Measured codability of pictures by an average uncertainty U of the distribution of names given as responses by a normative sample of 29 undergraduates. Exp. I showed that reaction time (RT) to name the displays sharply increased at U 2 bits for independent Ss. Since U covaries with frequency and age of acquisition of lexical responses, in Exp. II, 10 new Ss were treated as 10 independent experiments and their RT scores partitioned on frequency and age covariates. High U produces different functional stimuli and precluded pooling of data. Partitioned RTs to name high-U pictures were 200-970 msec longer than to name low-U pictures. High-U may possibly increase RT by intra-heuristic processes. Multiple regression analysis showed that RT for 6 Ss is predicted by age and frequency, 2 by age alone, 1 by frequency, and 1 by neither. Specific sets of predictor variables must be ascertained separately for each S. The structure of lexical storage and search algorithms to access its contents may differ in individuals of a language community although the content of storage is similar. (20 ref.) (PsycINFO Database Record (c) 2006 APA, all rights reserved)