The purpose of this study was to identify the nature of the information which preschool-age children must attend to and maintain within problems in order to solve a series of two-choice simultaneous discrimination problems. Twenty-four preschool children participated in the experiment. The stimuli used in these problems consisted of planometric geometric forms with seven values on each of the visual dimensions of color and form. Children were first overtrained on a two-choice simultaneous discrimination problem and subsequently were tested on a series of new problems. Prior to testing, trials of the previously overlearned problem were interpolated between the training and test trials. Also, to maintain attention to the originally trained cue and to test for its maintenance, three trials of the overlearned problem were presented between new problems. The new problems used in the test trials were of two types: those in which the correct cue value was on the same dimension as the original problem, necessitating an intradimensional shift in attention, and those in which the correct cue was on a different dimension from the original, thus involving an extradimensional shift. Each child received a total of eight, two-trial problems: four intradimensional and four extradimensional and interpolations in between, for a total of 54 trials. Results indicate that preschool children performed better when an extradimensional shift was called for than when an intradimensional shift was required. (Author/RH)