Feedback [in visual processing]

Most of the lowest levels of visual processing seem to involve only signals going successively from one layer in the eye or brain to the next. But presumably there is at least some feedback to previous layers, yielding in effect iteration of rules like the ones used in the main text. The resulting evolution process is likely to have attractors, potentially explaining the fact that in images such as "Magic Eye" random dot stereograms features can pop out after several seconds or minutes of scrutiny, even without any conscious effort.