KNOWLEDGE IN PERCEPTION AND ILLUSION

Following Hermann von Helmholtz, who described visual perceptions as u nconscious inferences from sensory data and knowledge derived from the past, perceptions are regarded as similar to predictive hypotheses of science, but are psychologically projected into external space and ac cepted as our most immediate reality. There are increasing discrepanci es between perceptions and conceptions with science's advances, which makes it hard to define 'illusion'. Visual illusions can provide evide nce of object knowledge and working rules for vision, but only when th e phenomena are explained and classified. A tentative classification i s presented, in terms of appearances and kinds of causes. The large co ntribution of knowledge from the past for vision raises the issue: how do we recognize the present, without confusion from the past. This da nger is generally avoided as the present is signalled by real-time sen sory inputs-perhaps flagged by qualia of consciousness.