Blocking by fixed and variable stimuli: Effects of stimulus distribution on blocking

An experiment with rats compared the ability of fixed and variable duration cues to produce blocking. Rats in group B (Blocking) were trained that both fixed- (F) and variable- (V) duration cues would be followed by food delivery. In a subsequent training stage F and V continued to be reinforced, but F was accompanied by X, and V by Y. In the test phase responding to X and Y was examined. Control group O (Overshadowing) received identical treatment, except that F and V were nonreinforced in the first training stage. In group B there was evidence for blocking, but only of X, which had been conditioned in compound with the fixed-duration F; there was no evidence for blocking of Y, which had been conditioned in compound with the variable-duration V. It is suggested that this result may occur because fixed cues reach a higher, more stable asymptote of associative strength than do their variable equivalents.     

Prediction and uncertainty in associative learning: examining controlled and automatic components of learned attentional biases

It has been suggested that attention is guided by two factors that operate during associative learning: a predictiveness principle, by which attention is allocated to the best predictors of outcomes, and an uncertainty principle, by which attention is allocated to learn about the less known features of the environment. Recent studies have shown that predictiveness-driven attention can operate rapidly and in an automatic way to exploit known relationships. The corresponding characteristics of uncertainty-driven attention, on the other hand, remain unexplored. In two experiments we examined whether both predictiveness and uncertainty modulate attentional processing in an adaptation of the dot probe task. This task provides a measure of automatic orientation to cues during associative learning. The stimulus onset asynchrony of the probe display was manipulated in order to explore temporal characteristics of predictiveness- and uncertainty-driven attentional effects. Results showed that the predictive status of cues determined selective attention, with faster attentional capture to predictive than to non-predictive cues. In contrast, the level of uncertainty slowed down responses to the probe regardless of the predictive status of the cues. Both predictiveness- and uncertainty-driven attentional effects were very rapid (at 250?ms from cue onset) and were automatically activated.     

The Role of Recollection and Familiarity in Nondemented Parkinson's Patients

The aim of the current study was to examine if recollection and familiarity decline in nondemented Parkinson's patients. To do so we compared a sample of older people with Parkinson's disease (n = 32) to a control sample of healthy older people (n = 32) on an associative recognition task in which we manipulated the repetition of the pairs during the study phase (half of the pairs were presented once and half twice) to obtain corrected estimates of recollection, familiarity, and false recognition based on the logic of the process-dissociation procedure. The results clearly show that recollection is impaired but familiarity is preserved in nondemented Parkinson's patients. The results show that memory for pairs in Parkinson's patients relies largely on the familiarity of each item and not on a precise recollection of associative information, supporting the idea that recollection-based monitoring processes are impaired in these patients.     

Comparing different kinds of words and word-word relations to test an habituation model of priming

Huber and O'Reilly (2003) proposed that neural habituation exists to solve a temporal parsing problem, minimizing blending between one word and the next when words are visually presented in rapid succession. They developed a neural dynamics habituation model, explaining the finding that short duration primes produce positive priming whereas long duration primes produce negative repetition priming. The model contains three layers of processing, including a visual input layer, an orthographic layer, and a lexical-semantic layer. The predicted effect of prime duration depends both on this assumed representational hierarchy and the assumption that synaptic depression underlies habituation. The current study tested these assumptions by comparing different kinds of words (e.g., words versus non-words) and different kinds of word-word relations (e.g., associative versus repetition). For each experiment, the predictions of the original model were compared to an alternative model with different representational assumptions. Experiment 1 confirmed the prediction that non-words and inverted words require longer prime durations to eliminate positive repetition priming (i.e., a slower transition from positive to negative priming). Experiment 2 confirmed the prediction that associative priming increases and then decreases with increasing prime duration, but remains positive even with long duration primes. Experiment 3 replicated the effects of repetition and associative priming using a within-subjects design and combined these effects by examining target words that were expected to repeat (e.g., viewing the target word ‘BACK' after the prime phrase ‘back to'). These results support the originally assumed representational hierarchy and more generally the role of habituation in temporal parsing and priming.     

Familiarity,Priming, and Perception in Similarity Judgments

We present a novel way of accounting for similarity judgments. Our approach posits that similarity stems from three main sources—familiarity, priming, and inherent perceptual likeness. Here, we explore each of these constructs and demonstrate their individual and combined effectiveness in explaining similarity judgments. Using these three measures, our account of similarity explains ratings of simple, color‐based perceptual stimuli that display asymmetry effects, as well as more complicated perceptual stimuli with structural properties; more traditional approaches to similarity solve one or the other and have difficulty accounting for both. Overall, our work demonstrates the importance of each of these components of similarity in explaining similarity judgments, both individually and together, and suggests important implications for other similarity approaches.     

Increased sensitivity to proactive interference in amnestic mild cognitive impairment is independent of associative and semantic impairment

Episodic memory deficit is the hallmark of amnestic mild cognitive impairment (aMCI). There is, however, an overlap in performance among patients with aMCI and elderly controls (EC). The memory deficit in aMCI therefore needs to be better characterized. Studies have shown that associative memory is selectively impaired in aMCI, and recent work suggested that aMCI may be hypersensitive to semantic proactive interference (PI). It is not known whether this increased PI is related to associative or semantic impairment. EC (n = 44) and patients with aMCI (n = 30) performed two tasks presenting a gradually increasing PI effect across four lists. One task used semantic cueing, the other phonological cueing. We controlled for associative memory by introducing it as a covariate and by matching our subjects for it. Patients with aMCI had a greater PI effect than EC matched for associative memory, regardless of the type of cueing. The increased PI effect in patients with aMCI is independent of their associative and semantic impairment.     

Effects of moderate chronic ethanol consumption on hippocampal nicotinic receptors and associative learning

A number of studies have reported that ethanol exposure induces changes in different brain systems. The hippocampus is a brain region that is very vulnerable to ethanol exposition, which functionally results in impairment of learning and memory processes reported in heavy drinkers. Hippocampal nicotinic receptors are involved in learning and memory. In this study, we determined the effects of ethanol on the main hippocampal subtypes of neural nicotinic receptors (α7 and α4β2) in rats non-selected for alcohol consumption, in order to check for possible changes on these receptors that could be linked with alterations in learning acquisition. Binding assays were carried out with [³H]methyllycaconitine ([³H]MLA) to study the α7 and [³H]nicotine to study α4β2 receptors. Auto-shaping, continuous ratio and extinction procedures were used as behavioral tests. The results show that moderate chronic ethanol consumption for 10 weeks produces: (a) a decrease of both hippocampal nicotinic receptor subtypes without alterations in affinity; (b) no differences in behavioral performance between control rats and ethanol-drinking rats in auto-shaping and continuous ratio; (c) an improvement of performance of extinction paradigm. These results indicate that chronic ethanol consumption, at moderate levels, induces changes in hippocampal nicotinic receptors but does not impair acquisition and performance of new associative learning and even improves some kind of paradigms. These results may have implications in the biochemical basis of interactions between alcohol and nicotine and the effects of these drugs on behavior.     

How to like yourself better, or chocolate less: Changing implicit attitudes with one IAT task

The current paper introduces a novel feature of implicit association tests (IATs) by demonstrating their potential to change implicit attitudes. We assume that such changes are driven by associative learning mechanisms caused by carrying out an IAT task. Currently, evaluative conditioning appears to be the only widespread paradigm for changing implicit attitudes. An IAT task could provide an alternative. In two experiments, participants initially reacted to only one IAT task. Implicit preferences subsequently assessed with different implicit measures depended on the initial IAT task. This was shown for implicit self-esteem and for implicit attitudes towards well-known candy brands. Findings are discussed in relation to task-order effects in IATs.     

Enhanced proliferation of progenitor cells following long-term potentiation induction in the rat dentate gyrus

The dentate gyrus (DG) is among the few areas in the mammalian brain where production of new neurons continues in the adulthood. Although its functional significance is not completely understood, several lines of evidence suggest the role of DG neurogenesis in learning and memory. Considering that long-term potentiation (LTP) is a prime candidate for the process underlying hippocampal learning and memory, these results raise the possibility that LTP and neurogenesis are closely related. Here, we investigated whether or not LTP induction in the afferent pathway triggers enhanced proliferation of progenitor cells in the DG. LTP was induced by tetanic stimulation in perforant path-DG synapses in one hemisphere, and the number of newly generated progenitor (BrdU-labeled) cells in the DG was quantified. Compared with the control hemisphere (stimulated with low-frequency pulses), the LTP-induced hemisphere contained a significantly higher number of newly generated progenitor cells in the dorsal as well as ventral DG. When CPP, an NMDA receptor antagonist, was administered, tetanic stimulation neither induced LTP nor enhanced progenitor cell proliferation, indicating that NMDA receptor activation, rather than tetanic stimulation per se, is responsible for enhanced progenitor proliferation in the control animal. Our results show that tetanic stimulation of perforant path sufficient to induce LTP increases progenitor proliferation in adult DG in an NMDA receptor-dependent manner.