Trends in Cognitive Sciences has a nice review on the 'top-down' cognitive direction of visual perception. We see more when we are expecting to see more. It's like this gray and black picture below. At first glance, we may not recognize it, but with further inspection we can fill in and organize what we see into a figure.
Many people are aware of these sorts of 'eye tricks' in the form of optical illusions. But, visual perception has extensive relevance to many aspects of learning, expertise, and some forms of disability.
Perceptual learning is big news because it highly trainable and involves 'rewiring' the brain. Computer-based programs are ideal for perceptual training, but existing commercial programs are fairly simplistic, although that probably won't be for long.
Training in visual perception has powerful implications for many groups and conditions, including athletes, workers who require visual discrimination as part of their occupations (quality control, air traffic controllers, umpires, chemists, architects, engineers etc.), visual experts (artists, bird watchers, antique appraisers, chess masters etc.), and children and adults who have conditions such as dyslexia, nonverbal learning disabilities, visual distractibility, prematurity (periventricular leukomalacia), or autism.
What can you do now, if you have a child with visual perceptual problems? First look for visual factors that may improve or detract from their visual ability. Vary the light intensity, color, and visual crowding. Could there be a problem with seeing movement? If so, slow it down. Try simplifying visual settings to see if it helps their visual search or orientation. Use words and touch to help them correct visual errors, spatial mistakes or size distortions. Have them draw and build, and give them plenty of time to study and compare what they see with what they perceive in terms of space. Many adults are able to compensate very well for visual perceptual problems, but they had to learn it gradually.
Visual Perceptual Learning
Cutting through the Clutter -PLos brief
The Principles of Artistic Illusions
Visual Shape Learning pdf