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Now, if you lengthen the delay a little, you see the word each time. There is even a specific delay where the subjects can see the stimulus half of the time. So now you are in business, because you have an experimental manipulation that you can reproduce in the lab, and that systematically creates a change in consciousness.

What do we see when we do these experiments? The first thing that we discovered is that, even when you cannot see a word or a picture, because it is presented in a subliminal condition, it does not mean that your cortex is not processing it.

For one fourth of a second, which is extraordinarily long for the brain, you can have identical activations, whether you are conscious or not. During this quarter of a second, the brain is not inactive and we can observe a number of instances of lexical access, semantic access and other processes (and subliminal processing can even continue after this point). But at about 270 milliseconds, 300 milliseconds in our experiments, we begin to see a huge divergence between conscious states and non-conscious states.

Our model proposes that this is really one of the main functions of consciousness: to provide an internal space where you can perform thought experiments, as it were, in an isolated way, detached from the external world.

However, if we now give you a task that involves two serial processing steps, you cannot do it. If I ask you to give me the number plus two, you can do it — but if I ask you to compute the initial number plus two, and then decide if the result of that +2 operation is larger or smaller than five, you cannot do it. It's a strange result, because the initial experiments show that you possess a lot of information about this subliminal digit. If you just named it, you would have enough information to do so correctly, much better than chance alone would predict. However when you are engaged in a chain of processing, where you have to compute x+2, and then decide if the outcome is larger or smaller than five, there are two successive steps that make performance fall back down to chance. Presumably, this is because you haven't had access to the workspace system that allows you to execute this kind of serial mental rule.

Now, after adaptation, the trick consists in presenting five identical tones: dit-dit-dit-dit-dit. This banal sequence becomes the novel situation now — the rare and unexpected one. Our claim is that only a conscious brain can take into account the context of the preceding series of tones, and can understand that five identical tones are something novel and unexpected.

The study is a big improvement over early experiments. In past studies, because researchers didn’t keep track of the same set of neurons, they had to reprogram the decoder every time to adapt to the new cortical activity. The changes also meant that the brain couldn’t form a cortical map of the prosthetic device. That limitation raised questions about whether paralyzed people would be able to use prosthetics with enough proficiency to make them really useful.

But perhaps more surprising, the researchers also tested a shuffled decoder. They took one of the existing decoders and randomly redistributed the weights in the equations among the neurons. This meant that the new decoder, unlike the early ones, had no relationship to actual movements of the monkey’s arm. It was a bit like giving a tennis player a hammer instead of a different racket.

What followed was a big surprise: After about just three days, the monkeys learned the new decoder. Just as before, practice allowed the neurons to develop a cortical map for the new task.