Are two words recalled or recognised as one? How age-of-acquisition affects memory for compound words

The age at which a person acquires knowledge of an item is a strong predictor of item retrieval, hereon defined as the Age of Acquisition (AoA) effect. This effect is such that early-acquired words are processed more quickly and accurately than late-acquired items. One account to explain this effect is the integrated account, where the AoA effect occurs in the early processes of lexical retrieval and hence should increase in tasks necessitating greater semantic processing. Importantly, this account has been applied to lexical processing, but not, to date, memory tasks. The current study aimed to assess whether the integrated account could explain memory tasks, using compound words, which differ from monomorphemic words regarding ease of mapping and semantic processes. Four-hundred-and-eighty participants were split into four groups of 120 participants for each of four experiments. Participants were required to recall unspaced and spaced compound words (Experiments 1 and 2, respectively) or make a recognition decision for unspaced and spaced compound words (Experiments 3 and 4, respectively). This approach allowed us to establish how semantic processing was involved in recalling and recognising the items. We found that (AoA) was related to all tasks such that irrespective of space, early-acquired compound words were recalled more accurately than late-acquired compound words in free recall. In recognition memory, late-acquired compound words were recognised more accurately than early-acquired compound words. However, the slope for the AoA was semantic processing influenced free recall to a greater extent than the recognition memory, with the AoA effect being larger in free recall than recognition memory. In addition, the AoA effect for the compound word was larger in spaced compound words than unspaced compound words. This demonstrates that the AoA effect in memory has multiple sources.