Is working memory capacity task dependent?

The complex span measure of working memory is a word/digit span measured while performing a secondary task. Two experiments investigated whether correlations between the complex span and reading comprehension depend on the nature of the secondary task and individual skill in that task. The secondary task did not have to be reading related for the span to predict reading comprehension. An arithmetic-related secondary task led to correlations with reading comprehension similar to those found when the secondary task was reading. The relationship remained significant when quantitative skills were factored out of the complex span/comprehension correlations. Simple digit and word spans (measured without a background task) did not correlate with reading comprehension and SAT scores. The second experiment showed that the complex span/comprehension correlations were a function of the difficulty of the background task. When the difficulty level of the reading-related or arithmetic-related background tasks was moderate, the span/comprehension correlations were higher in magnitude than when the background tasks were very simple, or, were very difficult.