In this paper we discuss the meaning of sensitivity and its implications in CA behavior. A new shift-invariant metric is given. The metric topology induced by this metric is perfect but not compact. More-over we prove that the new space is "suitable" for the study of the dy-namical behavior of CA. In this context sensitivity assumes a stronger meaning than before (usually S is given the product topology). Now cellular automata are sensitive if they are not only capable of "transport-ing" the information but if they are also able to create new information. We also provide an experimental evidence of the fact that (in the new topology) sensitivity is linked to the fractal dimension of the space-time pattern generated by cellular automata evolutions.
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