualia caused by the light. The entire reflex arc is irrevocable, and yet there are no qualia associated with it. You can't change your mind about it. You can't do anything about it, just as you couldn't do anything about the yellow filling in your blind spot in the doughnut example. So why does only the latter have qualia? The key difference is that in the case of the pupil's constriction, there is only one output—one final outcome—available and hence no qualia. In the case of the yellow disk, even though the representation that was created is irrevocable, you have the luxury of a choice; what you can do with the representation is open−ended. For instance, when you experienced yellow qualia, you could say yellow, or you could think of yellow bananas, yellow teeth, the yellow skin of jaundice and so on. And when you finally saw the dalmatian, your mind would be poised to conjure up any one of an infinite set of dog−related associations—the word "dog," the dog's bark, dog food or even fire engines. And there is apparently no limit to what you can choose. This is the second important feature of qualia: Sensations that are qualia−laden afford the luxury of choice. So now we have identified
two
functional features of qualia: irrevocability on the input side and flexibility on the output side.

There is a third important feature of qualia. In order to make decisions on the basis of a qualia−laden representation, the representation needs to exist long enough for you to work with it. Your brain needs to hold the representation in an intermediate buffer or in so−called immediate memory. (For example, you hold the phone number you get from the information operator just long enough to dial it with your fingers.) Again this 162

Figure 12.2
Random jumble of splotches. Gaze at this picture for a few seconds (or minutes) and you will
eventually see a dalmatian dog sniffing the ground mottled with shadows of leaves (hint: the dog's face is at
the left toward the middle of the picture; you can see its collar and left ear). Once the dog has been seen, it is
impossible to get rid of it.

Using similar pictures, we showed recently that neurons in the temporal lobes become altered permanently
after the initial brief exposure
—
once you have "seen" the dog (Tovee, Rolls and Ramachandran, 1996).

Dalmatian dog photographed by Ron James.

condition is not enough in itself to generate qualia. A biological system can have other reasons, besides making a choice, for holding information in a buffer. For example, Venus's−flytrap snaps shut only if its trigger hairs inside the trap are stimulated twice in succession, apparently retaining a memory of the first stimulus and comparing it with the second to

"infer" that something has moved. (Darwin suggested that this evolved to help the plant avoid inadvertently shutting the trap if hit by a dust particle rather than a bug. ) Typically in these sorts of cases, there is only one output possible: Venus's−flytrap
invariably
closes shut. There's nothing else it can do. The second important feature of qualia—choice—is missing. I think we can safely conclude, contrary to the panpsychists, that the plant does not have qualia linked to bug detection.

In Chapter 4, we saw how qualia and memory are connected in the story of Denise, the young woman living in Italy who suffered carbon monoxide poisoning and developed an unusual kind of "blindsight." Recall that she could correctiy rotate an envelope to post it in a horizontal or a vertical slot, even though she could not consciously perceive the slot's orientation. But if someone asked Denise first to look at the slot and then turned off the lights before asking her to post the letter, she could no longer do so. "She" seemed to forget the orientation of the slot almost immediately and was unable to insert the letter. This suggests that the part of 163

Denise's visual system that discerned orientation and controlled her arm movements—what we call the zombie or the how pathway in Chapter 4— not only was devoid of qualia, but also lacked short−term memory. But the part of her visual system—the what pathway—that would normally enable her to recognize the slot and perceive its orientation is not only conscious, it also has memory. (But "she" cannot use the what pathway because it is damaged; all that's available is the unconscious zombie and "it" doesn't have memory.) And I don't think this link between short−term memory and conscious awareness is coincidental.

Why does one part of the visual stream have memory and another not have it? It may be that the qualia−laden what system has memory because it is involved in making choices based on perceptual representations— and choice requires time. The how system without qualia, on the other hand, engages in continuous real−time processing running in a tightly closed loop—like the thermostat in your house. It does not need memory because it is not involved in making real choices. Thus simply posting the letter does not require memory, but choosing which letter to post and deciding where to mail it do require memory.

This idea can be tested in a patient like Denise. If you set up a situation in which she was forced to make a
choice,
the zombie system (still intact in her) should go haywire. For example, if you asked Denise to mail a letter and you showed her two slots (one vertical, one horizontal) simultaneously, she should fail, for how could the zombie system choose between the two? Indeed, the very idea of an unconscious zombie mak−

ing choices seems oxymoronic—for doesn't the very existence of free will imply consciousness?

To summarize thus far—for qualia to exist, you need potentially infinite implications (bananas, jaundice, teeth) but a stable, finite, irrevocable representation in your short−term memory as a starting point (yellow).

But if the starting point is revocable, then the representation will not have strong, vivid qualia. Good examples of the latter are a cat that you "infer" under the sofa when you only see its tail sticking out, or your ability to imagine that there is a monkey sitting on that chair. These do not have strong qualia, for good reason, because if they did you would confuse them with real objects and wouldn't be able to survive long, given the way your cognitive system is structured. I repeat what Shakespeare said: "You cannot cloy the hungry edge of appetite by bare imagination of a feast." Very fortunate, for otherwise you wouldn't eat; you would just generate the qualia associated with satiety in your head. In a similar vein, any creature that simply imagines having orgasms is unlikely to pass on its genes to the next generation.