We present strong evidence that a coupled-map-lattice model for
spatio-temporal intermittency belongs to the universality class of directed
percolation when the updating rules are asynchronous, i.e. when only one
randomly chosen site is evolved at each time step. In contrast, when the system
is subjected to parallel updating, available numerical evidence suggests that
it does not belong to this universality class and that it is not even
universal. We argue that in the absence of periodic external forcing, the
asynchronous rule is the more physical.Comment: 12 pages, RevTeX, includes 6 figures, submitted to Physical Review
Letters; changed version includes a better physical motivation for
asynchronous updates, extra references and minor change
