Since the study of Meyer and Schvaneveldt (1971), a large number of researches have shown facilitation effect in cognitive processing of a given word when it is preceded by a semantically (i.e. associatively) related word. In this study, we examined influence of association strength between context and target on visual word processing in Serbian language. Primary goal was to test cognitive relevance of the t-value and mutual information (MI) as measures of the association strength. The results showed that the mutual information affects response latencies in the visual lexical decision task: the higher the mutual information for two words (bigram), the shorter the reaction time. Contrariwise, cognitive relevance of the t-value as a measure of the words' association strength was not confirmed.