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Tatsuto Takeuchi, Karen K. De Valois, Harumi Saito; Perception of temporally-filtered moving natural images. Journal of Vision 2005;5(8):607. doi: 10.1167/5.8.607.
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© ARVO (1962-2015); The Authors (2016-present)
Unlike smoothly moving sinusoidal gratings, natural images that move contain many temporal frequencies. Human sensitivity to a pattern having a single temporal frequency has been measured. The purpose of this study is to examine how individual image components having different temporal frequencies affect our perception of the motion of moving natural images.
We prepared movies from natural images (running animals, aerial landscapes, river flow, moving car, and so on). Various filters were applied in the temporal frequency domain to the sequence of (luminance or color) variations of each pixel to obtain a temporally-filtered moving image.
In psychophysical experiments, we measured the perceived speed, motion direction and perceived smoothness of moving images. Subjects observed non-filtered and filtered movies in succession and judged which object in the two movies appeared to move faster and more smoothly. Subjects also observed a single filtered movie and judged the motion direction of an object in the movie.
Temporal filtering greatly affected the impression of motion. Perceived speed was underestimated not only when a low-pass filter was applied, but also in high-pass filtered images. Perceived smoothness was much greater in low-pass filtered moving images than in the original movies. The impression of motion direction was drastically diminished in the high-pass moving images. The appearance of band-pass moving images was more strongly negatively affected than that of low-pass moving images. Color information improved appearance when the temporal filter was applied only to the luminance components of moving images. We also manipulated the amount of filtering (number of pixels to which a filter was applied) and found that a small number of unfiltered pixels greatly improved the appearance of the moving images.
These results demonstrate that lower temporal frequency information in both luminance and color is critical for the appearance of moving natural images.
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