Empirical distribution of image speeds determined in a simulated environment. A) The probability distribution of the speeds on the image plane generated by the projection of objects moving randomly in the virtual environment illustrated in Figure 2B. By ordering how often objects moving in 3-D space project image sequences with different speeds, the accumulated experience of humans with projected speeds can be approximated. If motion percepts are determined empirically, then the amount of perceived lag shown in Figure 4B should be accurately predicted by the cumulative ranks of the image speeds in question. (After Wojtach et al., 2008)