Recentism - Recency Effect

Recency Effect

Two traditional classes of theories explain the recency effect.

Dual Store Models

These models postulate that later study list items are retrieved from a highly accessible short-term buffer, i.e. the short-term store (STS) in human memory. This allows items that are recently studied to have an advantage over those that were studied earlier, as earlier study items have to be retrieved with greater effort from one’s long-term memory store (LTS).

An important prediction of such models is that the presentation of a distractor, for example solving arithmetic problems for 10–30 seconds, during the retention period (the time between list presentation and test) attenuates such the recency effect. Since the STS has limited capacity, the distractor displaces later study list items from the STS so that at test, these items can only be retrieved from the LTS, and have lost their earlier advantage of being more easily retrieved from the short-term buffer. As such, dual-store models successfully account for both the recency effect in immediate recall tasks, and the attenuation of such an effect in the delayed free recall task.

A major problem with this model, however, is that it cannot predict the long-term recency effect observed in delayed recall, when a distractor intervenes between each study item during the interstimulus interval (continuous distractor task). Since the distractor is still present after the last study item, it should displace the study item from STS such that the recency effect is attenuated. The existence of this long-term recency effect thus raises the possibility that immediate and long-term recency effects share a common mechanism.

Single Store Models

According to single-store theories, a single mechanism is responsible for serial position effects.

A first type of model is based on relative temporal distinctiveness, in which the time lag between test and the study of each list item determines the relative competitiveness of an item’s memory trace at retrieval. In this model, end-of-list items are though to be more distinct, and hence more easily retrieved.

Another type of model is based on contextual variability, which postulates that retrieval of items from memory is cued not only based on one’s mental representation of the study item itself, but also of the study context. Since context varies and increasingly changes with time, on an immediate free-recall test, when memory items compete for retrieval, more recently studied items will have more similar encoding contexts to the test context, and are more likely to be recalled.

Outside of immediate free recall, these models are also able to predict the presence of the recency effect (or lack thereof) in delayed free recall and continual-distractor free recall conditions. Under delayed recall conditions, the state of test context would have drifted away with an increasing retention interval, leading to an attenuated recency effect. Under continual distractor recall conditions, while the increased interpresentation intervals reduces the similarities between the given study contexts and test context, the relative similarities amongst items remains unchanged. As long as the recall process is competitive, recent items will win out, so a recency effect is observed.

Ratio Rule

Overall, an important empirical observation regarding the recency effect is that it is not the absolute duration of retention intervals (RI, the time between end of study and test period) or of inter-presentation intervals (IPI, the time between different study items) that matters. Rather, the amount of recency is determined by the ratio of RI to IPI (the ratio rule). As a result, as long as this ratio is fixed, recency will be observed regardless of the absolute values of intervals, so that recency can be observed at all time scales, a phenomenon known as time scale invariance. This contradicts dual-store models, which assume that recency depends on the size of STS, and the rule governing the displacement of items in the STS.

Potential explanations either then explain the recency effect as occurring through a single, same mechanism, or re-explain it through a different type of model that postulates two different mechanisms for immediate and long-term recency effects. One such explanation is provided by Davelaar et al. (2005), who argue that there are dissociations between immediate and long-term recency phenomena that cannot be explained by a single-component memory model, and who argues for the existence of a STS that explains immediate recency, and a second mechanism based on contextual drift that explains long-term recency.