Learned avoidance of flavors signaling reduction in a nutrient.

Food-deprived rats learned to avoid a flavor negatively correlated with access to a rich nutrient, 20% maltodextrin (20M) solution. This avoidance in two-bottle choice tests was produced by training consisting of either an unpaired condition where sessions of unflavored 20M were intermixed with sessions of 2 or 3% maltodextrin (2M or 3M) flavored with salt (Experiment 1) or almond (Experiments 3 and 4) or a differential conditioning procedure where one flavor was mixed with 20M and another with 2M (Experiment 2). Avoidance was counter-conditioned by mixing the target flavor with 20M (Experiment 1), generalized to a neutral context (Experiment 3), and displayed strong resistance to extinction (Experiment 4). The results demonstrated that food avoidance learning can occur in the absence of an aversive unconditioned stimulus and indicated that unpaired control groups and differential conditioning procedures may be misleading in flavor preference learning research when further control conditions are absent. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of ethanol on encoding, consolidation, and expression of extinction following contextual fear conditioning.

Studies of contextual fear conditioning have found that ethanol administered prior to a conditioning session impairs the conditioned freezing response during a test session the next day. The present experiments examined the effects of ethanol on extinction, the loss of conditioned responding that occurs as the animal learns that a previously conditioned context no longer signals shock. Ethanol (1.5 g/kg) administered prior to single (Experiment 1) or multiple (Experiment 2) extinction sessions impaired extinction. Ethanol administered prior to a test session disrupted the expression of freezing after extinction (Experiments 3-5). There was some evidence that ethanol served as an internal stimulus signaling the operation of conditioning or extinction contingencies (Experiments 4-5). In Experiment 6, postsession injections of 1.5 g/kg ethanol had no effect on extinction with brief (3 min) or long (24 min) exposures to the context, but injections of 3 g/kg after long exposures impaired extinction. Together, these results indicate that ethanol affects extinction by acting on multiple learning and performance processes, including attention, memory encoding, and memory expression. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Responses eliminated by noncontingent or negatively contingent reinforcement recover in extinction

Autoshaped key pecking in pigeons was eliminated by presenting reinforcers only during non-CS periods (negatively contingent reinforcement) or in both non-CS and CS periods (noncontingent reinforcement). In either case, when all reinforcers were subsequently removed (simple extinction), responding recovered strongly (Experiment 1). Recovery in extinction occurred only if the CS was in a conditioned state when non-CS reinforcers were introduced (Experiment 2). Recovery from noncontingent reinforcement was virtually complete, since total responding in extinction after response elimination was not less than in control groups extinguished without an intervening response-elimination phase (Experiment 3). Recovery also occurred for nonautoshapable, instrumentally reinforced key pecking (Experiment 4). The hypothesis that recovery is due to reinstatement of the non-CS stimulus conditions of acquisition (absence of food) was not supported (Experiments 5 and 6). Other accounts of recovery are considered.     

Activity-based anorexia in rats as failure to adapt to a feeding schedule.

Progressive weight loss resulting from restriction to a daily 1.5-hr feeding period and access to a running wheel, the Activity-Based Anorexia (ABA) effect, was obtained in 3 experiments. However, bodyweight recovered when adaptation to the feeding schedule preceded access to the wheel (Experiment 1), when feeding was at the start of the dark period (Experiments 2 and 3), and when wheel access was denied in the 4 hrs before food (Experiment 4). It was concluded that ABA results from interference with adaptation to a new feeding schedule due to the development of anticipatory behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Resistance to extinction of conditioned odor perceptions: Evaluative conditioning is not unique.

A tasteless odor will smell sweeter after being sampled by mouth with sucrose and will smell sourer after being sampled with citric acid. This tasty-smell effect was found in experiments that compared odor-taste and color-taste pairings. Using odors and colors with minimal taste (Experiment 1), the authors found that repeated experience of odor-taste mixtures produced conditioned changes in odor qualities that were unaffected by intermixed color-taste trials (Experiment 2). An extinction procedure, consisting of postconditioning presentations of the odor in water, had no detectable effect on the changed perception of an odor (Experiments 3 and 4). In contrast, this procedure altered judgments about the expected taste of colored solutions. Evaluative conditioning (conditioned changes in liking) is claimed to be resistant to extinction. However, these results suggest that resistance to extinction in odors is related to the way they are encoded rather than to their hedonic properties. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effect of intertrial food presentations on anticipatory goal-tracking in the rat

Four experiments examined the sensitivity of anticipatory goal-tracking in the rat to stimulus-food contingency. Contingency was manipulated by varying the probability of food delivery in the absence of a food-tray-light or clicker conditional stimulus (CS), while holding constant the probability of food coincident with the CS. CS control of anticipatory food tray investigation was examined after a period of context extinction in all experiments. Acquisition of stimulus control was undermined by the scheduling of intertrial food deliveries (Experiment 1). The rate of intertrial food deliveries influenced subsequent acquisition of CS control when all intertrial food deliveries were omitted (Experiment 2). When intertrial food deliveries were added to the training regimen subsequent to acquisition of CS control, that control was impaired (Experiments 3 and 4).     

Expression of renewal is dependent on the extinction-test interval rather than the acquisition-extinction interval.

A recent finding suggested that when extinction occurs shortly after acquisition, renewal of an extinguished fear response (fear-potentiated startle) to a light conditioned stimulus (CS) is diminished (Myers, Ressler, & Davis, 2006). The present study attempted to extend this finding using a white-noise CS and freezing as the behavioral measure of fear. In Experiments 1A and 1B, we observed renewal whether extinction occurred 10 min or 24 hr after acquisition. In contrast, renewal was not observed if test occurred 10 min after extinction (Experiment 2). Experiment 3 demonstrated that expression of extinction at the 10-min extinction-test interval was attenuated by a pretest subcutaneous injection of the γ-aminobutyric acid (GABA) inverse agonist FG7142. These findings suggest that renewal is influenced more by the extinction-test interval than the acquisition-extinction interval. Further, the failure to see renewal 10 min after extinction suggests that there is a separate context memory that undergoes a different consolidation function than the CS-no US memory formed during extinction. Finally, the expression of extinction appears to be GABA dependent regardless of the extinction-test interval or the test context. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Categorization processes in mental comparisons.

Five experiments explore categorization and category-based congruity effects in mental comparisons. The first 4 experiments concentrate on categorization of infinite-set small items. The experiments vary the additional items presented and whether those items appear once (Experiments 1-2) or repeatedly (Experiments 3-4). Additional items include other small items (Experiment 1), relatively large items (Experiments 2-4), and items involving nonsize dimensions (Experiment 4). The critical small items show a complete congruity effect only in Experiments 1 and 3. Results suggest that categorization of infinite-set items may be based on range information alone (Experiment 1) but that multiple categorizations based on multiple ranges (Experiment 2) may require attentional effort. Results implicate categorization as a central process in mental comparison, despite differences in ease of categorization across paradigm. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The actor as context for social judgments: effects of prior impressions and stereotypes

Three experiments identified conditions under which trait judgments made about a behavior were more likely to influence later judgments of the behavior. In Experiment 1, participants made trait judgments about numerous behaviors presented with photos of actors. Some behaviors were repeated, paired with the same or a different actor. All repeated behaviors were judged faster than new behaviors. Facilitation was greatest when repeated behaviors were paired with the same actor, suggesting greater influence of prior judgments in this condition. Experiments 2 and 3 replicated this effect, and the pattern of response times (RTs) suggested a stronger association between the actor and behavior when a prior impression of the actor had been formed (Experiment 2) and when the behavior was stereotypic of the actor's group (Experiment 3). Level of prejudice moderated RT patterns in Experiment 3. Implications for context effects, the nature of trait inferences, and stereotype change are discussed.     

Repeated testing produces superior transfer of learning relative to repeated studying.

The present research investigated whether test-enhanced learning can be used to promote transfer. More specifically, 4 experiments examined how repeated testing and repeated studying affected retention and transfer of facts and concepts. Subjects studied prose passages and then either repeatedly restudied or took tests on the material. One week later, they took a final test that had either the same questions (Experiment 1a), new inferential questions within the same knowledge domain (Experiments 1b and 2), or new inferential questions from different knowledge domains (Experiment 3). Repeated testing produced superior retention and transfer on the final test relative to repeated studying. This finding indicates that the mnemonic benefits of test-enhanced learning are not limited to the retention of the specific response tested during initial learning but rather extend to the transfer of knowledge in a variety of contexts. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

On the nonautomaticity of visual word processing: Electrophysiological evidence that word processing requires central attention.

The present study used event-related potentials (ERPs) to determine the degree to which people can process words while devoting central attention to another task. Experiments 1-4 measured the N400 effect, which is sensitive to the degree of mismatch between a word and the current semantic context. Experiment 5 measured the P3 difference between low- and high-frequency words. Because these effects can occur only if a word has been identified, both ERP components index word processing. The authors found that the N400 effect (Experiments 1, 3, and 4) and the P3 difference (Experiment 5) were strongly attenuated for Task 2 words presented nearly simultaneously with Task 1. No such attenuation was found when the Task 1 stimulus was presented but required no response (Experiment 2). Strong attenuation was also evident when the Task 2 word was presented before the Task 1 stimulus (Experiment 4), suggesting that central resources are not allocated to stimuli first-come, first-served but rather are strategically locked to Task 1. The authors conclude that visual word processing is not fully automatic but rather requires access to limited central attentional resources. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of D-cycloserine on the extinction of appetitive operant learning.

Four experiments with rat subjects examined whether D-cycloserine (DCS), a partial NMDA agonist, facilitates the extinction of operant lever-pressing reinforced by food. Previous research has demonstrated that DCS facilitates extinction learning with methods that involve Pavlovian extinction. In the current experiments, operant conditioning occurred in Context A, extinction in Context B, and then testing occurred in both the extinction and conditioning contexts. Experiments 1A and 1B tested the effects of three doses of DCS (5, 15, and 30 mg/kg) on the extinction of lever pressing trained as a free operant. Experiment 2 examined their effects when extinction of the free operant was conducted in the presence of nonresponse-contingent deliveries of the reinforcer (that theoretically reduced the role of generalization decrement in suppressing responding). Experiment 3 examined their effects on extinction of a discriminated operant, that is, one that had been reinforced in the presence of a discriminative stimulus, but not in its absence. A strong ABA renewal effect was observed in all four experiments during testing. However, despite the use of DCS doses and a drug administration procedure that facilitates the extinction of Pavlovian learning, there was no evidence in any experiment that DCS facilitated operant extinction learning assessed in either the extinction or the conditioning context. DCS may primarily facilitate learning processes that underlie Pavlovian, rather than purely operant, extinction. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Aftereffects of the surprising presentation and omission of appetitive reinforcers on key-pecking performance in pigeons.

The reinforcement-omission effect (ROE), also known as frustration effect, refers to greater response strength immediately after nonreinforcement (N) than reinforcement (R). The ROE was traditionally interpreted as transient invigoration after N induced by primary frustration. Pigeons demonstrate similar ROEs whether outcomes are surprising (partial R) or expected (discrimination training) in runway (Experiment 1) and Skinner box situations (Experiments 2-3). Variations in the interval between N and the opportunity to respond indicate that the ROE results from an aftereffect of food consumption (Experiment 4). Increasing reinforcer magnitude increased the after-R effect, without modifying the after-N function (Experiment 5). These results are reviewed in the context of comparative research on spaced-trial successive negative contrast and related phenomena that have failed to appear in experiments involving nonmammalian vertebrates. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Temporal and spatial repetition blindness: Effects of presentation mode and repetition lag on the perception of repeated items.

In this study, participants were asked to identify briefly presented 5-letter (Experiments 1-3) or 2-letter (Experiment 4) strings. Identical items in a repeated trial were identified worse than their counterparts in a nonrepeated trial, indicating repetition blindness (RB; N. G. Kanwisher, 1987). In Experiment 1, RB occurred regardless of whether items were presented successively or simultaneously. In Experiments 2-4, RB occurred regardless of whether 2 simultaneously presented items were spatially close or far apart. The magnitude of RB, however, varied with presentation mode and repetition lag: RB was smaller in simultaneous than successive presentation, and RB increased and then decreased with the number of items separating 2 identical ones. These results provide important constraints in the interpretation of RB. A model that attributes RB to the refractoriness of perceptual recognition units is proposed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Maternal separation results in early emergence of adult-like fear and extinction learning in infant rats.

Recent studies in rats have shown that extinction occurring early in life is resistant to relapse and may represent the erasure of fear memories. In the present study we examined the effects of early life stress on extinction in the developing rat, which could have important implications for the treatment of anxiety disorders in those who have experienced early life stress. In the present study, we used maternal-separation on postnatal days (P) 2–14 as an early life stressor. On P17, maternally separated and standard-reared animals were trained to fear a noise associated with a footshock. The fear of this noise was then extinguished (through repeated nonreinforced noise presentations) on P18. Animals were tested for contextually mediated, stress-mediated, and GABA-mediated fear relapse the day after extinction. We found that young animals exposed to maternal-separation were more likely to exhibit context- and stress-mediated relapse after extinction than standard-reared animals (Experiments 1 and 2). Further, unlike standard-reared animals, maternally separated rats exhibited a return of fear when the inhibitory neurotransmitter GABA was blocked at test (Experiment 3). These effects were not the result of maternal separation increasing rats' sensitivity to footshock (Experiment 5) and may in part be related to superior long-term memory for contexts in P17 maternally separated rats (Experiment 4). Taken together, these results suggest that early life adversity may prepare young animals to respond more cautiously toward fear signals in their environment. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Attentional priming and visual search in pigeons.

Advance information about a target's identity improved visual search efficiency in pigeons. Experiments 1 and 2 compared information supplied by visual cues with information supplied by trial sequences. Reaction times (RTs) were lower when visual cues signaled a single target rather than two. RTs were lower (Experiment 1) or accuracy improved (Experiment 2) when a sequence of trials presented a single target rather than a mixture of 2. Experiments 3, 4, and 5 considered the selectivity of visual priming by introducing probe trials that reversed the usual cue–target relationship. RT was higher following such miscues than following the usual 1- or 2-target cuing relationships (Experiment 3); the miscuing effect persisted over variations in the target's concealment (Experiments 4 and 5), but did not occur when the target was presented alone (Experiment 4). Findings indicate that priming modifies an attentional mechanism and suggest that this effect accounts for search images. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Simultaneous presentation of similar stimuli produces perceptual learning in human picture processing.

Human participants received unsupervised exposure to difficult-to-discriminate stimuli (e.g., A and A′), created with a morphing procedure from photographs of faces, before learning a discrimination between them. Experiments 1 and 2 demonstrated that prior exposure enhanced later discrimination and that intermixed exposure (A, A′, A, A′...) resulted in better subsequent discrimination than blocked exposure (B, B, ...B′, B′...). Experiments 3 and 4 showed that simultaneous exposure to 2 similar stimuli facilitated the later acquisition of both a simultaneous and a successive discrimination, and this effect was observed even though simultaneous exposure to 2 stimuli fostered the development of an excitatory association between them (Experiment 5). The findings of Experiments 1 and 2 revealed a perceptual learning effect with pictures of faces, and the findings of Experiments 3-5 are difficult to reconcile with associative analyses of perceptual learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pavlovian analysis of interactions between hunger and thirst.

In four experiments we examined the effect of an irrelevant drive on classical conditioning with food and water. In the first experiment the irrelevant drive weakened the conditioned response in extinction. In Experiments 2 and 3, this suppressive effect was found also in acquisition. Furthermore, the presence of an irrelevant drive during nonreinforced presentations of the conditioned stimulus was found to protect the conditioned response from extinction. Experiment 4 showed that the depressive effect of the irrelevant drive is manifested only when the relevant drive is present. Taken together, these results suggest that an irrelevant drive can influence conditioned responding by modulating the representation of the unconditioned stimulus. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conversation memory: The effects of speaker status on memory for the assertiveness of conversation remarks.

We conducted three experiments to examine the effects of information about a speaker's status on memory for the assertiveness of his or her remarks. Subjects either read (Experiments 1 and 2) or listened to a conversation (Experiment 3) and were later tested for their memory of the target speaker's remarks with either a recognition (Experiment 1) or a recall procedure (Experiments 2 and 3). In all experiments the target speaker's ostensible status was manipulated. In Experiment 1, subjects who believed the speaker was high in status were less able later to distinguish between remarks from the conversation and assertive paraphrases of those remarks. This result was replicated in Experiment 2, but only when the status information was provided before subjects read the conversation and not when the information was provided after the conversation had been read. Experiment 2's results eliminate a reconstructive memory interpretation and suggest that information about a speaker's status affects the encoding of remarks. Experiment 3 examined this effect in a more ecologically representative context. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ontogeny of persistence: immediate and long-term persistence in rats varying in training age between 17 and 65 days

In Experiment 1, six age groups of rats were trained to run an alley for either partial (PRF) or continuous reinforcement (CRF). Training was during a 2-day period starting at six different ages, and extinction was initiated about 12 hr later. There was a clear partial reinforcement extinction effect (PREE) at all ages and, particularly after PRF training, an inverse relationship between resistance to extinction and age. In Experiment 2, retention and durability of persistence as well as immediate persistence were tested following acquisition at three different ages. The immediate extinction tests confirmed the results of Experiment 1. In the delayed extinction tests, greater resistance to extinction following PRF than following CRF was found in all age groups after both the retention and durability manipulations. In neither test was there an effect of age in original acquisition on the magnitude of adult persistence. These experiments confirm earlier findings of remarkable persistence in rats trained and tested at weanling age, show that the persistence is even greater in pre-weanlings, and show that it is retained into young adulthood.