What is it about the Mona Lisa, the Taj Mahal, or a dazzling nature scene that makes them so pleasing to contemplate? Is beauty really in the eye of the beholder, or is there some inherent quality that sets it apart? It’s an age-old question.
New research suggests that one visual wow factor may be related to a kind of laziness: What brings the most pleasure to the mind’s eye may be that which requires the least amount of energy for our visual systems to process. A team at the University of Toronto published the findings recently in PNAS Nexus.
Scholars have long proposed that pleasure may serve as a guide for humans and other living things as they navigate the universe: The things that are most delightful are also the ones that are most useful or beneficial to us. Some research seems to bear this out: The depiction of features of the environment that help the viewer adapt to their environment can make an image appear more pleasing, while those that could be harmful, such as the potential for concealed threats, often elicit dislike.
Read more: “What Is a Beautiful Experiment?”
But the University of Toronto researchers wanted to see if there were more fundamental ways that visual pleasure and fitness are linked, so they decided to measure the metabolic costs of aesthetic preference.
First, they tested a simplified model of the human visual system called a deep neural network by showing it nearly 5,000 real-world images of objects and scenes. Then they scanned the brains of actual humans while they were viewing the same images, to measure how much metabolic activity in the functioning human visual system—as measured by the number of active neurons—was associated with the aesthetic ratings of images. The beauty ratings for each image were determined through surveys of a population of more than 1,000 participants from Canada and the United States, who evaluated each image on a 5-point scale.
In both the humans and in the neural network model less really was more. The lighter the metabolic lift, the higher the aesthetic rank. The scientists also found that visual pleasure or, conversely, discomfort were closely related to how complex and “quintessential” an image was, and therefore how easy or hard it was to process.
The findings are specific to the perceptual system, not to any forms of higher cognition, the authors point out. The participants were asked to rate their level of pleasure when viewing each image, but were not encouraged to contemplate the forms further. So complex visual stimuli could elicit more pleasure with enough contemplation, the authors speculate. The scientists also suggest that the findings may hint at a reason why certain visual properties, such as spatial frequency or contours, can influence aesthetic experience: They may make it easier for the visual system to process and categorize a scene or object.
On a purely instinctual level, then, the most beautiful images may be the ones that make the brain’s job the easiest. 
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Lead image: Kotenko Oleksandr / Shutterstock
