Abstract
PURPOSE The propensity of successive discrete elements to be perceived as a single object in motion is called the strength of apparent motion (AM). We ask how space and time determine the strength of AM (SAM). There are two conflicting views on this matter. According to Korte's Third Law, if the temporal interval between the two elements is increased, their spatial distance must be increased in order to maintain the same SAM. On the other hand, according to Burt and Sperling (1981), if the temporal interval between the two elements is increased, their spatial distance must be decreased in order to maintain the same SAM. METHOD We used rapidly alternating patterns of regularly spaced dots, called motion lattices, in which observers can see alternative paths of AM. Within every path we varied spatial and temporal parameters and looked for conditions with different space-time combinations that yielded the same SAM. We found these points of perceptual equivalence between motion paths under different spatial scales. RESULTS We found that both Korte's law and the Burt/Sperling theory are correct, but under different spatial scales. Korte's law holds for large scales, whereas the Burt/Sperling theory holds for small scales. Between these two extremes, we found a spatial scale for which the SAM does not depend on the temporal interval between elements.