Episodic intertrial learning of younger and older adults: Effects of word frequency

ABSTRACT

Older adults have a demonstrable episodic memory deficit. The present study aimed to investigate whether the age deficit in episodic memory was influenced by stimulus characteristics known to produce differences in memory performance in younger adults, specifically word frequency. An intertrial paradigm was used whereby participants studied high- or low-frequency lists over several study-test trials, and the loss and gain of individual items was measured across trials; putative measures of consolidation and encoding. The results show that high-frequency words are recalled significantly better than low-frequency words. Older adults acquired high-frequency words at a greater rate across trials than they did for low-frequency words, an effect not evident in the younger adults. Older adults were found to have deficits in both encoding and consolidation as measured by losses and gains of items across trials. The results support the inter-item association theory of the word frequency effect on recall, with the age differences suggesting that memory deficits are sensitive to stimuli characteristics – one interpretation being that the ease of processing of the stimuli at encoding facilitates later recall.

Keywords:

• Episodic memory
• Word frequency
• Aging
• Consolidation
• Encoding
• Intertrial

Acknowledgments

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.

Notes

¹ 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.

² There was no significant main effect on recall for participants who completed the delayed recall task by phone compared to completing the task with pen and paper (F < 1). There was also no significant two-way interaction between method of delayed recall and age on saving scores (F < 1).

³ Furthermore, two sets of ANOVAs were used to investigate the recall over trials of younger and older adults studying high-frequency and low-frequency words. The first pair of ANOVAs separated the whole sample population on the basis of age and used a two-way ANOVA to investigate the recall of high-frequency and low-frequency words across five trials, hence a 2 × 5 design. The results confirm a significant two-way interaction between frequency and trial for younger and older adults, F(4, 132) = 5.03, p = .001, η² = .13 and F(4, 132) = 22.71, p < .001, η² = .32. The second pair of ANOVAs investigated the recall of low-frequency and high-frequency words, respectively comparing younger and older adults recall of such words over the five trials. Thus a 2 × 5 design was used. The results showed a significant two-way interaction for the recall of low-frequency words, F(4, 288) = 25.01, p < .001, η² = .26 and a significant two-way interaction for the recall of high-frequency words, F(4, 288) = 5.49, p < .001, η² = .07. The results of both pairs of ANOVAs confirmed that older adults show a steeper learning curve for high- than low-frequency words compared to younger adults as shown in Figure 1.