Academic journal article Memory & Cognition

Semantic Similarity Dissociates Short-From Long-Term Recency Effects: Testing a Neurocomputational Model of List Memory

Academic journal article Memory & Cognition

Semantic Similarity Dissociates Short-From Long-Term Recency Effects: Testing a Neurocomputational Model of List Memory

Article excerpt

The finding that recency effects can occur not only in immediate free recall (i.e., short-term recency) but also in the continuous-distractor task (i.e., long-term recency) has led many theorists to reject the distinction between short- and long-term memory stores. Recently, we have argued that long-term recency effects do not undermine the concept of a short-term store, and we have presented a neurocomputational model that accounts for both short- and long-term recency and for a series of dissociations between these two effects. Here, we present a new dissociation between short- and long-term recency based on semantic similarity, which is predicted by our model. This dissociation is due to the mutual support between associated items in the short-term store, which takes place in immediate free recall and delayed free recall but not in continuous-distractor free recall.

The concept of a limited-capacity short-term memory (STM) buffer has played a central role in theories of memory. Indeed, such a buffer is an essential component of computational models that account for quantitative data in tasks of immediate and delayed free recall, including the search of associative memory model (SAM; Raaijmakers & Shiffrin, 1981; see also Atkinson & Shiffrin, 1968; Kahana, 1996; Waugh & Norman, 1965) and the adaptive control of thought-rational model (ACT-R; Anderson, Bothell, Lebiere, & Matessa, 1998). However, the need to postulate the existence of such a buffer to account for free recall data seems to have fallen into disrepute (Bjork, 2001 ; Bjork & Whitten, 1974; Crowder, 1982; Glenberg & Swanson, 1986; Greene, 1986, 1992; Howard & Kahana, 1999; Nairne, Neath, Serra, & Byun, 1997; Neath, 1993; Tan & Ward, 2000; but see Healy & McNamara, 1996, and Raaijmakers, 1993, for a defense). Here, we present new data supporting the original notion that a short-term buffer is involved in producing the recency effect in immediate free recall. We will not address serial order recall, for which the evidence for a short-term buffer is thought to be weaker (Nairne, 2002).

One of the findings that initially suggested a role for a short-term buffer was the existence of a recency effect (the enhanced recall of the last items of a list) in immediate free recall (Atkinson & Shiffrin, 1968; Glanzer, 1972; Murdock, 1967). This effect was interpreted as reflecting the unloading of the most recent items from a limitedcapacity store, with earlier items having been displaced from the buffer by the more recent items. Because distractor tasks are thought to fill the capacity of the buffer, this helped explain why, when a distractor interval is inserted between list presentation and recall-a task known as delayed free recall-the recency effect is eliminated (Glanzer & Cunitz, 1966; Postman & Phillips, 1965).

A central reason for questioning the need for such a buffer was the discovery of recency effects in a paradigm that could not be interpreted as being mediated by the short-term buffer. The long-term memory (LTM) paradigm involved free recall of a list of words in which a distractor activity was inserted before and after every word in the list, including the last word (i.e., continuous-distractor free recall; see, e.g., Bjork & Whitten, 1974; Glenberg, Bradley, Kraus, & Renzaglia, 1983; Glenberg & Swanson, 1986; Tzeng, 1973). Because the absence of recency effects in delayed free recall had been perceived as one signature for the existence of a short-term buffer, the appearance of recency effects in continuous-distractor free recall, despite the distractor activity after the last item, led many investigators to question the existence of a buffer. Instead of postulating a short-term buffer, they argued that the recency effect reflects a more general property of memory and that a single memory store provides a more parsimonious account of recency effects (Crowder, 1982; Greene, 1986). …

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