fixation and prediction

LINK TO Professor Edward H. Adelson's proof and explabnation of his illusion at the MIT Department of Brain and Cognitive Sciences site.

No matter how much we intellectualize the various root causes of an optical illusion, and no matter how many times we revisit a favorite illusion, the fixed mode of seeing will not go away.

Optical illusions are set-piece, learning laboratories for how we perceive. They are artificial, contrived viewing situations. Like a good science experiments the variables are controlled. Optical illusions do not provide sufficient reason to reject the validity of what we see. Rather they pinpoint particular, stereotyped, genetically hard-wired aspects of a visual system that works extremely well.

Kimon Nicolaїdes and Betty Edwards

Improvisational Performance

Figure Drawing as Self-portraiture

Michael Markovitz

Astonishing as it seems the squares marked A and B in the famous Adelson illusion are exactly the same shade of gray. This is best proven by masking out the rest of the scene. The Photoshop color palette can also be used. What on earth is going on here?

We seem biologically predisposed to ignore color fluctuations caused by shadows and we tend to sharpen up and stereotype vertical and horizontal lines. No doubt the experience of previously seeing many geometric cylinders and checkerboards also plays into how the illusion is perceived. The conventions of “realistic” rendering with shading and shadow provides three-dimensional verisimilitude despite a cartoon-like appearance. It is reasonable to assume that semantic factors also come into play as we mentally name the squares and other shapes.

By a combination of nature and nurture fixed concepts become embedded as tacit knowledge. These fixed modes mostly lie below the level of conscious awareness. We are not at liberty to reject or jump out of them. In terms of the quest to draw—especially to draw something as familiar and compelling as other human beings—fixed concepts are both a blessing and a curse.

Take noses for example… Are we drawing the patterns of light and shade of this particular nose or the general concept of a nose? Do we dwell on the nose and hardly notice, say, the proportions of the forehead or the subtle convolutions of the chin? Must we always identify and name the nose? Do we slide into habit and always draw the same nose? Are those nasal orifices really jet black? Are we haunted by an idealized, Platonic nose?

Zeki and Platonic Concepts

Tacit Knowledge