When complex is easy on the mind: Internal repetition of visual information in complex objects is a source of perceptual fluency.

Across 3 studies, we investigated whether visual complexity deriving from internally repeating visual information over many scale levels is a source of perceptual fluency. Such continuous repetition of visual information is formalized in fractal geometry and is a key-property of natural structures. In the first 2 studies, we exposed participants to 3-dimensional high-fractal versus low-fractal stimuli, respectively characterized by a relatively high versus low degree of internal repetition of visual information. Participants evaluated high-fractal stimuli as more complex and fascinating than their low-fractal counterparts. We assessed ease of processing by asking participants to solve effortful puzzles during and after exposure to high-fractal versus low-fractal stimuli. Across both studies, we found that puzzles presented during and after seeing high-fractal stimuli were perceived as the easiest ones to solve and were solved more accurately and faster than puzzles associated with the low-fractal stimuli. In Study 3, we ran the Dot Probe Procedure to rule out that the findings from Study 1 and Study 2 reflected differences in attentional bias between the high-fractal and low-fractal stimuli, rather than perceptual fluency. Overall, our findings confirm that complexity deriving from internal repetition of visual information can be easy on the mind.