Furrow Illusions: Peripheral Motion

Motion looks different in the periphery!  Look straight at the red & yellow spots, and you can see they move horizontally.  But look away & view them in peripheral vision (out of the corner of your eye).  Their paths appear curved!  The yellow spots seem to bow outwards, the red spots inwards, attracted toward the background stripes.

The spots move in straight parallel lines, but in peripheral vision their paths look like circular arcs.

Left: Spots move straight, & look straight — no illusion.  Right: In peripheral vision the spot paths look curved.  Conclusion: Background must be local,not global, and spots must touch the stripes, not just be near them.

Spots move in circles on horizontal or vertical stripes.  In peripheral vision the spots appear to slide and shear on elliptical paths.

Moving bar, viewed peripherally, seems to change its length.

Red vertical lines appear to bow slightly outwards like sides of a barrel because of Hering’s (1861) geometrical illusion.  Red lines are repelled by radiating lines (orientation contrast).  Motion is illusion is opposite to this!  The spots kiss the red lines, but in peripheral vision they appear to bow inwards like a pincushion.  This is orientation assimilation, not contrast.

Top:  Footsteps illusion (Anstis 2001).  Blue & yellow squares move at constant speed, but appear to speed up and slow down.  Reason:  When dark blue edges lie on black stripes they have low luminance contrast and appear to slow down.  On white stripes they have high contrast and appear to speed up.
Bottom: Motion illusion.  In peripheral vision their speed does not change, but their perceived direction of motion does.  So the two illusions are different.

In central vision the spot is correctly seen as moving vertically.  But as you view it more & more peripherally, its perceived angle increases, up to a maximum of 45° in this case.