Fractal dimension links responses to a visual scene to its biodiversity.

Humans appear to have an innate, beneficial response and preference for natural over urban scenes, yet “natural” is an ambiguous concept that varies from culture to culture. In looking for a commonality to natural scenes that tends to be lacking in built scenes, many researchers have turned to fractal geometry, finding that fractal dimension can predict preference. Here, I calculated the fractal dimension of the dominant land-sky edge at a variety of sites having varying depths of water table and levels of biodiversity (specifically, “species richness”). I then investigated changes in human physiological arousal (magnitude of skin conductance responses) in response to images of those scenes. Sites with high biodiversity were shown to have a significantly higher associated fractal dimension than low-biodiversity sites, whereas shallow versus deep water-table sites showed no significant difference. When shown the images, the magnitude of skin conductance responses for human viewers showed a negative correlation with fractal dimension. Replicating earlier findings, ranked preference for a scene showed a positive correlation with fractal dimension. Taken together, these findings suggest an evolved response to stimuli associated with a healthy ecosystem: Patterns of healthy vegetative growth determine visual fractal dimension, which reduces physiological arousal upon observation, this being experienced as a positive emotional state and expressed as a preference for that environment.

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