Effect of extended training on generalization of latent inhibition: an instance of perceptual learning

Four experiments examined generalization of latent inhibition (LI) as a function of the length of preexposure in a conditioned taste aversion procedure with rats. Experiment 1 showed that one or four nonreinforced presentations of a flavor compound (BX) retarded subsequent conditioning to another compound (AX). However, after eight presentations of BX, conditioning to AX occurred at the same rate as with no preexposure. These results indicate that generalization of LI decreased as the length of preexposure to BX increased. Experiment 2 replicated this effect of reducing generalization, as well as demonstrating that LI actually increased as the length of preexposure to AX increased. Experiment 3 extended the generality of the effect to a procedure in which both BX and AX were preexposed. Experiment 4 demonstrated a similar reducing-generalization effect when generalization of LI from BX to X was assessed. All of these data are consistent with the notion that prolonged preexposure to BX enhances its discriminability. Different learning mechanisms that might be responsible for this perceptual learning effect are discussed.     

Changes in stimulus salience as a result of stimulus preexposure: Evidence from aversive and appetitive testing procedures

In two experiments, rats received preexposure to three compound flavor stimuli, AX, BX, and CX, where X represents a saline solution. AX and BX were presented in alternation; CX, on a separate block of trials. The value of X was then modified, being devalued by aversive conditioning in Experiment 1, and rendered valuable by the induction of a state of salt need in Experiment 2. When given a choice between BX and CX, the rats consumed more of BX than of CX in Experiment 1, and more of CX than of BX in Experiment 2, suggesting that B and C differed in their ability to modulate the response governed by the X element. It was suggested that blocked preexposure to CX reduces the salience of the C stimulus but that the salience of B is maintained by preexposure in which BX is alternated with AX. The implications of this result for the phenomenon of perceptual learning are discussed.     

Savings test for associations between neutral stimuli

Three experiments showed a savings procedure to be an effective and sensitive alternative to sensory preconditioning procedures as a measure of associations among neutral stimuli. Experiment 1 showed that within-compound associations developed more rapidly in reinforced appetitive serial compound conditioning when nonreinforced preexposure to the serial compound was given than when separate element or no preexposure was given. Experiment 2 showed the savings effect to be highly stimulus specific. Experiment 3 examined the facilitation of serial compound conditioning after either simultaneous or serial nonreinforced preexposure to the elements of the compound. The results of that experiment were consistent with those of analogous sensory preconditioning experiments. When preexposure involved only the two elements of the subsequently reinforced compound, serial preexposure produced more savings than simultaneous preexposure. But when preexposure involved a three-stimulus procedure like that used by Rescorla (1980b), simultaneous preexposure resulted in more savings. Advantages of the savings procedure over sensory preconditioning as a measure of association among neutral stimuli are discussed.     

The role of inhibitory associations in perceptual learning

Preexposure to two compound flavors (AX and BX) typically enhances their discriminability: An aversion conditioned to AX will generalize less to BX, especially if the preexposure regime has involved alternated presentations of AX and BX rather than presenting all AX trials before BX trials (or vice versa). One possible explanation of this finding is that alternating preexposure establishes inhibitory associations between the two unique features A and B, thus counteracting the generalization produced by excitatory associations between X and A and between X and B, which might result in either the retrieval of B on a conditioning trial to AX, or the retrieval of A on a test trial to BX. Three experiments on flavor aversion conditioning in rats tested these predictions. Experiment 1 suggested that the more important of these excitatory associations was that which allowed X to retrieve A on the test trial to BX. Experiment 2 suggested that the more important inhibitory association was that which allowed B to inhibit the representation of A on this test trial. Experiment 3 provided direct evidence of the role of this inhibitory B⊣A association.     

Perceptual learning transfer in an appetitive Pavlovian task

In two experiments, rats were given intermixed or blocked preexposure to two similar compound stimuli, AX and BX. Following preexposure, conditioning trials took place in which AX (Experiment 1) or a novel compound stimulus NX (Experiment 2) was paired with a food-unconditioned stimulus in an appetitive Pavlovian preparation. Animals that were given alternated preexposure showed lower generalization from AX to BX (Experiment 1) and from NX to a new compound, ZX (Experiment 2), than animals that were given blocked preexposure, a perceptual learning and a perceptual learning transfer effect, respectively.     

Flattening generalization gradients, context, and perceptual learning

The present research investigated the effects of physical context change and perceptual learning on generalization. In a video game, participants learned to suppress their mouse-clicking behavior in the presence of one stimulus (AX). Generalization was observed between the AX stimulus and another stimulus (BX) that was designed to be similar. When testing was conducted in a context different from that in which AX was used in training, responding to AX was attenuated, and responding to BX was enhanced. That is, the generalization gradient flattened. The latter effect was only evident in groups for which generalization had been reduced through a preexposure manipulation believed to produce perceptual learning. Experiment 2 demonstrated that the increase in generalization observed in the first experiment was due to the context change between the preexposure and test rather than to a change between the conditioning and test contexts. Implications for flattening generalization gradients and mechanisms of perceptual learning are discussed.     

Effects of compound or element preexposure on compound flavor aversion conditioning

Two experiments with rat subjects examined conditioning of an aversion to a compound flavor stimulus after preexposing the compound, its constituent elements, or no explicit flavor stimulus. Experiment 1 used a short-term procedure in which preexposure and conditioning treatments occurred on the same day; Experiment 2 used a long-term procedure in which more extensive preexposure was administered several days before conditioning. In both experiments, preexposure of the elements slowed conditioning to the compound more than did preexposure of the compound itself. These effects were apparently not mediated by changes in pseudoconditioned or neophobic responses. The results were related to Lubow’s conditioned attention theory of stimulus preexposure effects.     

Effects of elements or compound preexposure on conditioned taste aversion as a function of retention interval

The effects of element or compound preexposure and retention interval were examined in three experiments with the taste-aversion paradigm. In Experiment 1, preexposure to the elements of a compound flavor produced less latent inhibition to the compound than did preexposure to the compound itself when a 1-day preexposure-conditioning interval was used. However, preexposing the elements or the compound resulted in equivalent latent inhibition effects when a 21-day retention interval was used. In Experiment 2, a similar pattern of results was observed when the conditioning-test interval was manipulated. Experiment 3 explored the effect of element or compound preexposure when preexposure and test were carried out in different contexts. Attenuated latent inhibition following preexposure to the elements was found when preexposure and test were carried out in the same context. In contrast, preexposure to the elements resulted in as much latent inhibition as did preexposure to the compound when the context was switched from preexposure to testing. The implications of these findings for a retrieval-oriented view of latent inhibition are discussed.     

Effects of preexposure and retention interval placement on latent inhibition and perceptual learning in a choice-maze discrimination task

In two experiments, we examined how preexposure to discriminative stimuli and introduction of a 21-day retention interval affected the latent inhibition (LI) and perceptual learning (PL) of rats in a choice-maze discrimination task. Experimental groups were preexposed to three wall patterns, one in each of three arms of a maze. Control groups were preexposed only to white arms. PL groups were trained to discriminate A versus B, and LI groups, to discriminate A or B versus C. The A and B patterns shared many elements not shared with the C pattern. In Experiment 1, both at the end of training and after the subsequent retention interval, the PL groups performed better than controls, whereas the LI groups performed worse. In Experiment 2, inserting the 21-day retention interval between preexposure and discrimination training disrupted final measures of LI but not PL performance. Implications for current concepts of PL and LI are discussed.     

Further boundary conditions for the effects of perceptual disfluency on judgments of learning

The experience of fluency while learning might bias students’ metacognitive judgments of learning (JOLs) and impair the efficacy of their study behaviors. In the present experiments, we examined whether perceptual fluency affects JOLs (1) when people only experience one level of fluency, (2) when item relatedness is also available as a cue, and (3) across study-test trials. Participants studied a list of paired associates over two study-test trials and made JOLs for each item after studying it. We varied the perceptual fluency of the memory materials by making the font easy (fluent) or difficult (disfluent) to read. We also varied whether we manipulated the perceptual fluency of the items between-participants or within-participants and whether other memory factors—item relatedness and study time—were available for participants to use to inform their JOLs. We were only able to obtain effects of perceptual fluency on JOLs when we manipulated fluency within-participants and eliminated item relatedness as a cue for JOLs. The present results indicate that some effects of perceptual fluency on JOLs are not robust and might only occur under limited—and somewhat contrived—conditions. Therefore, these effects might be unlikely to bias students’ JOLs in actual learning situations.     

Reward devaluation disrupts latent inhibition in fear conditioning

Three experiments explored the link between reward shifts and latent inhibition (LI). Using consummatory procedures, rewards were either downshifted from 32% to 4% sucrose (Experiments 1–2), or upshifted from 4% to 32% sucrose (Experiment 3). In both cases, appropriate unshifted controls were also included. LI was implemented in terms of fear conditioning involving a single tone-shock pairing after extensive tone-only preexposure. Nonpreexposed controls were also included. Experiment 1 demonstrated a typical LI effect (i.e., disruption of fear conditioning after preexposure to the tone) in animals previously exposed only to 4% sucrose. However, the LI effect was eliminated by preexposure to a 32%-to-4% sucrose devaluation. Experiment 2 replicated this effect when the LI protocol was administered immediately after the reward devaluation event. However, LI was restored when preexposure was administered after a 60-min retention interval. Finally, Experiment 3 showed that a reward upshift did not affect LI. These results point to a significant role of negative emotion related to reward devaluation in the enhancement of stimulus processing despite extensive nonreinforced preexposure experience.     

Effects of perceptual training on the salience of information in a recall problem

Kindergarten children were given a salience-assessment task to determine each child's salience hierarchy for the dimensions of form, color, and position. The children were then assigned to either a control condition or one of 3 conditions providing different types of perceptual training with the child's least salient dimension. In a subsequent location recall task, children in all 3 training groups made significantly fewer errors recalling values of their least salient dimension than children in the control group. The results indicated that perceptual exposure alone was sufficient to increase the perceptual salience of the least salient dimension and its subsequent conceptual evaluation.     

The effects of compound stimulus preexposure of two elements differing in salience on the acquisition of conditioned suppression

Conditioned attention theory (CAT) of latent inhibition (LI) states that parallel learning processes occur during reinforced and nonreinforced stimulus presentation. The present experiments investigated the effects of nonreinforced preexposure of either a compound CS or elements of that compound which differed in salience. Three predictions were advanced: (1) Both the compound and its elements will show an increase in LI as a function of the number of preexposures; (2) the two elements will show different levels of LI, with more LI accruing to the more salient element; (3) overshadowing will occur during compound preexposure. Two experiments, using rats as subjects and a conditioned suppression test, are reported. In Experiment 1, groups received 0, 20, 40, or 80 nonreinforced preexposures to a compound whose elements differed in salience. The results of the subsequent test confirmed predictions 1 and 2. Experiment 2, in which groups were preexposed to either the elements or the compound, provided evidence for an overshadowing effect, confirming prediction 3 from CAT.     

Nonassociative habituation,US preexposure,and backward inhibitory conditioning with signaled and unsignaled USs

In a conditioned suppression experiment, rats received a single, massed session of conditioning in which one backward conditioned inhibitory stimulus (CS-) followed shocks that were signaled by a visual cue, and a second backward CS-followed shocks that were unsignaled. Conditioning was preceded by a preexposure phase in which some groups of rats were preexposed to unsignaled shock, while others were not preexposed and remained in the experimental apparatus in the absence of shock. The groups were further distinguished by whether US preexposure and conditioning occurred in the same or different contexts, and by whether conditioning began immediately or after a 24-h rest period in the home cage. Although the conditioning itself was effective in establishing the visual cue as a conditioned excitor in the nonpreexposed groups, it was not effective in establishing the two backward cues as reliable inhibitors with either signaled or unsignaled USs. After 210 US preexposures, however, the same conditioning sessions did yield conditioned inhibition to both CS-s. A 24-h rest period in the home cage reduced the magnitude of, but did not completely abolish, the facilitative effect of US preexposure on inhibitory conditioning. Other tests demonstrated that US preexposure had retarded excitatory conditioning to the visual cue. This interference with excitatory conditioning was unchanged in magnitude after the 24-h rest period. The facilitative effect of US preexposure on backward inhibitory conditioning, and the interference effect on excitatory conditioning, were both eliminated by a change in context between US preexposure and conditioning. These observations encourage predominantly associative accounts of the effects, but allow for a small nonassociative habituation component.     

Patterns of perceptual deficits in academically deficient juvenile delinquents

Patterns of perceptual deficits were investigated in a population of academically deficient juvenile delinquents. Comparisons were made with a group of youthful offenders with adequate academic skills. Auditory perceptual deficits appeared to be a more significant factor in accounting for the severe academic deficiencies observed in the delinquent subjects than did visual-perceptual deficits. However, multiple perceptual deficits involving both auditory and visual perceptual skills formed the basis of the majority of academic deficiencies and social maladaptation. The results indicate the potential ill effects of an undiagnosed and untreated learning disability on subsequent emotional development. Prevention of delinquency may begin with the preschool child who is at high-risk for developing behavioral problems in later years.     

Effect of perceptual processing strategies on problem solving of reflective and impulsive children

Several studies employing the "20 questions" test reported that reflective children asked proportionally more constraint-seeking (CS) questions than did impulsive children. The finding was interpreted as supporting the generally accepted view that reflective children are more mature and more efficient problem solvers than impulsive children. Inexplicably, the reflectives' higher proportion of CS questions was not associated with fewer questions to solution, that is, with greater efficiency. The present study examined an alternative hypothesis that differences in performance of impulsive and reflective children on the "20 questions" test are due to individual differences in preferred perceptual processing strategy rather than in cognitive maturity of problem-solving strategy. Efficiency of performance of reflective and impulsive children was shown to be related to type of stimuli and experimental conditions employed, supporting a perceptual rather than cognitive-maturational interpretation.     

Effect of different training methods on perceptual learning in impulsive children.

The effectiveness of different training and transfer test conditions in promoting perceptual learning in impulsive kindergarten children was investigated. Interproblem variability was found to be more effective than intraproblem variability, and a differentiation training procedure was found to be more effective than a matching training procedure. The results provide guidelines for designing effective training methods for improving discrimination learning and problem solving in impulsive children.     

Disruption of latent inhibition by interpolation of task-irrelevant stimulation between preexposure and conditioning

Latent inhibition refers to attenuated responding to a conditioned stimulus (CS) that was repeatedly presented without reinforcement prior to the CS-unconditioned stimulus (US) pairings. Using water-deprived rats as subjects, we observed that interpolating task-irrelevant stimulation between the preexposure and conditioning phases of a latent inhibition procedure attenuated latent inhibition (Experiments 1A, 1B, and 2). Apparently, interpolated stimulation segments the preexposure and conditioning treatments into two separate experiences, much in the same way that a change of context would. Consistent with this view, the interpolated stimulation did not disrupt latent inhibition if it was also presented during both preexposure and conditioning (Experiment 3). We view these results as analogous to those of Escobar, Arcediano, and Miller (2003), who suggested that the difficulty in observing latent inhibition in human adults is related to the segmentation between preexposure and conditioning caused by the usual interpolation of instructions in preparations with humans.     

The role of amount consumed in flavor preexposure effects and neophobia

Rats received either a small or a large amount of a novel saccharin solution prior to a conditioning episode in which the saccharin flavor was paired with lithium-induced toxicosis. When the time between the preexposure and the conditioning episode was 3.5 h, both the small and large amounts of saccharin decremented conditioning. However, when the time between the preexposure and the conditioning episode was 23.6 h, only the consumption of a large amount of saccharin decremented conditioning. In a second experiment, rats received either a short or a long exposure to the novel saccharin solution and were then given a choice test between the saccharin and water. Rats given the choice test immediately following their preexposure to saccharin avoided consuming it. If they received the choice test 4 h later, they consumed more of the saccharin irrespective of the length of the preexposure. In contrast, when they were given a choice test 24 h after the preexposure, only rats that had received a long preexposure displayed a significant preference for the saccharin. The present results demonstrate that the flavor preexposure effect and the attenuation of neophobia are both determined by the time between preexposure to the novel flavor and the conditioning episode or choice test and the amount of preexposure to the novel flavor. These findings are discussed in relation to the information-processing model developed by Wagner (1976, 1978) and are used to provide an account, in terms of this model, of the delay-gradient seen in flavor-aversion learning.     

Facilitation and impairment of conditioning in the preweanling rat after prior exposure to the conditioned stimulus

Olfactory aversion conditioning of preweanling rats, 10 or 18 days postnatal, was tested after some had been given nonreinforced experience with the to-be-conditioned odor stimulus. In three experiments, it was established that the amount of prior exposure to the CS determined the effectiveness of conditioning. For both ages, odor-shock conditioning was more likely impaired with longer durations of preexposure. This effect was more apparent in the older animals. Low to moderate degrees of prior exposure to the CS under some conditions facilitated, rather than impaired, olfactory conditioning in the 10-day-old rat. This result is in agreement with one previous study in which facilitation in learning was reported for this age after short-term preexposure to the CS. The present study adds to previous data on differential effects of CS preexposure on conditioning. Although the conditions under which facilitation rather than impairment occurs are not yet clear, age-related differences in the effects of CS preexposure were apparent in the present experiments.