His entry in the Polish Wikipedia says he read Cybernetics or Control and Communication in the Animal and the Machine by N. Wiener and A Mathematical Theory of Communication by C. E. Shannon when he was an assistant at the Jagiellonian University (1948-50).
Cited source is a book Świat na krawędzi, a series of interviews with Lem, written by Tomasz Fiałkowski (p. 56-57 specifically).
