1. Everything's an Inference
Without a profound simplification the world around us would be an infinite, undefined tangle that would defy our ability to orient ourselves and decide upon our actions ... We are compelled to reduce the knowable to a schema.
-Primo Levi, The Drowned and the Saved
First baseball umpire: "I call 'em as I see 'em."
Second umpire: "I call 'em as they are."
Third umpire: "They ain't nothin' till I call 'em."
When we look at a bird or a chair or a sunset, it feels as if we're simply registering what is in the world. But in fact our perceptions of the physical world rely heavily on tacit knowledge, and mental processes we're unaware of, that help us perceive something or accurately categorize it. We know that perception depends on mental doctoring of the evidence because it's possible to create situations in which the inference processes we apply automatically lead us astray.
Have a look at the two tables below. It's pretty obvious that one of the tables is longer and thinner than the other.
Obvious, but wrong. The two tables are of equal length and width.
The illusion is based on the fact that our perceptual machinery decides for us that we're looking at the end of the table on the left and the side of the table on the right. Our brains are wired so that they "lengthen" lines that appear to be pointing away from us. And a good thing, too. We evolved in a three-dimensional world, and if we didn't tamper with the sense impression-what falls on the eye's retina-we would perceive objects that are far away as being smaller than they are. But what the unconscious mind brings to perception misleads us in the two-dimensional world of pictures. As a result of the brain's automatically increasing the size of things that are far away, the table on the left appears longer than it is and the table on the right appears wider than it is. When the objects aren't really receding into the distance, the correction produces an incorrect perception.