Episodic intertrial learning of younger and older participants: Effects of age of acquisition

ABSTRACT

There is clear evidence of a deficit in episodic memory for older adults compared to younger adults. Using an intertrial technique previous research has investigated whether this deficit can be attributed to a decline in encoding or consolidation. On standard memory tests, these two aspects of memory function can be measured by examining the items forgotten or acquired across multiple learning trials. The present study assessed whether age deficits in episodic memory were affected by stimulus characteristics, specifically age of acquisition (AoA). A standard intertrial design was implemented whereby participants studied word lists over several study-test trials. The stimulus characteristics of AoA were manipulated using a pure-list technique. Our findings showed that older adults demonstrate an overall recall deficit which appeared to be a consequence of both an encoding deficit and consolidation weakness. Earlier-acquired words were recalled significantly better than later-acquired words and this was apparently due to both enhanced encoding and consolidation of earlier- over later-acquired words. The key finding is that older adults show a recall advantage for earlier- compared to later-acquired words over the entire experiment to a greater degree than younger adults.

Keywords:

• Age of acquisition
• Episodic memory
• Aging
• Recall
• Encoding
• Consolidation
• Retrieval
• Intertrial learning
• Inter-item association
• Connectionist models

This research was supported in part by a scholarship from the Harold Hyman Wingate Foundation and The Snowdon Awards Scheme. We are very grateful for the older adult volunteers who participated in this research. We would also like to thank research assistants Joseph Alderdice, Elizabeth Kim Murphy, Yvonne Kiera Bartlett, Serena Hannah, Katie Pickford, Shona Cleland, Rachel Carey, Emily Inston, Lauren Lewis, Lorna Murphy and Dayle Johnson. We would also like to thank Dr Peter Gardner and Dr Christopher J. A. Moulin for analytical advice.

Notes

¹  It is important to calculate GA and LA as percentages or proportions to remove scaling effects (see Dunlosky & Salthouse, 1996). If GA and LA were presented as raw data then it is possible that the statistics could be misleading; for example, if one considers two hypothetical participants studying 10 words on two trials. If Participant A recalls 2 words on trial one and 4 words on trial two, but the words which he recalled on trial two were completely different to the words he recalled on trial one, if GA was not calculated as percentages then the participant would score 4. The LA score would be 2. However, Participant B may recall 4 words on trial one and 6 words on trial two. He may recall 2 of the same words on trial one and two but forget 2 words which he had recalled on trial one. If the scores were not calculated as percentages this second participant would receive the same GA and LA score of 2. However, as calculated as percentages then Participant A has an LA score of 100% and a GA score of 50%. Participant two has a LA score of 50% and a GA score of 33.3%. It is necessary to convert to percentages, removing scaling effects because now it is possible to see that Participant A has a potential weaker LA, but stronger GA compared to Participant B.

²  Woodard, Dunlosky, and Salthouse (1999) are among a number of researchers who point out that the attribution of GA to encoding and LA to consolidation may be too simplistic. For example, it is possible that retrieval may contribute to both GA and LA, however, we will accept the general consensus that encoding and consolidation account for the majority of GA and LA, respectively. Please see the discussion for further information regarding this issue.

³  However, it must be acknowledged that Merritt et al. (2006) and DeLosh and McDaniel (1996) did not measure consolidation or retrieval.

⁴  The experimenter ensured that the participants rated each word at the same pace, however it was necessary to present both word lists on one sheet of paper to allow individuals to form inter-item associations between the to-be-remembered words for each word type (i.e., early- and later-acquired words).

⁵  Controlling for first task did not change any of the above ANOVA results.

⁶  It must be considered with some scepticism that AoA has a significantly larger effect on encoding than consolidation/retrieval. Although the results suggest no effect of AoA on LA in older adults when the sample population was separated on the basis of age, it is possible that the two constructs of GA and LA share some aspects of encoding and consolidation/retrieval (Woodward et al., 1999). Thus, it is difficult to conclude that AoA has a significantly greater effect of encoding in younger than older participants compared to consolidation and retrieval.