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Shin'ya Nishida; Perception of coherent pattern in motion. Journal of Vision 2003;3(9):273. doi: 10.1167/3.9.273.
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© ARVO (1962-2015); The Authors (2016-present)
The first stage of visual motion processing is a bank of direction and spatial-frequency selective sensors. If the analysis of moving pattern is completely independent between different frequency bands, it should not be possible to properly integrate pattern information across spatial frequencies that are signalling different directions of motion. An analysis of the multi-slit view however indicates that even when motion detection fails for certain frequencies, we can see a spatially coherent pattern in motion. In the multi-slit view, horizontally moving letters presented through an array of vertical slits can be effortlessly read in spite of only a fraction of the image being actually presented at any instant of time. This phenomenon can be ascribed to the brain's spatiotemporal interpolation by direction-selective integration of spatial pattern information (Nishida, VSS'02). In order to determine the degree to which pattern information is recovered by the interpolation, I conducted a psychophysical reverse-correlation experiment. The result suggested that observers could see image components whose horizontal frequencies were slightly higher than the Nyquist frequency of the slit sampling, although these components, when presented alone, should appear to move in the reverse direction (motion aliasing). Although this finding could indicate the perception of the fragmented (and left-right reversed) pattern information in the aliasing components, it was found that the addition of the over-Nyquist components significantly improved the discrimination of normal letters from mirror writings. In addition, this improvement occurred only when these components were presented together with sub-Nyquist low-frequency components, which resulted in coherent pattern motion in the correct direction. These findings suggest that the moving pattern analysis involves a cooperative interaction between different spatial frequency bands that helps us see coherent dynamic visual scene.
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