Imagine that there was a generally acknowledged test for artificial intelligence, to find out whether a computer program is truly intelligent. And imagine that a computer program passed this test for the first time. How would you feel about it?

The most likely answer is: disappointed.

We know this because it happened several times. The first time was in 1966, when ELIZA passed the Turing test. ELIZA was a chatbot who could fool some people to believe that they talk with a real human. Before ELIZA, people assumed that only an intelligent machine could do that, but it just turned out that it is really easy to fool others. Other tests for intelligence were playing chess, playing a whole variety of games, or recognizing cat images. Machines can do all this by now, and this is awesome. And yet, every success sparked new disappointment, because we didn't find any magic ingredient, some quality that would make a difference between intelligent and non-intelligent. When the groundbreaking GPT-3 and DALL-E suddenly could write news articles or poetry, or could dream up snails made of harp... the main improvement was that they used more raw computation power than the previous versions.

If you find this disappointing, then you will also be disappointed by "Consciousness and the Brain" by Stanislas Dehaene. The book is the condensed wisdom of three decades of cognitive research, and it tells you what consciousness is, how it operates, and why we have it. The book actually answers these questions. But if you were hoping that the book would Resolve Philosophy, tell you What Makes Humankind Unique, or whether Free Will exists, it doesn't do that.

It only tells you what consciousness is.

Consciousness: What is it Not?

In order to study consciousness, we first need to recognize it. Dehaene's approach to this is simple and bold: a perception or a thought is conscious if you can report on it. If a test subject sees the word "range" on a screen, and you ask her to report what word she has seen, then the answer might be

1) "I have seen the word range", or

2) "What word? There was no word!?"

In the first case, she has seen the word consciously, in the second not. This approach is more radical than it seems. Researchers are very cautious to take introspection at face value. And rightfully so, since our introspection is often wrong. The beauty of Dehaene's approach is that he only extracts a single bit of information (yes or no). It turns out that there are experiments which differ only in a minimal aspect (e.g., a slightly longer or shorter time delay), and which trigger either 1) or 2) reliably across many trials and many test subjects. I'll describe a few such setups later, but the point is that you can trust the reports because different people consistently give the same answer in the same situation.

It is important to understand that Dehaene's book is only about this definition of consciousness. It is not about cognition (in the sense of abstract reasoning) or meta-cognition (the ability to reflect about your own thoughts). It is not about self-consciousness (being aware of oneself). And of course, there are other definitions of consciousness. The most compelling alternative calls Dehaene's concept conscious access and distinguishes it from conscious perception. But for this review, I will stick with Dehaene's definition.

Another different, though related concept is attention. For Dehaene, attention is the gating mechanism that decides which information is allowed to enter consciousness. But this process itself is unconscious: we are not aware of all the options that were considered and discarded, only of the winner. This notion of attention is broadly in line with the mainstream of the field, though the exact definition varies.

Controlling Consciousness

To understand consciousness, the first step is to understand how unconscious processing works. Some glimpses come from blindsight patients, who lose the ability to see consciously due to brain damage. This can affect their whole field of vision, or just one hemisphere, or even just specific forms like lines. But they remain able to unconsciously process what they see. They will automatically walk around objects in their way, even though they swear that they don't see them. The effect can also be artificially produced in monkeys.

Fortunately, there are also ways to make perception unconscious in ordinary people:

- You don't always perceive images consciously if they are presented with a low contrast, or for a short time.

- Binocular rivalry occurs if your two eyes are presented with different images. In this case, most of the time you don't see a weird overlay of the two images, but instead your conscious perception flips between seeing either one or the other. It's a bit like staring at ambiguous images, but more consistent. So at any point in time, you perceive one of the images consciously and the other unconsciously.

- Attentional blinking describes the effect that after a conscious perception, you are consciously blind for anything that you see in the next 200-300ms. Let's say you watch a fast stream of digits, each only visible for 100ms, and occasionally the stream contains a letter instead of a number. You are supposed to detect the letters. When you see an "M", this enters your consciousness, and you detect it. But if 300ms (three images later), there is another letter "S", you will not see it consciously. Actually, you will be sure that there was no "S" in the stream.

- With Transcranial Magnetic Stimulation (TMS) we can stimulate specific brain regions. By stimulating sensory areas, we can induce hallucinations, and we can either make them conscious or unconscious by regulating the strength of TMS. By interfering with the right region at the right time, we can also prevent real perceptions from entering consciousness.

All these setups are useful, but they are not 100% reliable, more like 80% at best. For example, binocular rivalry is different in autistic people. But there is one setup which works always, for everyone, and that is masking. In masking you see some shapes (the "mask"), then very briefly an image, and then the shapes again. If the image is shown for 30ms, then people do not consciously see it, while for 60ms they do. This works with almost 100% accuracy, and has become the main workhorse for consciousness studies. You can even mask only a part of the screen if you want. While subjects are presented with masked words, numbers, and images, the researchers can measure the brain activity with EEG, MEG, fMRI, or even implanted electrodes (for epileptic patients who have the electrodes for unrelated medical reasons). They measure how the skin starts to sweat and the body tenses up from the unconscious perception. And mostly easily, they measure how it affects the performance in a subsequent, conscious task. For example, seeing the word "bank" unconsciously will make you react faster to a related word like "money", an effect known as priming.

Jul 16, 4:41pm: Your Book Review: Consciousness And The Brain → Consciousness And The Brain