The effect of spatial layout on motion segmentation

We present a series of experiments exploring the effect of the stimulus spatial configuration on speed discrimination and two different types of segmentation, for random dot patterns. In the first experiment, we find that parsing the image produces a decrease of speed discrimination thresholds such as was first shown by Verghese and Stone [Verghese, P., & Stone, L. (1997). Spatial layout affects speed discrimination threshold. Vision Research, 37(4), 397-406; Verghese, P., & Stone, L. S. (1996). Perceived visual speed constrained by image segmentation. Nature, 381, 161-163] for sinusoidal gratings. In the second experiment, we study how the spatial configuration affects the ability of a subject in localizing an illusory contour defined by two surfaces with different speeds. Results show that the speed difference necessary to localize the contour decreases as the stimulus patches are separated. The third experiment involves transparency. Our results show a little or null effect for this condition. We explain the first and second experiment in the framework of the model of Bravo and Watamaniuk [Bravo, M., & Watamaniuk, S. (1995). Evidence for two speed signals: a coarse local signal for segregation and a precise global signal for discrimination. Vision Research, 35(12), 1691-1697] who proposed that motion computation consists in, at least, two stages: a first computation of coarse local speeds followed by an integration stage. We propose that the more precise estimate of speed obtained from the integration stage is used to produce a new refined segmentation of the image perhaps, through a feedback loop. Our data suggest that this third stage would not apply to the processing of transparency.

[1]  J. Zanker,et al.  Motion vision : computational, neural, and ecological constraints , 2001 .

[2]  L. Stone,et al.  Speed tuning of motion segmentation and discrimination , 1999, Vision Research.

[3]  P. O. Bishop,et al.  Spatial vision. , 1971, Annual review of psychology.

[4]  Takeo Watanabe,et al.  High-Level Motion Processing , 1998 .

[5]  R. Wurtz,et al.  Sensitivity of MST neurons to optic flow stimuli. I. A continuum of response selectivity to large-field stimuli. , 1991, Journal of neurophysiology.

[6]  Kenneth H. Britten,et al.  Motion perception: How are moving images segmented? , 1999, Current Biology.

[7]  E H Adelson,et al.  Spatiotemporal energy models for the perception of motion. , 1985, Journal of the Optical Society of America. A, Optics and image science.

[8]  K. Tanaka,et al.  Analysis of motion of the visual field by direction, expansion/contraction, and rotation cells clustered in the dorsal part of the medial superior temporal area of the macaque monkey. , 1989, Journal of neurophysiology.

[9]  A. Watson,et al.  The optimal motion stimulus , 1995, Vision Research.

[10]  Nicholas E. Scott-Samuel,et al.  Sub-pixel accuracy: Psychophysical validation of an algorithm for fine positioning and movement of dots on visual displays , 1996, Vision Research.

[11]  K. Tanaka,et al.  Underlying mechanisms of the response specificity of expansion/contraction and rotation cells in the dorsal part of the medial superior temporal area of the macaque monkey. , 1989, Journal of neurophysiology.

[12]  A. Newton,et al.  The hydrophobic phosphorylation motif of conventional protein kinase C is regulated by autophosphorylation , 1999, Current Biology.

[13]  A. Yuille,et al.  A Theoretical Framework for Visual Motion , 1996 .

[14]  Felix Wichmann,et al.  The psychometric function: II. Bootstrap-based confidence intervals and sampling , 2001, Perception & psychophysics.

[15]  P. Verghese,et al.  Spatial Layout Affects Speed Discrimination , 1997, Vision Research.

[16]  Ning Qian,et al.  The organization of global motion and transparency , 2001 .

[17]  Alexander Thiele,et al.  A model of speed tuning in MT neurons , 2002, Vision Research.

[18]  Nicholas J. Priebe,et al.  Tuning for Spatiotemporal Frequency and Speed in Directionally Selective Neurons of Macaque Striate Cortex , 2006, The Journal of Neuroscience.

[19]  F A Wichmann,et al.  Ning for Helpful Comments and Suggestions. This Paper Benefited Con- Siderably from Conscientious Peer Review, and We Thank Our Reviewers the Psychometric Function: I. Fitting, Sampling, and Goodness of Fit , 2001 .

[20]  Vision Research , 1961, Nature.

[21]  G. Orban,et al.  Responses of macaque STS neurons to optic flow components: a comparison of areas MT and MST. , 1994, Journal of neurophysiology.

[22]  R. Wurtz,et al.  Sensitivity of MST neurons to optic flow stimuli. II. Mechanisms of response selectivity revealed by small-field stimuli. , 1991, Journal of neurophysiology.

[23]  J. van Santen,et al.  Elaborated Reichardt detectors. , 1985, Journal of the Optical Society of America. A, Optics and image science.

[24]  S. McKee.  A local mechanism for differential velocity detection , 1981, Vision Research.

[25]  Guillaume S Masson,et al.  Spatial scale of motion segmentation from speed cues , 2001, Vision Research.

[26]  P Girard,et al.  Feedback connections act on the early part of the responses in monkey visual cortex. , 2001, Journal of neurophysiology.

[27]  D H Brainard,et al.  The Psychophysics Toolbox. , 1997, Spatial vision.

[28]  D C Van Essen,et al.  Functional properties of neurons in middle temporal visual area of the macaque monkey. I. Selectivity for stimulus direction, speed, and orientation. , 1983, Journal of neurophysiology.

[29]  Thomas D Albright,et al.  Seeing the Big Picture Integration of Image Cues in the Primate Visual System , 1999, Neuron.

[30]  E. Adelson,et al.  Phenomenal coherence of moving visual patterns , 1982, Nature.

[31]  David Navon,et al.  The forest revisited: More on global precedence , 1981 .

[32]  Mary J. Bravo,et al.  Evidence for two speed signals: a coarse local signal for segregation and a precise global signal for discrimination , 1995, Vision Research.

[33]  Nicholas J. Priebe,et al.  The Neural Representation of Speed in Macaque Area MT/V5 , 2003, The Journal of Neuroscience.

[34]  Scott N. J. Watamaniuk,et al.  Temporal and spatial integration in dynamic random-dot stimuli , 1992, Vision Research.

[35]  Josée Rivest,et al.  Localizing contours defined by more than one attribute , 1996, Vision Research.

[36]  P. Atchley,et al.  Discrimination of speed distributions: Sensitivity to statistical properties , 1995, Vision Research.

[37]  D G Pelli,et al.  The VideoToolbox software for visual psychophysics: transforming numbers into movies. , 1997, Spatial vision.

[38]  J. Zanker,et al.  Combining direction and speed for the localisation of visual motion defined contours , 2008, Vision Research.

[39]  Preeti Verghese,et al.  Perceived visual speed constrained by image segmentation , 1996, Nature.

[40]  M. Graziano,et al.  Tuning of MST neurons to spiral motions , 1994, The Journal of neuroscience : the official journal of the Society for Neuroscience.

[41]  A. Watson,et al.  Motion-contrast sensitivity: visibility of motion gradients of various spatial frequencies , 1994 .

[42]  David Ascher,et al.  A Bayesian model for the measurement of visual velocity , 2000, Vision Research.