Mark Dow

Geek art

Directional edge contrast motion illusion comparison

    This is a comparison of several parameters variations of a simple motion illusion (short-range apparent motion). This percept is directly related to the "Four stroke apparent motion" illusion.
Prototypical edge contrast motion illusion
The prototype animation: 25 px. diameter circles, 76 x 76 px. frame,  2 px. maximum shift, 1/3 seconds/cycle (3 Hz., 8 frames at ~24 frames/s)
Matlab command:
>> nvolOut = ECC_animation_2x2( flRadius, imDim, flPxShiftMax, 1/3 );

Programs and code

Prototype frame 1 Prototype frame 2 Prototype frame 3 Prototype frame 4 Prototype frame 5 Prototype frame 6 Prototype frame 7 Prototype frame 8
The eight frames of the prototype.

Circles 2x2 CW P0 gray Circles 2x2 CW PCW gray Circles 2x2 CW PCCW gray Circles 2x2 CW PA gray
P0-gray (.vol.gz) PCW-gray (.vol.gz) PCCW-gray (.vol.gz) PA-gray (.vol.gz)

Circles 2x2 CW P0 linear Circles 2x2 CW PCW linear Circles 2x2 CW PCCW linear Circles 2x2 CW PA linear
P0-linear (.vol.gz) PCW-linear (.vol.gz) PCCW-linear (.vol.gz) PA-linear (.vol.gz)

>> ECC_animation_2x2( 25, 76, 24, .5 );

Circles 2x2 CW P90 linear .125s 3 frames <--90 degree phase offset
Circles 2x2 CW P45 linear .125s 3 frames Circles 2x2 CW P45 linear .16s 4 frames <--45 degree phase offset
Circles 2x2 CW P30 linear .125s 3 frames Circles 2x2 CW P30 linear .16s 4 frames Circles 2x2 CW P30 linear .25s 6 frames <--30 degree phase offset
Circles 2x2 CW P0 linear .125s 3 frames Circles 2x2 CW P0 linear .16s 4 frames Circles 2x2 CW P0 linear .25s 6 frames Circles 2x2 CW P0 linear .33s 9 frames Circles 2x2 CW P0 linear .5s 12 frames Circles 2x2 CW P0 linear .625s 15 frames
P0-3_frame (.vol.gz) P0-4_frame (.vol.gz) P0-6_frame (.vol.gz) P0-9_frame (.vol.gz) P0-12_frame (.vol.gz) P0-15_frame (.vol.gz)

Circles 2x2 CW P0 linear 1.0s 24 frames Circles 2x2 CW P0 linear 1.5s 36 frames Circles 2x2 CW P0 linear 1.66s 40 frames Circles 2x2 CW P0 linear 1.875s 45 frames Circles 2x2 CW P0 linear 2.5s 60 frames Circles 2x2 CW P0 linear 3.75s 90 frames
P0-24_frame (.vol.gz) P0-36_frame (.vol.gz) P0-40_frame (.vol.gz) P0-45_frame (.vol.gz) P0-60_frame (.vol.gz) P0-90_frame (.vol.gz)

1 px. maximum shift, 12 frame 2 px. maximum shift, 12 frame 4 px. maximum shift, 12 frame 6 px. maximum shift, 12 frame
1 px. maximum shift, 4 frame 2 px. maximum shift, 9 frame 4 px. maximum shift, 9 frame 6 px. maximum shift, 9 frame
1 px. maximum shift, 4 frame 2 px. maximum shift, 4 frame 4 px. maximum shift, 4 frame 4 px. maximum shift, 4 frame
1 px. maximum shift 2 px. maximum shift 4 px. maximum shift 6 px. maximum shift
P0-linear (.vol.gz) PCW-linear (.vol.gz) PCCW-linear (.vol.gz) PA-linear (.vol.gz)

[To Do: One-dimensional]

[To Do:

Plot a parameterized 1-D profile at several phases:

Write MATLAB  programs


-> edge_contrast_1D_animation.m

-> edge_contrast_1D.m
that generates a phased cyclic sequence of edge contrast vectors.
Test assembling an edge with variable width (and/or phase), angular frequency.
Build the edge necessary for the pinwheel tesselation:
Pinwheel tesselation template test


Checkerboard twist


    While writing the one-dimensional code (for a pinwheel "wedge" edge, EC_radial.m), this high symmetry "cone" structure came up. Do it exactly right, square tiling with no gap, smooth square-profile "teeth" and best continuity. Animated tiling.

checkerboard twist prototype


    Got them roughly alligned, mostly by trial and minimizing error. The geometry of the angles is opaque to me. I'll add the mirror in background, with some artificial fade with depth.

Mixed symmetry pair


A puzzle: The figure below is an arrangement of eight triangles, using three different triangular motifs (say a, b and c) along with a pi/2 rotation of each of the three (say -a, -b and -c). What is the spatial arrangement of the six?

  Diamond test animation


-b   c    -b

a   -a    a


See Mixed symmetries for details and code.

Programs and code

    The example frames and volumes were generated by the following MATLAB programs. The GIF animations were assembled from the serial frames using Jasc Software's Animation Shop. Parameter variations are made by both the program arguments and hardcoded items (see header comments for details).


    Space Software was used  to review the animations (utilizing the optional Matlab program output in volume format [.vol] ) and to generate serially numbered 2-D frames (File | Save As Serial Images).


Beta movement, Phi phenomena, Magni-phi and related phenomena

Visual dissociations of movement, position, and stereo depth: Some phenomenal phenomena

Richard L. Gregory and Priscilla F. Heard
Quarterly Journal of Experimental Psychology (1983) 35A, 217-237
Brain and Perception Laboratory, University of Bristol, Department of Anatomy, The Medical School, University Walk, Bristol BS8 1TD, England

"Helmholtz1867) described as "irradiation" the apparently greater size of a white compared with a dark square, or disc or whatever of the same physical size. The illusory size difference is reversed at low contrasts (Weale, 1974). It is also known that rapid increases in brightness gives apparent movement (gamma movement), though there is no agreed explanation for either phenomenon.

When narrow bordering stripes are added, further systematic phenomena occur. With intensity modulation of an edge-striped grey rectangle, which has a dark stripe on the left side and a light stripe on the right, the entire figure shifts, with reversed motion when the background luminance is modulated. By presenting a pair of such figures, mirror reversed one to each eye and fused stereoscopically, the question may be asked: Do these illusory shifts produce stereo depth? The answer is surprising: stereo is produced - but at the cross-over with luminance of the central grey rectangle with the background the depth change is opposite to that given by normal, non-illusory, opposed lateral shifts. We interpret this anomalous stereo depth as a switch of which edges of the stripes are fused, with the change of relative contrast of the edges of the dark and light stripes as the figure-background contrast is changed.

Measures of static shift, lateral movement, and stereo depth, give somewhat different functions. These are considered in terms of different signalled positions, stereo depth, and movement. This study brings out the importance, for explaining such perceptual anomalies, of distinguishing between neural signal channel characteristics and which stimulus features from the display are selected and accepted for perception. Although conceptually clearly distinct these are all too easily confused in psycho-physical experiments."

Anstis, S. M. and Rogers, B. J. (1986) Illusory continuous motion from oscillating positive-negative patterns: implications for motion perception. Perception 15, 627-640.

Carney T, Shadlen M N (1993) Dichoptic activation of the early motion system. Vision Research 33, 1977-1995.

George Mather, visual motion, depth perception research and demos, reference list

Art and Science in Motion Perception, an EPSRC Culture and Creativity Programme Network

80 Optical Illusions & Visual Phenomena, by Michael Bach, Freiburg University, Germany

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