Recently developed measures of clustering in free recall arc examined and shown to vary with characteristics of recall unrelated to relative amounts of clustering. Specifically, previous measures were shown to vary with such factors as number of categories recalled, the distribution of the total items recalled across categories, and total number of items recalled. For these reasons, comparisons between and within subjects, as well as comparisons between experiments, are most difficult. An adjusted ratio of clustering (ARC) measure, which does not vary with irrelevant characteristics of recall, is proposed.

This study provided a longitudinal assessment of skill development in addition for 26 normal and 12 mathematically disabled first-or second-grade children. At the first time of measurement, the children solved 40 simple addition problems. Ten months later, all subjects were readministered the addition task and a measure of working memory resources. Across times of measurement, the normal group showed increased reliance on memory retrieval and decreased reliance on counting to solve the addition problems, as well as an increase in speed of counting and of retrieving addition facts from long-term memory. The math-disabled group showed no reliable change in the mix of problem-solving strategies or in the rate of executing the counting or memory retrieval strategies. Finally, reliable differences, favoring the normal group, were found for the index of working memory resources.

Sixty young and 60 elderly adults completed a pencil-and-paper addition test and solved 40 computer-presented simple addition problems. Strategies and problem solution times were recorded on a trial-by-trial basis and were classified in accordance with the distributions of associations model of strategy choices. The elderly group showed a performance advantage on the ability measure and for the developmental maturity of the mix of problem-solving strategies, but the young group showed an advantage for overall solution times. A componential analysis of the overall solution times for memory retrieval trials, however, showed no reliable age difference for rate of retrieving addition facts from long-term memory but did suggest that the elderly adults might have been slower than the younger adults for rate of encoding digits and verbally producing an answer. Overall results are interpreted within the context of the strategy choice model.

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Typical varied serial-order conditions of paired-associate (PA) learning were compared with a constant serial order on all trials in 5 experiments involving systematic variations in method, kind of material, and other potentially relevant factors. The results showed a small but relatively consistent facilitation by constant serial order limited primarily to later stages of learning. Since a shift following the first correct response to each pair from constant to varied serial order produced as much facilitation as did completely constant-order conditions, it was concluded that complex associations involving serial position are developed during early stages of constant-order PA learning, but that these exercise a facilitating influence primarily through the reduction of inter-pair interference late in learning.