PLOS One

Understanding the visual elements that scan as "natural" could mean better design for built environments.

Natural space sharpens the mind and improves the mood. This much we know.

But what are the particular properties of green settings that enhance our mental well-being? To start to answer, you'd have to know what visually scans as "natural"—not just obvious stuff like trees, grass, or birds, but basic features like light, color, and lines. A new study led by Marc Berman, a University of Chicago psychology professor, parses out these visual cues. It's a step toward helping designers, planners, and architects develop spaces that offer maximum mental benefits.

First, Berman's team showed 20 participants a grid of 15 digital images of various city parks, asking them to reorganize the grid according to how similar or dissimilar the images were (like images went in one corner, non-like images went to another).

Once participants were finished, the researchers ran their image-charts through a multidimensional scaling (MDS) algorithm to determine the "dimensions" that organized them. (Berman compares the process to applying MDS to a list of distances between U.S. cities. "It would produce a chart that gives you two major dimensions: east/west versus north/south," he says.)

The image above shows the plotted results of two MDS dimensions for one set of images. The x-axis shows dimension one, or what seemed to the researchers to be the most significant organizing dimension among the images: naturalness. "To our eyes, left to right, it was going more natural to more built or urban," Berman says.

But MDS doesn't actually tell you what dimensions are, only that they're there. So the researchers asked another set of participants to label the x and y axes, and found that indeed, a majority labeled the x-axis with words like "nature," "organic," and "man-made." The y-axis, or dimension two, was a bit trickier; people seemed to interpret it as organized by space or open-ness. Says Berman, "The most clear-cut was the first dimension, so that’s what we focused on."

The point of all this charting and labeling was to determine whether people identify nature as nature in the same way—whether you and I both see green space when we look at a picture of a park. After a final correlation test, Berman's team found that yes, people do have consistent views on what appears natural—a rarity in behavioral research.

But, then, to return to the first question: What makes those images look "natural"? Using image-processing software, Berman's team found that the most significant visual features were color saturation, the degree of diversity in the image's hues, and the number of straight edges versus non-straight edges.

The image above compares color diversity properties. (A) has less diversity in both hue and color saturation than (B), making it more natural-looking. Below, a look at how the researchers pulled out straight edges (B) from an image (A). Fewer straight edges increased an image's being perceived as natural. "Edge density" (C) also mattered—the more densely clustered the edges, the more natural an image looked.

The research has caveats, of course. Does looking at a Pollock painting, with all its curvy lines and across-the-canvas hues, produce the same salubrious affects as looking at a park? And how does abstracting nature into an image change its visual impact? These are questions Berman and his collaborators will keep pursuing.

Yet Berman, who calls himself an "environmental neuroscientist," says that the implications of this new research—sussing out what low-level, visual features scan as natural—could one day be hugely valuable to planners and landscape architects as they develop green space that's both aesthetically pleasing and brain-enhancing.

In fact, he says, it applies to all built environments. "If you’re in the office, and you have a window out to nature, you focus better. If you’re in a hospital, you recover faster. If you live in public housing, access to nature can lower crime," Berman says, referring to other studies in the field. "We’re taking it to a lower-level to say, what is it about that nature view that’s producing those effects? Because if someone doesn't have that window, maybe you could design a wallpaper that you might want in your home or work environment. You can design the built environment in more informed ways."

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