Abstract
Human observers show a strong aesthetic preference for images with amplitude spectral slope similar to that of natural scenes. However, the effect of the orientation in the 2D spectrum, which is quite different for different categories of scenes, is unclear. Here, we investigated the effect of the shape of amplitude spectrum on aesthetic preference. The test stimuli were scrambled grayscale images (8 x 8 degree) with 1/f^α spectrum averaged across orientation. However, spectrum slope varied as a function of orientation. The slope α was from -2.5 to -0.5 with 0.5 step at vertical/horizontal orientation. The slope of was ranged from α - 0.3 to α + 0.3 at the 45-degree oblique orientation. The observers pressed a key to indicate the aesthetics value as well as naturalness of the test stimuli on a 6-point Lickert scale. Our results showed that the preference rating was an inverted-U shape function of the averaged spectral slope. The peak of the preference function, however, shifted from averaged slope -2 to -1.25 with the slope difference between obligate and vertical/horizontal orientation. The naturalness ratings also showed an inverted-U shape function. However, it did not show a peak shift. Thus, the human aesthetic preference not only depends on the orientation averaged amplitude spectral slope as the previous research showed, but also on the shape of the 2D spectrum. The effect of the 2D spectral distribution on aesthetic preference, however, cannot be fully explained by naturalness of the test images. It implied that other factors than naturalness was involved, in which the properties were summarized by human visual system in evolution process.