Макс Тегмарк - Life 3.0 - Being Human in the Age of Artificial Intelligence

To me, consciousness is the elephant in the room. Not only do you know that you’re conscious, but it’s all you know with complete certainty—everything else is inference, as René Descartes pointed out back in Galileo’s time. Will theoretical and technological progress eventually bring even consciousness firmly into the domain of science? We don’t know, just as Galileo didn’t know whether we’d one day understand light and matter. *4Only one thing is guaranteed: we won’t succeed if we don’t try! That’s why I and many other scientists around the world are trying hard to formulate and test theories of consciousness.

Experimental Clues About Consciousness

Lots of information processing is taking place in our heads right now. Which of it is conscious and which isn’t? Before exploring consciousness theories and what they predict, let’s look at what experiments have taught us so far, ranging from traditional low-tech or no-tech observations to state-of-the-art brain measurements.

What Behaviors Are Conscious?

If you multiply 32 by 17 in your head, you’re conscious of many of the inner workings of your computation. But suppose I instead show you a portrait of Albert Einstein and tell you to say the name of its subject. As we saw in chapter 2, this too is a computational task: your brain is evaluating a function whose input is information from your eyes about a large number of pixel colors and whose output is information to muscles controlling your mouth and vocal cords. Computer scientists call this task “image classification” followed by “speech synthesis.” Although this computation is way more complicated than your multiplication task, you can do it much faster, seemingly without effort, and without being conscious of the details of how you do it. Your subjective experience consists merely of looking at the picture, experiencing a feeling of recognition and hearing yourself say “Einstein.”

Psychologists have long known that you can unconsciously perform a wide range of other tasks and behaviors as well, from blink reflexes to breathing, reaching, grabbing and keeping your balance. Typically, you’re consciously aware of what you did, but not how you did it. On the other hand, behaviors that involve unfamiliar situations, self-control, complicated logical rules, abstract reasoning or manipulation of language tend to be conscious. They’re known as behavioral correlates of consciousness, and they’re closely linked to the effortful, slow and controlled way of thinking that psychologists call “System 2.”5

It’s also known that you can convert many routines from conscious to unconscious through extensive practice, for example walking, swimming, bicycling, driving, typing, shaving, shoe tying, computer-gaming and piano playing.6 Indeed, it’s well known that experts do their specialties best when they’re in a state of “flow,” aware only of what’s happening at a higher level, and unconscious of the low-level details of how they’re doing it. For example, try reading the next sentence while being consciously aware of every single letter, as when you first learned to read. Can you feel how much slower it is, compared to when you’re merely conscious of the text at the level of words or ideas?

Indeed, unconscious information processing appears not only to be possible, but also to be more the rule than the exception. Evidence suggests that of the roughly 10 7bits of information that enter our brain each second from our sensory organs, we can be aware only of a tiny fraction, with estimates ranging from 10 to 50 bits.7 This suggests that the information processing that we’re consciously aware of is merely the tip of the iceberg.

Taken together, these clues have led some researchers to suggest that conscious information processing should be thought of as the CEO of our mind, dealing with only the most important decisions requiring complex analysis of data from all over the brain.8 This would explain why, just like the CEO of a company, it usually doesn’t want to be distracted by knowing everything its underlings are up to—but it can find them out if desired. To experience this selective attention in action, look at that word “desired” again: fix your gaze on the dot over the “i” and, without moving your eyes, shift your attention from the dot to the whole letter and then to the whole word. Although the information from your retina stayed the same, your conscious experience changed. The CEO metaphor also explains why expertise becomes unconscious: after painstakingly figuring out how to read and type, the CEO delegates these routine tasks to unconscious subordinates to be able to focus on new higher-level challenges.

Where Is Consciousness?

Clever experiments and analyses have suggested that consciousness is limited not merely to certain behaviors, but also to certain parts of the brain. Which are the prime suspects? Many of the first clues came from patients with brain lesions: localized brain damage caused by accidents, strokes, tumors or infections. But this was often inconclusive. For example, does the fact that lesions in the back of the brain can cause blindness mean that this is the site of visual consciousness, or does it merely mean that visual information passes through there en route to wherever it will later become conscious, just as it first passes through the eyes?

Although lesions and medical interventions haven’t pinpointed the locations of conscious experiences, they’ve helped narrow down the options. For example, I know that although I experience pain in my hand as actually occurring there, the pain experience must occur elsewhere, because a surgeon once switched off my hand pain without doing anything to my hand: he merely anesthetized nerves in my shoulder. Moreover, some amputees experience phantom pain that feels as though it’s in their nonexistent hand. As another example, I once noticed that when I looked only with my right eye, part of my visual field was missing—a doctor determined that my retina was coming loose and reattached it. In contrast, patients with certain brain lesions experience hemineglect, where they too miss information from half their visual field, but aren’t even aware that it’s missing—for example, failing to notice and eat the food on the left half of their plate. It’s as if consciousness about half of their world has disappeared. But are those damaged brain areas supposed to generate the spatial experience, or were they merely feeding spatial information to the sites of consciousness, just as my retina did?

The pioneering U.S.-Canadian neurosurgeon Wilder Penfield found in the 1930s that his neurosurgery patients reported different parts of their body being touched when he electrically stimulated specific brain areas in what’s now called the somatosensory cortex (figure 8.3).9 He also found that they involuntarily moved different parts of their body when he stimulated brain areas in what’s now called the motor cortex. But does that mean that information processing in these brain areas corresponds to consciousness of touch and motion?

Fortunately, modern technology is now giving us much more detailed clues. Although we’re still nowhere near being able to measure every single firing of all of your roughly hundred billion neurons, brain-reading technology is advancing rapidly, involving techniques with intimidating names such as fMRI, EEG, MEG, ECoG, ePhys and fluorescent voltage sensing. fMRI, which stands for functional magnetic resonance imaging, measures the magnetic properties of hydrogen nuclei to make a 3-D map of your brain roughly every second, with millimeter resolution. EEG (electroencephalography) and MEG (magnetoencephalography) measure the electric and magnetic field outside your head to map your brain thousands of times per second, but with poor resolution, unable to distinguish features smaller than a few centimeters. If you’re squeamish, you’ll appreciate that these three techniques are all noninvasive. If you don’t mind opening up your skull, you have additional options. ECoG (electrocorticography) involves placing say a hundred wires on the surface of your brain, while ePhys (electrophysiology) involves inserting microwires, which are sometimes thinner than a human hair, deep into the brain to record voltages from as many as a thousand simultaneous locations. Many epileptic patients spend days in the hospital while ECoG is used to figure out what part of their brain is triggering seizures and should be resected, and kindly agree to let neuroscientists perform consciousness experiments on them in the meantime. Finally, fluorescent voltage sensing involves genetically manipulating neurons to emit flashes of light when firing, enabling their activity to be measured with a microscope. Out of all the techniques, it has the potential to rapidly monitor the largest number of neurons, at least in animals with transparent brains—such as the C. elegans worm with its 302 neurons and the larval zebrafish with its about 100,000.