Wednesday, November 20, 2019

The Oblique Effect

Our visual systems are equipped with special cells in the visual cortex whose job is to detect vertically aligned edges, bars, and lines.

There are other simple cells that detect horizontal edges. And there's a third group of cells that detect diagonal ones.

Ivan Shishkin
According to Dr. Peter Hills, PhD., "Humans have more cells for horizontal and vertical bars than for oblique lines. Cats have cells for all orientations. So, humans find detecting horizontal and vertical lines easier than those of other angles. In other words, they have greater visual acuity for horizontal and vertical lines."

Our relative deficiency at judging diagonal angles compared to verticals and horizontals is known as the oblique effect. According to Wikipedia, "People are very good at detecting whether a picture is hung vertically, but are two- to fourfold worse for a 45-degree oblique contour, even when a comparison is available."

Another remarkable fact is that the relative number of these cells depends on the visual environment that we grow up in. People raised in forests have more vertical cells than people raised on the plains.
Quotes from Cognitive Psychology For Dummies
Wikipedia on The Oblique Effect.


Drake Gomez said...

Interesting to learn that there is a physiological basis for something that I think most artists have intuitively known all along. As for judging 45-degree angles, I often tell my students to question whether any diagonal would bisect (diagonally) an imaginary square. If so, it must be 45 degrees. I suppose this works because it goes back to the ability to more accurately judge verticals and horizontals, and to visualize them in the form of a square.

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