For over 100 years, psychologists have known that most people prefer curviness over angularity in practically everything - from lines and shapes to faces, paintings and interior spaces.
Moreover, the phenomenon has been observed across cultures, in infants and even in great apes.
Yet, it remains unclear what it is about our perception of curvature that translates into this widespread preference.
"Now we have this advantage that we can probe the brain to see the mechanisms that are really driving this process," says Oshin Vartanian, an associate professor in the department of psychology at the University of Toronto who is appointed to Defence Research and Development Canada.
Using brain imaging data and computational measures of curvature, Vartanian worked with U of T PhD student Delaram Farzanfar, Dirk Bernhardt-Walther, a U of T associate professor of psychology, and an international group of collaborators to solve the mystery.
For the study, published recently in Scientific Reports , participants completed two tasks when presented with images of curvy and angular interior spaces. They judged each as either "beautiful" or "not beautiful" and decided whether they would choose to "enter" or "exit" the space.
Researchers found that there are regions in the brain that are sensitive to scenes participants perceive to be curvy, but only when they are judging its beauty. When a participant is asked to decide whether they would enter or exit the space, those regions are not sensitive to perceived curvature.
This observation suggests that the context within which we perceive curvature makes a difference in how our brain responds to it.
The regions of the brain that lit up to scenes participants perceive to be curvy, in the fusiform gyrus, are involved in higher-order visual processing like object recognition. They are also sensitive to the perception of faces.
In other words, these findings suggest that the region of our brain that specializes in distinguishing one face from another might also be sensitive to processing curvature in other contexts - such as looking at architectural spaces.
Researchers also found that images of spaces that participants perceived as curvy did not always match with computational measures of those same spaces. However, a region in the primary visual cortex shows sensitivity to computational curvature, regardless of the task.
"It's entirely possible that when a person looks at an image, they form a mental representation that's three-dimensional," Vartanian says. Such a representation eludes mathematical measurements of two-dimensional images.
Bernhardt-Walther adds that, going forward, researchers need to have a broader view of what parts of an image translate into a sense of curviness that people perceive as aesthetically pleasant.
"Artists and designers are way ahead of scientists. They already use organic, curvy lines to evoke a sense of comfort, aesthetic pleasure and hominess," says Bernhardt-Walther. "Our work provides a scientific underpinning for their intuitions and may guide them on using curvature more deliberately as a design element to generate aesthetically pleasing forms or, alternatively, to use angularity to challenge and engage the viewers."
Farzanfar, meanwhile, says the research is not only relevant to the work of neuroscientists and psychologists, but to artists, designers, architects and city planners.
"I think as we understand how spaces impact our mood and cognition, we can create better environments for our health and enrich the experience of modern life for many people," she says.
