Mark Dow

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.

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 );

P0-gray (.vol.gz)	PCW-gray (.vol.gz)	PCCW-gray (.vol.gz)	PA-gray (.vol.gz)

P0-linear (.vol.gz)	PCW-linear (.vol.gz)	PCCW-linear (.vol.gz)	PA-linear (.vol.gz)

	<--90 degree phase offset
		<--45 degree phase offset
			<--30 degree phase offset
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)

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)

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

EC_radial.m

-> 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:

Checkerboard twist

2008-11-12 

    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.

2008-11-15 

    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.

 

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?

 

     -c        

-b   c    -b

a   -a    a

      b

Programs and code

References

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

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.