Aesthetic preferences may have evolved as the brain’s energy-saving mechanism
One can spend hours watching a calm sunset or a clear night sky. These scenes are not only easy to watch, they can also be easy on the brain. People tend to like visual stimuli that require little cognitive effort to processthe researchers reported in December Nexus PNAS.
The brain is the most energy-consuming organ of the bodyand visual processing alone accounts for almost half of its energy consumption. Researchers have long studied how the visual system conserves energy. But the new study approaches the question from a different angle. “Not only is the visual system optimized for efficiency, but we might also have aesthetic preferences for efficient stimuli to process,” says Mick Bonner, a neuroscientist at Johns Hopkins University who was not involved in the study.
Neuroscientist Dirk Bernhardt-Walther of the University of Toronto and his colleagues suspected that such preferences might have evolved as cognitive shortcuts, helping organisms avoid excessive effort when navigating their environment.
To probe the energy consumed in visual processing, the researchers turned to an existing functional MRI dataset, in which four individuals viewed 5,000 images while their brain activity was monitored. Measurements of oxygen consumption in different parts of the brain provided an indicator of metabolic activity. The team also fed these images through an artificial neural network trained to recognize objects and scenes, using the proportion of “neurons” activated as an indicator of metabolic expenditure.
The researchers then compared these metabolic cost estimates – both human and artificial – to the aesthetic ratings of the images, collected from more than 1,000 online survey respondents who rated each image on a five-point scale. In both cases, the metabolic effort required to process the images was inversely proportional to their aesthetic ratings.
This negative correlation was stronger in high-level visual regions of the brain, such as the fusiform area of the face. responsible for face recognitionand the corresponding layers of the artificial neural network. This suggests, Bernhardt-Walther says, that most energy savings occur during advanced stages of visual processing such as object recognition rather than during low-level functions such as edge or contrast detection.
Previous studies have shown that people tend to like faces, and even cars, that look closer to the average than those that look different. We prefer the platonic version, says Bernhardt-Walther, probably because outliers force the brain to expend energy updating its internal models of what a face or a car looks like.
Metabolic cost may also explain pleasurable experiences beyond sight. Think of joy to solve a riddle after juggling and weighing several solutions. “The “aha!” The experience is deeply pleasurable because metabolic needs suddenly decrease,” explains Bernhardt-Walther.
Bonner says future work should examine whether metabolic costs directly cause aesthetic preferences, or whether both come from a common characteristic such as familiarity. Furthermore, we do not know what properties make certain stimuli more pleasant and more effective for the brain to process than others. “What precisely makes an image easier for the visual system to process remains a huge open question,” he says.
