Even men use this trick!

What do babies and fish have in common?

Patrick Cavanagh, Stuart Anstis, Daphne Maurer, Terri Lewis

Fishes and babies can neither read nor speak, yet we persuaded them to tell us what colors they see. We showed them special moving colored patterns on a computer screen. If they saw the colors, the babies followed the movement with their eyes, and the fishes followed it by moving their whole bodies, swimming after the patterns in an innate optomotor response.

We made a movie only four frames long which looped repetitively. Each frame filled the whole computer screen with vertical colored stripes. In the left hand column, the stripes at Time 1 were light red and dark green, and at Time 2 they were light & dark yellow. The yellow stripes were shifted sideways by half a bar width, so the stripes appeared to jump sideways — but which way? The brain could not pair up succcessive stripes on the basis of color, because all the stripes at Time 2 were the same color (yellow). So the brain had to pair them up on the basis of luminance. If the red stripes were lighter than the green, the stripes appeared to jump to the right toward the nearest light yellow stripe (left-hand column). If the red stripes were darker than the green, the stripes appeared to jump to the left toward the nearest dark yellow stripe (right-hand column). The movie translates lightness into motion.

We titrated red against green luminance until, at equiluminance, perceived motion disappeared for adult obsesrvers, babies stopped making pursuit eye movements, and fishes stopped swimming in circles. Red-deficient observers rquire more red to make an equiluminous mathc, and green-deficients require more green. We were able to identify individual color-defective babies. Conclusions: Outputs from cones into the luminance pathways were in place within the first months of life. Also, guppy fish are more green-sensitive and less red-senstivie than humans.

Who What makes your heart flutter?

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.