How meaningfulness and initial learning degree influence associative storage and retrieval processes: A multinomial processing tree and power function analysis.

The effects of meaningfulness and initial learning on memory retention remain debated, largely due to methodological differences and a reliance on observed retention measures that confound underlying storage and retrieval processes. This study investigated how these encoding factors distinctly influence storage and retrieval of associative memory over time. Participants learned noun-noun pairs varying in associative meaningfulness (high, low) and initial learning degree (high, medium, low), followed by free-then-cued recall tests at four retention intervals (35 s, 1 hr, 1 day, 3 days). We employed a two-step modeling approach: a multinomial processing tree (MPT) model isolated storage and retrieval probabilities, and a power forgetting function modeled the time-dependent decay of storage probability. The results revealed that high associative meaningfulness significantly increased storage probability but decreased retrieval probability. Higher initial learning boosted both storage and retrieval processes. Furthermore, the power forgetting function revealed that higher meaningfulness and greater initial learning were associated with a higher initial storage probability and a slower relative forgetting rate. These findings clarify longstanding contradictions by demonstrating that meaningfulness and initial learning have dissociable effects on the latent cognitive processes underlying retention: meaningfulness primarily enhances storage probability but impedes retrieval, whereas initial learning strengthens both processes. Together, these findings provide a deeper understanding of how encoding conditions shape the memory decay over time.