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.     

Reply to Farrell and Lewandowsky: Recency—contiguity interactions predicted by the temporal context model

Farrell and Lewandowsky (2008) argued that the temporal context model (TCM; Howard & Kahana, 2002) cannot explain nonmonotonicities in the contiguity effect seen at extreme lags. However, TCM actually predicts these nonmonotonicities to the extent that end-of-list context persists as a retrieval cue during recall and to the extent that end-of-list context generates a recency effect. We show that the observed nonmonotonicity in the contiguity effect interacts with the recency effect, as predicted by TCM. In conditions, such as immediate and continualdistractor free recall, that exhibit strong recency, one observes more prominent nonmonotonicities in the contiguity effect than in conditions, such as delayed free recall, that attenuate recency. The nonmonotonicities in the contiguity effect at extreme lags, and the interactions between recency and contiguity, result from the role of end-of-list context as a retrieval cue in TCM. Results of an additional simulation based on the Howard and Kahana (2002) version of TCM may be downloaded from http://pbr.psychonomic-journals.org/content/supplemental.     

The conditional-recency dissociation is confounded with nominal recency: Should unitary models of memory still be devaluated?

The conditional-recency dissociation between immediate and delayed free recall FR; Farrell (Journal of Experimental Psychology: Learning, Memory, and Cognition, 36, 324–347, 2010) has critical implications regarding the prolonged debate between unitary and dual-store models of memory. In immediate FR, when the availability of items is controlled for, the recency of the final list item increases across the first few output positions. No such increase is found in delayed FR, with a trend in the opposite direction. This dissociation challenges temporal context TCM; Howard & Kahana (Journal of Mathematical Psychology, 46, 269–299, 2002) and distinctiveness SIMPLE; Brown, Neath, & Chater (Psychological Review, 114, 539–576, 2007) unitary models of memory and suggests the involvement of a short-term buffer in immediate FR. We show that this dissociation is confounded with the different magnitudes of nominal recency (i.e., the prevalence of the final list item) found in immediate as compared to delayed FR. By reshuffling output orders and comparing the empirical results to those of a null hypothesis of no output-order effect, we controlled for the greater prevalence of the final list item that has been observed in immediate FR. Under this control, we found no evidence for a dissociation in the tendency to recall the final list item across output positions. This finding suggests that the conditional-recency dissociation imposes no new constraint on unitary models of memory. More generally, we demonstrate how biases that influence measures of output-order tendencies (e.g., conditional recency) can be controlled for, thus yielding “purer” measures of these variables.     

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.     

Age dissociates recency and lag recency effects in free recall

The temporal relations among word-list items exert a powerful influence on episodic memory retrieval. Two experiments were conducted with younger and older adults in which the age-related recall deficit was examined by using a decomposition method to the serial position curve, partitioning performance into (a) the probability of first recall, illustrating the recency effect, and (b) the conditional response probability, illustrating the lag recency effect (M. W. Howard & M. J. Kahana, 1999). Although the older adults initiated recall in the same manner in both immediate and delayed free recall, temporal proximity of study items (contiguity) exerted a much weaker influence on recall transitions in older adults. This finding suggests that an associative deficit may be an important contributor to older adults' well-known impairment in free recall.     

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.     

Multiple mechanisms for recency with vowels and consonants

Three experiments were conducted to test the hypothesis that the difference in recency effect between vowel-contrasting and stop-contrasting lists of syllables in immediate ordered recall can be explained by item discriminability and regular short-term memory mechanisms, without any recourse to echoic memory or precategorical acoustic storage (PAS). In Experiment 1, the short-term memory mechanisms were manipulated by reducing amount of output interference and length of retention interval. The partial-report technique was used. The most important finding was the usual final-position recency effect (difference in recall between the fifth and sixth serial positions) for the vowel lists but not for the stop lists, regardless of the type of report. Thus the PAS theory could not be rejected. In Experiments 2 and 3, the last item was differentiated from the other items of the list, either by lengthening the interstimulus interval between the last and the next-to-last (Experiment 2) or by increasing the intensity of the last item (Experiment 3). In both cases, an increase of the final-position recency effect was found even for stop lists. Since a drop in recall errors was also obtained for the fourth item when its intensity was increased (von Restorff effect), this final-position recency effect for stop lists is likely to be due to item discriminability, and not to echoic memory for the last item. Item discriminability appeared to be the critical factor.     

Phonological short-term store and the nature of the recency effect: Evidence from neuropsychology

The recency effect in immediate recall of lists of unrelated words was investigated in P.V., a left hemisphere-damaged patient, who had a grossly reduced auditory verbal span, attributed to a selective impairment of a phonological short-term store. No recency effect was evident in free recall of auditorily presented material. When the patient was instructed to recall the final items of the list first, the recency performance remained defective, even though P.V. was able to adopt a recall from end order. In the case of visual presentation, P.V.'s free recall performance was within the normal range and a clear recency occurred in the recall from end condition. These results are consistent with the view that the standard recency effect in immediate free recall of auditorily presented material represents the output of a phonological short-term store to which ordinal retrieval strategies, in P.V.'s case unimpaired, are applied. Finally, the contributions of the phonological short-term store and the process of rehearsal to the recency effect and to immediate memory span performance are discussed.     

Recency effects in delayed recall of mouthed stimuli

Auditory presentation leads to greater recency effects in recall than does visual presentation. This phenomenon (the modality effect) is found in both free and serial recall and in both immediate and delayed recall. Silent mouthing of visually presented stimuli also leads to enhanced recency effects in immediate serial recall. Two experiments reported here extend the generality of the mouthing effect by demonstrating that enhanced recency effects of mouthed stimuli occur in delayed serial and free recall. These results are inconsistent with theories that attribute the modality effect to a purely auditory sensory memory.     

A Distributed Representation of Temporal Context

The principles of recency and contiguity are two cornerstones of the theoretical and empirical analysis of human memory. Recency has been alternatively explained by mechanisms of decay, displacement, and retroactive interference. Another account of recency is based on the idea of variable context (Estes, 1955; Mensink & Raaijmakers, 1989). Such notions are typically cast in terms of a randomly fluctuating population of elements reflective of subtle changes in the environment or in the subjects' mental state. This random context view has recently been incorporated into distributed and neural network memory models (Murdock, 1997; Murdock, Smith, & Bai, 2001). Here we propose an alternative model. Rather than being driven by random fluctuations, this formulation, the temporal context model (TCM), uses retrieval of prior contextual states to drive contextual drift. In TCM, retrieved context is an inherently asymmetric retrieval cue. This allows the model to provide a principled explanation of the widespread advantage for forward recalls in free and serial recall. Modeling data from single-trial free recall, we demonstrate that TCM can simultaneously explain recency and contiguity effects across time scales.     

Oscillator-based memory for serial order

A computational model of human memory for serial order is described (OSCillator-based Associative Recall [OSCAR]). In the model, successive list items become associated to successive states of a dynamic learning-context signal. Retrieval involves reinstatement of the learning context, successive states of which cue successive recalls. The model provides an integrated account of both item memory and order memory and allows the hierarchical representation of temporal order information. The model accounts for a wide range of serial order memory data, including differential item and order memory, transposition gradients, item similarity effects, the effects of item lag and separation in judgments of relative and absolute recency, probed serial recall data, distinctiveness effects, grouping effects at various temporal resolutions, longer term memory for serial order, list length effects, and the effects of vocabulary size on serial recall.     

Adult age differences in temporal and item memory

Three experiments tested whether the relationship between age differences in temporal and item memory depends on the degree to which the item memory measure relies on memory for context. The authors predicted a stronger relationship of temporal memory to free recall than to recognition memory. Results showed that age differences in temporal memory could be eliminated after controlling for free recall but not recognition memory performance. Under some conditions recognition memory accounted for a significant portion of age-related variance in temporal memory. These results challenge past research that has interpreted age differences in temporal and item memory as independent and suggest that a generalized decline in context memory may underlie reduced performance in older adults on all types of memory tests.     

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.     

Distinctiveness and Very Short-term Serial Position Effects

The serial position function reflects better memory for the first and last few items in a list than for the middle items. Four experiments examined the effects of temporal spacing on the serial position function for five-item lists that took between 0.5 seconds and 1.1 seconds to present. As with recall of far longer-lasting lists, recency and other robust serial position effects were observed with both free and serial recall. We demonstrate that temporal schedules of presentation control recall probability in predictable ways, and conclude that very fleeting lists obey similar principles as do longer-lasting lists. We compare both sets of findings with predictions from the dimensional distinctiveness framework.     

Evidence for similar principles in episodic and semantic memory: The presidential serial position function

When people recall a list of items that they have just experienced (an episodic memory task), the resulting serial position function looks strikingly similar to that observed when people are asked to recall the presidents of the United States (a semantic memory task). Despite the similarity in appearance, there is disagreement about whether the two functions arise from the same processes. A local distinctiveness model of memory, SIMPLE, successfully fit the presidential data using two underlying dimensions: one corresponding to item (or presidential) distinctiveness and the other to order (or positional) distinctiveness. According to the model, presidential primacy and recency are due to the same mechanisms that give rise to primacy and recency effects in both shortand long-term episodic memory. All of these primacy and recency effects reflect the relative distinctiveness principle (Surprenant & Neath, 2009): Items will be well remembered to the extent that they are more distinct than competing items at the time of retrieval.     

Serial recall of two-voice lists: Implications for theories of auditory recency and suffix effects

Substantial recency effects are found in immediate serial recall of auditory items. These recency effects are greatly reduced when an irrelevant auditory stimulus (a stimulus suffix) is presented. A number of accounts that have been proposed to explain these phenomena assume that auditory items are susceptible to masking or overwriting in memory. Later items overwrite earlier items, leading to an advantage for the last item, unless it is masked by a suffix. This assumption is called into question by evidence that presenting list items in two voices has no beneficial effect in immediate serial recall. In addition, it is shown that suffix effects on both terminal and preterminal list items are influenced by the physical similarity of the suffix to the terminal item and not by the physical similarity of the suffix to preterminal items.     

Examining the relationship between free recall and immediate serial recall: the effect of concurrent task performance

In 3 experiments, participants saw lists of 16 words for free recall with or without a 6-digit immediate serial recall (ISR) task after each word. Free recall was performed under standard visual silent and spoken-aloud conditions (Experiment 1), overt rehearsal conditions (Experiment 2), and fixed rehearsal conditions (Experiment 3). The authors found that in each experiment, there was no effect of ISR on the magnitude of the recency effect, but interleaved ISR disrupted free recall of those words that would otherwise be rehearsed. The authors conclude that ISR and recency cannot both be outputs from a unitary limited-capacity short-term memory store and discuss the possibility that the process of rehearsal may be common to both tasks.     

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.     

Amnesia,rehearsal, and temporal distinctiveness models of recall

Classical amnesia involves selective memory impairment for temporally distant items in free recall (impaired primacy) together with relative preservation of memory for recency items. This abnormal serial position curve is traditionally taken as evidence for a distinction between different memory processes, with amnesia being associated with selectively impaired long-term memory. However recent accounts of normal serial position curves have emphasized the importance of rehearsal processes in giving rise to primacy effects and have suggested that a single temporal distinctiveness mechanism can account for both primacy and recency effects when rehearsal is considered. Here we explore the pattern of strategic rehearsal in a patient with very severe amnesia. When the patient’s rehearsal pattern is taken into account, a temporal distinctiveness model can account for the serial position curve in both amnesic and control free recall. The results are taken as consistent with temporal distinctiveness models of free recall, and they motivate an emphasis on rehearsal patterns in understanding amnesic deficits in free recall.     

What can we learn about immediate memory from the development of children's free recall?

We ask the question: Which aspects of immediate memory performance improve with age? In two studies, we reexamine the widely held view that primary memory capacity estimates derived from children's immediate free recall are age invariant. This was done by assessing children's immediate free-recall accuracy while also measuring the order in which they elected to recall items (Experiment 1) and by encouraging children to begin free recall with items from towards the end of the presented list (Experiment 2). Across samples aged between 5 and 8 years we replicated the previously reported age-related changes in free-recall serial position functions when aggregated across all trials of the standard task, including an absence of age differences in the recency portion of this curve. However, we also show that this does not reflect the fact that primary memory capacity is constant across age. Instead, when we incorporate order of report information, clear age differences are evident in the recall of list-final items that are output at the start of a participant's response. In addition, the total amount that individuals recalled varied little across different types of free-recall tasks. These findings have clear implications for the use of immediate free recall as a means of providing potential indices of primary memory capacity and in the study of the development of immediate memory.