Extracting functional equivalence from reversing contingencies.

In 2 experiments assessing acquired equivalence, human participants were initially presented with 4 cues, 2 of which were paired with 1 outcome and 2 of which were paired with a 2nd outcome. These contingencies were then reversed across several training blocks such that, although each cue was paired equally often with each of the two outcomes across blocks, cues A and B always signaled the same outcome within blocks (as did cues C and D). In both experiments, performance on a subsequent transfer discrimination was enhanced when participants were required to generalize between stimuli that had been paired with the same outcome within each block of training. Additional tests did not yield evidence of a bias toward a specific set of cue–outcome contingencies in either experiment. Moreover, interviews conducted at the end of Experiment 2 revealed that performance on the transfer discrimination was enhanced only in participants who discovered the equivalence relationships during initial training. The results challenge simple associative, and attentional, accounts of acquired equivalence and favor the view that this effect is mediated by comparisons of the similarity of adjacent cue–outcome structures. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of posterior parietal and frontal neocortical lesions in the squirrel monkey.

2 groups of squirrel monkeys with frontal or parietal cortical lesions and an unoperated control group (N = 12) received the following in the order mentioned: brightness discrimination; 3 forms of a spatial pattern discrimination in which the essential cue and site of reinforcement were separated (SSP); delayed response; form discrimination; and 3 forms of a spatial pattern discrimination in which the essential cue and site of reinforcement were identical. Ss with frontal lesions were impaired on delayed response, and those with parietal lesions were impaired on form and SSP discriminations. Neither group was impaired on brightness discrimination. Results confirm and extend previous findings that the posterior parietal cortex of nonhuman primates is critically involved in visually guided spatial discriminations when the primary cue and the site of reinforcement are separated. (46 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Intertrial interval as a contextual stimulus: Further analysis of a novel asymmetry in temporal discrimination learning.

Four experiments investigated discrimination learning when the duration of the intertrial interval (ITI) signaled whether or not the next conditional stimulus (CS) would be paired with food pellets. Rats received presentations of a 10-s CS separated half the time by long ITIs and half the time by short ITIs. When the long ITI signaled that the CS would be reinforced and the short interval signaled that it would not be (Long+/Short?), rats learned the discrimination readily. However, when the short ITI signaled that the CS would be reinforced and the long interval signaled that it would not (Short+/Long?), discrimination learning was much slower. Experiment 1 compared Long+/Short? and Short+/Long? discrimination learning with 16-min/4-min or 4-min/1-min ITI combinations. Experiment 2 found no evidence that Short+/Long? learning is inferior because the temporal cue corresponding to the short interval is ambiguous. Experiment 3 found no evidence that Short+/Long? learning is poor because the end of a long ITI signals a substantial reduction in delay to the next reinforcer. Long+/Short? learning may be faster than Short+/Long?because elapsing time involves exposure to a sequence of hypothetical stimulus elements (e.g., A then B), and feature-positive discriminations (AB+/A?) are learned quicker than feature-negative discriminations (A+/AB?). Consistent with this view, Experiment 4 found a robust feature-positive effect when sequentially presented CSs played the role of elements A and B. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A configural analysis for feature-negative discrimination learning.

In 4 experiments, rats were initially trained with an A+ AXo discrimination in which Stimulus A by itself signaled the delivery of food, A+, whereas the simultaneous presentation of A and X was followed by nothing, AXo. In each experiment, X was then paired with food prior to a test phase in which A and X were again presented for a discrimination. The discrimination was of the form A+ AXo in Exps 1 and 2, whereas it was of the form X+ AXo for Exps 3 and 4. In all 4 experiments, the test discrimination was acquired more rapidly than a control discrimination. The results are interpreted in terms of the original A+ AXo discrimination resulting in the growth of an association between a representation of the entire AX compound and the effects of nonreinforcement. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Configural processes in human associative learning.

The extent to which human discrimination learning is based on elemental or configural stimulus representations was examined in 7 experiments. In Experiments 1a and 1b, participants were able to learn nonlinear discrimination problems in a food-allergy task. In unique-cue theories, such learning is explained by individual stimulus elements acquiring independent connections with the outcome and also combining to form unique cues that function elementally. In Stage 1 of Experiments 2, 3, and 4a–c, Food A signaled an allergy outcome (O) (A?→?O) when presented alone but signaled no allergy (AB?→?no O) when paired with Food B. In Stage 2, Food B was paired with the allergy (B?→?0). In a test phase, the original discrimination between A and AB was found to be intact, at variance with the unique-cue theory. By contrast, in Experiments 5a, 5b, and 6, an effect of the B?→?O trials on the A–AB discrimination was observed with training procedures previously found by D. A. Williams (1995) to encourage elemental processing. Experiment 7 showed that the influence of B?→?0 trials on the A–AB discrimination was unaffected by pretreatments designed to foster an elemental processing strategy.… (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The discrimination of structure: III. Representation of spatial relationships.

Pigeons received a discrimination in which the spatial relationship between 2 adjacent rectangles filled with different colors signaled the trial outcome. Test trials then involved the same rectangles separated horizontally by a gap. The tests in Experiment 1 disrupted the discrimination more when the rectangles were tall and thin than when they were short and wide. Experiment 2 revealed that the width of the rectangles rather than their height determined the extent to which separating them would disrupt the original discrimination. The results are explained in terms of a template-matching account of pattern recognition with the additional assumption, supported by Experiment 3, that the size of a template can be altered to improve its match with a test pattern. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Status, age, and sex effects on performance of discrimination tasks in group-tested rhesus monkeys (Macaca mulatta).

To assess the relation between performance and social or demographic variables, this study group tested a captive monkey colony on visual and manual discrimination problems. Animals could choose between differently colored, sand-filled boxes, where hue signaled the initial probability of finding buried food items. Dominant animals and subadults were most successful in locating and retrieving incentives, but sex did not affect performance. Rank effects occurred without overt aggression, suggesting deference by subordinates as a mediating mechanism. Age effects may reflect changing attention patterns only evident in complex arenas where cue salience becomes diluted. Because these findings differ from studies of singly tested animals, they show that, in a social context, an individual's rank and age may define opportunities to gain or efficiently use information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The associative interference hypothesis in verbal discrimination transfer: A note on the Eckert and Kanak review.

E. Eckert and N. Kanak (see record 1975-02303-001) suggested that in addition to the frequency theory, the hypothesis of associative interference is necessary to explain the negative transfer observed in the discussed verbal discrimination transfer paradigm. The present note suggests that the associative interference inferred in this paradigm is a correlate of the negative transfer but does not specify the mechanism needed to explain such transfer. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Modulation by the stimulus properties of excitation

Three experiments with pigeons investigated the role of excitation in a Pavlovian modulatory paradigm where the reinforcement contingencies of a conditioned stimulus (CS) were signaled by modulatory stimuli. In Experiment 1, excitatory training of the modulator that signaled reinforcement, the positive modulator, had a greater facilitative impact on discrimination learning than did excitatory training of both modulators. Although this could have resulted from simple excitatory summation, Experiment 2 revealed that excitatory training of the negative modulator also enhanced learning more than did excitatory training of both modulators. In Experiment 3, responding to CSs that had come under the control of differentially excitatory modulators was similarly controlled by new stimuli that had received simple differential excitatory training. Results suggest that excitation can play a modulatory role in Pavlovian conditioning.     

Examination of affect and egotism as mediators of bias in causal attributions.

Investigated the relationship between affect and self-attributions following positive (P) and negative (N) behavioral outcomes. In the presence (high publicity) or absence (low publicity) of observers, 63 college students delivered therapeutic instructions that were expected to have a P or N effect and that resulted in a P or N effect on a supposedly phobic patient. Principal findings were that (a) Ss made greater attributions to self for P than for N outcomes; (b) both during and following performance, P outcome Ss reported more P and less N affect than did N outcome Ss; (c) both during and following performance, P outcome Ss reported greater feelings of egotism than did N outcome Ss; and (d) under N outcome conditions, high publicity Ss made lower self-attributions and subsequently also reported greater feelings of egotism than did low publicity Ss. The results support the notion that the observed P–N outcome differences in self-attributions reflect motivational biases in the causal inference process. (19 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

There are two types of psychometric function: A theory of cue combination in the processing of complex stimuli with implications for categorical perception.

Psychometric functions are customarily fitted using normal distribution functions. However, categorical perception identification tasks give functions that are more sigmoid than the normal distribution (M. Treisman, A. Faulkner, P. L. N. Naish, & B. S. Rosner, see record 1995-42700-001). This can be explained by a theory of discrimination, cue combination theory (CCT), presented here. This theory assumes that complex stimuli (e.g., speech sounds) are composed of components or cues that vary in informativeness. The decision mechanisms sample individual cue dimensions and combine the information from each. The model generates a normal psychometric function if all cues sampled are informative. If not, the function becomes more sigmoid. CCT offers accounts of discrimination (categorical and continuous) and sensory reaction times, adaptation, sequential effects, contextual effects, trading relations, speed and accuracy, perceptual learning, and the separable-integral distinction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of the dorsomedial striatum in behavioral flexibility for response and visual cue discrimination learning.

These experiments examined the effects of dorsomedial striatal inactivation on the acquisition of a response and visual cue discrimination task, as well as a shift from a response to a visual cue discrimination, and vice versa. In Experiment 1, rats were tested on the response discrimination task followed by the visual cue discrimination task. In Experiment 2, the testing order was reversed. Infusions of 2% tetracaine did not impair acquisition of the response or visual cue discrimination but impaired performance when shifting from a response to a visual cue discrimination, and vice versa. Analysis of the errors revealed that the deficit was not due to perseveration of the previously learned strategy, but to an inability to maintain the new strategy. These results contrast with findings indicating that prelimbic inactivation impairs behavioral flexibility due to perseveration of a previously learned strategy. Thus, specific circuits in the prefrontal cortex and striatum may interact to enable behavioral flexibility, but each region may contribute to distinct processes that facilitate strategy switching. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Inescapable shock and attention to internal versus external cues in a water discrimination escape task.

In these experiments we examined discrimination learning in a water escape task following exposure to escapable, yoked inescapable, or no electric shock. Inescapable shock did not have an effect on swim speeds in any of the experiments. Inescapable shock interfered with the acquisition of a position (left–right) discrimination when an irrelevant brightness cue (black and white stimuli) was present. However, inescapable shock did not affect the acquisition of the position discrimination when the irrelevant brightness cue was removed. Inescapably shocked Subjects showed facilitated learning relative to escapably shocked and nonshocked subjects when the brightness cue was included as a relevant cue. These data may resolve discrepancies between studies that did, and did not, find inescapable shock to interfere with the acquisition of discriminations. Moreover, they point to attentional processes as one locus of the cognitive changes produced by inescapable shock and suggest the exposure to inescapable shock biases attention away from "internal" response-related cues toward "external" cues. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Olfaction and the "data" memory system in rats.

Conducted studies to characterize the memory system involved in successive olfactory discrimination learning in rats. Two odors emanated from different arms of a radical maze; 1 of the arms contained a water reward. After training on 4 to 5 pairs of odors Ss learned to discriminate the members of a new pair in 5–20 trials. Experiments in which either member of the pair was compared with a novel cue indicated that the Ss learn both positive and negative odors, rather than ignoring the negative cue. The memories for the odors were apparently persistent, and no evidence for retroactive interference from subsequent training was obtained. Animals trained on 3 component odors with 2 in common did not recognize the elements that were unshared when these were presented by themselves. Even when 1 of the 2 shared components was combined with the differentiating component into a cue the new cue was treated as a novel odor. Inclusion of a previously learned simple odor in a complex odor did affect the learning of that odor. Findings, combined with those of previous studies in which lesions were used, suggest that learning that a series of odor discriminations involves a version of the "data" memory system described by cognitive psychologists. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Observation and discrimination learning in the rat: Specific and nonspecific effects.

After watching the performance of a model rat (N = 10), 48 Os (naive male hooded rats) were trained on a visual pattern discrimination. Results show that the observational experience facilitated discrimination learning if the same cue pattern was positive for the model and the O; it retarded learning in Ss trained on the reversal of the observed discrimination. These results depend on the viewing of a model contiguous with the cue pattern. A 2nd type of facilitating effect followed visual exposure to the cue patterns presented without a model S. When such an observational condition involved stimulus change, discrimination learning was facilitated regardless of the cue to be approached. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Trauma-focused imaginal exposure for individuals with comorbid posttraumatic stress disorder and alcohol dependence: Revealing mechanisms of alcohol craving in a cue reactivity paradigm.

With a sample (N = 43) of participants meeting current diagnostic criteria for both alcohol dependence and posttraumatic stress disorder (PTSD), the authors tested the hypothesis that alcohol craving elicited by a trauma cue might be attenuated if trauma-elicited negative emotion were reduced following trauma-focused imaginal exposure. In a laboratory-based experiment, participants were randomly assigned to either trauma-focused imaginal exposure or imagery-based relaxation. A cue reactivity paradigm was used to assess alcohol craving prior to, and after completion of, the 6 clinical sessions. Attrition was high but did not differ between experimental conditions. For study completers, PTSD symptoms decreased in the exposure condition but not in the relaxation condition. Alcohol craving and distress elicited by trauma images decreased in the exposure condition but did not change in the relaxation condition. Results support the hypothesis that negative emotion is a mechanism of alcohol craving. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Explicitly unpaired procedure as a response elimination technique in autoshaping.

In 4 experiments, with 113 wild and White Carneaux pigeons, autoshaped keypecking was eliminated by presenting an excitatory keylight and food in an explicitly unpaired relation. However, keypecking recovered when all food presentations were subsequently omitted (simple extinction). Exps I and II suggested that the recovery effect could not be explained by nonassociative processes, because both response elimination and response recovery were specific to the keylight involved in the explicitly unpaired relation. Exp III suggested that the effect could not be explained in terms of a food-related cue protecting the keylight from extinction, because food–keylight spacing did not affect the degree of subsequent recovery. Exp IV evaluated the possibility that signaling food presentations during response elimination might influence the degree of recovery. Greater recovery occurred after explicitly unpaired food presentations had been signaled than when they were unsignaled, suggesting that signaling reduced the development of inhibition during the response elimination phase. Implications for current theories of associative learning are discussed. (38 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Uterine contractions at the time of embryo transfer alter pregnancy rates after in-vitro fertilization

To investigate the possible consequences of uterine contractions (UC) as visualized by ultrasound (US) on in-vitro fertilization (IVF)-embryo transfer outcome, we studied prospectively 209 infertile women undergoing 220 cycles of controlled ovarian stimulation. Inclusion criteria were age < or = 38 years, a morphologically normal uterus, and at least three good quality embryos transferred. Just before embryo transfer, women underwent 5 min digital recordings of the uterus using US image analysis software for UC assessment. Plasma progesterone and oestradiol concentrations were measured. Four groups were defined according to UC frequency: < or = 3.0 (n = 53), 3.1-4.0 (n = 50), 4.1-5.0 (n = 43), and > 5.0 (n = 74) UC/min respectively. Patients, controlled ovarian hyperstimulation and embryology characteristics were comparable in all groups. A stepwise decrease in clinical and ongoing pregnancy rates as well as in implantation rates occurred from the lowest to the highest UC frequency groups (53, 36, 21; 46, 32, 20; 23, 19, 10; and 14, 11, 4%; P < 0.001). Plasma progesterone and UC frequency were negatively correlated (r = -0.34, P < 0.001). Direction of UC did not affect embryo transfer outcome. As this study was controlled strictly for confounding variables and UC were assessed objectively by a computerized system, its results indicate that high frequency UC on the day of embryo transfer hinder IVF-embryo transfer outcome, possibly by expelling embryos out of the uterine cavity. The negative correlation between UC frequency and progesterone concentrations supports the uterine relaxing properties of progesterone.     

Morphine promotes autonomic learning.

Morphine (0.01-10 mg/kg) promoted rapid autonomic learning of discriminative, Pavlovian conditioned heart rate decelerations to tone signals in male and female rabbits, and the higher doses (1-10 mg/kg) promoted decelerative heart rate orienting reflexes to novel tones. Morphine does dependently reduced heart rate acceleration to signaled shock but had no effect on heart rate acceleration to unsignaled shock. Morphine did not impair retention of cardiac conditioned reflexes, and its U-shaped dose effect, increasing conditioned heart rate discrimination early in training, reappeared in extinction. The authors propose that morphine promotes autonomic learning of preparatory, compensatory reflexes to signaled stressors that reduce their stressful effects. This action may mimic the normal, adaptive function of an endogenous messenger released by the Pavlovian contingency. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acquisition of superexcitatory properties by an irrelevant background stimulus.

Six appetitive conditioning experiments with rats demonstrated that an irrelevant X accompanying a negative patterning discrimination (XA+, XB+, XAB-) acquires extraordinarily high levels of conditioned excitation. Responding to X was similar to that evoked by 2 excitors in combination (Experiment 1) and was greater than responding to a separately reinforced Y (Experiments 2-5). Superexcitatory properties were not acquired by X in the nonpatterning discriminations of Experiments 2-4. Experiment 5 found that A and B, if anything, were weakly excitatory. Making them more strongly excitatory after conditioning did not interfere with retention of the original discrimination (Experiment 6). Results support a counterintuitive prediction of associative theories that, under carefully arranged conditions, irrelevant stimuli may acquire superexcitatory properties. (PsycINFO Database Record (c) 2010 APA, all rights reserved)