Function Of Associative Strength Research Articles

Conditioned inhibitory and excitatory gain modulations of visual cortex in fear conditioning: Effects of analysis strategies of magnetocortical responses.

In unpredictable environments, stimuli that predict potential danger or its absence can change rapidly. Therefore, it is highly adaptive to prioritize incoming sensory information flexibly as a function of prior experience. Previously, these changes have only been conceptualized as excitatory gain increases in sensory cortices for acquired fear-relevant stimuli during associative learning. However, formal descriptions of associative processes by Rescorla and Wagner predict both conditioned excitatory and inhibitory processes in response systems for fear and safety cues, respectively. Magnetocortical steady-state visual evoked fields (ssVEFs) have been shown to vary in amplitude as a function of associative strength. Therefore, we wondered why previous studies reporting ssVEF modulations by fear learning did not observe conditioned inhibition of ssVEF responses for the safety cue. Three analysis strategies were applied: (1) traditional analysis of ssVEF amplitude at occipital MEG sensors, (2) applying a general linear model (GLM) at each sensor, and (3) fitting the same GLM to cortically localized ssVEF responses. First, we replicated previous findings of increased ssVEFs for acquired fear-relevant stimuli using all three analysis strategies. Critically, we demonstrated conditioned inhibition of ssVEF responses for fear-irrelevant cues for specific gradiometer sensor types using the traditional analysis technique and for all sensor types when applying a GLM to the sensor space. However, sensor space effects were rather small. In stark contrast, cortical source space effect sizes were most pronounced. The results of opposing CS+ and CS- modulations in sensory cortex reflect predictions of the Rescorla-Wagner model and current neurobiological findings.

Early dynamics of the semantic priming shift.

Semantic processing of sequences of words requires the cognitive system to keep several word meanings simultaneously activated in working memory with limited capacity. The real- time updating of the sequence of word meanings relies on dynamic changes in the associates to the words that are activated. Protocols involving two sequential primes report a semantic priming shift from larger priming of associates to the first prime to larger priming of associates to the second prime, in a range of long SOAs (stimulus-onset asynchronies) between the second prime and the target. However, the possibility for an early semantic priming shift is still to be tested, and its dynamics as a function of association strength remain unknown. Three multiple priming experiments are proposed that cross-manipulate association strength between each of two successive primes and a target, for different values of short SOAs and prime durations. Results show an early priming shift ranging from priming of associates to the first prime only to priming of strong associates to the first prime and all of the associates to the second prime. We investigated the neural basis of the early priming shift by using a network model of spike frequency adaptive cortical neurons (e.g., Deco & Rolls, 2005), able to code different association strengths between the primes and the target. The cortical network model provides a description of the early dynamics of the priming shift in terms of pro-active and retro-active interferences within populations of excitatory neurons regulated by fast and unselective inhibitory feedback.

Dopaminergic neuromodulation of semantic priming in a cortical network model

Semantic priming between items stored and associated in memory underlies contextual recall. Response times to process a given target item are shorter when following presentation of a related prime item than when it is unrelated. The study of priming effects allows investigating the structure of semantic networks as a function of association strength and number of links relating the prime and target. Behavioral data from divided visual field experiments in healthy subjects show a variability in the magnitude of priming effects when the left or right hemisphere is primary involved. Data from schizophrenic patients also exhibit variability in priming magnitude compared to data from healthy subjects. Mathematical models of cortical networks allow theorists to understand the link between the physiology of single neurons and synapses and network behavior. Computational modelling can replicate electrophysiological recordings of cortical neurons in monkeys, that exhibit two types of task-related activity, ‘retrospective’ (related to a previously shown stimulus) and ‘prospective’ (related to a stimulus expected to appear, due to learned association between both stimuli). Experimental studies of associative priming report priming effects on behavioral data in both human and monkeys. Cortical network models can account for a large variety of priming effects observed in human, and for the dependence of retrospective activity on dopamine neuromodulation. Here, we investigate how variable levels of dopamine in a model of a cortical network can modulate prospective activity to vary the magnitude of semantic priming. We simulate a biologically realistic network of integrate and fire neurons to study the effects of dopaminergic neuromodulation of NMDA receptors of glutamatergic and gabaergic neurons on semantic priming dynamics. Results support the possibility that different levels of dopaminergic neuromodulation can subtend hemispheric differences in semantic priming, corresponding to focused priming in the left hemisphere and to extended priming in the right hemisphere. Furthermore, results can account for priming perturbations in schizophrenia depending on the level of dopamine.

Learning-dependent timing of Pavlovian eyelid responses: differential conditioning using multiple interstimulus intervals.

This study demonstrates that individual animals can concurrently acquire differently timed conditioned eyelid responses using a differential conditioning procedure in which distinctive conditioned stimuli (CSs) are individually paired with an unconditioned stimulus, with each using a different interstimulus interval (ISI). This promotes robust conditioning, and the timing of the conditioned responses is appropriate for the respective ISIs, differs for each CS to the extent that the ISIs are dissimilar, and is apparent in individual trials. This procedure was used to demonstrate that response timing is not a function of associative strength. These data suggest response timing is mediated by an ability to make temporal discriminations during the CS. The within-animals comparisons made possible by this differential conditioning should facilitate lesion and unit recording analyses of the neural basis of response timing.

Verbal discrimination learning as a function of associative strength between noun pair members.

Verbal discrimination learning as a function of associative strength between noun pair members.

Mediation effects in verbal chaining paradigms as a function of associative strength and the number of stages.

Mediation effects in verbal chaining paradigms as a function of associative strength and the number of stages.

Extra-list errors in paired associate learning by retarded and normal children.

This study compared the proportions of extra-list intrusions in errors by retarded and normal Ss on a paired-associate task. Associative strength of the paired items was varied. Results indicated that retardates imported a significantly greater proportion of responses than normals under both levels of associative strength. Ss did not import differential proportions of responses as a function of associative strength.

Learning and Retention of Letter Pairs as a Function of Association Strength

Three experiments on paired-associate learning and retention of letter pairs tested the Underwood-Postman hypothesis that extraexperimental associations interfere with learning and produce forgetting. As hypothesized, in experiments with seven- and ten-year-old children and with adults, highly associated (high-strength) letter pairs were learned faster and, on the whole, retained better over one week than low-strength pairs. The positive retention effects, not observed in previous studies, are partly attributed to the use of the correction procedure as a control for the overlearning of easy items in low-strength lists that is unavoidable with standard methods. This overlearn- ing is believed to reduce the probability of detecting any differential retention of high- and low-strength lists. Developmental differences in children were small for original learning and insignificant for forgetting. A single postcriterion trial, however, facilitated retention-test performance. Theoretical implications are discussed.

Verbal discrimination learning as a function of associative strength between the word-pair members

Derivations from associative generalization experiments and the frequency theory of verbal discrimination learning were tested in four experiments. Exps. I and IV used the usual simultaneous verbal discrimination procedure, Exp. II used a successive discrimination procedure, and Exp. III used a differential discrimination procedure. Exps. I-III were conducted with college S s and Exp. IV was conducted with fourth-grade children. In all four experiments discriminations were required between pairs of words of high, intermediate or zero free-association strength, and in all cases the difficulty of the discrimination was positively related to association strength although the overall difficulty of learning was related to the type of discrimination task employed. The results were interpreted as supporting the frequency theory of verbal discrimination learning.

Conceptual behavior as a function of associative strength between representational responses

The influence of associative strength between representational responses on conceptual categorizing behavior was investigated in two experiments. The first study failed to produce a significant effect of level of associative strength, high or low, on the ability of S s to execute a reversal shift in a concept-identification task requiring sorting nouns into two sense-impression categories. In the second study only one sorting category was used, and the S after identifying the correct concept was required to shift to a second concept which was either a high- or low-associate of the first concept. The shift was executed significantly more rapidly when the second concept was a high-associate of the first.

Short-Term Retention as a Function of Associative Strength and Retention Intervals

The effects of association strength, retention intervals, and repetition of task on paired-associate acquisition by retardates were studied. 30 retardates with an MA range of 5.6 to 9.8 were divided randomly into 3 groups of 10 subjects each, corresponding to each of the retention intervals—zero seconds, 2 seconds, and 4 seconds delay of recall. 12 paired-associate pictures representing high, medium, and low association value were presented randomly to each subject. After each presentation, subjects were required to recall the response picture associated with each stimulus picture. The results showed that associative strength and retention intervals have a significant effect on mentally retarded children's retentive process. This study suggests that the factor of immediate feedback and the use of meaningful materials should play an important role in the educational curriculum and the teaching method with exceptional children.

Acquisition of paired associates as a function of associative strength of competing responses.

Acquisition of paired associates as a function of associative strength of competing responses.

Extra-List Intrusions in Immediate Free Recall as a Function of Associative Strength in Children

After collecting word-association norms for 12 high frequency responses to 36 stimulus words drawn from the Minnesota norms (3), Deese (2) found that the relative frequency of occurrence of a stimulus word as an associate to these responses was significantly correlated with the extent to which the stimulus word occurred as an extra-list intrusion in tests of immediate free recall. Using college students as Ss, the product-moment correlation between the frequency of occurrence of the stimulus word as an associate and the frequency of occurrence of the stimulus word as an intrusion was ,873. The purpose of the present study was to examine this same relationship in grade school children. The procedure employed by Deese (2) was followed as closely as possible with three exceptions: fewer recall lists and words per list were used. the recall tests were administered in groups rather than individually (1) and the word associations were collected by having E read the stimulus words aloud instead of having the stimulus words printed on sheets of paper. Ss were school children drawn from the 4th, 5th, and 6th grades. In Part I of the experiment, 19 free recall tests consisting of 10 high frequency responses each were administered to 29 Ss each from these grades. The stimulus and response words were culled from word-association norms collected by Simon, Lotsof, and Pease (4) from 399 4th. 5th. and 6th grade children. Jn Part I1 of the experiment, word-association norms were collected from 90 different Ss drawn from the same population as that employed in Part I of the experiment. For all grades combined, the product-moment correlation between the number of times the stimulus word occurred as a free association in Part I1 and the number of times the stimulus word occurred as an intrusion in Pan I was ,725 (p< .01). The correlations for the 4th, 5th, and 6th grades, respectively, were ,675, ,719, and ,604 (p < .O1 in all three instances). None of the latter ss were significantly different from one another. These results agree well with those reported by Deese (1) and suggest that his findings may reliably be extended to include children in the 4th, 5th, and 6th grades.

Associative strength and degree of competition in verbal paired-associate learning

The present study dealt with paired-associate learning in elementary school age children as a function of associative strength and degree of competition. Two conditions were compared, each involving S-R pairs mediated by weak as well as strong associative strengths. The pairs mediated by strong associative strengths were identical in both conditions. In Condition I the S-R pairs mediated by weak associative strengths were constructed so as to maximize generalization of their response items to the stimulus items for the strongly associated S-R pairs. Performance on these latter S-R pairs in Condition I was found to be significantly poorer in comparison to identical S-R items in Condition II which minimized the presence of competing associations.

Incidental Learning: A Function of Associative Strength and Distance Between S-R Pairs

Incidental Learning: A Function of Associative Strength and Distance Between S-R Pairs