Semantic similarity dissociates short- from long-term recency effects: Testing a neurocomputational model of list memory

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 (ie., 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.     

Dissociation of short- and long-term face memory: evidence from long-term recency effects in temporal lobe epilepsy

We tested whether memory deficits in temporal lobe epilepsy (TLE) are better described by a single- or dual-store memory model. To this aim, we analyzed the influence of TLE and proactive interference (PI) on immediate and 24-h long-term recency effects during face recognition in 16 healthy participants and 18 right and 21 left non-surgical TLE patients. PI in healthy participants or TLE erased the long-term recency effect, but left the immediate recency effect unaffected. Although the immediate recency effect was still visible in right TLE patients, the number of detected recency items during immediate recognition was decreased in right TLE compared to left TLE. Right TLE was also related to decreased detection of pre-recency items during delayed recognition compared to left TLE, and decreased detection of pre-recency items during immediate recognition under PI. The results show that the temporal lobes are necessary for the long-term recency effect, but not for the immediate recency effect, and thus speak for a dissociation of short- and long-term memory for faces. Right TLE is related to more severe long-term memory deficits than left TLE and is also related to additional short-term memory deficits for faces.     

Recency effect in recall of a word list when an immediate memory task is performed after each word presentation

Subjects studied 12-word lists for free recall. During presentation of the lists, each word was followed by a supraspan sequence of digits, which the subjects tried to reproduce. This task, unlike those used in previous research with this continual distractor procedure, presumably taxed immediate memory capacity to the full. Nevertheless, the word recall data showed a pronounced recency effect. Moreover, the magnitude of the recency effect was found to be just as great with this task as with a more typical task in which the demands on immediate memory are likely to be fewer. These findings reinforce the emerging view that the recency effect need not be the product of immediate memory.     

Contextual variability and serial position effects in free recall.

In immediate free recall, words recalled successively tend to come from nearby serial positions. M. J. Kahana (1996) documented this effect and showed that this tendency, which the authors refer to as the lag recency effect, is well described by a variant of the search of associative memory (SAM) model (J. G. W. Raaijmakers & R. M. Shiffrin, 1980, 1981). In 2 experiments, participants performed immediate, delayed, and continuous distractor free recall under conditions designed to minimize rehearsal. The lag recency effect, previously observed in immediate free recall, was also observed in delayed and continuous distractor free recall. Although two-store memory models, such as SAM, readily account for the end-of-list recency effect in immediate free recall, and its attenuation in delayed free recall, these models fail to account for the long-term recency effect. By means of analytic simulations, the authors show that both the end of list recency effect and the lag recency effect, across all distractor conditions, can be explained by a single-store model in which context, retrieved with each recalled item, serves as a cue for subsequent recalls.     

Serial position functions for recognition of olfactory stimuli

Two experiments examined item recognition memory for sequentially presented odours. Following a sequence of six odours participants were immediately presented with a series of two-alternative forced-choice (2AFC) test odours. The test pairs were presented in either the same order as learning or the reverse order of learning. Method of testing was either blocked (Experiment 1) or mixed (Experiment 2). Both experiments demonstrated extended recency, with an absence of primacy, for the reverse testing procedure. In contrast, the forward testing procedure revealed a null effect of serial position. The finding of extended recency is inconsistent with the single-item recency predicted by the two-component duplex theory (Phillips & Christie, 1977). We offer an alternative account of the data in which recognition accuracy is better accommodated by the cumulative number of items presented between item learning and item test.     

The influence of word frequency on recency effects in directed free recall

Leading theoretical explanations of recency effects are designed to explain the reported absence of a word frequency effect on recall of words from recency serial positions. The present study used a directed free-recall procedure (J. J. Dalezman, 1976) and manipulated the frequency composition of the word lists (pure and mixed). Overall, with pure lists, a greater proportion of high-frequency (HF) words were recalled than low-frequency (LF) words, and with mixed lists, a greater proportion of LF words were recalled than HF words. Of importance, this recall advantage for one frequency over the other as a function of list composition was evident across the last three serial positions, indicating an influence of word frequency on recency effects that is dependent on the frequency composition of the lists. These results challenge one of the major assumptions on which several theories of recency effects have been based.     

Recency effects in direct and indirect memory tasks

In three experiments, subjects learned two lists under incidental conditions and were then given either a part-word or a word (extralist associate) cue. Each cue was related to one word in each list. Half the subjects were given production instructions (an indirect memory test), and half were given cued recall instructions (a direct memory test). When the interval between List 2 and the test was shortened, recency effects were found for part-word cues for both cued recall and production instructions. Little or no recency effects were found with word cues. These results are incompatible with a simple distinction between the types of memory trace or information that are tapped by direct as opposed to indirect memory tasks. Possible causes for the recency effect and for the difference between word and part-word cues are discussed.     

Semantic cuing and the scale insensitivity of recency and contiguity

In recalling a set of previously experienced events, people exhibit striking effects of recency, contiguity, and similarity: Recent items tend to be recalled best and first, and items that were studied in neighboring positions or that are similar to one another in some other way tend to evoke one another during recall. Effects of recency and contiguity have most often been investigated in tasks that require people to recall random word lists. Similarity effects have most often been studied in tasks that require people to recall categorized word lists. Here we examine recency and contiguity effects in lists composed of items drawn from 3 distinct taxonomic categories and in which items from a given category are temporally separated from one another by items from other categories, all of which are tested for recall. We find evidence for long-term recency and for long-range contiguity, bolstering support for temporally sensitive models of memory and highlighting the importance of understanding the interaction between temporal and semantic information during memory search.     

Effects of association and repetition in memory for temporal order

Temporal order recognition memory has been examined previously with tasks involving a recency judgment between a pair of items in a preceding string. Recency judgments are impaired when the earlier item is repeated. The present study employed the comparative recency judgment paradigm, with the lists composed of words. The effect of the inclusion in the list of a high associate of the earlier test item was examined and compared to the effect of repetition. Associative interference was observed, but not in all conditions. Direction of association was a significant factor. The results were interpreted in terms of a model of word recognition proposed by Morton.     

Serial position-dependent false memory effects*

ABSTRACT

Evidence for false recognition within seconds of encoding suggests that semantic-associative influences are not restricted to long-term memory, consistent with unitary memory accounts but contrary to dual store models. The present study sought further relevant evidence using a modified free recall converging associates task where participants studied 12-item lists composed of 3 semantically distinct quartets (sublists) related to a separate, non-presented theme word (i.e., words 1–4/theme1, 5–8/theme2, and 9–12/theme3). This list construction permits assessment of false recall errors from each sublist, and, particularly, the primacy and recency sublists that have been linked to long- and short-term memory stores. Experiment 1 tested immediate free recall for items. Associative false memories were evident from all sublists, however, significantly less so from the recent sublist, which also showed the highest levels of veridical memory. By inserting a brief (3?s) distractor prior to recall, Experiment 2 selectively reduced veridical memory and increased false memory for the recent sublist while leaving the primacy sublist unaffected. These recall results converge with prior evidence indicating the immediacy of false recognition, and can be understood within a unitary framework where the differential availability of verbatim features and gist-based cues affect memory for primacy and recency sublists.     

Conditions for positive and negative recencies in running memory-span recognition

A positive recency effect in a running-span recognition procedure was obtained in Experiment 1 for hits and for intratrial false alarms. In running recall procedures, recency does not fit well with an active updating hypothesis. In Experiment 2, in which the beginning of the target set was marked with a cue upon presentation, the recency effects disappeared. In Experiments 3 and 4 participants were forced to maintain 2 items in memory until the last one was presented for recognition. These three items were the target set. When the last item presentation was uncertain—because of the variable length list—an unexpected negative recency effect appeared. An explanation for this change from positive to negative recency is offered based on the sharing of attentional resources put forward by others for similar procedures.     

The word frequency effect in recognition memory versus repetition priming

The role of word frequency in recognition memory and repetition priming was investigated by using a manipulation of attention. In Experiment 1, the lexical decision task produced greater repetition priming for low-frequency words than for high-frequency words following either the attended or the unattended study condition. The recognition memory test, on the other hand, showed a low-frequency word advantage only following the attended study condition. Furthermore, this advantage was limited to the measure of recognition memory based on conscious recollection of the study episode. In Experiment 2, a speeded recognition memory test replicated the pattern obtained with the unspeeded recognition memory test in Experiment 1. These results argue against the view that the word frequency effects in recognition memory and repetition priming have the same origin. Instead, the results suggest that the word frequency effect in recognition memory has its locus in conscious recollection.     

Scaling behavior in the temporal context model

The Temporal Context Model (TCM) postulates a distributed representation of temporal context that provides the cue for episodic recall tasks. TCM, coupled with the Luce Choice Rule for determining probability of recall, a conjunction referred to as TCMFR, is able to explain the existence of the long-term recency effect, as well as predicting the persistence of associative effects even with the inclusion of a delay between items. Here, quantitative predictions of TCMFR such as the magnitude of the delay interval is increased in continuous-distractor free recall are developed. The magnitude of the recency effect is operationally defined as the ratio of the probability of first recall (PFR) of the last list item to the PFR of the next-to-last item. Properties of associative effects are operationalized by using analogous measures derived from conditional response probability (CRP) curves. TCMFR predicts a decrease in recency with increasing delay. The rate of this decay and the qualitative pattern of change with increasing delay depend on the rate of contextual drift. For a range of values of the rate of contextual drift, TCMFR also predicts a transient increase in the recency effect as the length of the delay increases from zero. The model predicts that contiguity effects in free recall should follow a similar pattern, but that associative asymmetry, ubiquitously observed in free recall, should decay monotonically with increases in the delay interval.     

A dual-probe recognition memory task for use during sustained operations

Although memory has been shown to be greatly affected by sleep loss, there is an absence of data on the effect of sustained work on recognition memory. This is unfortunate because recognition, unlike free recall, can be analyzed to separate effects on memory sensitivity from effects on report bias. Based upon work with single-probe recognition memory tasks, we developed a clual-probe recognition task for practical use in sustained work paradigms. The task requires 20 min to complete and yields an array of performance variables that can be used to conduct signal detection analyses, to assess serial-position effects, and to evaluate speed-accuracy functions.     

Recency, immediate recognition memory, and reaction time

Four classes of possible mechanisms for short-term item recognition are distinguished: (I) pure list-search, (II) direct-access activation (or trace strength) discrimination, (III) mixtures (of I and II), and (IV) response-association. Manipulations of recency, particularly of negative probe items, provide critical tests between them. Two experiments are reported using Sternberg' s 1966 varied-set reaction time paradigm, coupled with procedures intended to minimize rehearsal and control the recency of probes and memory set items. RT and error rate were greater for negative probe items that had recently been presented than for items less recently presented, and this effect increased with positive set size. In contrast, positive RT was, except for the initial item, a decreasing function of recency (= serial position), and there was no additional effect of set size per se. A brief filled delay between list and probe increased positive RT but not the slope of the set size function. These and other findings appear to reject models of Classes I and IV and, while implying some direct discrimination of an item's recency, require modification of the models of Classes II and III. The implications are discussed with respect to the relation between the two versions of Sternberg's paradigm and also in connection with facilitatory “priming” effects in memory.     

Mental imagery and the distinction between primary and secondary memory

Previous research has shown that the imageability of stimulus material affects the secondary memory (SM) component of free recall, but not the primary memory (PM) component, and that a negative recency effect is only observed for material of high imageability. It was found that interactive imagery instructions affected the SM component, but not the PM component; separative imagery instructions led to an increased PM component and a reduced SM component. A negative recency effect can be observed in an initial, delayed recall test. However, it is removed by imagery mnemonic instructions. This supports the idea that the negative recency effect is caused by the fact that subjects do not normally image the last few words presented in a free-recall task.     

Serial position effects in recognition memory for odors: A reexamination

Seven experiments examined recognition memory for sequentially presented odors. Following Reed (2000), participants were presented with a sequence of odors and then required to identify an odor from the sequence in a test probe comprising 2 odors. The pattern of results obtained by Reed (2000, although statistically marginal) demonstrated enhanced recognition for odors presented at the start (primacy) and end (recency) of the sequence: a result that we failed to replicate in any of the experiments reported here. Experiments 1 and 3 were designed to replicate Reed (2000), employing five-item and seven-item sequences, respectively, and each demonstrated significant recency, with evidence of primacy in Experiment 3 only. Experiment 2 replicated Experiment 1, with reduced interstimulus intervals, and produced a null effect of serial position. The ease with which the odors could be verbally labeled was manipulated in Experiments 4 and 5. Nameable odors produced a null effect of serial position (Experiment 4), and hard-to-name odors produced a pronounced recency effect (Experiment 5); nevertheless, overall rates of recognition were remarkably similar for the two experiments at around 70%. Articulatory suppression reduced recognition accuracy (Experiment 6), but recency was again present in the absence of primacy. Odor recognition performance was immune to the effects of an interleaved odor (Experiment 7), and, again, both primacy and recency effects were absent. There was no evidence of olfactory fatigue: Recognition accuracy improved across trials (Experiment 1). It is argued that the results of the experiments reported here are generally consistent with that body of work employing hard-to-name visual stimuli, where recency is obtained in the absence of primacy when the retention interval is short.     

Primacy and recency in primed free association and associative cued recall

Two experiments compared the serial positions of primed words in an implicit free association test with words recalled in a cued recall test. In both tests, weakly or strongly related word pairs were studied, and the first words of each pair formed the test cues. In the implicit test, weakly related words pairs showed primacy and extended recency effects but strongly related word pairs did not. In the explicit test, both weakly and strongly related word pairs showed primacy and extended recency effects. These functional dissociations between implicit and explicit memory tests indicate that strongly related word pairs are encoded together because they have unitized memory representations that function as integrated units without requiring any additional associative links to be made, but that an additional system or process is required to strengthen weakly related word pairs during encoding. In addition, a further additional system or process is accessed by explicit retrieval.