Editing Long-term memory (section)

====Unitary model====
Not all researchers agree that short- and long-term memory are separate systems. The alternative Unitary Model proposes that short-term memory consists of temporary activations of long-term representations (that there is one memory that behaves variously over all time scales, from milliseconds to years).<ref>{{Citation |last=Cowan |first=Nelson |title=Essence of Memory |date=2008 |volume=169 |pages=323–338 |series=Progress in Brain Research |chapter=Chapter 20 What are the differences between long-term, short-term, and working memory? |publisher=Elsevier |doi=10.1016/s0079-6123(07)00020-9 |isbn=978-0-444-53164-3 |pmc=2657600 |pmid=18394484}}</ref><ref>{{cite journal |last1=Brown |first1=G. D. A. |last2=Neath |first2=I. |last3=Chater |first3=N. |year=2007 |title=A ratio model of scale-invariant memory and identification |journal=Psychological Review |volume=114 |issue=3 |pages=539–576 |citeseerx=10.1.1.530.3006 |doi=10.1037/0033-295X.114.3.539 |pmid=17638496}}</ref> It has been difficult to identify a sharp boundary between short- and long-term memory. Eugen Tarnow, a physics researcher, reported that the recall probability versus latency curve is a straight line from 6 to 600 seconds, with the probability of failure to recall only saturating after 600 seconds.<ref name="Tarnow2">Tarnow, Eugen (2007). [http://cogprints.org/4273/1/The_structure_of_short_term_memory_-_Tarnow.pdf Properties of the Short Term Memory Structure]</ref> If two different stores were operating in this time domain, it is reasonable to expect a discontinuity in this curve. Other research has shown that the detailed pattern of recall errors looks remarkably similar to recall of a list immediately after learning (it is presumed, from short-term memory) and recall after 24 hours (necessarily from long-term memory).<ref>{{cite journal |last1=Nairne |first1=J. S. |last2=Dutta |first2=A. |year=1992 |title=Spatial and temporal uncertainty in long-term memory |journal=Journal of Memory and Language |volume=31 |issue=3 |pages=396–407 |doi=10.1016/0749-596x(92)90020-x}}</ref>

Further evidence for a unified store comes from experiments involving continual distractor tasks. In 1974, Bjork and Whitten, psychology researchers, presented subjects with word pairs to remember; before and after each word pair, subjects performed a simple multiplication task for 12 seconds. After the final word-pair, subjects performed the multiplication distractor task for 20 seconds. They reported that the recency effect (the increased probability of recall of the last items studied) and the primacy effect (the increased probability of recall of the first few items) was sustained. These results are incompatible with a separate short-term memory as the distractor items should have displaced some of the word-pairs in the buffer, thereby weakening the associated strength of the items in long-term memory.<ref>{{cite journal |last1=Bjork |first1=R.A. |last2=Whitten |first2=W.B. |year=1974 |title=Recency-sensitive retrieval processes in long-term free recall |url=https://deepblue.lib.umich.edu/bitstream/2027.42/22374/1/0000823.pdf |journal=Cognitive Psychology |volume=6 |issue=2 |pages=173–189 |doi=10.1016/0010-0285(74)90009-7 |hdl-access=free |hdl=2027.42/22374}}</ref>

[[Ovid Tzeng]] (1973) reported an instance where the recency effect in [[free recall]] did not seem to result from a short-term memory store. Subjects were presented with four study-test periods of 10-word lists, with a continual distractor task (20-second period of counting-backward). At the end of each list, participants had to free recall as many words as possible. After recall of the fourth list, participants were asked to recall items from all four lists. Both the initial and final recall showed a recency effect. These results violated the predictions of a short-term memory model, where no recency effect would be expected.<ref>{{cite journal |last1=Tzeng |first1=O.J.L. |year=1973 |title=Positive recency in delayed free recall |journal=Journal of Verbal Learning and Verbal Behavior |volume=12 |issue=4 |pages=436–439 |doi=10.1016/s0022-5371(73)80023-4}}</ref>

Koppenaal and Glanzer (1990) attempted to explain these phenomena as a result of the subjects' adaptation to the distractor task, which allowed them to preserve at least some short-term memory capabilities. In their experiment, the long-term recency effect disappeared when the distractor after the last item differed from the distractors that preceded and followed the other items (e.g., arithmetic distractor task and word reading distractor task). Thapar and Greene challenged this theory. In one of their experiments, participants were given a different distractor task after every study item. According to Koppenaal and Glanzer's theory, no recency effect would be expected as subjects would not have had time to adapt to the distractor; yet such a recency effect remained in place in the experiment.<ref>{{cite journal |last1=Koppenaal |first1=L |last2=Glanzer |first2=M. |year=1990 |title=An examination of the continuous distractor task and the long-term recency effect |journal=Memory & Cognition |volume=18 |issue=2 |pages=183–195 |doi=10.3758/bf03197094 |pmid=2319960 |doi-access=free}}</ref>