Faith, Meaning, and Experience

Part 1, Top-Down versus Bottom-Up Processing

At school I teach a class called "Cognition and Learning." It's a basic introduction to learning theory (classical, operant, and social learning) and cognitive science. 

Perhaps the greatest finding in cognitive science is that the brain is not a passive computational machine, taking in sensory input and crunching through all that raw data. The brain is, rather, active and anticipatory. The brain doesn't have time to churn through all the sensory input to compute, from scratch, the virtual real-time simulation we call consciousness. The brain has to guess, hypothesize, and anticipate. The brain has to fill in gaps with expectations, assumptions, and prior knowledge. The brain uses heuristics and rules of thumb. 

For most of our waking lives, the brain does this flawlessly. But sometimes we can trick the brain into making a wrong guess. A famous example is the Ames Room illusion. 

Whenever the brain compares visual images on the retina, it has to make a guess about if the two images represent a difference of size or distance. For example, a smaller image of a person on the retina can mean that a person is short or that they are average-sized but further away. By using a lot of visual cues, along with some general assumptions about the world, the brain can quickly sort out if an object is small versus far away. The Ames Room illusion, however, tricks the brain into making a wrong guess about size versus distance. Most rooms are square, so the brain is generally correct in assuming that people within a small room are about the same distance away. If so, any visual differences in their sizes has to be due to differences in their height, smaller versus taller people standing side by side in a room together. But in the Ames Room a person seems to shrink or grow as they walk around the room. How is that happening? Because the brain is tricked into thinking the room is square when it's actually trapezoidal. As the person walks around the room they are actually walking toward or away from the viewer. Normally, the brain would see this changing image as a change in distance. The person isn't "shrinking" but is simply walking away from me. Nor is the person "growing," they are simply approaching. The brain makes the reasonable guess that people stay the same size, so any change in their visual image--larger or smaller--has to be a change in distance. But the Ames Room, through cunning arrangement of the room, tricks the brain out of that assumption. If a person in the room can't be getting closer or farther from me the brain switches to the only other explanation left to it: The person is changing in size. People in the Ames Room look tiny or giant, rather than farther or closer way.

I'm using the Ames Room to illustrate the point I made above. The brain works with assumptions and hypotheses. And most of the time these guesses work. In a complex visual world, the brain has to quickly judge if things are small or far away, large or close at hand. And we hardly notice that the brain does this work so quickly and so well. 

The Ames Room illustrates what is called bottom-up versus top-down processing. Again, a lot of us think the brain is a "bottom-up" processor, that the brain pulls in raw sensory data to build up from scratch our experience of consciousness. It's like putting a puzzle together, each bit of sensory data a puzzle piece fit together until the fuller picture is revealed in consciousness. But most of our cognitive processes are not bottom-up, they are top-down. The brain begins with assumptions, predictions, prior knowledge, and expectations and then imposes those guesses and hypotheses upon incoming sensory data. We have the puzzle pieces in front of us, the sensory data, but we also have the picture on the cover of puzzle box set before us. We know where the pieces are "going" as we are putting the puzzle together. This is top-down processing, the brain sees what it expects to see.

Change blindness is another fun example of this. The work of Daniel Simons has shown how people often fail to notice changes in their environment, even big and obvious changes. Follow the link for an example of a classic Simons' study, where people don't notice that the person they are talking is replaced with a different person. Here's another version of that study. Change blindness is due to top-down processing. The brain makes the good guess that people don't change while we're talking to them, and uses that expectation to "fill in" its visual surroundings, seeing but not really seeing. And thus missing the change. 

But you know all this already! We all know that we see what we want to see and hear what we want to hear. Much of what we experience is coming from our own minds and is being projected onto the world. Our "experience" is a complex product of both bottom-up and top-down processing, the world we are experiencing along with how those experiences are being shaped and filled in by our beliefs, assumptions, expectations, knowledge, prior experiences, and desires. 

Now, what does all this cognitive science have to do with God? Well, ponder this question: How is your experience of God, or lack of experience, being affected by your top-down processing? How are your beliefs and assumptions about the world, your categories of the possible and impossible, shaping your experience of the world as a spiritual person? 

How are you seeing but not really seeing?