Article summary with A comparison of visual working memory and episodic memory performance in younger and older adults by Lugtmeijer a.o. - 2019

It is well-established that visual working memory and episodic memory performance decline with age. That is, older people exhibit decreases in performance on working memory and episodic memory. However, although it is well-known that memory function is not a unitary construct, it is largely unknown whether age-associated differences are similar in different memory systems. To fill this gap of knowledge, the present study compared the performance of younger and older adults on both working memory and episodic memory performance.

Which theoretical frameworks focus on the effect of aging on memory? 

Several theories of the effect of aging on memory have been proposed, of which two theoretical frameworks are of particular interest here.

Associative deficit hypothesis

The first theoretical framework is that of the associative deficit hypothesis, which states that older adults exhibit a disproportionate decrement in memory for bound, associative information (for example context memory), relative to memory for the associated items, and that this is because of problems with binding and retrieval. Context memory aids the retrieval of memories and has been found to be more impaired in older adults in comparison to younger adults. 

Irrelevant information deficit hypothesis

The second theoretical framework is called the irrelevant information deficit hypothesis. According to this theory, older adults have relatively more problems in inhibiting irrelevant information and updating in the presence of distraction, which results in inefficient coding and impaired performance. 

Scientific evidence 

Studies resulted in inconclusive results regarding the effects of aging on memory, which may be explained by task differences. Working memory is a multifaceted system that combines various processes, such as encoding, maintenance, attention, and inhibition. As such, it is not surprising that different working memory tasks tap only partly overlapping components of working memory resulting in a weak correlation between tasks. In addition, the degree of age-related decline may also depend on task characteristics. More complex working memory tasks may be more sensitive to aging than less complex ones. One way to reduce task differences and assess the relationship between the subsystems is to use the same stimuli in a within-subjects design. So far, only three studies examined working memory and episodic memory by testing incidental encoding during the working memory task with a subsequent memory task. 

What was the design of the present study?

Research questions

In this study, the following three research questions were formulated:

1. Do working memory and episodic memory performance show similar age differences when using the same stimuli?
2. How are working memory and episodic memory performance related in younger and older adults?
3. Are there age-related differences in response patterns?

Hypotheses

Based on the above mentioned theories, a set of hypotheses can be produced. The associative deficit hypothesis predicts similar age-associated differences on the working memory and subsequent memory tasks. The correlation between performances on the two tasks is expected to be positive, indicating that both systems are related by a common mechanism. Second, the irrelevant information deficit hypothesis predicts worse performance of older adults on the working memory task, but a possible advantage on the subsequent memory task. Lack of inhibition of irrelevant objects from different lags than two might impair performance on the first task, the N-back task, while encoding of irrelevant location information during the working memory task in older adults might result in an advantage on the subsequent memory task. 

Participants

To answer these questions, 30 younger adults (age between 20 and 30 years) and 30 older adults (aged above 60 years) were tested on both working memory and episodic memory tasks. Participants from these two groups were matched on gender and educational level based on the Dutch educational system, ranging from 1 (low) to 7 (highly educated).

Instruments

To assess general cognitive functioning, a brief battery of neuropsychological tests including the MoCA was used. IQ was estimated using the Dutch version of the National Adult Reading Test. Visual working memory was assessed using the Corsi Block-Tapping Task. Visual recognition was assessed using the Doors and People Test.

Two experimental tasks were conducted. A so-called N-back task was used to assess working memory. In this task, participants have to respond when an item in a sequence of presentations matches the item N trials before. The N-task that the authors of this paper used was designed comprising easy-to-name objects to avoid a floor effect on the subsequent memory task and contained no relevant associations apart from temporal order to reduce the chance of recruitment of long-term memory during the working memory task. The N-back task was followed by an unexpected memory task, during which object location associations incidentally encoded during the working memory task were tested. Here, participants had to indicate whether the object was presented in the same corner on the screen now as during the 2-back task. The total duration of the experimental procedure varied between 50 and 60 minutes. 

What were the main outcomes of the study? 

Do working memory and episodic memory performance show similar age differences when using the same stimuli?

• To analyse the performance of both groups on both tasks, a repeated measures ANOVA was conducted. 
• The main effect of task was significant, with better performance on the 2-back task than on the subsequent memory task. 
• The main effect of group was also significant, with younger adults performing better than older adults.
• Yet, to answer this question, there was no significant group by task interaction.  

How are working memory performance and episodic memory performance related in younger and older adults?

• To answer this question, Pearson product-moment correlations were calculated. Overall, performance on the 2-back task was not significantly related to subsequent memory performance. In older adults, no significant correlation was found, while in younger adults, the two tasks correlated significantly. 

Are there age-related differences in response patterns?

• 2-back task: Older adults had a tendency toward fewer hits and a non-significant difference in false alarms. 
• Subsequent memory task: The number of hits and false alarms on the subsequent memory task did not significantly differ between the two age-groups. 

To conclude, the results showed that older adults performed worse than younger adults on both working memory and subsequent memory tasks with the same stimuli. A moderate to large effect size was found. No significant interaction effect was found, suggesting that there possibly the differences are similar for both age groups when using the same stimuli. However, some caution is warranted when drawing this conclusion. Although the authors aimed at designing the tasks to be similar, there are several differences that might have influenced the results.