Molander, B., and Garvill, J. Effects of first stage variations of stimulus meaningfulness and response meaningfulness in the A-B, B-C, A-C paradigm. Uneå Psychological Reports, No. 85, 1975. - With CVC-syllables as low meaningfulness material and common nouns as high meaningfulness material, two levels of stimulus meaningfulness and two levels of response meaningfulness were corrbined to form the four first stage conditions HH, LH, HL and LL in the A-B, B-C, A-C paradigm. The results of the experiment, which was performed according to standard PA learning procedures, indicated that stimulus meaningfulness as well as response meaningfulness contributed to the mediation effects in stage three. The mediation effects, however, seemed to be directly related to first stage performance rather than to meaningfulness per se. The results also suggested that intra-pair and intralist similarity may be important acquisition variables in studies on mediation.