The afterimages were responsible for the fact that no interruptions were noticeable, while the movement itself resulted simply from the passing of one position into another.

What else is the perception of movement but the seeing of a long series of different positions?
If instead of looking through the zooetrope we watch a real trotting horse on a real street, we see its whole body in ever new progressing positions and its legs in all phases of motion; and this continuous series is our perception of the movement itself.
This seems very simple.

Yet it was slowly discovered that the explanation is far too simple and that it does not in the least do justice to the true experiences.

With the advance of modern laboratory psychology the experimental investigations frequently turned to the analysis of our perception of movement.

In the last thirty years many researches, notably those of Stricker, Exner, Hall, James, Fischer, Stern, Marbe, Lincke, Wertheimer, and Korte have thrown new light on the problem by carefully devised experiments.