Interesting excerpt from "Drawing on the Right Side of the Brain"...
One further complication of seeing needs mentioning. The eyes gather visual information by constantly scanning the environment. But visual data from "out there", gathered by sight, is not the end of the story. At least part, and perhaps much of what we see is changed, interpreted, or conceptualized in ways that depend on a person's training, mind-set, and past experiences. We tend to see what we expect to see or what we decide we have seen. This expectation or decision, however, often is not a conscious process. Instead, the brain frequently does the expecting and the deciding, without our conscious awareness, and then alters or rearranges - or even simply disregards - the raw data of vision that hits the retina. Learning perception through drawing seems to change this process and to allow a different, more direct kind of seeing. The brain's editing is somehow put on hold, thereby permitting one to see more fully and perhaps more realistically.