Demonstrations of neophobia and enhanced neophobia in the albino rat.

The conditions under which neophobia and enhanced neophobia occur in the albino rat were studied. Neophobia to a .1% saccharin solution was demonstrated in a 10-min single-bottle test. This neophobia was enhanced by pairing water ingestion with a radiation exposure of 100 r. or an injection of lithium chloride 24 hr prior to the saccharin test. In addition, it was found that the differences in consumption of saccharin in a 10-min single-bottle test due to neophobia and enhanced neophobia were produced by consistent differences in drinking rates which appeared early in the 10-min period. The disappearance of neophobia and enhanced neophobia in a 1-hr single-bottle test suggested that the effects of neophobia and enhanced neophobia are short-lived and are best measured in a brief single-bottle test. Finally, enhanced neophobia was not found when 2 days of water drinking were interposed between LiCl poisoning and saccharin testing.     

The role of background stimuli during pavlovian conditioning

An investigation was carried out into the part played by background stimuli during Pavlovian conditioning. Groups of rats were presented with tone CSs and unavoidable foot-shock USs. Both CS-US conditional probabilities and US intensity were manipulated across groups. Subsequently all animals were tested for their reactions to the environment in which they had previously been trained. During tests neither the CS nor the US was presented. It was found that the degree to which rats avoided the environment was inversely related to the probability of the CS being followed by a US and directly related to the level of US intensity to which they had been exposed during training. The results largely supported Rescorla and Wagner's (1972) theory of Pavlovian conditioning.     

Personality and conditioning with appetitive and aversive stimuli

Two studies examining relationships of extraversion (E), neuroticism (N) and psychoticism (P) to conditioning performance are reported. In the first, 31 male volunteers developed electrodermal CRs to appetitive or aversive stimuli of either weak or strong rated intensity. Factor analysis yielded general factors of classical CR acquisition and extinction across reinforcement type. Stability and E loaded the acquisition factor, these Ss, from post-hoc analysis, revealing superior conditioning in the strong appetitive condition. In the second study, 20 of these 31 Ss participated in two series of discrimination motor reaction time trials, in which attainment of criterion RT was reinforced by appetitive slides, and slower-than-criterion responding by aversive slides. Introversion was correlated with greater response acquisition under both conditions, although post-hoc analysis suggested that improvement under positive reinforcement did not differ from simple practice. Results are congruent with a model combining reinforcer preference with response potential to describe personality-conditioning relationships.     

Electrodermal pavlovian conditioning with prepared and unprepared stimuli

One-trial learning referred to by Guthrie has been suggested to occur in autonomic conditioning, if the conditional stimuli (CSs) are so-called prepared ones. To test this idea, half of 28 subjects were given spider or snake slides as “prepared” CSs, while the remainder were given neutral slides as “unprepared” CSs. A shock was employed as the unconditional stimulus (UCS), with a CS-UCS interval of 8 seconds. Electrodermal activity and probe reaction times were the dependent measures of conditioning, conceived in cognitive, information-processing terms as the learning of the CS/UCS contingency. Evidence for the usual CS/UCS contingency learning emerged in both indicators, and during both acquisition and extinction, but none for one-trial learning, perhaps because the UCS was insufficiently aversive.     

Effects of neophobia and habituation on the poison-induced avoidance of exteroceptive stimuli in the rat.

Two experiments on the role of neophobia in poison-induced aversions to exteroceptive stimuli are reported. In Experiment 1, rats were given either 10 or 25 days of habituation to the test situation prior to conditioning. Those animals with the longer habituation period avoided a complex of novel exteroceptive stimuli while those with the shorter habituation period did not. In Experiment 2 rats initially avoided the more novel of two containers, but gradually came to eat equal amounts from both. A single pairing of toxicosis with consumption from either the novel or the familiar container reinstated the avoidance of the novel container in both cases. The results were discussed in terms of an interaction between habituation and conditioning procedures. It was suggested that previously reported differences between interoceptive and exteroceptive conditioning effects may have been influenced by the differential novelty of the two classes of stimuli in the test situation. It was further suggested that non-contingently poisoned control groups should routinely be included in poison avoidance conditioning studies.     

Contextual factors in neophobia and its habituation: The role of absolute and relative novelty

In four experiments we investigated the role of contextual cues in the habituation of neophobia in rats. Experiment 1 showed that the consumption of a novel flavour increased across a series of presentations in one context (A) but fell when the flavour was subsequently presented in a second, novel, context (B). In Experiments 2 and 3, subjects again received exposure to a flavour in context A, but also were familiarized with the test context, B. These subjects consumed the flavour with equal readiness, whether it was presented in Context A or in Context B at test. Experiment 4 replicated the results of Experiment 1 and also showed that the consumption of a novel flavour was not influenced by whether it was presented in a novel or a familiar context. Several mechanisms by which the novelty or familiarity of the context might interact with the novelty or familiarity of the flavour were discussed.     

Electrodermal conditioning to potentially phobic stimuli: Effects of instructed extinction

It was hypothesized that electrodermal responses to potentially phobic stimuli “conditioned” through verbal threats about an aversive UCS should be equally resistant to instructed extinction as the responses obtained by actual CS-UCS pairings. Two groups of human subjects were exposed to pictures of either snakes and spiders (phobic CSs), or circles and triangles (neutral CSs) in a differential Pavlovian conditioning paradigm. Changes in skin conductance were recorded. Half of the subjects in each group were threatened with a shock-UCS while the other half were given shock-reinforced CS presentations. At the onset of extinction, all subjects in each of the four groups were informed that no more UCSs were to be delivered, and the shock electrodes were removed. All groups showed evidence of conditioning during acquisition. During extinction there was an immediate drop in responding in the two neutral groups, whereas the two phobic groups showed reliable evidence of resistance to extinction, with no differences between the threatened- and the CS-UCS-group. The observed resistance to extinction found in the phobic groups implies a similarity to the irrationality of real-life phobias. Furthermore, the data are in accordance with analysis of electrodermal fear-conditioning as a case of prepared learning.     

Personality and conditioning: a test of four models

Four experiments were conducted to test hypotheses derived from 4 alternative models of individual differences in instrumental conditioning. A standard go--no-go discrimination learning task was used in each of the 4 experiments. The results indicate that individual differences in performance of this discrimination are more consistently and strongly associated with impulsivity and anxiety than with extraversion and neuroticism. In each of the experiments, high anxiety hindered the learning of a go--no-go discrimination more among high impulsive Ss than among low impulsive Ss, and in 2 of the experiments high anxiety actually facilitated learning among low impulsive Ss. These findings are incompatible with Eysenck's and Gray's hypotheses regarding extraversion but are not inconsistent with Newman's. Aspects of these results do support Spence's and Gray's models of anxiety and instrumental conditioning. However, both of these models were contradicted by other trends in the data. A modification of Gray's model of impulsivity and anxiety that emphasizes the role of expectancies was proposed to fit these data.     

Background stimuli and the inter-stimulus interval during pavlovian conditioning

An experiment was carried out to investigate the part played by background stimuli during Pavlovian conditioning. Groups of rats were presented with tone CSs and unavoidable footshock USs. Two components of the inter-stimulus interval, namely CS duration and the duration of a trace interval, were manipulated across groups. Subsequently subjects were tested for their reactions to background stimuli by being re-exposed to the training environment in the absence of both the CS and US. The degree to which rats failed to avoid this environment was found to relate to CS duration by an inverted U curve. The manipulation of the trace interval however did not significantly affect avoidance.     

Emotional conditioning to masked stimuli and modulation of visuospatial attention

Two studies investigated the effects of conditioning to masked stimuli on visuospatial attention. During the conditioning phase, masked snakes and spiders were paired with a burst of white noise, or paired with an innocuous tone, in the conditioned stimulus (CS)+ and CS- conditions, respectively. Attentional allocation to the CSs was then assessed with a visual probe task, in which the CSs were presented unmasked (Experiment 1) or both unmasked and masked (Experiment 2), together with fear-irrelevant control stimuli (flowers and mushrooms). In Experiment 1, participants preferentially allocated attention to CS+ relative to control stimuli. Experiment 2 suggested that this attentional bias depended on the perceived aversiveness of the unconditioned stimulus and did not require conscious recognition of the CSs during both acquisition and expression.     

Stimulus generalization: the ordering and spacing of test stimuli

Twenty-four pigeons learned a successive discrimination between 500 mmu (S+) and 574 mmu (S-). When tested in extinction, some birds received stimuli around S+, with no S- presentations. These birds showed a positive peak shift, with maximum responding not at 550 mmu, but displaced to 538 mmu and 544 mmu. Other birds were tested with stimuli around S-, with no S+ presentations. These birds showed a negative shift, with least responding not at 574 mmu, but at 586 mmu. Though the first group was tested around S+ and the second around S-, total responding between groups did not differ. When retested on the other half of the continuum, however, birds that had gone from the S+ half to the S- half responded fewer times than those that had gone from the S- half to the S+ half. In a second experiment, reducing stimulus spacing from 6 mmu to 2 mmu produced flatter gradients and decreased the amount of positive shift. In a third experiment, birds were tested across the whole continuum with stimuli presented in serial order. A sequence from 538 mmu to 586 mmu produced no responding after the first part of the session; a sequence from 586 mmu to 538 mmu produced responding throughout the session.     

Aversive and appetitive electrodermal classical conditioning using pictures as stimuli

The principal goal of this study was to verify whether it was possible to obtain both aversive and appetitive electrodermal classical conditioning, using pictures as conditioned stimuli (CS), and unconditioned stimuli (US). Additionally, we tried to verify whether, as a consequence of such conditioning, diminution of the unconditioned response (UR) was observed. With this aim, IAPS (?International Affective Picture System?) pictures were selected as stimuli. A picture showing a burnt face was used as the aversive US (USav), and a picture showing a scene with erotic content was used as the appetitive US (USap). As the aversive CS (CSav), and appetitive CS (CSap), two images with intermediate values of valence and arousal showing male faces were selected. In the experimental group, 10 CSav/USav and 10 CSap/USap trials were presented. In the control group 10 CSav, CSap, USav, and USap trials were presented in pseudorandom order. Skin conductance response (SCR) elicited by both the CSs and the USs was scored. Results showed aversive conditioning, but neither appetitive conditioning nor UR diminution. Problems to obtain conditioning using pictures as stimuli and possible options to overcome them in future research are discussed.     

Learning with arbitrary versus ecological conditioned stimuli: Evidence from sexual conditioning

Laboratory investigations of Pavlovian conditioning typically involve the association of an arbitrary conditioned stimulus (CS) with an unconditioned stimulus (US) that has no inherent relation to the CS. However, arbitrary CSs are unlikely to become conditioned outside the laboratory, because they do not occur often enough with the US to result in an association. Learning under natural circumstances is likely only if the CS has a preexisting relation to the US. Recent studies of sexual conditioning have shown that in contrast to an arbitrary CS, an ecologically relevant CS is resistant to blocking, extinction, and increases in the CS-US interval and results in sensitized responding and stronger second-order conditioning. Although the mechanisms of these effects are not fully understood, these findings have shown that signature learning phenomena are significantly altered when the kinds of stimuli that are likely to become conditioned under natural circumstances are used. The implications of these findings for an ecological approach to the study of learning are discussed.     

Evaluative conditioning in the picture-picture paradigm with random assignment of conditioned stimuli to unconditioned stimuli

Human participants were allocated to 1 of 3 groups. In the conditioning group, each conditioned stimulus (CS)-unconditioned stimulus (US) pair was presented 7 times during the acquisition phase. Participants who were assigned to the extinction group saw 5 additional presentations of each CS in isolation after the 7 presentations of each CS-US pair. In the latent inhibition group, the CS-only trials were presented before the CS-US trials. Overall, a significant evaluative conditioning effect was observed. This effect cannot be dismissed on the basis of the arguments developed by A. P. Field and G. C. L. Davey (1997, 1998, 1999), and the results thus provide strong evidence for the associative nature of evaluative conditioning. The results are also in line with other findings, which showed that evaluative conditioning is resistant to extinction.     

Autonomic conditioning to monetary and social stimuli and aggression in children

Poor conditioning to punishment, such as loud tones or electric shock, has been proposed as an important factor involved in the etiology of aggressive and psychopathic behavior. However, it is not known whether the association holds when monetary or social stimulus is used as the unconditioned stimulus, and if aggressive individuals also have impaired conditioning to rewards. In this study, skin conductance responses in a conditioning task involving both monetary/social reward and punishment as unconditioned stimuli were assessed in 340 male and female 8‐ to 9‐year‐old children from the community. Children reported their reactive and proactive aggression using the Reactive and Proactive Aggression Questionnaire (RPQ; Raine et al., 2006). Results showed that monetary/social reward and punishment were effective in eliciting physiological classical conditioning in children, and that reduced reward conditioning was associated with high levels of proactive aggression in particular. Findings highlight the importance of distinguishing between reactive and proactive aggression when examining antisocial behavior in children, and suggest that reward‐oriented treatment programs may not be effective for children with more proactive, instrumental aggressive behavior.