A Test for Consciousness?

Michelson-Gale-Pearson experiment/Universal History Archive/UIG/Bridgeman Images


Will we ever really know what, or even where, consciousness is? Is there any way to get at it scientifically, conclusively? Week by week we hear claims from neuroscientists that would appear to confirm the prevailing “internalist” view of consciousness. If the brain creates a representation in our heads of the world around us through the firing of neurons, the argument goes, then we can identify neural activity that corresponds to particular aspects of consciousness. They tell us that if this part of the brain is damaged it will affect our eyesight. If that part suffers, we will have difficulty moving through space. They show us images based on scans of electrical and chemical activity in the brain and how those images change when our experience changes. Yet there has been no progress in bridging the gap between this activity in the brain and the nature of our experience, the richness of our sensations of color, sound, touch, motion, or simply awareness.

How, then, can the internalist theory be tested and demonstrated scientifically? Will it ever really be possible to prove beyond all doubt that this neural activity is our experience? And if that can’t be done, is there any proof for an alternative account of consciousness? What about the hypothesis that Riccardo Manzotti has been setting out in these dialogues, that consciousness is actually external to the body? Are there any scientific experiments that could settle this debate?


—Tim Parks

This is the tenth in a series of conversations on consciousness between Riccardo Manzotti and Tim Parks.

Tim Parks: Riccardo, let me start with a very simple experiment, something anyone can try, that seems very much in favor of the internalists. When we look intensely at a field of red color and then shift our eyes to a white or grey surface, we see, admittedly only for a few seconds, but nevertheless very distinctly, an area of green. Since it is clear to anyone who has not been looking at red that there is no green on this white background, is it not evident that colors are generated in the brain?

Riccardo Manzotti: Well, first, you don’t see green but cyan, a greenish blue color.

Parks: Who cares! Surely the only thing that matters is that one is seeing a color that isn’t there.

Manzotti: I care, we should all care. When doing science we must be precise. It’s actually rather extraordinary that in current textbooks and even in scientific papers people are still claiming one sees a green afterimage after looking intently at red.

Parks: But…

Manzotti: It’s more important than you think. Let’s put in the colors right here for people to see and have them make up their own minds.

So, readers should stare at the red square for at least twenty seconds— if they’re using a small screen, they’ll need to get right up close—then move their eyes and look steadily at the light grey, whitish square, where they will now see a color afterimage. But what exactly?

Color A, or color B? If you are a standard color perceiver, a trichromat, what you have just seen is much closer to color A than B, that is, to cyan rather than green.

Parks: Ok, it works for me. And so?

Manzotti: Well, white, as you know, or this light grey is made up of all the colors. And it just so happens that if we take the red out of the white, we’re left with cyan. Not green.

Parks: But still, the paper is white, or greyish, not cyan. At least to anyone who hasn’t been staring at red.

Manzotti: If you had stared at green rather than red, then when you turned to the white you would see white minus green, which is magenta. And if you stared at red and then looked at a field of yellow rather than white you would see a green afterimage, which is yellow minus red.

Parks: Ah. What you’re saying is that what we see is dependent on what’s out there.

Manzotti: Right. And we can predict what we’re going to see. Staring at an intense color, the eye experiences something called chromatic fatigue. It becomes briefly blind to that color. So when it turns to look elsewhere, for a few seconds it does not pick up the color it’s blind to. Turning to white after looking at red, you see the cyan in the white. Then white takes over again.

Parks: So I’m seeing something that’s really there.

Manzotti: You are. That’s why it matters that we establish the exact color we’re seeing. Because it’s not produced in the head. It depends on what’s out there. It is what’s out there, for your altered perceptive faculties. And before we move on, let me just say that this is a classic example of how an orthodoxy—in this case the idea that experience, and in particular color, is all generated in the brain—leads to some sloppy science and even a denial of what anyone can go and check for themselves.


Parks: Let’s see if I can do better with my next challenge. Internalists often mention Wilder Penfield’s experiments. He managed to get people to have hallucinations by stimulating parts of their brains electrically during open brain surgery. Other neuroscientists have even managed to relate stimulation of a particular neuron to “seeing” a particular face, obviously in the absence of that face. Again this suggests that experience is generated by the brain; we don’t need the world around to see something.

Manzotti: Have you checked out the hallucinations Penfield reports?

Parks: No.

Manzotti: They are all rather everyday ordinary experiences. Seeing one’s wife entering the room. Hearing a friend’s voice.

Parks: And so?

Manzotti: Well, if experience were actually generated freely by the brain, isn’t it odd that it remains so strictly tied to the world? Why no colors that have never been seen before? Sounds never heard in reality? Why no experiences that clearly have nothing to do with the outer world? Even when we dream we are aware that the bizarre aspects of dreams are due to their superimposition or mixing of different elements of known experience. An elephant that’s pink, or green. A dog that can talk. Whatever.

Parks: But surely the point is that we’re seeing something that’s not there.

Manzotti: Tim, we discussed this in our conversation on dreams. The question of what’s “there” or what’s “now” is complex. The objects that make up our experience can be milliseconds or years away from our bodies. Photons take time to travel, neurons take time to send electrical signals. We have already suggested that although ongoing ordinary experience of the world follows a privileged neural path that makes it possible for the body to deal with phenomena immediately around it, there are also other paths, eddies as it were, where neural activity mills, or is somehow delayed, then released later in dreams, or when a surgeon stimulates a part of the brain electrically. But this does not mean the brain is creating experience.

Parks: I’m not entirely convinced by this. You can’t prove, scientifically, this idea of experience being buffered or delayed in neural eddies.

Manzotti: At this stage, no. Neuroscientists can’t disprove it, or prove that the experience is “generated” in the head. But let’s remember, we do science by forming a hypothesis, making predictions in line with that hypothesis, and inventing experiments that prove or disprove the hypothesis.

Parks: So how would that work in the case of consciousness?

Manzotti: Hypothesis: All our experience is made of physical things that have had some causal relationship with our bodies. In fact, if it could be demonstrated that someone has had an experience made up of elements that were never causally related to his or her body, my theory would collapse and—

Parks: Sorry. What about the congenitally blind painter, Turkish I think, who claims to see colors in his mind?

Manzotti: Esref Armagan. Okay. He was born with no eyes. However, he has spent all his life among people who talk about color and he refers to color with the common terms, the sky is blue, the grass is green, etc. But the colors have to be chosen for him when he paints them. He can’t see them, so it’s impossible for us to know what it means when he says he experiences them. There are many cases of congenitally blind people writing about color, but they usually admit these are simply words they learned. If color was concocted in their heads, without any contact with the outer world, why would they ascribe the right colors to the right objects, as it were, having never seen those objects?

Parks: I can see we’re not going to get very far with this. Your general prediction is that every experience will be traceable back to an actual physical property in the world. But when it comes to fleeting feelings and intuitions, any such tracing back becomes extremely complicated. And I want to be brutally definite. Can you invent a clear and concrete experiment and predict an outcome of that experiment that would prove your position? Accepting of course, that if the outcome is different, you are wrong.

Riccardo: Yes. Let me propose two. Neither is easy, but then again neither is impossible, and both are certainly easier than much of what neuroscience gets up to these days. The first requires a little surgery and a willing guinea pig.


Parks: Yourself?

Manzotti: I’m up for it, yes. Though no doubt some people will raise ethical objections. So, take an afferent nerve from a part…

Parks: What is an afferent nerve?

Manzotti: Simply a bundle of axons carrying an electrical impulse, or action potential, from an external physical phenomenon to the central nervous system. For example, mechanoreceptors are cells that respond to mechanical forces, such as pressure or distortion. They generate action potentials that head off towards the brain via the spinal cord. They allow the external world to be the cause of effects in the brain.

Parks: Ok.

Manzotti: Take an afferent nerve from a part of the body that is not of crucial importance, for instance a tactile nerve in the back. Then connect it to a transducer…

Parks: Explain.

Manzotti: A transducer is a device that picks up a phenomenon and transforms it into an electrical impulse. For example, artificial retinas and artificial cochleas are transducers, picking up visual and auditory phenomena. Connected to nerves in the eye or ear they offer forms of sight and hearing.

Parks: And what’s the phenomenon that the transducer in this experiment picks up? The one we’re going to attach to the nerve in your back.

Manzotti: Well, it has to be a transducer for a phenomenon human beings cannot pick up with their bodies. Ultrasound, infrared, electromagnetic fields. Let’s say infrared. After all, some species of snakes experience infrared.

Parks: We take the nerve in your back and hook it up to an infrared transducer. Your prediction?

Manzotti: Since my hypothesis is that experience is not created in the brain but selected by the brain and the body in the external world, it follows that if we extend the mechanisms of selection, we should be able to extend our experience accordingly. So I predict that as soon as that external phenomenon—in this case infrared—becomes able, through the transducer connected to the afferent nerve, to affect what is going on in my brain, I will begin to perceive the additional external phenomenon. I will have an experience of infrared if only because infrared is now causally connected to my brain.  

Parks: This sounds a bit like those attempts to convey visual information through tactile stimulators attached to the back of a blind person. A camera, or visual transducer I suppose you’d say, sends signals to a sort of plate placed on the back, and the person then learns to interpret the signals visually.

Manzotti: Right. But there are two important differences. First, those systems are not directly attached to the nerves. Second, the point of that research is to allow a person who is blind, but was once able to see, to learn a skill, that is, to respond appropriately to a new kind of visual stimuli—something he or she has done in the past reacting to stimuli from the eyes before he or she became blind. In my experiment, the transducer is fixed directly to the nerve, which puts the body in causal contact with a new phenomenon, not something previously experienced.

Parks: So, we do the experiment, and either you have a new experience, which is an awareness of infrared, or you don’t. But couldn’t the internalists claim that the nerve was, yes, stimulated from without, but that nevertheless what is experienced is experienced within, and is a representation of infrared, not the phenomenon itself?

Manzotti: Ha! They could. We would have established a need for the outside world to have the experience, but not the location of the experience.

Parks: So you’re only halfway there, or not even.

Manzotti: I said there were two experiments and the second attempts to deal with this objection. The idea this time is to prove that it is possible to have different experiences with the exact same neuronal activity. And the experiences would be different because the external world would be different.

Parks: How on earth are you going to do that?

Manzotti: First we need some optical reversing, or inverting, goggles, the kind that make everything look upside down. We know from previous experiments that if you wear the goggles continuously for a few days you adapt and your perception adjusts. You see things the right way up, the way they are, despite the goggles. Right? So, in this experiment, before giving a subject the goggles we present him with a simple visual stimulus, say, a big capital T. Then after he has worn the goggles a few days and adapted to them, we present him the same stimulus, but inverted—an upside down capital T.

Parks: I’m getting confused. Why?

Manzotti: Well, at this point we have a double inversion: the inverted T with the inverting goggles will cause the viewer the exact same retinal activity he had previously when there was an upright T without the goggles.

Parks: Got it. We’ve created the same retinal activity with different stimuli.

Manzotti: Right. And my prediction is that despite the retinal activity being the same, the viewer will see the stimulus upside down, as it really is.

Parks: Because he’s adapted to the goggles. Cunning.

Manzotti: Naturally, we would record the neural activity in both cases using a high-res fMRI (functional Magnetic Resonance Imaging). Here I’m predicting that the cascade of neural activity in the cortical area would be the same, while the experiences, as we’ve said, would be different and, crucially, correct, on both occasions. This, I think, would demonstrate that the experience is not a neural representation, not in the head, since in the head we have the same activity on both occasions, while the experience is different. Therefore, the experience must exist outside the brain.

Parks: Wait a minute! Wouldn’t the adaptation process that the wearer has gone through produce some variation in brain activity, and wouldn’t it be that variation that accounts for the different experience?

Manzotti: Yes and no. First, I should say that we’ll be recording neural activity related to visual stimuli, the way neuroscientists do when they establish neural correlates for visual experience. Haynes and Rees, for example, in 2006 succeeded in matching specific brain activity with specific visual experience. More remarkably, in 2011 Nishimoto managed to reconstruct the external visual stimuli that volunteers were responding to on the basis of their brain activity.

In light of these results, then, you might suppose that the adaptation that occurs when someone wears reversing goggles is the result of an inversion that takes place inside the brain. Yet we have no indication that anything of the kind takes place. It’s worth remembering that ever since the early 1600s, when Kepler did his work on human vision, scientists and philosophers have been puzzled by the optical inversion that occurs inside the retina and have looked for some corresponding re-inversion in the brain. Nothing has ever been found. As to adaptation to inverting goggles, evidence collected by Linden and Kallenbach in 1999 suggests that no change occurs in the orientation of neural activity in the visual cortex. Of course, one could always object that current brain imaging techniques have their limitations and that there may be hidden neural activities not yet observed, but the burden of proof would then be on the internalists to find such activity. This is an empirical question and needs to be settled empirically, not on the basis of prejudice or dogma.

Parks: Coming at this from another angle, don’t we already know that the same type of neural firing along a single axon can be correlated to different senses? In which case, even assuming your experiment works, would it really be such a revolutionary result?

Manzotti: You’re right, yes. And we also know that the same byte of memory can have different meanings, and again that the primary auditory cortex and the primary visual cortex have very similar structures with similar neural activity, yet one correlates to auditory experiences and the other to visual experiences. The point of my experiment is to create such a clear-cut situation that scientists would have to consider the obvious conclusion from all this data: that the experience is not located in the brain, but in the truly different phenomenon outside.

Parks: But do you believe that either of your experiments will be carried out in the near future?

Manzotti: At present we are stuck in a dead end where the orthodoxy, internalism, is entirely dominant, but no progress is being made as to the nature of consciousness for the simple reason that, as we showed in our earlier dialogues, this orthodoxy makes no sense at all. Rather than doing any real science, we are hearing fantasies about downloading consciousness into computers and the like. Perhaps in our next conversation we could consider this state of affairs and challenge internalists to disprove the hypothesis I have put forward.

Parks: By all means, let’s see where everyone stands and where they think they’re moving.

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