Figure 3 ~ Now you see it, now you dont

Take a look at the visual illusion of figure 3. Twelve pots, printed in light gray, surrounded a black cross. Now stare intently at the central cross. After a few seconds, you should see some of the gray dots fade in and out of existence. For a few seconds, they vanish from your awareness; then they pop back again. Sometimes the entire set goes away, temporarily leaving you with a blank page -- only to return a few seconds later with a seemingly darker shade of gray.

An objectively fixed visual display can pop in and out of our subjective awareness, more or less at random. This profound observation forms the basis of the modern science of consciousness. In the 1990s, the late Nobel Prize winner Francis Crick and the neurobiologist Christof Koch jointly realized that such visual illusions gave scientists a means to track the fate of conscious versus unconscious stimuli in the brain.

Conceptually at least, this research program poses no major difficulty. During the experiment with the twelve dots, for instance, we can record the discharges of neurons from different places in the brain during moments in which the dots are seen, and compare these recordings with those made during moments in which the dots are not seen. Crick and Koch singled out vision as a domain ripe for such investigations, not only because we are beginning to understand the great detail the neural pathways that carry visual information from the retina to the cortex, but also because there are myriad visual illusions that can be used to contrast vision and invisible stimuli. Do they share anything. Is there a single pattern of brain activity that underlies all the conscious states and that provides a unifying ‘signature’ of conscious access in the brain? Finding such a signature pattern would be a major step forward for consciousness research.

In their down-to-earth manner, Crick and Koch had cracked the problem open. Following their lead, dozens of laboratories started studying consciousness through elementary visual illusions such as the one you just experienced. Three features of this research program suddenly put conscious perception with in experimental reach. First, the illusions did not require an elaborate notion of consciousness --just the simple act of seeing or not seeing, what I have called conscious access. second, a great many illusions were available for study -- as we shall see, cognitive scientists have invented dozens of techniques to make words, pictures, sounds, and even gorillas disappear at will. And third, such illusions are eminently subjective -- only you can tell when and where the dots disappear in your mind. Yet the results are reproducible: anyone who watches the figure reports having the same kind of experience. There is no point in denying it: we all agree that something real, peculiar, and fascinating is going on in our awareness. We have to take it seriously. ~ Page 18/19