Recognition memory: One-component strength functions In the “short-term to long-term transition region”

Experimental manipulationofthe upper bound on the retention interval (30 sec, with average duration of 11 sec, vs. 2 min, with average duration of 18 sec) failed to produce evidence for independent adjustment of initial long-term and short-term storage strengths. Very accurate strength functions of retention time were obtained; these were fitted equally well by a two-component equation and a one-componentequation derived from a theory postulating sequential employment of an active attentional buffer and a one-trace passive storage system. The latter theory appears to be capable of accounting for both post-attentional and two-phase experimental strength data, using fewer free parameters than strength theories which postulate the simultaneous existence of short-term and long-term traces. Other arguments for two traces are also discussed In relation to the postulate of a single post-attentional trace.     

Dual trace theory and the consolidation of long-term memory

Retention functions were determined for four Ss for recognition memory of letters at 14 different delays from 3 sec to 5 min and two levels of storage load (1 and 6 letter lists), the retention interval being filled with backward counting. Memory strength retention functions were fit extremely well by assuming that two traces, short-term memory and long-term memory, are operative in this type of memory task. Only the short-term memory trace appears to be present during the first 8 or 10 sec of the retention interval, and this short-term trace decays exponentially with a time constant in the vicinity of 10 sec. Long-term memory is subject to a consolidation process which does not begin until about 10 sec after the study period and which is substantially complete at about 30 sec after the study period. Storage load has a very large effect on the degree of acquisition (learning) for both short and long-term traces, but storage load appears to have only a moderate effect or no effect on the decay rate of the short-term trace. There is some suggestion that the duration of the consolidation phase is shortened by an increase in storage load.     

Forgetting the once-seen face: estimating the strength of an eyewitness's memory representation

The fidelity of an eyewitness's memory representation is an issue of paramount forensic concern. Psychological science has been unable to offer more than vague generalities concerning the relation of retention interval to memory trace strength for the once-seen face. A meta-analysis of 53 facial memory studies produced a highly reliable association (r=.18, d=0.37) between longer retention intervals and positive forgetting of once-seen faces, an effect equally strong for both face recognition and eyewitness identification studies. W. A. Wickelgren's (1974, 1975, 1977) theory of recognition memory provided statistically satisfactory fits to 11 different empirical forgetting functions. Applied to the results of field studies of eyewitness memory, the theory yields predictions relevant to fact finders' evaluations of eyewitness credibility. A plausible upper limit for witness initial memory strength corresponds to a probability of .67 of being correct on a fair six-person lineup. Furthermore, not only can the percentage of remaining memory strength be determined for any retention interval, but this strength estimate can be translated into an estimated probability of being correct on a fair lineup of a specified size.     

Single-trace fragility theory of memory dynamics

In single-trace fragility theory, forgetting is produced by two factors, time and interference. Memory traces are assumed to have two partially coupled dynamic properties, strength and fragility. Strength determines the probability of correct recall and recognition, while fragility determines the susceptibility of the trace to the time-decay process but not to the interference process. Consolidation is assumed to be a continual reduction in the fragility of the memory trace rather than any change in strength or availability. Decreasing fragility accounts for the continually decreasing forgetting rate, the temporal character of retrograde amnesia and recovery therefrom, and the type of internal clock necessary for nonassociative recency judgments. Data are presented to indicate that interference is independent of the interval between original and interpolated learning, that nonassociative recency discriminability approaches a limit at about 30 min, and that the decay rate of long-term retention in amnesic patients is the same as in normal Ss.     

The role of the interpolated task in short-term retention

It has been proposed that a single set of operations based on classical interference theory is adequate to describe the phenomena of both short- and long-term memory. An article by Keppel and Underwood (1962) argues that short-term forgetting is due to proactive interference and, by implication, not a result of trace decay. An experiment which varied retention interval and the nature of the interpolated task, gave results which indicate that when the amount forgotten and the nature of errors are considered, a decay model is supported, the proactive interference suggestion being untenable.     

Cortical barrel lesions impair whisker-CS trace eyeblink conditioning

Whisker deflection is an effective conditioned stimulus (CS) for trace eyeblink conditioning that has been shown to induce a learning-specific expansion of whisker-related cortical barrels, suggesting that memory storage for an aspect of the trace association resides in barrel cortex. To examine the role of the barrel cortex in acquisition and retrieval of trace eyeblink associations, the barrel cortex was lesioned either prior to (acquisition group) or following (retention group) trace conditioning. The acquisition lesion group was unable to acquire the trace conditioned response, suggesting that the whisker barrel cortex is vital for learning trace eyeblink conditioning with whisker deflection as the CS. The retention lesion group exhibited a significant reduction in expression of the previously acquired conditioned response, suggesting that an aspect of the trace association may reside in barrel cortex. These results demonstrate that the barrel cortex is important for both acquisition and retention of whisker trace eyeblink conditioning. Furthermore, these results, along with prior anatomical whisker barrel analyses suggest that the barrel cortex is a site for long-term storage of whisker trace eyeblink associations.     

Measurement of trace strength in memory for pictures

Four experiments using a yes-no recognition task with snapshots examined (1) the effect of presenting not one but two items simultaneously, either both targets or both distractors, for a single judgment at a retention test trial; (2) the rate of forgetting; (3) the interaction between retention interval and the exposure duration at acquisition; (4) acquisition as a function of the number of times a picture was presented. In each case performance was assessed by calculating the discriminability index d'. The results supported the hypotheses that trace strength is lognormally distributed, that forgetting is exponential, and that in acquisition trace strength is a linear function of the number of presentations.     

Practice and retention: a unifying analysis.

What is the strength of a memory trace that has received various practices at times tj in the past? The strength accumulation equation proposes the following: strength = sigma tj-d, where the summation is over the practices of the trace. This equation predicts both the power law of practice and the power law of retention. This article reports the fits of the predictions of this equation to 5 experiments. Across these experiments, participants received as many as 240 trials of practice distributed over intervals as long as 400 days. The experiments also varied whether participants were just practicing retrieving an item or practicing applying a relatively complex rule. A model based on this equation successfully fit all the data when it was assumed that the passage of psychological time slowed after the experimental session. The strength accumulation equation was compared with other conceptions of the retention function and the relationship of the retention function to the practice function.     

Trace susceptibility theory

A new theory for the dynamics of trace susceptibility to storage loss is developed and tested. According to the trace susceptibility theory, storage loss occurs when a critical feature for the support of recall is no longer bound to the other features of the trace. The storage loss occurs because of the retroactive influence of other traces, and the storage retention function is precisely characterized by an underlying Weibull distribution. Predictions of the trace susceptibility theory were tested against predictions of a multistore model. The results support the trace susceptibility theory. Finally, the relation between the trace susceptibility theory and proactive interference effects was developed.     

A model for stochastic drift in memory strength to account for judgments of learning

Previous research has shown that judgments of learning (JOLs) made immediately after encoding have a low correlation with actual cued-recall performance, whereas the correlation is high for delayed judgments. In this article, the authors propose a formal theory describing the stochastic drift of memory strength over the retention interval to account for the delayed-JOL effect. This is done by first decomposing the aggregated memory strength into exponential functions with slow and fast memory traces. The mean aggregated memory strength shows power-function forgetting curves. The drift of the memory strength is large for immediate JOLs (causing a low predictability) and weak for delayed JOLs (causing a high predictability). Consistent with empirical data, the model makes a novel prediction of JOL asymmetry, or that immediate weak JOLs are more predictive of future performance than are immediate strong JOLs. The JOL distributions for immediate and delayed JOLs are also accounted for.     

Memory strength affects reporting of misinformation

A model of long-term retention was used to examine whether and how the strength of original information (differences in learning and testing time) and the strength of misleading information (differences in timing and frequency) influence 3- to 5-year-olds' memory for an event. In three experiments, preschoolers viewed a slide presentation depicting an event, some of them were asked misleading questions, and memory for event details was tested. There was little evidence of memory impairment, but exposure to misleading information encouraged reporting of this information. Differences in learning influenced reporting in that children exposed to the event once reported more misled details than those who saw the event multiple times. Furthermore, preschoolers who saw the event once were just as susceptible to misleading information whether exposed to misinformation once or three times; however, preschoolers who had seen the event multiple times were susceptible only to repeated presentations of misinformation. Given that the reporting of misinformation is determined by the degree of integrity of both the original and misleading information, it is important to control for differences in trace strength for both types of information in future research.     

Role of the phosphoinositide 3-kinase-Akt-mammalian target of the rapamycin signaling pathway in long-term potentiation and trace fear conditioning memory in rat medial prefrontal cortex

Phosphatidylinositol 3-kinase (PI3K) and its downstream targets, including Akt (also known as protein kinase B, PKB), mammalian target of rapamycin (mTOR), the 70-kDa ribosomal S6 kinase (p70S6k), and the eukaryotic initiation factor 4E (eIF4E)-binding protein 1 (4E-BP1), may play important roles in long-term synaptic plasticity and memory in many brain regions, such as the hippocampus and the amygdala. The present study investigated the role of the PI3K/Akt-mTOR signaling pathway in the medial prefrontal cortex (mPFC), also a crucial neural locus for the control of cognition and emotion. Western blot analysis of mPFC tissues showed an activation of phosphorylation of Akt at the Ser473 residues, mTOR, p70S6k, and 4E-BP1 in response to long-term potentiation (LTP)-inducing high-frequency stimulation (HFS). Infusion of PI3K inhibitors (wortmannin and LY294002) and an mTOR inhibitor (rapamycin) into the mPFC in vivo suppressed HFS-induced LTP as well as the phosphorylation of PI3K/Akt-mTOR signaling pathway. In parallel, these inhibitors interfered with the long-term retention of trace fear memory examined 3 d and 6 d after the trace fear conditioning training, whereas short-term trace fear memory and object recognition memory were kept intact. These results provide evidence of involvement of activation of the PI3K/Akt-mTOR signaling pathway in the mPFC for LTP and long-term retention of trace fear memory.     

Inverse temporal contributions of the dorsal hippocampus and medial prefrontal cortex to the expression of long-term fear memories

Retrograde amnesia following disruptions of hippocampal function is often temporally graded, with recent memories being more impaired. Evidence supports the existence of one or more neocortical long-term memory storage/retrieval site(s). Neurotoxic lesions of the medial prefrontal cortex (mPFC) or the dorsal hippocampus (DH) were made 1 day or 200 days following trace fear conditioning. Recently encoded trace fear memories were most disrupted by DH lesions, while remotely encoded trace and contextual memories were most disrupted by mPFC lesions. These data strongly support the consolidation theory of hippocampus function and implicate the mPFC as a site of long-term memory storage/retrieval.     

On the participation of mTOR in recognition memory

Evidence indicates that activation of the neuronal protein synthesis machinery is required in areas of the brain relevant to memory for consolidation and persistence of the mnemonic trace. Here, we report that inhibition of hippocampal mTOR, a protein kinase involved in the initiation of mRNA translation, immediately or 180min but not 540min after training impairs consolidation of long-term object recognition memory without affecting short-term memory retention or exploratory behavior. When infused into dorsal CA1 after long-term memory reactivation in the presence of familiar objects the mTOR inhibitor rapamycin (RAP) did not affect retention. However, when given immediately after exposing animals to a novel and a familiar object, RAP impaired memory for both of them. The amnesic effect of the post-retrieval administration of RAP was long-lasting, did not happen after exposure to two novel objects or following exploration of the training arena in the absence of other stimuli, suggesting that it was contingent with reactivation of the consolidated trace in the presence of a behaviorally relevant and novel cue. Our results indicate that mTOR activity is required in the dorsal hippocampus for consolidation of object recognition memory and suggest that inhibition of this kinase after memory retrieval in the presence of a particular set of cues hinders persistence of the original recognition memory trace.     

State-trace analysis: A method of testing simple theories of causation

An independent variable measures some aspect of a treatment applied to a person; a dependent variable measures some aspect of the treatment's effect upon the person. Two dependent variables will often covary with each other because they are affected by a common independent variable. A state trace is a graph which plots the value of one dependent variable as a function of another. (Thus, a state trace is a generalization of the yes-no receiver-operating-characteristic curve.) By appropriately analyzing state traces, it is possible to test theories concerning (a) the mechanisms by which independent variables affect dependent variables and (b) how these mechanisms differ from one population of persons to another. As an illustration, a study of long-term memory in normal persons, schizophrenics, and persons with organic brain syndrome is presented. The effects of number of word presentations and length of retention interval upon probability of word recall and recognition were investigated. The results were analyzed by state-trace analysis.     

Toward a quantitative theory for performance differences between anticipation and study-test procedures: The retention interval model

In an effort to account quantitatively for performance differences between study-test and anticipation methods, a rudimentary theory, the retention interval model, is proposed. This model postulates three different theoretical functions for the three operationally distinguishable and qualitatively different events in the retention interval: intercycle rest, intervening-study-events and intervening-test-events intervals. The retention interval model satisfactorily accounted for 144 data points based on 35, 136 observations (164 subjects) by using only 30 estimated parameters in three experiments (48 points via 10 parameters per experiment), with massed as well as spaced practice, under both anticipation and study-test (RT) methods. In spite of a restrictive parameter estimation mode, close agreements were achieved between the model and data. The retention interval appears to generate powerful effects in determining the absolute performance levels for both anticipation and study-test learning procedures in the various intercycle intervals.     

Trace fear conditioning is reduced in the aging rat

Auditory trace fear conditioning is a hippocampus-dependent learning task that requires animals to associate an auditory conditioned stimulus (CS) and a fear-producing shock-unconditioned stimulus (US) that are separated by an empty 20-s trace interval. Previous studies have shown that aging impairs learning performance on hippocampus-dependent tasks. This study measured heart rate (HR) and freezing fear responses to determine if aging impairs hippocampus-dependent auditory trace fear conditioning in freely moving rats. Aging and Young rats received one long-trace fear conditioning session (10 trials). Each trial consisted of a tone-CS (5 s) and a shock-US separated by an empty 20-s trace interval. The next day rats received CS-alone retention trials. Young rats showed significantly larger HR and freezing responses on the initial CS-alone retention trials compared to the Aging rats. A control group of aging rats received fear conditioning trials with a short 1-s trace interval separating the CS and US. The Aging Short-Trace Group showed HR and freezing responses on the initial CS alone retention trials that were similar to the Young Long-Trace Group, but greater than the Aging Long-Trace Group. A second aging control group received unpaired CSs and USs, and showed no HR or freezing responses on CS-alone retention trials. These data show that HR and freezing are effective measures for detecting aging-related deficits in trace fear conditioning.     

Long-term spontaneous improvement of performance is related to the strength of the initial training: theoretical implications

In a recent study we established that following a partial acquisition of a brightness discrimination escape task (15 trials), Sprague-Dawley albino rats exhibited a long-term spontaneous improvement of performance (LTSI) after 7 to 14 days. Some evidence suggests a relation between the strength of the initial training and the delay of the optimal retention performance. This study investigates such a possibility in studying performance of rats (number of trials needed to reach a criterion of 10 errorless trials) following nine different retention intervals: 10 min, and 1, 3, 5, 7, 10, 14, 21, and 28 days, after a strengthened initial training (25 trials). Under those conditions, LTSI occurred after a delay of 5 to 7 days. Theoretical implications for an inverse relationship between the strength of initial training and the length of delay leading to LTSI are discussed.     

Long-term consolidation and retention of learning-induced tuning plasticity in the auditory cortex of the guinea pig.

The major goal of this study was to determine whether classical conditioning produces long-term neural consolidation of frequency tuning plasticity in the auditory cortex. Local field potentials (LFPs) were obtained from chronically implanted adult male Hartley guinea pigs that were divided into conditioning (n = 4) and sensitization control (n = 3) groups. Tuning functions were determined in awake subjects for average LFPs (approximately 0.4 to 36.0 kHz, -20 to 80 dB) immediately before training as well as 1 h and 1, 3, 7, and 10 days after training; sensitization subjects did not have a 10-day retention test. Conditioning consisted of a single session of 30 to 45 trials of a 6-s tone (CS, 70 dB) that was not the best frequency (BF, peak of a tuning curve), followed by a brief leg shock (US) at CS offset. Sensitization control animals received the same density of CS and US presentations unpaired. Heart rate recordings showed that the conditioning group developed conditioned bradycardia, whereas the sensitization control group did not. Local field potentials in the conditioning group, but not in the sensitization group, developed tuning plasticity. The ratio of responses to the CS frequency versus the BF were increased 1 h after training, and this increase was retained for the 10-day period of the study. Both tuning plasticity and retention were observed across stimulus levels (10-80 dB). Most noteworthy, tuning plasticity exhibited consolidation (i.e., developed greater CS-specific effects across retention periods), attaining asymptote at 3 days. The findings indicate that LFPs in the auditory cortex have three cardinal features of behavioral memory: associative tuning plasticity, long-term retention, and long-term consolidation. Potential cellular and subcellular mechanisms of LFP tuning plasticity and long-term consolidation are discussed.     

Direct remembering,mediated remembering,and atypical forgetting functions

Atypical forgetting functions have been demonstrated in several recent studies of delayed matching to sample, in which experimental conditions are altered partway through the retention interval. The forgetting functions are atypical in that accuracy or discriminability is not always a negatively accelerated monotonic function of increasing retention interval duration, but may increase at later times in the retention interval. Atypical forgetting functions reflect changes in levels of discrimination. A switch from a lower level to a higher level of discrimination, or vice versa, can occur at any time in the retention interval. The behavioral theories of remembering proposed by Nevin, Davison, Odum, and Shahan (2007), and White and Brown (2014), offer quantitative predictions of forgetting functions that differ in intercept or slope. Both theories are able to account for atypical forgetting functions, by assuming time‐independent changes in the mediating effect of attending to sample and comparison stimuli (in Nevin et al.'s model) or in the direct effect of the context of reinforcement of the conditional discrimination (in White & Brown's model). Despite differences in their main assumptions, the theories have an edge over any theory that assumes that forgetting is time‐dependent.