Sandra Blakeslee and Matthew Blakeslee (mother and son) co-authored a terrific new book, The Body Has a Mind of its Own, which we recommended and provided a review of a couple of weeks ago (here). In this post, we offer a brief excerpt from the book — a section providing a brief, fascinating description of the brain’s organization and the process of perception.
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[It is helpful to understand] a bit more about how the brain is organized. Almost all of your higher mental functions are carried out in the cortex—a thin sheet of tissue that is wrapped around older brain structures. About the size of a formal dinner napkin, it is massively folded so it can fit inside your skull. The entire cortical sheet has six layers of cells, each as thick as a single business card.
Although the cortex physically resembles a thin sheet, it is functionally organized into regions that specialize in different tasks, such as vision, hearing, touch, movement, and making plans. Furthermore, these regions are organized in hierarchies. Imagine a deck of cards laid out, faceup, side by side. Functionally the ace is higher than the jack, which is functionally higher than the eight, which is functionally higher than the two. The functional hierarchies in your brain are far more complex than playing cards, but the analogy should give you an idea of how hierarchies can exist in a nearly two-dimensional plane.
In the cortex, so-called lower areas absorb raw sensory information and pass it over to higher areas where it is processed and then passed over to still higher areas. But there is no ultimate top area where everything “comes together” . . . . On the contrary. Once information reaches higher regions, it is fed back down the hierarchy. Anatomists have found that in most areas of the cortex, for every fiber carrying information up the hierarchy, there are as many as ten fibers carrying processed information back down the hierarchy.
Researchers are still exploring the meaning of this massive feedback architecture, but one function is now clear: Your mind operates via prediction. Perception is not a process of passive absorption, but of active construction. When you see, hear, or feel something, the incoming information is always fragmentary and ambiguous. As it percolates up the cortical hierarchy, each area asks: “Is this what I expect? Is this what I predict? Does this conform to what I already know is the case?” So your brain is constantly comparing incoming information to what it already knows or expects or believes. As higher areas make sense of the input—“Yes, this is something I have seen before”—the information is fed back to lower areas to confirm that what you believe is happening really is happening.
But in many cases it goes beyond mere confirmation, and the back-fed prediction or belief actually alters the upward-flowing information to make it conform. The fact that the information travel “backward” down the cortical hierarchy all the way from higher, mentally sophisticated regions into lower levels of basic sensory processing means your predictions and beliefs can work against you. They do this by interfering with your ability to see things afresh, or even notice major contradictions between your expectation and what is actually present to your senses. For example, pity the ubiquitous husband who totally fails to notice that his wife has come home with a new hairstyle.
In other words, your understanding of reality is a far cry from reality itself. Your understanding of reality is constructed in large part according to your expectations and beliefs, which are based on all your past experiences which are held in the cortex as predictive memory. This is worth repeating: Many of your perceptions—what you see, hear, feel, and think is real—are profoundly shaped and influenced by your beliefs and expectations. And this includes beliefs about your body.