This study was concerned with the implementation of certain mathematical results that give optimal ways to present stimulus items in learning experiments. This optimization theory is based on a stimulus‐sampling model of a learning experiment. We assumed that this particular model of learning would describe paired‐associate learning and then compared the effects of training subjects in several paired‐associate experiments by the optimal strategy and by another simple presentation strategy. Our empirical results did not support the adequacy of the assumed model of learning for representing the learning processes in these experiments. In particular, it appears that suitable models of these learning situations must incorporate some mode of representation of short‐term retention.

2 groups of 15 high school Ss received instruction in logic from a computer controlled autoinstructional device. In 1 group all Ss received a fixed sequence of 233 items. In the 2nd group each of the Ss received a different number and sequence of items, depending on the S's performance during the lesson. Branching decisions were based on errors and on the S's evaluation of his own readiness to advance to new topics. Posttest scores were significantly higher (.05 level) for the branching group than for the fixed sequence group; training time differences were not significant.

"In Experiment I, three groups of 17 subjects were used to test 2 hypotheses concerning optional branching. A fixed-sequence group received items in fixed order; a back-branching group receiving the same items as the first group, was permitted to back up one item at a time to review earlier items; a third group received the same items cast in statement form and organized into paragraphs permitting subjects to choose material at their own option. A significant difference on a posttest in favor of the third group was obtained when the first and third groups were compared. In Experiment II, a computer-controlled teaching machine was used to evaluate the effectiveness of adapting sequences of teaching items on logic. Members of a branching group received sequences of items determined by the errors that were made during instruction. Each member of a fixed sequence group was paired at random with one member of the branching group . . . . Covariance analysis of criterion scores using aptitude and training time as control variables yielded no significant difference between branching and fixed-sequence conditions."

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