Edge Induction

It was twilight in Tannersville, New York. A light rain had been coming down steadily all day. I set up my easel under a store awning because I stupidly forgot an umbrella. The aroma of French onion soup beckoned from the restaurant across the street.

The sun must have set by now because the light was failing. The light from the sky seemed to have bluish cast in contrast to the warm lights that were coming on. But I wasn't sure. I could practically feel the cones in my eyes shutting down. Honestly I could hardly see what colors I was mixing on the palette, because I forgot a flashlight, too.

As I studied the scene I realized that I could easily see the sharply defined contours of the utility pole and the roofline against the bright sky. But I couldn’t make out the clapboards or the signs; in fact I really couldn’t see the windows or doors at all—except on the bright white building in the center of the picture. So I tried to paint the scene as I saw it: blurry and tentative.

This illustrates a principle called “edge induction.” When a subject is poorly lit or in shadow, some of the edges will be below the threshold where our eyes can discern a contour. A camera might be able to pick up all the edges in these dim zones, but not the human eye.

It's not just a matter of what the rods and cones can respond to. What happens without you knowing it is that your brain takes over where your eyes leave off. In dim conditions your visual cortex starts interpolating or inventing contours based on the few edges that you truly can see and on your prior knowledge of how things should look.

The brain wants to confirm the contours first, and then it quickly fills them in with textures, tones, and colors—almost like a coloring book. This happens instantly at an unconscious level, as was demonstrated in a study published last summer by researchers at Vanderbilt University.

The visual cortex is always busy constructing a detailed fabrication of the world, whether it has all the information or not, and it tricks you into thinking you’re seeing edges that really aren’t visible.

Painters shouldn’t seek out edges that aren’t there; in fact poetry often springs from deliberately placing edges into obscurity, as Meissonier did in this portrait of Dumas.

Let edges and details go out of focus in sub-threshold or shadow areas, as Gerome did with the shadow-side eye in this portrait of a peasant. If you like a painterly handling, here’s the place to use sketchy, soft brushstrokes. It’s perfectly OK to deny the viewer the chance to scrutinize the details too much.

For more about that Vanderbilt University study and the phenomenon of edge induction, link.
The last three images came from Art Renewal Center, link.

Tomorrow is the Art by Committee sketch challenge. Please get your sketches in by Tuesday at 6:00 pm. Eastern Time, USA. To read about the challenge, link, and then scroll down.