The Atheist's Guide to Reality_ Enjoying Life Without Illusions - Alex Rosenberg [75]
FIGURE 6.
When we look at Figure 6, the brain produces sensations of different brightnesses of the three target diamonds on each cube, even though the actual luminance values of all the diamonds is exactly the same. Because of the past history of how shadows have shaped the neural networks in the optical system from retina to brain, each of the three diamonds on each cube elicit a different sensation of brightness (even though they are all the same color).
Treating different packages of source, object, and medium as “the same” in luminance—by responding in the same way to them—is crucial to tracking things in the environment over time. It’s what enables us and other mammals to see a fire or the surface of a pond or a cliff edge as “the same,” even when clouds obscure the sun, when the flames or the waves change their reflective properties, or when smoke or mist obscures the fire or pond’s surface or the cliff’s drop-off.
The inverse optics problem is just one of many inverse sensory problems. There is an inverse acoustical problem, an inverse tactile problem, an inverse olfactory problem. They are all solved in similar ways. Humans and other animals navigate the world using a “rearview mirror.” It was created by a Darwinian process of natural selection operating in Earth’s environment over the last billion years or so. This hardwired rearview mirror gets a bit of fine-tuning in each of us, from birth onward. The fine-tuning results from operant conditioning, another Darwinian process of blind variation and environmental filtration for guesses that successfully navigate the demands of current environments. In your particular visual system and in mine, no amount of fine-tuning can overcome the evolutionary past. That is why the illusions in Figures 4, 5, and 6 continue to work, even when you know that they are illusions and you know how they trick us.
This research shows that conscious introspection persistently foists illusions on us. The visual system works so fast and so smoothly that we think of it as a continually updated “motion-picture record” of our surroundings. But this is an illusion. The visual system is continually producing the illusion of matching a target—the outside world—by processing variations—in luminance differences, for example—through the filter of stored guesses from previous environments. With luck, of course, there will be enough similarity between past and present environment for the inputs to produce behavior that is still adaptive. The illusions, of course, show that this is not always the case.
In a world where physics fixes all the facts, where there are no future purposes or past designs, where the second law drives all adaptation, Mother Nature had no alternative. She could only have built sensory systems that track the past, not the instantaneous present, still less the future, near or far. The surprise is that ongoing vision—“now sight”—tracks the distant past of our species along with our own childhood pasts. But the rearview mirror through which we watch the landscape go by is entirely hidden from introspection. Natural selection has produced in us the confident feeling that along with a little foresight, we have a lot of now sight, when all we ever really have is hindsight.
WE HAVE SEEN that consciousness can’t be trusted to be right about the most basic things: the alleged need for visual experiences to see colors and shapes, the supposed role of conscious decisions in bringing about our actions, even the idea that we have now sight instead of hindsight. If it can be wrong about these things, it can be wrong