Forgotten but not gone: savings for pictures and words in long-term memory

Five experiments examined the relearning of words, simple line-drawing pictures, and complex photographic pictures after retention intervals of 1 to 10 weeks. For those items that were neither recalled nor recognized, the identical item was relearned better than an unrelated control item, as measured by a recall test following relearning. This relearning advantage in recall held for all three classes of material and extended to the cross-modality case (i.e., picture-word and word-picture) and the same-referent case (i.e., two pictures of the same object). However, recognition tests of relearning failed to detect this same relearning advantage for apparently forgotten items. Taken together, these findings conflict with the existing account of savings. Most fundamental, the classic argument that relearning serves a trace-strengthening function is undetermined by the observed recall-recognition contrast. An alternative explanation of savings is suggested wherein relearning assists retrieval of information, thereby affecting recall in particular.     

Attentional capture by items that match episodic long-term memory representations

A remarkable ability of the human visual system is the implementation of attentional control settings (ACSs) that govern what stimuli capture or hold attention. We provide evidence that ACSs can be specified by episodic long-term memory representations. In all experiments, participants memorized 30 images of objects that they then monitored for in an attention task, inducing an episodic-based ACS. In Experiments 1a and 1b, only studied cues in a cueing task captured attention. We confirmed these cueing effects reflect capture by testing for inhibition of return in Experiment 2a, and controlled for perceptual masking by cues in Experiment 2b. In Experiment 3 we determined that ACSs are specifically supported by episodic retrieval, by dividing studied images into two sets and designating one as the targets in a rapid serial visual presentation task: Only target-set matching distractors produced a spatial blink (captured attention). These results extend our understanding of the representations specifying ACSs.     

Short-term memory for repeated and non-repeated items

Digit sequences containing repeated items are retained differently in short-term memory from sequences containing no repeated items. The repeated items are remembered better or worse than items in the corresponding positions of “all-different” sequences depending on the number of times the item is repeated, the number of items repeated, the number of items intervening between the occurences of a repeated item, and the position of the repeated items in relation to the beginning and end of the sequence. In every type of repetition studied, except one, memory for the non-repeated items in sequences with repeated items is better than for the corresponding items of all-different sequences. This is true in some cases despite significant specific interference between the (non-repeated) items following the separated occurrences of repeated items. The negative effects in memory for repeated items and the positive effects in memory for non-repeated items are greater when the items are presented at the rate of five per sec. than at one per sec., contrary to the hypothesis that differential rehearsal is responsible for these effects. The results are interpreted as supporting an “associative,” as opposed to a “non-associative,” theory of short-term memory, as this distinction is defined in the paper.     

Recognition memory for prose items in noise

Using a probe-recognition technique the signal detection theory parameters d' and Beta were estimated for three types of probe (common surnames, uncommon surnames and synonyms) for material contained in a prose passage. Subjects were presented with the prose passage either in the presence of noise (85dBA) or in quiet (60dBA). In two experiments the effects of noise on auditory and visual presentation of the passage were studied. In both cases the recognition test took place in quiet. Noise decreased values of Beta for rare names and increased Beta for common names in both auditory and visual versions of the task. Noise influenced d' values in the auditory version only, with d' increasing for common names in loud noise. The results support the view that noise influences performance by disturbing the pigeon-holing mechanism with the qualification that when material may not be recapitulated (as in the auditory presentation in the present study) greater attention may be allocated to easily recognizable material. The findings give little support to theories of noiseinduced deficits in performance based on the masking of inner speech.     

Source memory for unrecognized items: Predictions from multivariate signal detection theory

We report three experiments investigating source memory for words that were called "new" on a recognition test. In each experiment, participants could accurately specify the source of words that they failed to recognize. Results also demonstrated that source memory for unrecognized items varied with the bias to respond "old" in recognition decisions: Participants displayed unrecognized source memory when they were told that 25% of the recognition test words were old (promoting conservative responding) but not when they were told that 75% of the test words were old (promoting liberal responding). Our results were successfully predicted by a multivariate signal detection approach to recognition/source memory.     

Proactive interference from items previously stored in visual working memory

This study investigates the fate of information that was previously stored in visual working memory but that is no longer needed. Previous research has found inconsistent results, with some showing effective release of irrelevant information and others showing proactive interference. Using change detection tasks of colors or shapes, we show that participants tend to falsely classify a changed item as "no change" if it matches one of the memory items on the preceding trial. The interference is spatially specific: Memory for the preceding trial interferes more if it matches the feature value and the location of a test item than if it does not. Interference results from retaining information in visual working memory, since it is absent when items on the preceding trials are passively viewed, or are attended but not memorized. We conclude that people cannot fully eliminate unwanted visual information from current working memory tasks.     

Serial-position effects for items and relations in short-term memory

Two experiments used immediate probed recall of words to investigate serial-position effects. Item memory was tested through probing with a semantic category. Relation memory was tested through probing with the word's spatial location of presentation. Input order and output order were deconfounded by presenting and probing items in different orders. Primacy and recency effects over input position were found for both item memory and relation memory. Both item and relation memory declined over output position. The finding of a U-shaped input position function for item memory rules out an explanation purely in terms of positional confusions (e.g., edge effects). Either these serial-position effects arise from variations in the intrinsic memory strength of the items, or they arise from variations in the strength of item–position bindings, together with retrieval by scanning.     

Seven-month-old infants chunk items in memory

Although working memory has a highly constrained capacity limit of three or four items, both adults and toddlers can increase the total amount of stored information by "chunking" object representations in memory. To examine the developmental origins of chunking, we used a violation-of-expectation procedure to ask whether 7-month-old infants, whose working memory capacity is still maturing, also can chunk items in memory. In Experiment 1, we found that in the absence of chunking cues, infants failed to remember three identical hidden objects. In Experiments 2 and 3, we found that infants successfully remembered three hidden objects when provided with overlapping spatial and featural chunking cues. In Experiment 4, we found that infants did not chunk when provided with either spatial or featural chunking cues alone. Finally, in Experiment 5, we found that infants also failed to chunk when spatial and featural cues specified different chunks (i.e., were pitted against each other). Taken together, these results suggest that chunking is available before working memory capacity has matured but still may undergo important development over the first year of life.     

Retrieval of propositional information from long-term memory

Three experiments are reported in which subjects learn propositions like A hippie is in the park. The experiments manipulate the number of such propositions involving a particular person (e.g., hippie) or a particular location (e.g., park). After learning the material, subjects are asked to judge whether particular probe propositions are from the study set. Times to make these judgments about probe propositions increase with the number of study propositions involving the person or location used in the probe proposition. A model is presented which assumes a subject simultaneously accesses memory from all concepts in a probe proposition and serially searches through all study propositions involving each concept. Search of memory terminates as soon as one search process from a concept finds the probe proposition or exhausts the study propositions attached to that concept.     

Remembering the forgotten? Reminiscence, hypermnesia and memory for order

Three experiments established that repeated testing affects item and order retention differently: Hypermnesia was found with repeated free recall tests, whereas net performance declined significantly across successive free reconstruction of order tests. Overall order performance declined over tests under a variety of encoding conditions (pictures, words, and relational and item-specific processing) and retrieval conditions (intentional and incidental learning). Although net performance dropped across tests, participants did show reliable order recovery (reminiscence) between tests. The implications of these data for general theories of hypermnesia and order are discussed.     

Hierarchical encoding in visual working memory: ensemble statistics bias memory for individual items

Influential models of visual working memory treat each item to be stored as an independent unit and assume that there are no interactions between items. However, real-world displays have structure that provides higher-order constraints on the items to be remembered. Even in the case of a display of simple colored circles, observers can compute statistics, such as mean circle size, to obtain an overall summary of the display. We examined the influence of such an ensemble statistic on visual working memory. We report evidence that the remembered size of each individual item in a display is biased toward the mean size of the set of items in the same color and the mean size of all items in the display. This suggests that visual working memory is constructive, encoding displays at multiple levels of abstraction and integrating across these levels, rather than maintaining a veridical representation of each item independently.     

Competition between two memory traces for long-term recognition memory

Previous studies investigating the processes which underlie memory consolidation focused almost exclusively on isolated learning events. Here I studied the competition of two similar memory traces for consolidation non-conditioned recognition memory in adult male C57BL/6JOlaHsd mice using the olfactory cues based social discrimination procedure. My results show that the interference phenomena that cause forgetting are time-dependent, and that retroactive interference can be discriminated from proactive interference. Furthermore, both types of interference can be suppressed by subcutaneous anisomycin treatment immediately after presentation of the interference stimulus. These findings imply that interference phenomena, which result from the competition of two similar memory traces for long-term recognition memory, are related to the progress of memory consolidation and linked to protein synthesis.     

The tenacious nature of memory binding for arousing negative items

In two experiments, we investigated whether people are better or worse at updating memory for the location of emotional pictures than of neutral pictures. We measured participants’ memories for the locations of both arousing negative pictures and neutral pictures while manipulating practice (encountering the same event repeatedly) and interference (encountering the same picture in a different location). Memory for the context of emotional items was less likely to be corrected when erroneous and was less likely to be correctly updated when the context changed. These results suggest that initial item-context binding is more tenacious for emotional items than for neutral items, even when such binding is incorrect.     

From sensory to long-term memory: evidence from auditory memory reactivation studies

Everyday experience tells us that some types of auditory sensory information are retained for long periods of time. For example, we are able to recognize friends by their voice alone or identify the source of familiar noises even years after we last heard the sounds. It is thus somewhat surprising that the results of most studies of auditory sensory memory show that acoustic details, such as the pitch of a tone, fade from memory in ca. 10-15 s. One should, therefore, ask (1) what types of acoustic information can be retained for a longer term, (2) what circumstances allow or help the formation of durable memory records for acoustic details, and (3) how such memory records can be accessed. The present review discusses the results of experiments that used a model of auditory recognition, the auditory memory reactivation paradigm. Results obtained with this paradigm suggest that the brain stores features of individual sounds embedded within representations of acoustic regularities that have been detected for the sound patterns and sequences in which the sounds appeared. Thus, sounds closely linked with their auditory context are more likely to be remembered. The representations of acoustic regularities are automatically activated by matching sounds, enabling object recognition.     

No source memory for unrecognized items when implicit feedback is avoided

In a recent empirical study, Starns, Hicks, Brown, and Martin (Memory & Cognition, 36, 1–8 2008) collected source judgments for old items that participants had claimed to be new and found residual source discriminability depending on the old-new response bias. The authors interpreted their finding as evidence in favor of the bivariate signal-detection model, but against the two-high-threshold model of item/source memory. According to the latter, new responses only follow from the state of old-new uncertainty for which no source discrimination is possible, and the probability of entering this state is independent of the old-new response bias. However, when missed old items were presented for source discrimination, the participants could infer that the items had been previously studied. To test whether this implicit feedback led to second retrieval attempts and thus to source memory for presumably unrecognized items, we replicated Starns et al.’s (Memory & Cognition, 36, 1–8 2008) finding and compared their procedure to a procedure without such feedback. Our results challenge the conclusion to abandon discrete processing in source memory; source memory for unrecognized items is probably an artifact of the procedure, by which implicit feedback prompts participants to reconsider their recognition judgment when asked to rate the source of old items in the absence of item memory.     

Trade-off between memory for verbal items and their visual attributes.

Instructions to attend to the case and color in which words were presented led to improved retention of these visual attributes but depressed recognition performance. This trade-off between item and attribute memory occurred at three presentation rates (1.5, 5.5, and 10.5 sec/item), suggesting that visual attributes of verbal stimuli are rarely stored unless subjects expect that knowledge of physical form will be useful later. Visual attributes of high-imagery words were retained better than visual attributes of low imagery words by subjects instructed to attend to case and color, but not by subjects asked only to attend to word meaning. Implications of these findings for the hypothesis that visually presented verbal stimuli are stored as literal copies are discussed.     

Pop-out and pop-in: Visual working memory advantages for unique items

Attentional control is thought to play a critical role in determining the amount of information that can be stored and retrieved from visual working memory (VWM). We tested whether and how task-irrelevant feature-based salience, known to affect the control of visual attention, affects VWM performance. Our results show that features of a task-irrelevant color singleton are more likely to be recalled from VWM than non-singleton items and that this increased memorability comes at a cost to the other items in the display. Furthermore, the singleton effect in VWM was negatively correlated with an individual’s baseline VWM capacity. Taken together, these results suggest that individual differences in VWM storage capacity may be partially attributable to the ability to ignore differences in task-irrelevant physical salience.     

Infants' recognition memory, forgetting, and savings.

In four experiments infants of 5–6 months of age were tested for recognition memory of briefly presented visual stimuli. In the first experiment infants showed relatively more looking at a novel picture when it was paired with a picture they had just studied for 10 or 20 sec. This differential response to novelty served as evidence of immediate recognition memory. In the second experiment these same 10- or 20-sec study times were used but were not sufficient to produce reliable evidence of memory over a long (48 hr) retention interval or even as short an interval as 40 sec. The third experiment demonstrated substantial delayed recognition if a brief reexposure of materials was introduced immediately prior to the recognition test. This reminder required less than the minimal study time found necessary to produce immediate recognition memory in Experiment 1. The results of the fourth experiment indicated that the savings effects that occurred in Experiment 3 were not solely due to familiarity with the testing procedures. The implications of savings effects in infants' memory are discussed.     

Self-reference in memory: Recognition of personality items

The hypothesis that the “self” concept is active in memory was tested in a series of recognition experiments involving first- and third-person sentences under several instructional conditions. The results confirmed the hypothesis and indicated a degree of sentence specificity for the effect. These results were interpreted as congruent with the notion that the “self” can be seen as a cognitive structure with both a memory component as well as an involvement in the evaluation and processing of incoming materials.