Perceiving direction of deformation-based motion

Transparent liquid flow deforms its background through light refraction, creating complex spatiotemporal patterns that challenge the visual system in discerning flow direction. This study investigates how the visual system perceptually resolves the direction of transparent liquid flow. Using two-dimensional 1/f noise as background, we sequentially deformed the noise with pre-defined displacement maps displaced across frames, systematically manipulating spatial frequency and displacement magnitude. Participants reported the perceived direction of deformation-based motion. The results emphasize the critical role of the relationship between the minimum wavelength and displacement magnitude. Performance declined when the displacement magnitude exceeded a certain proportion relative to the wavelength. Conversely, performance also dropped significantly under conditions of small displacements combined with low cut-off frequencies. Further analysis revealed the local deformation possibly hinders the detection of deformation-based motion. These findings enhance understanding of how global and local motion cues interact, providing insight into the visual systems processing of deformation-induced motion and transparency.