Measuring working memory capacity with greater precision in the lower capacity ranges.

Working memory capacity is usually measured as the number of stimuli correctly remembered. However, these measures lack precision when assessing individuals with low capacity. This study aimed to create a more precise measure of visuospatial working memory capacity, using intra-level differences in difficulty between items. In two experiments, children aged 4-6 years (N = 97) were tested on a large number of items. Data showed a large variability of difficulty within each level and the factors contributing to this variability were identified. This variability can be used to provide a precise measure of working memory capacity in the lower ranges.