Distractor effect on the latent inhibition of conditioned flavor aversion in rats

Using a conditioned flavor aversion procedure with rats as subjects, the effect of the addition of a distractor stimulus on the magnitude of the latent inhibition effect was examined. Experiment 1 showed that latent inhibition to vinegar was attenuated by the addition of sucrose during preexposure. On the other hand, sucrose added during conditioning to vinegar did not attenuate latent inhibition. It was also found that the degree of latent inhibition to the vinegar-sucrose compound solution was less when vinegar alone was preexposed (i.e., when sucrose was added only during conditioning) than when the compound solution was preexposed (i.e., when sucrose was added both during preexposure and during conditioning). Experiment 2 gave similar results but with sucrose assigned as the target flavor and vinegar as the distractor. These findings are in full agreement with the generalization decrement account of latent inhibition.     

Asymmetry of generalization decrement in causal learning

Two experiments required volunteers to learn which of various “planes” caused high levels of pollution. Novel test items were then rated as causes of pollution. Items created by adding novel features were rated at the same level as that of the original training items but items created by removing features received reduced ratings. This asymmetry of generalization decrement was not predicted by a well-known configural model of stimulus representation (Pearce, 1987, 1994) but was predicted by a recently proposed model of stimulus representation, the replaced-elements model (Brandon, Vogel, & Wagner, 2000).     

The influence of generalization decrement on the outcome of a feature-positive discrimination

In a feature-positive discrimination subjects receive training in which reinforced presentations of a compound, AB⁺, are intermixed among non-reinforced presentations of one element, A^o. The three reported experiments compared the results of this procedure when using a light or a tone as the feature-positive stimulus, B. In all three experiments, the tone elicited a stronger conditioned response than the light when it was presented alone. The main concern of Experiments 2 and 3 was to examine whether this effect was due to training being incomplete for subjects receiving the light as the B element. In Experiment 2 it was found that extended discrimination training did not diminish the difference between the properties of the light and the tone. Experiment 3 revealed that this effect was not due to differences in the asymptotic associative strength of either A or the compound. It is argued that these results are not readily compatible with contemporary theories of learning, and an alternative account is presented.     

The interactive effects of stimulus generalization decrement and contextual pre-exposure cues upon fear incubation

Models of fear incubation may be described as explanations for the interference of Pavlovian extinction. From this perspective, the effects of several parameters upon the incubation phenomenon were examined. Fear incubation was found to be attenuated by manipulations associated with stimulus generalization decrement (Experiment 1), as well as pre-exposure manipulations (Experiment 2). These findings were incorporated within existing models of incubation.     

Extinction and latent inhibition of within-event learning are context specific

Exposure to a solution composed of an odor (almond) and a taste (salt) produced a context-independent preference when rats were subsequently tested with almond under a salt appetite. Postcompound exposure to either the almond or the salt alone reduced almond preferences but only when rats were tested in the extinction context. Exposure to either the almond or the salt in 1 context in advance of exposure to the compound in a different context also reduced preferences but only when the rats were tested in the context in which the element had been pre-exposed. These results show that extinction and latent inhibition of within-event learning are context specific.     

Distractor inhibition is more effective at a central than at a peripheral location

The "distractor eccentricity effect" refers to the finding of reduced interference from an incompatible distractor at a central relative to a peripheral location (Chen, 2008). The present study examines the mechanism that underlies the distractor eccentricity effect, and relates it to the inattentional blindness explored by Mack and Rock (1998), which was also more marked at a foveal than at a parafoveal location. The results suggest that these two visual phenomena may reflect the same underlying mechanism--a gradient of increasing attentional suppression from the periphery to the center.     

The effects of preexposure-test and conditioning-test intervals on the magnitude of latent inhibition

Using the conditioned taste aversion paradigm, two experiments were conducted to examine the effects of the interval between preexposure and test and that between conditioning and test on the magnitude of latent inhibition. Experiment 1 revealed that the degree of latent inhibition was attenuated when rats were given a 21‐day interval between preexposure and test. It was also found that this attenuation was more marked in subjects which were given conditioning immediately after preexposure than those which were conditioned shortly before the test. Retention interval between preexposure and test was reduced to 12 days in Experiment 2, and exactly the same pattern of results as those found in Experiment 1 was obtained. These findings suggest that the memory of conditioning as well as that of preexposure decreases its retrievability after a long retention interval, although the former is more retainable than the latter.     

Potentiation of latent inhibition

Rats were given exposure either to an odor (almond) or a compound of odor plus taste (almond plus saline), prior to training in which the odor served as the conditioned stimulus. It was found, for both appetitive and aversive procedures, that conditioning was retarded by preexposure (a latent inhibition effect), and the extent of the retardation was greater in rats preexposed to the compound (i.e., latent inhibition to the odor was potentiated by the presence of the taste). In contrast, the presence of the taste during conditioning itself overshadowed learning about the odor. We argue that the presence of the salient taste in compound with the odor enhances the rate of associative learning, producing a rapid loss in the associability of the odor. This loss of associability will generate both overshadowing and the potentiation of latent inhibition that is observed after preexposure to the compound.     

Distractor effects during processing of words under load

The perceptual load model of attention (Lavie, 1995) suggests that processing of irrelevant distractors depends on the extent to which a relevant task engages full perceptual capacity. Word recognition models suggest that letter perception is facilitated in words relative to nonwords. These models led us to hypothesize that increasing the number of letters would increase perceptual load more for nonwords than for words, and thus would be more likely to exhaust capacity and eliminate distractor processing for nonwords than for words. In support of this hypothesis, we found that increasing the number of search letters increases RTs more for nonwords than for words and only reduces distractor interference for nonwords. Thus, although readers process words more efficiently than nonwords, they also become more prone to distraction when processing words.     

Context specificity of conditioning and latent inhibition: Evidence for a dissociation of latent inhibition and associative interference

Conditioning may generalize from one context to another when latent inhibition (the effect on subsequent conditioning of prior unreinforced exposure to the stimulus) does not. Experiment 1 studied conditioned approach and licking by rats to a stimulus paired with the delivery of water and confirmed that latent inhibition could be abolished by a change of context, while prior aversive conditioning to the stimulus, produced by pairing it with mild shock, interfered with the acquisition of conditioned approach and licking regardless of this change of context. Thus even when conditioning and latent inhibition were measured in the same way, the former generalized across contexts, and the latter did not. Experiment 2 showed that the effects not only of unreinforced exposure to a stimulus but also of presentation of the stimulus uncorrelated with the delivery of water were confined to the context in which they occurred. Thus the generalization of conditioning from one context to another and the failure of latent inhibition to generalize cannot be attributed to the occurrence of rein-forcers during conditioning and their absence in latent inhibition. This conclusion was confirmed in Experiment 3, where animals received both aversive conditioning trials and unreinforced presentations of other stimuli in the treatment phase of the experiment, but were then conditioned to one of these stimuli paired with water. Once again, the effects of aversive conditioning transferred perfectly from one context to another, while those of unreinforced presentations did not. Latent inhibition, these results suggest, is not easily explained by supposing that animals associate an unreinforced stimulus with zero consequences and have to unlearn this association when the stimulus is then paired with a reinforcer.     

Stimulus generalization of excitation and inhibition

Five sign-tracking experiments with pigeons investigated the breadth of stimulus generalization of excitatory and inhibitory conditioning. Using a compound stimulus test procedure, these experiments found evidence for a narrower generalization of associative strength in excitation than in inhibition. They also found a narrower associative gradient with a more strongly conditioned excitatory stimulus, although this did not seem to account for the difference between exciters and inhibitors. These results confirm earlier findings comparing generalization after acquisition and extinction and raise various theoretical issues about generalization.     

Stimulus generalization of excitation and inhibition

Five sign-tracking experiments with pigeons investigated the breadth of stimulus generalization of excitatory and inhibitory conditioning. Using a compound stimulus test procedure, these experiments found evidence for a narrower generalization of associative strength in excitation than in inhibition. They also found a narrower associative gradient with a more strongly conditioned excitatory stimulus, although this did not seem to account for the difference between exciters and inhibitors. These results confirm earlier findings comparing generalization after acquisition and extinction and raise various theoretical issues about generalization.     

The influence of a distractor during compound preexposure on latent inhibition

Nonreinforced exposure to a nontarget stimulus that was followed by nonreinforced exposure to a target/nontarget simultaneous compound stimulus resulted in enhanced latent inhibition of the target. Conditioning was slower after this treatment than after nonreinforced exposure to the target stimulus alone (Experiment 1). However, a salient auditory stimulus presented immediately after the compound in the second phase reduced levels of latent inhibition, relative to the enhanced latent inhibition produced when no such extracompound stimulus was presented (Experiments 2 and 3). This effect was not noted if the salient auditory cue was presented 10 sec after the termination of the compound stimulus (Experiment 4). In Experiment 5, there was no disruption of simple latent inhibition produced by a salient stimulus. These results are consistent with enhanced latent inhibition's being produced by the formation of within-compound associations, which are disrupted by the salient extracompound stimuli.     

Transient effects of acquisition history on generalization in a matching-to-sample task

This study examined the role of learning history on the acquisition of a matching-to-sample task. Twelve preschool children learned four stimulus classes through instructions, shaping, or imitation. After reaching criterion, the subjects were exposed to changed discrimination contingencies to determine how each learning history affected the acquisition of responses appropriate to the new contingencies. All subjects reached criterion on the new relations, although the subjects with a shaping history adapted slightly more quickly than those subjects with a history of instructions or imitation. Given sufficient exposure to changed contingencies, rule-driven insensitivity to contingencies was overcome by experience with consequences. This result may be specific to younger subjects, but it suggests that instructions can be used in education without creating insensitivity to contingencies.     

An alertness decrement hypothesis of response inhibition to repeatedly presented stimuli

Both inhibitory and facilitative effects of repeated stimulus presentation have been observed. Two-factor theory attributes both kinds of effects to changes in specific components of attention. The theory claims that repeated exposure (a) decreases the alerting capacity of a stimulus and (b) facilitates encoding. The purpose of the present research was to provide further evidence that alertness decrement underlies the inhibitory effects of stimulus repetition. Adults were exposed to 30 presentations of a colored circle prior to performing a choice-reaction time (RT) task on which the targets were the familiarized stimulus and a novel stimulus. A warning signal occurred at one of three intervals prior to target onset. It was predicted from the literature on the temporal characteristics of alertness that the relative speed of responding to the familiarized stimulus would vary as a function of the warning signal-target interval. As predicted, responses to the familiarized stimulus were (a) slower than to the novel stimulus at intervals of 0 and 2,500 ms, but (b) faster than to the novel stimulus at 450 ms. The convergence of these findings with the alertness literature suggests an alertness decrement interpretation of response decrements to repeatedly presented stimuli.     

Obsessive-compulsive disorder patients display enhanced latent inhibition on a visual search task

Latent inhibition (LI) is a phenomenon that reflects the ability to ignore irrelevant stimuli. LI is attenuated in some schizophrenic patient groups and in high schizotypal normal participants. One study has found enhanced LI in patients with obsessive-compulsive disorder (OCD [Swerdlow, N. R., Hartston, H. J., & Hartman, P. L., 1999. Enhanced visual latent inhibition in obsessive-compulsive disorder. Biological Psychiatry, 45, 482-488]). The present experiment replicated this finding using a within-subject visual search LI task, with OCD patients displaying more LI than healthy controls. The contrasting LI effects in schizophrenia and OCD are discussed in terms of how these groups differentially process relevant and irrelevant stimuli, and how that outcome affects subsequent behavior.     

The effects of acute exercise on temporal generalization

Sixteen healthy college students performed a multiple-trial referenced temporal generalization task and an episodic temporal generalization task before and during moderate-intensity aerobic exercise. The same tasks were performed in a resting control condition. Working memory tasks were also administered before, during, and after exercise to determine whether exercise affected working memory processes. Temporal generalization gradients demonstrated leftward shifts during exercise when compared to rest, indicating that the subject perceived intervals to elapse more slowly. This finding is consistent with an increased pacemaker speed. Subjective lengthening of stimuli as the task progressed did not occur during exercise or rest. No significant differences were observed on the episodic timing task, nor were any differences found on the working memory tasks. These findings provide support for the notion that exercise influences the internal clock in a manner similar to other arousal-inducing manipulations.