Verbal and spatial acquisition as a function of distributed practice and code-specific interference.

Theories of memory must account for memory performance during both the acquisition (i.e., ongoing learning) and retention (i.e., following disuse) stages of training. One factor affecting both stages is whether repeated encounters with a set of material occur with no delay between blocks (massed) or alternating with another intervening task (spaced). Whereas the retention advantage for spaced over massed practice is well accounted for by some current theories of memory, theories of decay or general interference predict massed, rather than spaced, advantages during acquisition. In a series of 3 experiments, we show that the effects of spacing on acquisition depend on the relationship between primary and delay tasks. Specifically, massed acquisition advantages occur only in the presence of code-specific interference (the engagement in two alternating tasks both emphasizing the same processing code, such as verbal or spatial processing codes; e.g., learning letter-number pairs and reading text), whereas spaced acquisition advantages are observed only when code-specific interference is absent. These results present a challenge for major theories of memory. Furthermore, we argue that code-specific interference is important for researchers of the spacing and interleaving effects to take into consideration, as the relationship between the alternating tasks used has a substantial impact on acquisition performance.