Investigated the effects on information processing of (a) the use of self-paced serial reactions vs. discrete reactions, (b) the use of different types of stimuli and responses, and (c) the use of 3 levels of stimulus uncertainty. Reaction time was an increasing linear function of the average amount of information transmitted. The self-paced and discrete tasks gave very similar results. The findings are interpreted as indicating the importance of overlearning in determining S-R compatibility effects. Also, S's familiarity in dealing with specific subsets drawn from familiar alphabets may affect his information-handling rates when restricted subsets of stimuli and responses are used. (PsycINFO Database Record (c) 2006 APA, all rights reserved)