When Two Patterns of Dots Moving Horizontally in Opposite Directions

Multiple Choice

When two patterns of dots moving horizontally in opposite directions are superimposed, they may produce motion transparency. Which characteristics of the patterns produce transparency?

A) The dots in each pattern must move at the same speeds
B) The patterns must be of the same size
C) The dots in each pattern must have the same lifetime
D) The dots on one pattern must be vertically displaced from the dots in the other