Predictability and heritability of individual differences in fear learning

Our objective was to characterize individual differences in fear conditioning and extinction in an outbred rat strain, to test behavioral predictors of these individual differences, and to assess their heritability. We fear-conditioned 100 Long-Evans rats, attempted to extinguish fear the next day, and tested extinction recall on the third day. The distribution of freezing scores after fear conditioning was skewed, with most rats showing substantial freezing; after fear extinction, the distribution was bimodal with most rats showing minimal freezing, but a substantial portion showing maximal freezing. Longer rearing episodes measured prior to conditioning predicted less freezing at the beginning of extinction, but differences in extinction learning were not predicted by any baseline exploratory behaviors. We tested the heritability of extinction differences by breeding rats from the top and bottom 20 % of freezing scores during extinction recall. We then ran the offspring through the same conditioning/extinction procedure, with the addition of recording ultrasonic vocalizations throughout training and testing. Only a minority of rats emitted distress vocalizations during fear acquisition, but the incidence was less frequent in the offspring of good extinguishers than in poor extinguishers or randomly bred controls. The occurrence of distress vocalizations during acquisition predicted higher levels of freezing during fear recall regardless of breeding line, but the relationship between vocalization and freezing was no longer evident following extinction training, at which point freezing levels were influenced only by breeding and not by vocalization. The heritability (h ²) of extinction recall was estimated at 0.36, consistent with human estimates.     

A computer program for determining optimal data transformations minimizing skew

A program is presented that solves for an optimal transformation of data that minimizes skew. Various possible transformations are represented by a function that depends upon a single parameter, λ. A process of iterative approximations is employed to find a value of λ that will transform the data so as to produce a third moment equal to zero. The transformation found by this process may be used as computed or used to indicate which of the commonly employed transformations will most adequately counteract skew. The use of this program in processing data before analysis of variance is discussed.     

Instability in memory phenomena: A common puzzle and a unifying explanation

In mixed lists, stable free recall advantages are observed for encoding conditions that are unusual, bizarre, or attract extensive individual item elaboration relative to more common encoding conditions; but this recall advantage is often eliminated or reversed in pure lists. We attempt to explain this ubiquitous memory puzzle with an item-order account that assumes that (1) free recall of unrelated lists depends on order and item information; (2) unusual items attract greater individual item-processing but disrupt order encoding regardless of list composition; and (3) list composition determines differences in order encoding across unusual and common items. We show that the item-order account provides a unifying explanation of five memory phenomena for which the requisite data exist. The account also successfully anticipates pure-list reversals, in which the standard mixed-list recall pattern is obtained in pure, structured lists, a finding that competing accounts cannot handle. Extending the item-order account to other “established” recall phenomena may prove fruitful.     

Retrospective questions and correlations

In survey research it is not uncommon to ask questions of the following type: “How many times did you undertake actiona in reference periodT of length τ?.” The relationship is established between τ and the correlation of the number of reported actions with some background variable. To this end it is assumed that the process of actions satisfies a renewal model with individual heterogeneity. Also a model has to be formulated for possible recall effects. Applications are given in the field of medical consumption.     

On-line analysis of the GSR

This study reports the use of the λ, a measure of sequential dependency developed by Lathrop (1964) in connection with electrodermal activity. Thirteen female subjects, ranging in age from 19 to 53, participated in a simple repeat-stimulus habituation experiment: GSR data in percent-change and λ were compared. A high, positive correlation was obtained. Consequently, the use of λ is advocated because it shows both initial value and sequential dependency and meets the criteria for analysis based on the probability of statistics such ast andF.     

Decomposing retrieval and integration in memory for actions: A multinomial modeling approach

Typically, action phrases are recalled better if participants are asked to enact the phrases than if they are just asked to remember them. When investigating which processes constitute this enactment effect a difficulty is that observable effects in standard memory tests are ambiguous because such tests require several processes. In the present article, we introduce a multinomial model that decomposes observable memory performance into a retrieval parameter and a parameter concerning the item-specific processing and integration of an action phrase. These parameters are estimated from free recall and cued recall performance. The model fitted the data of two experiments designed to test it. Experiment 1 demonstrated the basic usefulness of the model by showing expected differences in the integration parameter in the absence of unexpected differences in the retrieval parameter. Experiment 2 extended the conditions under which the model is useful by showing expected differences in the retrieval parameter even in the presence of unexpected differences in the integration parameter. Together, these findings support our theoretical framework according to which enactment generally boosts integration of action phrases, but increases retrieval only for phrases with context cues.     

Decomposing retrieval and integration in memory for actions: a multinomial modeling approach

Typically, action phrases are recalled better if participants are asked to enact the phrases than if they are just asked to remember them. When investigating which processes constitute this enactment effect a difficulty is that observable effects in standard memory tests are ambiguous because such tests require several processes. In the present article, we introduce a multinomial model that decomposes observable memory performance into a retrieval parameter and a parameter concerning the item-specific processing and integration of an action phrase. These parameters are estimated from free recall and cued recall performance. The model fitted the data of two experiments designed to test it. Experiment 1 demonstrated the basic usefulness of the model by showing expected differences in the integration parameter in the absence of unexpected differences in the retrieval parameter. Experiment 2 extended the conditions under which the model is useful by showing expected differences in the retrieval parameter even in the presence of unexpected differences in the integration parameter. Together, these findings support our theoretical framework according to which enactment generally boosts integration of action phrases, but increases retrieval only for phrases with context cues.     

Chronic stress and sex differences on the recall of fear conditioning and extinction

Chronic stress effects and sex differences were examined on conditioned fear extinction. Male and female Sprague–Dawley rats were chronically stressed by restraint (6 h/d/21 d), conditioned to tone and footshock, followed by extinction after 1 h and 24 h delays. Chronic stress impaired the recall of fear extinction in males, as evidenced by high freezing to tone after the 24 h delay despite exposure to the previous 1 h delay extinction trials, and this effect was not due to ceiling effects from overtraining during conditioning. In contrast, chronic stress attenuated the recall of fear conditioning acquisition in females, regardless of exposure to the 1 h extinction exposure. Since freezing to tone was reinstated following unsignalled footshocks, the deficit in the stressed rats reflected impaired recall rather than impaired consolidation. Sex differences in fear conditioning and extinction were observed in nonstressed controls as well, with control females resisting extinction to tone. Analysis of contextual freezing showed that all groups (control, stress, male, female) increased freezing immediately after the first tone extinction trial, demonstrating contextual discrimination. These findings show that chronic stress and sex interact to influence fear conditioning, with chronic stress impairing the recall of delayed fear extinction in males to implicate the medial prefrontal cortex, disrupting the recall of the fear conditioning acquisition in females to implicate the amygdala, and nonstressed controls exhibiting sex differences in fear conditioning and extinction, which may involve the amygdala and/or corticosterone levels.     

The learning theory model of neurosis—A new approach

This paper is concerned with the development of a learning theory model of neurosis which would not be susceptible to the many criticisms which can be made of former models. Two widely favoured models—those of Freud and Skinner—are rejected because they are either non-falsifiable or tautological. The Watson and Mowrer models are rejected because they have been experimentally invalidated. The model here suggested differs from previous ones in several important respects. In the first place, it replaces the classical law of extinction by a more modern version which allows for incubation (enhancement) effects of exposure to CS-only stimuli, as well as for extinction effects. In the second place, the model emphasizes the importance of individual differences, and suggests precise relations between personality and the conditioning of neurotic behaviours. In the third place, the model lays stress on innate fear patterns and ‘preparedness’ as important factors in the genesis of conditioned fear responses. In the fourth place, the concept of ‘pain’ in the classical animal literature, and its use in creating models of neurosis, is supplemented by other concepts (‘frustrative non-reward’, ‘approach-avoidance’ conflict) which are more relevant to human neurosis. In the fifth place, and most important. the notion of ‘traumatic’, single-trial conditioning is abandoned, and a new theory based on incubation is proposed. It is suggested that the new theory is more adequate than previous ones to account for the known facts of human neurosis, and that it suggests novel types of experiment in both the animal and human fields which can be used to test its adequacy.     

Ability correlates of memory performance in adulthood and aging

The predictive relationships between an array of cognitive process and intellectual ability variables and text- and word-recall performance were examined. A sample of 584 men and women from 3 age groups (19-36, 55-69, and 70-86 years) completed a battery of 23 tasks marking 2 latent criterion variables and 10 latent predictor variables. The results indicated that (a) individual differences in process and ability variables predict performance on text and word recall, accounting for approximately half of the variance; (b) the pattern of predictors is quite similar for text and word recall; (c) age-related differences in text and word recall can be substantially accounted for by individual differences in constituent abilities, particularly indicators of verbal speed and working memory; and (d) there is some evidence to suggest that the pattern of ability-performance relationships varies across age, but such interactions appear to be relatively small.     

Reorganization of learning-associated prefrontal synaptic plasticity between the recall of recent and remote fear extinction memory

We have previously shown that fear extinction is accompanied by an increase of synaptic efficacy in inputs from the ventral hippocampus (vHPC) and mediodorsal thalamus (MD) to the medial prefrontal cortex (mPFC) and that disrupting these changes to mPFC synaptic transmission compromises extinction processes. The aim of this study was to examine whether these extinction-related changes undergo further plasticity as the memory of extinction becomes more remote. Changes in synaptic efficacy in both vHPC-mPFC and MD-mPFC inputs were consequently analyzed when the memory was either 1 d or 7 d old. Increases of synaptic efficacy in the vHPC-mPFC pathway were observed when the memory was 1 d old, but not 7 d after initial extinction. In contrast, potentiation of synaptic efficacy in the MD-mPFC pathway increased over time. In rats that received low-frequency vHPC stimulation immediately after extinction, both vHPC-mPFC and MD-mPFC inputs failed to develop potentiation, and the recall of extinction (both recent and remote memories) was impaired. These findings suggest that post-extinction potentiation in vHPC-mPFC inputs may be necessary for both the recall of recent memory and post-extinction potentiation in the MD-mPFC inputs. This late potentiation process may be required for the recall of remote extinction memory.     

A test of current explanations of the effect of item familiarity on memory

The effects of item familiarity in memory have been variously ascribed to differences in storage or retrieval efficiency, response availability, and response bias. The experiments reported here attempted to discriminate between these explanations, using a model of the response process based on signal-detection theory. Memory for English surnames varying in frequency of occurrence was tested under free recall and recognition conditions. In both conditions, common names appeared more often among the incorrect responses, reflecting a response bias in their favour; but storage and/or retrieval of these names, as measured by the parameter d', was less efficient than for uncommon ones. The finding of similar results in recognition and recall shows that the effect remains even when differences in response availability are removed by the use of a probe.     

Deviation from hierarchical structure in recall: Is there an “optimal” structure?

Past research has suggested that proportionally more superordinate than sub-ordinate propositions are recalled from expository texts, following a hierarchical analysis of the text structure. Since free recall has typically followed this hierarchical pattern, several researchers have assumed that the related memory structures are isomorphic to the text structure. However, few of these studies have examined how individual differences and text structure interact to affect free recall. In two experiments, the assumption of hierarchical patterns of children's recall of expository text was tested. In Experiment 1, high- and average-ability fourth graders (9 years old) were asked to read and recall a passage. Experiment 2 was a replication and extension of Experiment 1. In this experiment, fourth and sixth graders (9 and 11 years old) read and recalled a different passage. The combined results of both experiments support the notion that there is probably no one optimal hierarchical structure for storage and retrieval of expository text.     

Recalling safety: cooperative functions of the ventromedial prefrontal cortex and the hippocampus in extinction

Anxiety disorders are commonly treated with exposure-based therapies that rely on extinction of conditioned fear. Persistent fear and anxiety following exposure therapy could reflect a deficit in the recall of extinction learning. Animal models of fear learning have elucidated a neural circuit for extinction learning and recall that includes the amygdala, ventromedial prefrontal cortex (vmPFC), and hippocampus. Whereas the amygdala is important for extinction learning, the vmPFC is a site of neural plasticity that allows for the inhibition of fear during extinction recall. We suggest that the vmPFC receives convergent information from other brain regions, such as contextual information from the hippocampus, to determine the circumstances under which extinction or fear will be recalled. Imaging studies of human fear conditioning and extinction lend credence to this extinction network. Understanding the neural circuitry underlying extinction recall will lead to more effective therapies for disorders of fear and anxiety.     

The proper role of clusters in mathematical models of continuous recall

Previous research has shown that the number of words cumulatively recalled (N) at time (t) is a negatively accelerated function that reaches an asymptote as t → ∞. Research has also shown that the increase in N with t occurs in bursts or clusters. Several models purport to account for this cumulative recall curve in terms of cluster characteristics. The present research shows that previous models have not in fact successfully linked continuous recall to cluster characteristics. This research demonstrates that cluster models need to employ three empirical characteristics of clusters: T_b, the time between clusters; T_w, the average time between words within a cluster; and W_c, the number of words within a cluster. It is shown that these three quantities determine the cumulative recall curve, and these three quantities may in turn be characterized by four parameters. Of these four parameters, only three actually characterize the cumulative recall curve. Two parameters determine the initial slope and final asymptote of the curve, while a third parameter, which we introduce for the first time, characterizes the curve's shape. This latter parameter may be interpreted as the ratio ofthe time spent in retrieving and discarding a cluster that has been previously recalled to the amount of time spent in retrieving and outputting a newly encountered cluster. It is pointed out that previous success in fitting the cumulative recall data with a two-parameter function may be explained by the fact that this parameter lies in a restricted range about unity. Further experimental work is suggested to elucidate the behavior of this new parameter. Two models are then proposed to account for these characteristics of clusters and the shape of the recall curve.     

Reliability coefficients as a function of individual differences induced by a learning process assuming identical organisms

In this article we show that a particular mathematical learning model, the Bower-Trabasso (1964) concept identification model taken together with an assumption of independence of replicate measurements, implies the existence of substantial and statistically significant performance differences across individuals. The individual differences in turn imply a sizeable reliability coefficient. These results contradict naive intuition, for this model (like many other mathematical models of learning) assumes that all individuals begin the experiment with identical parameter values for the process under study. Thus at least one such model has the characteristic of implying the generation of individual performance differences among originally identical organisms.Examination of data from an experiment by Cotton shows that the Hoyt reliability coefficient under classical test theory, a lower bound for the (composite) reliability of total scores for a series of trials, increases with the number of trials analyzed and exceeds the corresponding theoretical values implied by the Bower-Trabasso model. An experiment by Levine was also analyzed because its use of blank trials between feedback trials permitted direct calculation of composite reliability (or more properly stated composite consistency). For this experiment, the theoretical development just discussed (Case I) was used together with Restle's hypothesis selection model specialized to include a local consistency assumption, the so-called P₂ model of Gregg and Simon (Case II). Moderate conformity of empirical and theoretical reliabilities was found, with discrepancies between observed and predicted values usually being smaller with Case II. However, the Hoyt reliability coefficient is not a lower bound for composite reliability in Case II, because composite reliability is underestimated when identical stimuli are not used for comparable trials.Despite the Bower-Trabasso assumption of no initial differences, it seems reasonable to attribute the difference between predicted and obtained reliabilities to preexisting individual differences. Implications of the tentative conclusion that individual differences in concept identification performance are attributable to a combination of preexisting differences and differences induced in a current task are discussed briefly.     

Checking the Assumptions of Rasch's Model for Speed Tests

Two new tests for a model for the response times on pure speed tests by Rasch (1960) are proposed. The model is based on the assumption that the test response times are approximately gamma distributed, with known index parameters and unknown rate parameters. The rate parameters are decomposed in a subject ability parameter and a test difficulty parameter. By treating the ability as a gamma distributed random variable, maximum marginal likelihood (MML) estimators for the test difficulty parameters and the parameters of the ability distribution are easily derived. Also the model tests proposed here pertain to the framework of MML. Two tests or modification indices are proposed. The first one is focused on the assumption of local stochastic independence, the second one on the assumption of the test characteristic functions. The tests are based on Lagrange multiplier statistics, and can therefore be computed using the parameter estimates under the null model. Therefore, model violations for all items and pairs of items can be assessed as a by-product of one single estimation run. Power studies and applications to real data are included as numerical examples.     

Adding sound to lipread lists: The effects on serial recall of adding an auditory pulse train and a pure tone to silently lipread lists

These investigations examined subjects’ serial recall of lipread digit lists accompanied by an auditory pulse train. The pulse train indicated the pitch of voiced speech (buzz-speech) of the seen speaker as she was speaking. As a purely auditory signal, it could not support item identification. Such buzz-speech recall was compared with silent lipread list recall and with the recall of buzz-speech lists to which a pure tone had been added (buzz-and-beep lists). No significant difference in overall accuracy of recall emerged for the three types of lipread list; however, there were significant differences in the shape of the serial recall function for the three list types. Recency characterized the silent and the buzz-speech lists, and these lists differed in their varying susceptibilities to a range of speechlike suffixes. By contrast, adding a pure tone to a buzz-speech list (buzz-and-beep) produced little recency and no further recall loss as a function of suffix type. We discuss these effects with reference to the contrast betweensensory-similarity and speechlikeness accounts of auditory recency and suffix effects. Sensory similarity accounts cannot capture the effects reported here, but processing in a speech mode (buzz-and-beep) need not always lead to recency effects like those resulting from clearly heard or lipread lists.     

When the event is more than the sum of its parts: 9-month-olds' long-term ordered recall

Research suggests that 9-month-old infants are able to recall single object-specific actions over delays of 24 hours. In the present research we investigated whether 9-month-olds are able to recall over more extended delays, and to recall the temporal order of events, as well as the individual actions in them. In addition, we investigated whether recall can be enhanced by pre- and/or re-exposure to target events. Using elicited imitation of novel, multi-step event sequences, we demonstrated that, as a group, 9-month-olds are able to recall target actions after delays of five weeks. However, after this long delay, only 45% of the infants recalled the temporal order of the events. Re-exposure to events during the delay interval proved necessary for boys, but not for girls; pre-exposure to events did not affect later recall. The implications of individual differences in infants' recall ability for the understanding of the development of the neural correlates of declarative memory are discussed.