many cubes do you see simultaneously... One or
you perceive when the spinning mask becomes concave?
Impressive, isn't it?
some of the dots move you will recognize a familiar
figure in motion, but without its apparent contour (a
figure is usually distinguished from its background
by a line border called a contour). There are
circumstances when a figure can be perceived
although contour does not exist. This can occur
when a figure is in motion relative to a background.
The figure shown opposite is visible only during
its motion (when motion ends the figure ceases
to be visible...)
direction is the rotation? Observe attentively the
right gear below. You should be able to see it rotates
clockwise or anticlockwise while the red pointer always rotates
clockwise. To get the effects to switch direction,
blink or look away briefly.
Another example. Which direction rotates
the large blue gear above? Same effect as in the previous
sequences of this animation are made by modifying the
width of the alternate black and white horizontal lines
which form the background motif. The animation creates
a funny "boing" effect