Effects of dot density, patch size and contrast on the upper spatial limit for direction discrimination in Random-dot Kinematograms

Two-frame random-dot kinematograms (RDKs) of different dot density, area and contrast were used to study the spatial properties of the human visual motion system. It was found that the maximum spatial displacement at which observers could reliably discriminate the direction of motion (dmax) increased gradually by a factor of up to 6.4 as dot density was decreased from 50 to 0.025% for high Michelson contrast (0.997) stimuli. As stimulus area was reduced from 645 deg2, this trend gradually disappeared so that by a stimulus area of 2.56 deg2, there was no effect of density upon dmax. A further experiment investigated the effects of reducing Michelson contrast from 0.77 to 0.2 on dmax over this same range of dot densities. It was found that at the highest densities, dmax declined as contrast was reduced. Furthermore, for contrasts at and below 0.4, dmax was invariant of density over the range 50-5%. These results can be accounted for by the fact that both reducing contrast, while keeping density fixed, and reducing density, while maintaining a fixed high contrast, reduce the stimulus mean luminance. For all contrasts, decreasing density below 5% led to an increase in dmax. However, the rate of this increase was slower for the lower contrast stimuli. A two-stage model based on bandpass filtering followed by an informationally limited motion detection stage is proposed and shown to provide a good account of these data.

[1]  V. Lollo,et al.  Effects of adapting luminance and stimulus contrast on the temporal and spatial limits of short-range motion , 1990, Vision Research.

[2]  O. Braddick,et al.  Direction discrimination for band-pass filtered random dot kinematograms , 1990, Vision Research.

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

[4]  Walter F. Bischof,et al.  On the half-cycle displacement limit of sampled directional motion , 1991, Vision Research.

[5]  Petersik Jt.  The two-process distinction in apparent motion. , 1989 .

[6]  R. Sekuler,et al.  Masking of motion by broadband and filtered directional noise , 1979 .

[7]  G A Orban,et al.  Discrimination of opposite directions measured with stroboscopically illuminated random-dot patterns. , 1989, Journal of the Optical Society of America. A, Optics and image science.

[8]  J T Petersik.  The two-process distinction in apparent motion. , 1989, Psychological bulletin.

[9]  C. O. Roelofs,et al.  Some aspects of apparent motion , 1953 .

[10]  J. Lappin,et al.  The detection of coherence in moving random-dot patterns , 1976, Vision Research.

[11]  O. Braddick.  A short-range process in apparent motion. , 1974, Vision research.

[12]  V. Lollo,et al.  Perception of directional sampled motion in relation to displacement and spatial frequency: Evidence for a unitary motion system , 1990, Vision Research.

[13]  J. Pokorny.  Foundations of Cyclopean Perception , 1972 .

[14]  D J Field,et al.  Relations between the statistics of natural images and the response properties of cortical cells. , 1987, Journal of the Optical Society of America. A, Optics and image science.

[15]  K. Nakayama,et al.  Temporal and spatial characteristics of the upper displacement limit for motion in random dots , 1984, Vision Research.

[16]  S. M. Axstis.  PHI MOVEMENT AS A SUBTRACTION PROCESS , 1970 .

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

[18]  S. Anstis.  The perception of apparent movement. , 1980, Philosophical transactions of the Royal Society of London. Series B, Biological sciences.

[19]  O J Braddick,et al.  Temporal Properties of the Short-Range Process in Apparent Motion , 1985, Perception.

[20]  P. Cavanagh,et al.  Perception of Motion in Equiluminous Kinematograms , 1985, Perception.

[21]  C. Baker,et al.  Spatial receptive-field properties of direction-selective neurons in cat striate cortex. , 1986, Journal of neurophysiology.

[22]  B Julesz,et al.  Cooperative and non-cooperative processes of apparent movement of random-dot cinematograms. , 1985, Spatial vision.

[23]  M. Fahle,et al.  Effects of pattern element density upon displacement limits for motion detection in random binary luminance patterns , 1992, Proceedings of the Royal Society of London. Series B: Biological Sciences.

[24]  M. J. Morgan,et al.  Spatial filtering precedes motion detection , 1992, Nature.

[25]  B. Julesz,et al.  Displacement limits for spatial frequency filtered random-dot cinematograms in apparent motion , 1983, Vision Research.

[26]  Brian J. Rogers,et al.  Motion detection is limited by element density not spatial frequency , 1996, Vision Research.

[27]  Walter F. Bischof,et al.  Beyond the displacement limit: An analysis of short-range processes in apparent motion , 1985, Vision Research.

[28]  E. Peli.  Contrast in complex images. , 1990, Journal of the Optical Society of America. A, Optics and image science.

[29]  K. Nakayama,et al.  Detection and discrimination of sinusoidal grating displacements. , 1985, Journal of the Optical Society of America. A, Optics and image science.

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

[31]  O J Braddick,et al.  Low-level and high-level processes in apparent motion. , 1980, Philosophical transactions of the Royal Society of London. Series B, Biological sciences.

[32]  Richard A Eagle,et al.  What determines the maximum displacement limit for spatially broadband kinematograms , 1996 .

[33]  P. A. Kolers.  Aspects of motion perception , 1972 .

[34]  S. Ullman,et al.  The interpretation of visual motion , 1977 .

[35]  C. Baker,et al.  The basis of area and dot number effects in random dot motion perception , 1982, Vision Research.

[36]  Allan Pantle,et al.  An energy model of interframe interval effects in single-step apparent motion , 1994, Vision Research.

[37]  M. J. Keck,et al.  Influence of the spatial periodicity of moving gratings on motion response. , 1980, Investigative ophthalmology & visual science.

[38]  V. Ramachandran,et al.  Displacement thresholds for coherent apparent motion in random dot-patterns , 1983, Vision Research.

[39]  B. Julesz,et al.  Cooperative phenomena in apparent movement perception of random-dot cinematograms , 1984, Vision Research.

[40]  David C. Burr,et al.  Receptive field properties of human motion detector units inferred from spatial frequency masking , 1989, Vision Research.