Editing Serial-position effect (section)

==Recency effect==
{{See also|Recency bias}}
Two traditional classes of theories explain the recency effect.

===Dual-store models===
These models postulate that study items listed last are retrieved from a highly accessible short-term buffer, i.e. the [[Short-term memory|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|long-term memory store]] (LTS).

An important prediction of such models is that the presentation of a distraction, for example solving [[Arithmetic|arithmetic problems]] for 10–30 seconds, during the retention period (the time between list presentation and test) attenuates the recency effect. Since the STS has limited capacity, the distraction 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 distraction intervenes between each study item during the [[interstimulus interval]] (continuous distractor task).<ref name="Bjork 1974">Bjork & Whitten (1974). ''Recency sensitive retrieval processes in long-term free recall'', Cognitive Psychology, 6, 173–189.</ref> Since the distraction 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.<ref>{{cite journal | last1 = Greene | first1 = R. L. | year = 1986 | title = Sources of recency effects in free recall | journal = Psychological Bulletin | volume = 99 | issue = 12| pages = 221–228 | doi=10.1037/0033-2909.99.2.221}}</ref>

===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 the study of each list item and the test determines the relative competitiveness of an item’s memory trace at retrieval.<ref name="Bjork 1974"/><ref>{{cite journal | last1 = Neath | first1 = I. | last2 = Knoedler | first2 = A. J. | year = 1994 | title = Distinctiveness and serial position effects in recognition and sentence processing | journal = Journal of Memory and Language | volume = 33 | issue = 6| pages = 776–795 | doi=10.1006/jmla.1994.1037}}</ref> In this model, end-of-list items are thought 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.<ref>{{cite journal | last1 = Howard | first1 = M. W. | last2 = Kahana | first2 = M. | year = 1999 | title = Contextual variability and serial position effects in free recall | journal = Journal of Experimental Psychology: Learning, Memory, and Cognition | volume = 24 | issue = 4| pages = 923–941 | doi=10.1037/0278-7393.25.4.923| pmid = 10439501 | citeseerx = 10.1.1.360.18 }}</ref><ref>{{cite journal | last1 = Howard | first1 = M. W. | last2 = Kahana | first2 = M. J. | year = 2002 | title = A distributed representation of temporal context | journal = Journal of Mathematical Psychology | volume = 46 | issue = 3| pages = 269–299 | doi=10.1006/jmps.2001.1388}}</ref> 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 immediate free recall, these models can also predict the presence or absence of the recency effect in delayed free recall and continual-distractor free-recall conditions. Under delayed recall conditions, the test context would have drifted away with increasing retention interval, leading to attenuated recency effect. Under continual distractor recall conditions, while increased interpresentation intervals reduce the similarities between study context and test context, the relative similarities among 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 research|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 [[Rational choice theory|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.{{citation needed|date=October 2017}}

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),<ref>{{cite journal | last1 = Davelaar | first1 = E. K. | last2 = Goshen-Gottstein | first2 = Y. | last3 = Ashkenazi | first3 = A. | last4 = Haarmann | first4 = H. J. | last5 = Usher | first5 = M. | year = 2005 | title = The demise of short-term memory revisited: Empirical and computational investigations of recency effects | journal = Psychological Review | volume = 112 | issue = 1| pages = 3–42 | doi=10.1037/0033-295x.112.1.3 | pmid=15631586| s2cid = 16327806 }}</ref> who argue that there are [[Dissociation (psychology)|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. The recency effect as well as the '''ratio''' changes in [[Alzheimer's disease]] and therefore can be used as an indicator of this disease condition from the earliest stages of neurodegeneration <ref>{{cite journal | vauthors = Kovács KA | title = Relevance of a Novel Circuit-Level Model of Episodic Memories to Alzheimer's Disease | journal = International Journal of Molecular Sciences | volume = 23 | issue = 1 | pages = 462 | date = December 2021 | doi = 10.3390/ijms23010462 | pmid = 35008886 | pmc = 8745479 | doi-access = free }}</ref>