Proactive Interference in Short-Term Memory as a Function of Prior-Item Retention Interval

Magnitude and sources of proactive interference in visual memory

Proactive interference - the disruptive effect of old memories on new learning - is a long-established forgetting mechanism, yet there are doubts about its impact on visual working memory and uncertainty about the kinds of information that cause proactive interference. The present study aimed to assess these issues in three experiments using a modified recent probes task. Participants encoded four target images on each trial and determined whether a probe matched one of those targets. In Experiment 1, probes matching targets from trial N-1 or N-3 damaged responding in relation to a novel probe. Proactive interference was also produced by probes differing in state to a previously experienced target. This was further assessed in Experiments 2 and 3. Here, probes differing in colour to a previous target, or matching the general target category only, produced little proactive interference. Conversely, probes directly matching a prior target, or differing in state information, hindered task performance. This study found robust proactive interference in visual working memory that could endure over multiple trials, but it was also produced by stimuli closely resembling an old target. This challenges the notion that proactive interference is produced by an exact representation of a previously encoded image.

Buildup and release from proactive interference - Cognitive and neural mechanisms

Interference from related memories is generally considered one of the major causes of forgetting in human memory. The most prevalent form of interference may be proactive interference (PI), which refers to the finding that memory of more recently studied information can be impaired by the previous study of other information. PI is a fairly persistent effect, but numerous studies have shown that there can also be release from PI. PI buildup and release have primarily been studied using paired-associate learning, the Brown-Peterson task, or multiple-list learning. The review first introduces the three experimental tasks and, for each task, summarizes critical findings on PI buildup and release, from both behavioral and imaging work. Then, an overview is provided of suggested cognitive mechanisms operating on the encoding and retrieval stages as well as of neural correlates of these mechanisms. The results indicate that, in general, both encoding and retrieval processes contribute to PI buildup and release. Finally, empirical gaps in the current work are emphasized and suggestions for future studies are provided.

Short Term Forgetting in the Absence of Proactive Interference

It has been claimed that the short-term forgetting shown by the Peterson technique is entirely due to proactive interference from prior experimental items. Two experiments investigated this by studying forgetting when prior items were avoided by testing subjects only once. Both experiments showed significant forgetting, although the degree of forgetting was less than with a multitrial procedure. On the basis of this and other results it is suggested that the Peterson technique comprises two components, a primary memory component which decays within 6 sec, and a more stable secondary memory component. Forgetting with the multitrial procedure is attributed principally to the need to use temporal retrieval cues to avoid confusion between successive items; longer retention intervals are associated with reduced temporal discriminability and hence poorer recall.

Effects of Proactive Interference and Rehearsal on the Primary and Secondary Components of Short-Term Retention

Under the conditions of the distractor paradigm, short-term retention declines to a minimum in a very brief period. The rapid forgetting can be said to reflect the declining contribution of the short-term store or primary memory and the asymptote can be taken as a measure of the contribution of the long-term store or secondary memory. It was shown that manipulating proactive effects by varying the recency of prior material affected only the primary memory component of the short-term retention function. On the other hand manipulating the difficulty of the subsidiary task performed during the retention period with proactive effects held constant affected both the primary and the secondary components. The results were discussed with respect to the relation between the two memory components and the idea that proactive effects are limited to long-term store.

Decay theory of immediate memory: From Brown (1958) to today (2014)

This work takes a historical approach to discussing Brown's (1958) paper, "Some Tests of the Decay Theory of Immediate Memory". This work was and continues to be extremely influential in the field of forgetting over the short term. Its primary importance is in establishing a theoretical basis to consider a process of fundamental importance: memory decay. Brown (1958) established that time-based explanations of forgetting can account for both memory capacity and forgetting of information over short periods of time. We discuss this view both in the context of the intellectual climate at the time of the paper's publication and in the context of the modern intellectual climate. The overarching theme we observe is that decay is as controversial now as it was in the 1950s and 1960s.

Revisiting the time course of inter-trial feature priming in singleton search

Current theories of the locus of inter-trial priming effects in efficient visual search posit an early perceptual component that reflects the short-term influence of a memory trace for low-level stimulus attributes. Despite the fact that this memory trace is hypothesized to be short term, and should therefore have a diminishing influence on performance over time, there has been relatively little study of the effect of time alone on singleton priming effects. The present series of experiments addresses this issue by systematically examining the effect of time on the priming of pop-out (PoP) effect. In Experiment 1, we show that the PoP effect does indeed diminish with increases in the RSI between trials, and does so in accord with a power-law function. In Experiment 2, we show that temporal discriminability of trial n - 1 from the trial that precedes it does not contribute to PoP effects. The results of Experiment 3 revealed two key results: (1) the PoP effect survives an equivalent number of intervening trials across very different RSI conditions; and (2) the cumulative target repetition benefit does depend on the RSI between trials. Together, the results favor neither a simple passive decay nor a strong episodic retrieval account of the PoP effect.

The scope and control of attention as separate aspects of working memory

The present study examines two varieties of working memory (WM) capacity task: visual arrays (i.e., a measure of the amount of information that can be maintained in working memory) and complex span (i.e., a task that taps WM-related attentional control). Using previously collected data sets we employ confirmatory factor analysis to demonstrate that visual arrays and complex span tasks load on separate, but correlated, factors. A subsequent series of structural equation models and regression analyses demonstrate that these factors contribute both common and unique variance to the prediction of general fluid intelligence (Gf). However, while visual arrays does contribute uniquely to higher cognition, its overall correlation to Gf is largely mediated by variance associated with the complex span factor. Thus we argue that visual arrays performance is not strictly driven by a limited-capacity storage system (e.g., the focus of attention; Cowan, 2001), but may also rely on control processes such as selective attention and controlled memory search.

Reversing the course of forgetting

Forgetting functions were generated for pigeons in a delayed matching-to-sample task, in which accuracy decreased with increasing retention-interval duration. In baseline training with dark retention intervals, accuracy was high overall. Illumination of the experimental chamber by a houselight during the retention interval impaired performance accuracy by increasing the rate of forgetting. In novel conditions, the houselight was lit at the beginning of a retention interval and then turned off partway through the retention interval. Accuracy was low at the beginning of the retention interval and then increased later in the interval. Thus the course of forgetting was reversed. Such a dissociation of forgetting from the passage of time is consistent with an interference account in which attention or stimulus control switches between the remembering task and extraneous events.

Reversing the signaled magnitude effect in delayed matching to sample: delay-specific remembering

Pigeons performed a delayed matching-to-sample task in which large or small reinforcers for correct remembering were signaled during the retention interval. Accuracy was low when small reinforcers were signaled, and high when large reinforcers were signaled (the signaled magnitude effect). When the reinforcer-size cue was switched from small to large partway through the retention interval, accuracy accordingly changed from low to high. The opposite happened when the cue was switched from large to small. This dissociation of forgetting from the passage of time raises the possibility that remembering is delay-specific. The reversal of the signaled magnitude effect during the retention interval is consistent with an attentional account in which the stimulus control of remembering is influenced by extraneous events.

Moving and memorizing: motor planning modulates the recency effect in serial and free recall

Motor planning has generally been studied in situations where participants carry out physical actions without a particular purpose. Yet in everyday life physical actions are usually carried out for higher-order goals. We asked whether two previously discovered motor planning phenomena--the end-state comfort effect and motor hysteresis--would hold up if the actions were carried out in the service of higher-order goals. The higher-order goal we chose to study was memorization. By focusing on memorization, we asked not only how and whether motor planning is affected by the need to memorize, but also how memory performance might depend on the cognitive demands of motor planning. We asked university-student participants to retrieve cups from a column of drawers and memorize as many letters as possible from the inside of the cups. The drawers were opened either in a random order (Experiment 1) or in a regular order (Experiments 2 and 3). The end-state comfort effect and motor hysteresis were replicated in these conditions, indicating that the effects hold up when physical actions are carried out for the sake of a higher-order goal. Surprisingly, one of the most reliable effects in memory research was eliminated, namely, the tendency of recent items to be recalled better than earlier items--the recency effect. This outcome was not an artifact of memory being uniformly poor, because the tendency of initial items to be recalled better than later items--the primacy effect--was obtained. Elimination of the recency effect was not due to the requirement that participants recall items in their correct order, for the recency effect was also eliminated when the items could be recalled in any order (Experiment 3). These and other aspects of the results support recent claims for tighter links between perceptual-motor control and intellectual (symbolic) processing than have been assumed in the past.

No temporal decay in verbal short-term memory

Many models of short-term memory (STM) ascribe an important role to temporal decay and forgetting because of the passage of time alone. We argue against decay as the primary form of forgetting from STM, and suggest that new experimental methodologies and recent models provide new perspectives on the old issue of the causes of forgetting. We show that several classic sources of evidence for time-based forgetting can be re-interpreted in terms of an interference-based view, and that new experiments provide compelling evidence against decay. We conclude that progress requires moving beyond demonstrations of qualitative effects and focusing instead on testing quantitative predictions of models.

The Importance of Temporal Distinctiveness for Forgetting Over the Short Term

Rapidly forgetting information once attention is diverted seems to be a ubiquitous phenomenon. The cause of this rapid decline has been debated for decades; some researchers claim that memory traces decay as a function of time out of the focus of attention, whereas others claim that prior memory traces cause confusability by interfering with the current trace. Here we demonstrate that performance after a long delay can be better than performance after a short delay if the temporal confusability between the current item and previous items is reduced. These results provide strong evidence for the importance of temporal confusability, rather than decay, as the cause of forgetting over the short term.

What are the differences between long-term, short-term, and working memory?

In the recent literature there has been considerable confusion about the three types of memory: long-term, short-term, and working memory. This chapter strives to reduce that confusion and makes up-to-date assessments of these types of memory. Long- and short-term memory could differ in two fundamental ways, with only short-term memory demonstrating (1) temporal decay and (2) chunk capacity limits. Both properties of short-term memory are still controversial but the current literature is rather encouraging regarding the existence of both decay and capacity limits. Working memory has been conceived and defined in three different, slightly discrepant ways: as short-term memory applied to cognitive tasks, as a multi-component system that holds and manipulates information in short-term memory, and as the use of attention to manage short-term memory. Regardless of the definition, there are some measures of memory in the short term that seem routine and do not correlate well with cognitive aptitudes and other measures (those usually identified with the term "working memory") that seem more attention demanding and do correlate well with these aptitudes. The evidence is evaluated and placed within a theoretical framework depicted in Fig. 1.

Time does not cause forgetting in short-term serial recall

Time-based theories expect memory performance to decline as the delay between study and recall of an item increases. The assumption of time-based forgetting, central to many models of serial recall, underpins their key behaviors. Here we compare the predictions of time-based and event-based models by simulation and test them in two experiments using a novel manipulation of the delay between study and retrieval. Participants were trained, via corrective feedback, to recall at different speeds, thus varying total recall time from 6 to 10 sec. In the first experiment, participants used the keyboard to enter their responses but had to repeat a word (called the suppressor) aloud during recall to prevent rehearsal. In the second experiment, articulation was again required, but recall was verbal and was paced by the number of repetitions of the suppressor in between retrieval of items. In both experiments, serial position curves for all retrieval speeds overlapped, and output time had little or no effect. Comparative evaluation of a time-based and an event-based model confirmed that these results present a particular challenge to time-based approaches. We conclude that output interference, rather than output time, is critical in serial recall.

The effects of periodic visual occlusion on ball catching

Four experiments were conducted to examine the effects of periodic visual occlusion on one-handed ball catching. Tennis balls were projected one at a time over distances of 8-12 m, and liquid-crystal visual occlusion spectacles provided intermittent vision by opening and closing the lens shutters at different frequencies. As well as frequency, we manipulated duty cycle, or the proportion of time that the lenses were open. Generally, catching performance deteriorated as frequency was reduced. Although longer visual samples (i.e., increased duty cycle) mediated this effect to some extent, the most potent variable was the time between visual samples; performance deteriorated rapidly when this interval was greater than 80 ms (i.e., 10 Hz with 20-ms lens open times). Presumably this occurred because subjects had difficulty integrating visual information separated by longer temporal intervals.

Neural network for encoding immediate memory in phonological processing

The aim of this fMRI study was to identify neuroanatomical substrates of immediate memory underlying phonological processing. To distinguish encoding of immediate memory from rehearsal, participants were required to match tones from the first and last positions of a three-syllable list to their following probes in an immediate-recognition paradigm. The first position task included intervening distractors between the target and probe. Increased activations were found in the left inferior frontal gyrus, right lateral cerebellum, and medial frontal gyrus for the target tone in first position. This network mediates articulatory encoding in immediate-response, and articulatory rehearsal in delayed-response paradigms. These findings support a working memory model in which rehearsal is optional, while encoding is an obligatory component of the phonological loop.

Remembering over the short-term: the case against the standard model

Psychologists often assume that short-term storage is synonymous with activation, a mnemonic property that keeps information in an immediately accessible form. Permanent knowledge is activated, as a result of on-line cognitive processing, and an activity trace is established "in" short-term (or working) memory. Activation is assumed to decay spontaneously with the passage of time, so a refreshing process-rehearsal-is needed to maintain availability. Most of the phenomena of immediate retention, such as capacity limitations and word length effects, are assumed to arise from trade-offs between rehearsal and decay. This "standard model" of how we remember over the short-term still enjoys considerable popularity, although recent research questions most of its main assumptions. In this chapter I review the recent research and identify the empirical and conceptual problems that plague traditional conceptions of short-term memory. Increasingly, researchers are recognizing that short-term retention is cue driven, much like long-term memory, and that neither rehearsal nor decay is likely to explain the particulars of short-term forgetting.

VERBAL LEARNING AND MEMORY: Does the Modal Model Still Work?

This chapter focuses on recent research concerning verbal learning and memory. A prominent guiding framework for research on this topic over the past three decades has been the modal model of memory, which postulates distinct sensory, primary, and secondary memory stores. Although this model continues to be popular, it has fostered much debate concerning its validity and specifically the need for its three separate memory stores. The chapter reviews research supporting and research contradicting the modal model, as well as alternative modern frameworks. Extensions of the modal model are discussed, including the search of associative memory model, the perturbation model, precategorical acoustic store, and permastore. Alternative approaches are discussed including working memory, conceptual short-term memory, long-term working memory, short-term activation and attention, processing streams, the feature model, distinctiveness, and procedural reinstatement.

An in-depth analysis of lead effects in a delayed spatial alternation task: assessment of mnemonic effects, side bias, and proactive interference

This study examined the effects of chronic postweaning lead (Pb) exposure in Long-Evans rats on a series of spatial alternation tasks. All tasks were administered in automated testing chambers, with a nosepoke as the critical response. While neither Pb-exposed group (median blood lead levels: 19 and 39 micrograms/dl, respectively) was impaired in learning the alternation rule, both groups performed more poorly than controls on the alternation task with variable intertrial delays (0, 10, 20, and 40 s). The deficit was constant across delays, arguing against memory dysfunction. Analyses of the responses on individual trials shed further light on the impaired and spared processes in the Pb-exposed rats. First, these analyses revealed stronger side biases in the higher exposure group. One interpretation is that these animals experienced impatience when the longer delays were included, making it more difficult for them to inhibit a prepotent response to a preferred side. In contrast, these trial-by-trial analyses revealed that several other factors-retention interval, semantic proactive interference, and temporal discriminability-exerted similar effects on performance in the control and lead-exposed animals. The use of logistic regression for these trial-by-trial analyses provided a means of simultaneously assessing the influence of several variables on performance, a significant advantage when there is confounding or interactions between variables.

Short-term memory: where do we stand?

Two empirical challenges to the traditional "modal model" of short-term memory are that neither the Brown-Peterson distractor technique nor the recency effect in recall is well accommodated by that position. Additionally, the status of memory stores as such, has declined in response to proceduralist thinking. At the same time, the concept of coding, on which the modal model is silent, is increasingly central to memory theory. People need to remember things in the short term, but a dedicated store does not need to be the agency.

Parafoveal identification asymmetry in a lateral masking effect

The degree to which the identification of a parafoveally presented letter target was impaired by being flanked by a foveal or peripheral nontarget at a target-mask interval of zero, 75, or 150 msec, was examined. Peripheral placement of the nontarget was more disruptive than foveal placement, and this asymmetry was significantly more pronounced at a 75-msec interval than at either of the other two. This finding is consonant with explanations of the asymmetry based on target visibility rather than on criterion or response factors.

Short-term retention of tactile stimulation

In three experiments subjects were required to reproduce after varying delays the locus of a tactile stimulation delivered to the upper-side of the arm. During the retention periods subjects either performed a subsidiary, arithmetic task or rested. Recall, as measured by accuracy in reproducing the locus of stimulation, decreased as a function of retention interval, asymptoting after approximately 5 s. Performance was poorer in the subsidiary task condition than in the rest condition; however, the effect of the subsidiary task appeared to be more on subject recall strategies than on rehearsal capacity. No evidence of proactive interference effects was found, and a decay interpretation of forgetting of discrete tactile stimuli in the short-term memory distractor paradigm was favoured.