Neutral auditory words immediately followed by painful electric shock may show reduced next-day recollection.

In this study, we investigated the effect of experimentally delivered acute pain on memory. Twenty-five participants participated in experimental sessions on consecutive days. The first session involved a categorization task to encourage memory encoding. There were two conditions, presented in randomized order, in which participants listened to a series of words, which were repeated three times. In one condition, one-third of the word items were immediately followed by a painful electrical shock. This word-shock pairing was consistent across repetition and the pain-paired items were presented unpredictably. In the other condition, all word items were not associated with pain. Response times over these repeated presentations were assessed for differences. Explicit memory was tested the following day, employing a Remember-Know assessment of word recognition, with no shocks employed. We found evidence that recollection may be reduced for pain-paired words, as the proportion of correct Remember responses (out of total correct responses) was significantly lower. There were no significant reductions in memory for non-pain items that followed painful stimulation after a period of several seconds. Consistent with the experience of pain consuming working memory resources, we theorize that painful shocks interrupt memory encoding for the immediately preceding experimental items, due to a shift in attention away from the word item.

Midazolam and Ketamine Produce Distinct Neural Changes in Memory, Pain, and Fear Networks during Pain.

BACKGROUND: Despite the well-known clinical effects of midazolam and ketamine, including sedation and memory impairment, the neural mechanisms of these distinct drugs in humans are incompletely understood. The authors hypothesized that both drugs would decrease recollection memory, task-related brain activity, and long-range connectivity between components of the brain systems for memory encoding, pain processing, and fear learning. METHODS: In this randomized within-subject crossover study of 26 healthy adults, the authors used behavioral measures and functional magnetic resonance imaging to study these two anesthetics, at sedative doses, in an experimental memory paradigm using periodic pain. The primary outcome, recollection memory performance, was quantified with d' (a difference of z scores between successful recognition versus false identifications). Secondary outcomes were familiarity memory performance, serial task response times, task-related brain responses, and underlying brain connectivity from 17 preselected anatomical seed regions. All measures were determined under saline and steady-state concentrations of the drugs. RESULTS: Recollection memory was reduced under midazolam (median [95% CI], d' = 0.73 [0.43 to 1.02]) compared with saline (d' = 1.78 [1.61 to 1.96]) and ketamine (d' = 1.55 [1.12 to 1.97]; P < 0.0001). Task-related brain activity was detected under saline in areas involved in memory, pain, and fear, particularly the hippocampus, insula, and amygdala. Compared with saline, midazolam increased functional connectivity to 20 brain areas and decreased to 8, from seed regions in the precuneus, posterior cingulate, and left insula. Compared with saline, ketamine decreased connectivity to 17 brain areas and increased to 2, from 8 seed regions including the hippocampus, parahippocampus, amygdala, and anterior and primary somatosensory cortex. CONCLUSIONS: Painful stimulation during light sedation with midazolam, but not ketamine, can be accompanied by increased coherence in brain connectivity, even though details are less likely to be recollected as explicit memories.

Familiarity acts as a reduction in objective complexity.

High-complexity stimuli are thought to place extra demands on working memory when processing and manipulating such stimuli; however, operational definitions of complexity are not well established, nor are the measures that would demonstrate such effects. Here, we argue that complexity is a relative quantity that is affected by preexisting experience. Experiment 1 compared cued-recall performance for Chinese and English speakers when the stimuli involved Chinese features that varied in the number of strokes or involved Ethiopic features unfamiliar to both groups. Chinese pseudocharacters (two radicals) had half the strokes of Chinese pseudowords (two characters). The response terms were English words familiar to both groups. English speakers performed equivalently with the Ethiopic and pseudocharacters, but much worse on the pseudowords. In contrast, Chinese speakers performed equivalently with pseudowords or pseudocharacters, but worse with Ethiopic cues. Experiment 2 showed that the lack of a complexity effect for Chinese speakers was not due to greater ease of rehearsal of pseudowords compared with pseudocharacters. Experiment 3 ruled out that Chinese speakers are just better at learning paired associates involving Mandarin by demonstrating that while complexity did not affect them, other features of the stimuli did. Taken together, it appears that complexity is not an absolute property based on the number of visual elements, but rather a relative property affected by one's prior knowledge.

Forgetting Is a Feature, Not a Bug: Intentionally Forgetting Some Things Helps Us Remember Others by Freeing Up Working Memory Resources.

In the present study, we used an item-method directed-forgetting paradigm to test whether instructions to forget or remember one item affect memory for subsequently studied items. In two experiments (Ns = 138 and 33, respectively), recall was higher when a word pair was preceded during study by a to-be-forgotten word pair. This effect was cumulative: Performance increased when more preceding study items were to be forgotten. The effect decreased when memory was conditioned on instructions for items appearing farther back in the study list. Experiment 2 used a dual-task paradigm that suppressed, during encoding, verbal rehearsal or attentional refreshing. Neither task removed the effect, ruling out that rehearsal or attentional borrowing is responsible for the advantage conferred from previous to-be-forgotten items. We propose that memory formation depletes a limited resource that recovers over time and that to-be-forgotten items consume fewer resources, leaving more resources available for storing subsequent items. A computational model implementing the theory provided excellent fits to the data.

Memory for non-painful auditory items is influenced by whether they are experienced in a context involving painful electrical stimulation.

In this study, we sought to examine the effect of experimentally induced somatic pain on memory. Subjects heard a series of words and made categorization decisions in two different conditions. One condition included painful shocks administered just after presentation of some of the words; the other condition involved no shocks. For the condition that included painful stimulations, every other word was followed by a shock, and subjects were informed to expect this pattern. Word lists were repeated three times within each condition in randomized order, with different category judgments but consistent pain-word pairings. After a brief delay, recognition memory was assessed. Non-pain words from the pain condition were less strongly encoded than non-pain words from the completely pain-free condition. Recognition of pain-paired words was not significantly different than either subgroup of non-pain words. An important accompanying finding is that response times to repeated experimental items were slower for non-pain words from the pain condition, compared to non-pain words from the completely pain-free condition. This demonstrates that the effect of pain on memory may generalize to non-pain items experienced in the same experimental context.

Item strength affects working memory capacity.

Do the processing and online manipulation of stimuli that are less familiar require more working memory (WM) resources? Is it more difficult to solve demanding problems when the symbols involved are less rather than more familiar? We explored these questions with a dual-task paradigm in which subjects had to solve algebra problems of different complexities while simultaneously holding novel symbol-digit associations in WM. The symbols were previously unknown Chinese characters, whose familiarity was manipulated by differential training frequency with a visual search task for nine hour-long sessions over 3 weeks. Subsequently, subjects solved equations that required one or two transformations. Before each trial, two different integers were assigned to two different Chinese characters of the same training frequency. Half of the time, those characters were present as variables in the equation and had to be substituted for the corresponding digits. After attempting to solve the equation, subjects had to recognize which two characters were shown immediately before that trial and to recall the integer associated with each. Solution accuracy and response times were better when the problems required one transformation only; variable substitution was not required; or the Chinese characters were high frequency. The effects of stimulus familiarity increased as the WM demands of the equation increased. Character-digit associations were also recalled less well with low-frequency characters. These results provide strong support that WM capacity depends not only on the number of chunks of information one is attempting to process but also on their strength or familiarity.

Cortical Networks Involved in Memory for Temporal Order.

We examined the neurobiological basis of temporal resetting, an aspect of temporal order memory, using a version of the delayed-match-to-multiple-sample task. While in an fMRI scanner, participants evaluated whether an item was novel or whether it had appeared before or after a reset event that signified the start of a new block of trials. Participants responded "old" to items that were repeated within the current block and "new" to both novel items and items that had last appeared before the reset event (pseudonew items). Medial-temporal, prefrontal, and occipital regions responded to absolute novelty of the stimulus-they differentiated between novel items and previously seen items, but not between old and pseudonew items. Activation for pseudonew items in the frontopolar and parietal regions, in contrast, was intermediate between old and new items. The posterior cingulate cortex extending to precuneus was the only region that showed complete temporal resetting, and its activation reflected whether an item was new or old according to the task instructions regardless of its familiarity. There was also a significant Condition (old/pseudonew) × Familiarity (second/third presentations) interaction effect on behavioral and neural measures. For pseudonew items, greater familiarity decreased response accuracy, increased RTs, increased ACC activation, and increased functional connectivity between ACC and the left frontal pole. The reverse was observed for old items. On the basis of these results, we propose a theoretical framework in which temporal resetting relies on an episodic retrieval network that is modulated by cognitive control and conflict resolution.

He who is well prepared has half won the battle: an FMRI study of task preparation.

The neural mechanism underlying preparation for tasks that vary in difficulty has not been explored. This functional magnetic resonance imaging study manipulated task difficulty by varying the working memory (WM) load of the n-back task. Each n-back task block was preceded by a preparation period involving a screen that indicated the level of difficulty of the upcoming task. Consistent with previous work, activation in some brain regions depended on WM load in the task. These regions were used as regions of interest for the univariate and multivariate (classification) analyses of preparation periods. The findings were that the patterns of brain activation during task preparation contain information about the upcoming task difficulty. (1) A support vector machine classifier was able to decode the n-back task difficulty from the patterns of brain activation during task preparation. Those individuals whose activation patterns for anticipated 1- versus 2- versus 3-back conditions were classified with higher accuracy showed better behavioral performance on the task, suggesting that task performance depends on task preparation. (2) Left inferior frontal gyrus, intraparietal sulcus, and anterior cingulate cortex parametrically decreased activation as anticipated task difficulty increased. Taken together, these results suggest dynamic involvement of the WM network not only during WM task performance, but also during task preparation.

An attentional-adaptation account of spatial negative priming: evidence from event-related potentials.

Negative priming (NP) refers to a slower response to a target stimulus if it has been previously ignored. To examine theoretical accounts of spatial NP, we recorded behavioral measures and event-related potentials (ERPs) in a target localization task. A target and distractor briefly appeared, and the participant pressed a key corresponding to the target's location. The probability of the distractor appearing in each of four locations varied, whereas the target appeared with equal probabilities in all locations. We found that response times (RTs) were fastest when the prime distractor appeared in its most probable (frequent) location and when the prime target appeared in the location that never contained a distractor. Moreover, NP effects varied as a function of location: They were smallest when targets followed distractors in the frequent distractor location-a finding not predicted by episodic-retrieval or suppression accounts of NP. The ERP results showed that the P2, an ERP component associated with attentional orientation, was smaller in prime displays when the distractor appeared in its frequent location. Moreover, no differences were apparent between negative-prime and control trials in the N2, which is associated with suppression processes, nor in the P3, which is associated with episodic retrieval processes. These results indicate that the spatial NP effect is caused by both short- and long-term adaptation in preferences based on the history of inspecting unsuccessful locations. This article is dedicated to the memory of Edward E. Smith, and we indicate how this study was inspired by his research career.

Repetition related changes in activation and functional connectivity in hippocampus predict subsequent memory.

Using fMRI, this study examined the relationship between repetition-related changes in the medial temporal lobe (MTL) activation during encoding and subsequent memory for similarity of repetitions. During scanning, subjects classified pictures of objects as natural or man-made. Each object-type was judged twice with presentations of either identical pictures or pictures of different exemplars of the same object. After scanning, a surprise recognition test required subjects to decide whether a probe word corresponded to pictures judged previously. When a subject judged the word as "old," a second judgment was made concerning the physical similarity of the two pictures. Repetition related changes in MTL activation varied depending on whether or not subjects could correctly state that pictures were different. Moreover, psychophysiological interactions analyses showed that accuracy in recalling whether the two pictures were different was predicted by repetition-related changes in the functional connectivity of MTL with frontal regions. Specifically, correct recollection was predicted by increased connectivity between the left posterior hippocampus and the right inferior frontal gyrus, and also by decreased connectivity between the left posterior hippocampus and the left precentral gyrus on the second stimulus presentation. The opposite pattern was found for trials that were incorrectly judged on the nature of the repetition. These results suggest that successful encoding is predicted by a combination of increases and decreases in both the MTL activation and functional connectivity, and not merely by increases in activation and connectivity as suggested previously.

Why it's easier to remember seeing a face we already know than one we don't: preexisting memory representations facilitate memory formation.

In two experiments, we provided support for the hypothesis that stimuli with preexisting memory representations (e.g., famous faces) are easier to associate to their encoding context than are stimuli that lack long-term memory representations (e.g., unknown faces). Subjects viewed faces superimposed on different backgrounds (e.g., the Eiffel Tower). Face recognition on a surprise memory test was better when the encoding background was reinstated than when it was swapped with a different background; however, the reinstatement advantage was modulated by how many faces had been seen with a given background, and reinstatement did not improve recognition for unknown faces. The follow-up experiment added a drug intervention that inhibited the ability to form new associations. Context reinstatement did not improve recognition for famous or unknown faces under the influence of the drug. The results suggest that it is easier to associate context to faces that have a preexisting long-term memory representation than to faces that do not.

Dynamic changes in the medial temporal lobe during incidental learning of object-location associations.

The role of the medial temporal lobe (MTL) in associative memory encoding has been the focus of many memory experiments. However, there has been surprisingly little investigation of whether the contributions of different MTL subregions (amygdala, hippocampus [HPC], parahippocampal [PHc], perirhinal cortex [PRc], and temporal polar cortex [TPc]) shift across multiple presentations during associative encoding. We examined this issue using event-related functional magnetic resonance imaging and a multivoxel pattern classification analysis. Subjects performed a visual search task, becoming faster with practice to locate objects whose locations were held constant across trials. The classification analysis implicated right HPC and amygdala early in the task when the speed-up from trial to trial was greatest. The same analysis implicated right PRc and TPc late in learning when speed-up was minimal. These results suggest that associative encoding relies on complex patterns of neural activity in MTL that cannot be expressed by simple increases or decreases of blood oxygenation level-dependent signal during learning. Involvement of MTL subregions during encoding of object-location associations depends on the nature of the learning phase. Right HPC and amygdala support active integration of object and location information, while right PRc and TPc are involved when object and spatial representations become unitized into a single representation.

Procedural learning and associative memory mechanisms contribute to contextual cueing: Evidence from fMRI and eye-tracking.

Using a combination of eye tracking and fMRI in a contextual cueing task, we explored the mechanisms underlying the facilitation of visual search for repeated spatial configurations. When configurations of distractors were repeated, greater activation in the right hippocampus corresponded to greater reductions in the number of saccades to locate the target. A psychophysiological interactions analysis for repeated configurations revealed that a strong functional connectivity between this area in the right hippocampus and the left superior parietal lobule early in learning was significantly reduced toward the end of the task. Practice related changes (which we call "procedural learning") in activation in temporo-occipital and parietal brain regions depended on whether or not spatial context was repeated. We conclude that context repetition facilitates visual search through chunk formation that reduces the number of effective distractors that have to be processed during the search. Context repetition influences procedural learning in a way that allows for continuous and effective chunk updating.

Memory resources recover gradually over time: The effects of word frequency, presentation rate, and list composition on binding errors and mnemonic precision in source memory.

Normative word frequency has played a key role in the study of human memory, but there is little agreement as to the mechanism responsible for its effects. To determine whether word frequency affects binding probability or memory precision, we used a continuous reproduction task to examine working memory for spatial positions of words. In three experiments, after studying a list of five words, participants had to report the spatial location of one of them on a circle. Across experiments we varied word frequency, presentation rate, and the proportion of low-frequency words on each trial. A mixture model dissociated memory precision, binding failure, and guessing rate parameters from the continuous distribution of errors. On trials that contained only low- or only high-frequency words, low-frequency words led to a greater degree of error in recalling the associated location. This was due to a higher word-location binding failure and not due to differences in memory precision or guessing rates. Slowing down the presentation rate eliminated the word frequency effect by reducing binding failures for low-frequency words. Mixing frequencies in a single trial hurt high-frequency and helped low-frequency words. These findings support the idea that word frequency can lead to both positive and negative mnemonic effects depending on a trade-off between an HF encoding advantage and a LF retrieval cue advantage. We suggest that (1) low-frequency words require more resources for binding, (2) that these resources recover gradually over time, and that (3) binding fails when these resources are insufficient. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Opposing patterns of neural priming in same-exemplar vs. different-exemplar repetition predict subsequent memory.

The present neuroimaging study examines how repetition-related neural attenuation effects differ as a function of the perceptual similarity of the repetition and subsequent memory. One previous study (Turk-Browne et al., 2006) reported greater attenuation effects for subsequent hits than for misses. Another study (Wagner et al., 2000) found that neural attenuation is negatively correlated with subsequent memory. These opposing results suggest that repetition-related neural attenuation for subsequent hits and misses may be driven by different factors. In order to investigate the factors that affect the degree of neural attenuation, we varied perceptual similarity between repetitions in a scanned encoding phase that was followed by a subsequent memory test outside the scanner. We demonstrated that the degree of neural attenuation in the object processing regions depends on the interaction between perceptual similarity across repeated presentations and the quality their encodings. Specifically, the same areas that decreased neural signal for repetitions of same exemplars that were subsequently recognized with confidence that the repetitions were identical showed a decrease in neural signal for different-exemplar misses but not for the corresponding subsequently recognized hits. Our results imply that repetition-related neural attenuation should be related to the more efficient processing of perceptual properties of the stimuli only if subjects are able to subsequently remember the stimuli. Otherwise, the cause of attenuation may be in the failure to encode the stimuli on the second presentation as shown by the pattern of neural attenuation for the different-exemplar misses.

Greater discrimination difficulty during perceptual learning leads to stronger and more distinct representations.

Despite the conventional wisdom that it is more difficult to find a target among similar distractors, this study demonstrates that this disadvantage is short-lived, and that high target-to-distractor (TD) similarity during visual search training can have beneficial effects for learning. Participants with no prior knowledge of Chinese performed 12 hour-long sessions over 4 weeks, where they had to find a briefly presented target character among a set of distractors. At the beginning of the experiment, high TD similarity hurt performance, but the effect reversed during the first session and remained positive throughout the remaining sessions. This effect was due primarily to reducing false alarms on trials in which the target was absent from the search display. In addition, making an error on a trial with a specific character was associated with slower visual search response times on the subsequent repetition of the character, suggesting that participants paid more attention in encoding the characters after false alarms. Finally, the benefit of high TD similarity during visual search training transferred to a subsequent N-back working-memory task. These results suggest that greater discrimination difficulty likely induces stronger and more distinct representations of each character.

Frequency effects on memory: A resource-limited theory.

We present a review of frequency effects in memory, accompanied by a theory of memory, according to which the storage of new information in long-term memory (LTM) depletes a limited pool of working memory (WM) resources as an inverse function of item strength. We support the theory by showing that items with stronger representations in LTM (e.g., high frequency items) are easier to store, bind to context, and bind to one another; that WM resources are involved in storage and retrieval from LTM; that WM performance is better for stronger, more familiar stimuli. We present a novel analysis of preceding item strength, in which we show from nine existing studies that memory for an item is higher if during study it was preceded by a stronger item (e.g., a high frequency word). This effect is cumulative (the more prior items are of high frequency, the better), continuous (memory proportional to word frequency of preceding item), interacts with current item strength (larger for weaker items), and interacts with lag (decreases as the lag between the current and prior study item increases). A computational model that implements the theory is presented, which accounts for these effects. We discuss related phenomena that the model/theory can explain. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Knowing we know before we know: ERP correlates of initial feeling-of-knowing.

Subjects performed a rapid feeling-of-knowing task developed by (Reder, L. M., & Ritter, F. (1992). What determines initial feeling of knowing? Familiarity with question terms, not with the answer. Journal of Experimental Psychology: Learning, Memory, and Cognition, 18, 435-451), while event-related potentials (ERPs) were recorded to identify the time course of "feeling-of-knowing" signals. Subjects were shown a series of math problems, some of which were repeated multiple times during the course of the experiment, and subjects had to rapidly decide whether the answer to a given problem could be quickly retrieved from memory (retrieval trials) or had to be calculated on scrap paper (calculate trials). Behavioral results replicated the 1992 study, showing that subjects can estimate whether the answer is known much faster than the answer can be retrieved. ERPs time-locked to the onset of the math problem showed that accurate retrieval trials were associated with greater positivity for an early frontal P2 component (epoched from 180 to 280ms) and a frontal-central P3 component (epoched from 300 to 550ms). Moreover, this feeling-of-knowing signal was not found for subjects who never obtained a successful on-time retrieval. We interpret these findings as suggesting that initial feeling-of-knowing relies on a rapid assessment of the "perceptual fluency" with which the stimulus is processed. If a stimulus is deemed sufficiently familiar, the activation level of an internal problem representation is used to arrive at a decision of whether to search for the answer or to calculate it.

Memory systems do not divide on consciousness: Reinterpreting memory in terms of activation and binding.

There is a popular hypothesis that performance on implicit and explicit memory tasks reflects 2 distinct memory systems. Explicit memory is said to store those experiences that can be consciously recollected, and implicit memory is said to store experiences and affect subsequent behavior but to be unavailable to conscious awareness. Although this division based on awareness is a useful taxonomy for memory tasks, the authors review the evidence that the unconscious character of implicit memory does not necessitate that it be treated as a separate system of human memory. They also argue that some implicit and explicit memory tasks share the same memory representations and that the important distinction is whether the task (implicit or explicit) requires the formation of a new association. The authors review and critique dissociations from the behavioral, amnesia, and neuroimaging literatures that have been advanced in support of separate explicit and implicit memory systems by highlighting contradictory evidence and by illustrating how the data can be accounted for using a simple computational memory model that assumes the same memory representation for those disparate tasks.

The two processes underlying the testing effect- Evidence from Event-Related Potentials (ERPs).

Theoretical explanations of the testing effect (why people learn better from a test than a re-study) have largely focused on either the benefit of attempting to retrieve the answer or on the benefit of re-encoding the queried information after a successful retrieval. While a less parsimonious account, prior neuroimaging evidence has led us to postulate that both of these processes contribute to the benefit of testing over re-study. To provide further empirical support for our position, we recorded ERPs while subjects attempted to recall the second word of a pair when cued with the first. These ERPs were analyzed based on the current response accuracy and as a function of accuracy on the subsequent test, yielding three groups: the first and second tests were correct, the first was correct and the second was not, both were incorrect. Mean amplitude waveforms during the first test showed different patterns depending on the outcome patterns: Between 400 and 700 ms the amplitudes were most positive when both tests were correct and least positive when both were incorrect; mean amplitudes between 700 and 1000 ms only differed as a function of subsequent memory. They were more positive when the second test was correct. Importantly, the later component only predicted subsequent memory when the answers were not overlearned, i.e. only correctly recalled once previously. We interpret the 400-700 ms time window as a component reflecting a retrieval attempt process, which differs as a function of both current and subsequent accuracy, and the later time window as a component reflecting a re-encoding process, which only involves learning from tests, both of which are involved in the testing effect.