Luis Aguado

Interval between preexposure and test determines the magnitude of latent inhibition: Implications for an interference account

The effect of a retention interval on latent inhibition was studied in three experiments by using rats and the conditioned taste-aversion procedure. In Experiment 1, we demonstrated an apparent loss of latent inhibition (i.e., a strengthening of the aversion) in preexposed subjects that experienced a retention interval of 12 days between conditioning and the test. In Experiment 2, we found no effect of this retention interval on the habituation of neophobia produced by the phase of exposure to the flavor. In Experiment 3, we showed that interposing a retention interval between preexposure and conditioning produced effects exactly comparable to those seen in Experiment 1. The implications of these results for rival theories of latent inhibition, as an acquisition deficit or as a case of interference at retrieval, are discussed.

Effects of the NMDA receptor antagonist ketamine on flavor memory: Conditioned aversion, latent inhibition, and habituation of neophobia

In four experiments with rats, the effects of the NMDA antagonist ketamine on several forms of gustatory learning were studied. Replicating previous findings, in Experiment 1 ketamine was shown to impair one-trial acquisition of a flavor aversion at the dose of 25 mg/kg, but also produced a significant state-dependency effect. In Experiment 2 ketamine did not alter the process of habituation of neophobia to a new flavor. Abolition of latent inhibition by ketamine injected before preexposure in Experiment 3a was not replicated in Experiment 3b when ketamine was injected before all phases of the experiment. Finally, in Experiment 4 rats injected with ketamine showed slower acquisition of a flavor aversion with a multiple-trial procedure but finally reached a level similar to that shown by saline controls. The implications of these results for an interpretation of the effects of ketamine on flavor aversion learning in terms of interference with flavor memory storage are discussed.

Symmetrical interaction of sex and expression in face classification tasks

Classification of faces as to their sex or their expression—with sex and expression varying orthogonally—was studied in three experiments. In Experiment 1, expression classification was influenced by sex, with angry male faces being classified faster than angry female faces. Complementarily, sex classification was faster for happy than for angry female faces. In Experiment 2, mutual interaction of sex and expression was also found when the participants were asked to classify top and bottom face segments. In Experiment 3, a face inversion effect was found for both sex and expression classification of whole faces. However, a symmetrical interaction between sex and expression was again found. The results are discussed in terms of configural versus feature processing in the perception of face sex and expression and of their relevance to face perception models that postulate independent processing of different facial features. 2009 The Psychonomic Society, Inc.

Tests for inhibition after extinction of a conditioned stimulus in the flavour aversion procedure.

In four experiments, rats received flavour aversion conditioning followed by extinction. The flavour was then subjected to retardation and summation tests. Experiment 1 showed that reacquisition of an extinguished flavour aversion was retarded with respect to the performance shown by rats for whom the flavour was novel. No retardation was found, however, with respect to a control group that had been given non-reinforced pre-exposure to the flavour. Experiment 2 demonstrated that extinction showed the same sensitivity to the effects of a retention interval as did latent inhibition, consistent with the view that the retardation effect was a consequence of the occurrence of latent inhibition during extinction. An extinguished stimulus was also found to alleviate the response governed by a separately trained excitor in a summation test (Experiments 3 and 4), but the size of this effect did not exceed that produced by a control stimulus when the procedure used ensured an equivalent aversion to the test excitor in the two cases. These results challenge the proposal that extinction can turn a stimulus into a net inhibitor.

Effects of Prime Task on Affective Priming By Facial Expressions of Emotion

Priming of affective word evaluation by pictures of faces showing positive and negative emotional expressions was investigated in two experiments that used a double task procedure where participants were asked to respond to the prime or to the target on different trials. The experiments varied between-subjects the prime task assignment and the prime-target interval (SOA, stimulus onset asynchrony). Significant congruency effects (that is, faster word evaluation when prime and target had the same valence than when they were of opposite valence) were observed in both experiments. When the prime task oriented the subjects to an affectively irrelevant property of the faces (their gender), priming was observed at SOA 300 ms but not at SOA 1000 ms (Experiment 1). However, when the prime task assignment explicitly oriented the subjects to the valence of the face, priming was observed at both SOA durations (Experiment 2). These results show, first, that affective priming by pictures of facial emotion can be obtained even when the subject has an explicit goal to process a non-affective property of the prime. Second, sensitivity of the priming effect to SOA duration seems to depend on whether it is mediated by intentional or unintentional activation of the valence of the face prime.

Following the time course of face gender and expression processing: a task-dependent ERP study.

The effects of task demands and the interaction between gender and expression in face perception were studied using event-related potentials (ERPs). Participants performed three different tasks with male and female faces that were emotionally inexpressive or that showed happy or angry expressions. In two of the tasks (gender and expression categorization) facial properties were task-relevant while in a third task (symbol discrimination) facial information was irrelevant. Effects of expression were observed on the visual P100 component under all task conditions, suggesting the operation of an automatic process that is not influenced by task demands. The earliest interaction between expression and gender was observed later in the face-sensitive N170 component. This component showed differential modulations by specific combinations of gender and expression (e.g., angry male vs. angry female faces). Main effects of expression and task were observed in a later occipito-temporal component peaking around 230 ms post-stimulus onset (EPN or early posterior negativity). Less positive amplitudes in the presence of angry faces and during performance of the gender and expression tasks were observed. Finally, task demands also modulated a positive component peaking around 400 ms (LPC, or late positive complex) that showed enhanced amplitude for the gender task. The pattern of results obtained here adds new evidence about the sequence of operations involved in face processing and the interaction of facial properties (gender and expression) in response to different task demands.

Illness-Induced Context Aversion Learning in Rats With Lesions of the Dorsal Hippocampus

In 2 experiments, rats with electrolytic lesions of the dorsal hippocampus and sham-operated control subjects were given injections of lithium chloride after exposure to a distinctive context. This procedure establishes a context-illness association in intact subjects. In Experiment 1, the strength of the context aversion was assessed by measuring the subjects willingness to consume a novel flavor in the context. It was found that lesioned subjects showed less suppression of consumption than controls. Experiment 2 tested the ability of the context to block subsequent flavor-aversion learning and revealed less effective blocking in lesioned rats. These results are consistent with the view that hippocampal lesions retard context conditioning; unlike previous work that has made use of conditioned freezing as the measure of context conditioning, the present results are not explicable in terms of lesion-induced changes in general activity.

Neuroscience of Pavlovian Conditioning: A Brief Review

Current knowledge on the neuronal substrates of Pavlovian conditioning in animals and man is briefly reviewed. First, work on conditioning in aplysia, that has showed amplified pre-synaptic facilitation as the basic mechanism of associative learning, is summarized. Then, two exemplars of associative learning in vertebrates, fear conditioning in rodents and eyelid conditioning in rabbits, are described and research into its neuronal substrates discussed. Research showing the role of the amygdala in fear conditioning and of the cerebellum in eyelid conditioning is reviewed, both at the circuit and cellular plasticity levels. Special attention is given to the parallelism suggested by this research between the neuronal mechanisms of conditioning and the principles of formal learning theory. Finally, recent evidence showing a similar role of the amygdala and of the cerebellum in human Pavlovian conditioning is discussed.

Priming effects on the N400 in the affective priming paradigm with facial expressions of emotion

We studied the effect of facial expression primes on the evaluation of target words through a variant of the affective priming paradigm. In order to make the affective valence of the faces irrelevant to the task, the participants were assigned a double prime–target task in which they were unpredictably asked either to identify the gender of the face or to evaluate whether the word was pleasant or unpleasant. Behavioral and electrophysiological (event-related potential, or ERP) indices of affective priming were analyzed. Temporal and spatial versions of principal components analyses were used to detect and quantify those ERP components associated with affective priming. Although no significant behavioral priming was observed, electrophysiological indices showed a reverse priming effect, in the sense that the amplitude of the N400 was higher in response to congruent than to incongruent negative words. Moreover, a late positive potential (LPP), peaking around 700xa0ms, was sensitive to affective valence but not to prime–target congruency. This pattern of results is consistent with previous accounts of ERP effects in the affective priming paradigm that have linked the LPP with evaluative priming and the N400 with semantic priming. Our proposed explanation of the N400 priming effects obtained in the present study is based on two assumptions: a double check of affective stimuli in terms of valence and specific emotion content, and the differential specificities of facial expressions of positive and negative emotions.

Faces in context: Modulation of expression processing by situational information

Numerous studies using the event-related potential (ERP) technique have found that emotional expressions modulate ERP components appearing at different post-stimulus onset times and are indicative of different stages of face processing. With the aim of studying the time course of integration of context and facial expression information, we investigated whether these modulations are sensitive to the situational context in which emotional expressions are perceived. Participants were asked to identify the expression of target faces that were presented immediately after reading short sentences that described happy or anger-inducing situations. The main manipulation was the congruency between the emotional content of the sentences and the target expression. Context-independent amplitude modulation of the N170 and N400 components by emotional expression was observed. On the other hand, context effects appeared on a later component (late positive potential, or LPP), with enhanced amplitudes on incongruent trials. These results show that the early stages of face processing where emotional expressions are coded are not sensitive to verbal information about the situation in which they appear. The timing of context congruency effects suggests that integration of facial expression with situational information occurs at a later stage, probably related to the detection of affective congruency.