Try drawing a 3-d box. What exactly about it makes it look 3-d, even though we all know that a drawing on paper is 2-d? In order to make the box look 3-d, you first have to make sure that all the lines are connected. You also have to make sure the lines are at a certain angle to induce the 3-d effect. But why exactly do we use these strategies to make our visual system perceive depth or dimension in something that is 2-d?
Artists use these strategies and capitalize on how the brain perceives and processes information through the visual system. Artists can manipulate an image to induce the perception of 3-d or depth by creating an illusion. For instance, if an artist wants to convey depth in an image, they have to draw lines in certain ways to form angles consistent with a 3-d corner, which in turn causes viewers to perceive depth in the image. Artists can also manipulate the perception of depth by changing the steepness or the pattern of the angles (Shapely & Maertens, 2008). For example, Disfigured Circle (1970) by Bridget Riley is a piece of modern art that produces the perception of depth and 3-d by aligned angles.
The perception of depth can also be created by occlusion, or the absence of lines (Shapley & Maertens, 2008). In the Kanizsa triangle example, the viewer perceives the illusion of a triangle shape in the middle because of the presence of the contours surrounding the perceived triangle (Kanizsa, 1979).
Angle alignment can also evoke the presence of other types of illusions (Shapely & Maertens, 2008). For instance, the pattern of zigzag lines creates an illusory contour and the perception of folds.
Shapley and Maertens (2008) examined this effect of angles on illusions by testing whether misaligned angles created the same perception of depth as aligned angles. When the angles were misaligned by only 10% of the line length, the apparent depth of the image disappeared (Shapley & Maertens, 2008). These results highlight the importance of connecting angles in a precise way in order to induce the perception of depth in an image.
When you first encounter an image, your perception of the image is processed through the ventral pathway visual cortex (Connor, Brincat, & Pasupathy, 2007). Though the process is very complex and some parts are still undiscovered, it is well-known that incoming information through the retina is processed by the ventral pathway, which codes the object’s information into separate categories. This information is then sent to other parts of the brain that are specialized in processing these categories, such as face, body, and scene processing (Connor, Brincat, & Pasupathy, 2007). Previous research has shown that in macaque monkeys, one-fourth of the neurons in the V2 visual area of the visual system are activated when viewing angled lines (Plebe, 2007). This gives evidence that the 3-d processing of illusions may possibly occur within the V2 area of the visual system.
Though much remains to be discovered about the underlying neuronal mechanisms of the visual system, there are many ways to capitalize on the makeup of the visual system to create 3-d perception. The connection of lines and alignment of angles is necessary for 3-d perception of an image (Shapley & Maertens, 2008). Artists manipulate this aspect of the human visual system in order to induce a 3-d effect in 2-d artwork. Next time you encounter a piece of art that evokes this 3-d perception, it is important to appreciate the artist’s hard work in angle alignment, because it’s not always easy to get the right angle!
Connor, C. E., Brincat, S. L., & Pasupathy, A. (2007). Transformation of shape information in the ventral pathway. Current opinion in neurobiology, 17(2), 140-147.
Kanizsa, G. (1979). Organization in vision: Essays on Gestalt perception. Praeger Publishers.
Plebe, A. (2007). A model of angle selectivity development in visual area V2. Neurocomputing, 70(10), 2060-2063.
Shapley, R., & Maertens, M. (2008). Angle alignment evokes perceived depth and illusory surfaces. Perception, 37(10), 1471-1487.