Second-order motion conveys depth-order information.

Psychophysical and neurophysiological studies have revealed that the visual system is sensitive to both "first-order" motion, in which moving features are defined by luminance cues, and "second-order" motion, in which motion is defined by nonluminance cues, such as contrast or flicker. Here we show psychophysically that common types of second-order stimuli provide potent cues to depth order. Although motion defined exclusively by nonluminance cues may be relatively rare in natural scenes, the depth-order cues offered by second-order stimuli arise ubiquitously as a result of occlusion of one moving object by another. Our results thus shed new light on the ecological importance of second-order motion. Furthermore, our results imply that visual cortical areas that have been shown to be responsive to second-order motion may be extracting information not just about object motion as has been assumed, but also about the relative depth of objects.

[1]  Alan C. Evans,et al.  Cortical specialization for processing first- and second-order motion. , 2003, Cerebral cortex.

[2]  Adriane E Seiffert,et al.  Functional MRI studies of human visual motion perception: texture, luminance, attention and after-effects. , 2003, Cerebral cortex.

[3]  J. Hennig,et al.  The Processing of First- and Second-Order Motion in Human Visual Cortex Assessed by Functional Magnetic Resonance Imaging (fMRI) , 1998, The Journal of Neuroscience.

[4]  Thomas D. Albright,et al.  The interpretation of visual motion: Evidence for surface segmentation mechanisms , 1996, Vision Research.

[5]  Keith Langley,et al.  Computational analysis of non-Fourier motion , 1994, Vision Research.

[6]  T D Albright,et al.  Form-cue invariant motion processing in primate visual cortex. , 1992, Science.

[7]  A. Yonas,et al.  Kinetic occlusion: Further studies of the boundary-flow cue , 1990, Perception & psychophysics.

[8]  G. Sperling,et al.  Drift-balanced random stimuli: a general basis for studying non-Fourier motion perception. , 1988, Journal of the Optical Society of America. A, Optics and image science.

[9]  Valdis Berzins,et al.  Dynamic Occlusion Analysis in Optical Flow Fields , 1985, IEEE Transactions on Pattern Analysis and Machine Intelligence.

[10]  William B. Thompson,et al.  Analysis of Accretion and Deletion at Boundaries in Dynamic Scenes , 1984, IEEE Transactions on Pattern Analysis and Machine Intelligence.

[11]  George A. Kaplan,et al.  Kinetic disruption of optical texture: The perception of depth at an edge , 1969 .

[12]  C. Baker,et al.  Processing of second-order stimuli in the visual cortex. , 2001, Progress in brain research.

[13]  P. Cavanagh,et al.  Motion: the long and short of it. , 1989, Spatial vision.

[14]  W. B. Thompson,et al.  Relative motion: Kinetic information for the order of depth at an edge , 1987, Perception & psychophysics.

[15]  J. Gibson,et al.  The Change from Visible to Invisible: A Study of Optical Transitions* , 1969 .