The role of within-compound associations in learning about absent cues

When two cues are reinforced together (in compound), most associative models assume that animals learn an associative network that includes direct cue–outcome associations and a within-compound association. All models of associative learning subscribe to the importance of cue–outcome associations, but most models assume that within-compound associations are irrelevant to each cue’s subsequent behavioral control. In the present article, we present an extension of Van Hamme and Wasserman’s (Learning and Motivation 25:127–151, 1994) model of retrospective revaluation based on learning about absent cues that are retrieved through within-compound associations. The model was compared with a model lacking retrieval through within-compound associations. Simulations showed that within-compound associations are necessary for the model to explain higher-order retrospective revaluation and the observed greater retrospective revaluation after partial reinforcement than after continuous reinforcement alone. These simulations suggest that the associability of an absent stimulus is determined by the extent to which the stimulus is activated through the within-compound association.     

Revisiting the role of within-compound associations in cue-interaction phenomena

Although it is thought that within-compound associations are necessary for the occurrence of both backward blocking and unovershadowing, it is not known whether this variable plays a similar role in mediating the two phenomena. Similarly, the roles of within-compound associations in forward blocking and in reduced overshadowing have not been tested independently. The present experiments evaluated how the strength of within-compound associations affects backward blocking, unovershadowing, forward blocking, and reduced overshadowing. Using an allergy task, the strength of within-compound associations was varied by taking advantage of the participants’ prior knowledge of common and uncommon food pairings. Backward blocking and unovershadowing effects were present only when highly memorable compound cues were used. Moreover, the magnitudes of both retrospective revaluation effects were affected by the strength of within-compound associations. Forward blocking and reduced overshadowing effects were independent of within-compound associations. These results have important theoretical implications for causal learning research.     

An elemental model of retrospective revaluation without within-compound associations

When retrospective revaluation phenomena (e.g., unovershadowing: AB+, then A?, then test B) were discovered, simple elemental models were at a disadvantage because they could not explain such phenomena. Extensions of these models and novel models appealed to within-compound associations to accommodate these new data. Here, we present an elemental, neural network model of conditioning that explains retrospective revaluation apart from within-compound associations. In the model, previously paired stimuli (say, A and B, after AB+) come to activate similar ensembles of neurons, so that revaluation of one stimulus (A?) has the opposite effect on the other stimulus (B) through changes (decreases) in the strength of the inhibitory connections between neurons activated by B. The ventral striatum is discussed as a possible home for the structure and function of the present model.     

Overshadowing and CS duration: counteraction and a reexamination of the role of within-compound associations in cue competition

In the present experiments, we examined the role of within-compound associations in the interaction of the overshadowing procedure with conditioned stimulus (CS) duration, using a conditioned suppression procedure with rats. In Experiment 1, we found that, with elemental reinforced training, conditioned suppression to the target stimulus decreased as CS duration increased (i.e., the CS duration effect), whereas, with compound reinforced training (i.e., the overshadowing procedure), conditioned suppression to the target stimulus increased as CS duration increased. In subsequent experiments, we replicated these findings with sensory preconditioning and demonstrated that extinction of the overshadowing stimulus results in retrospective revaluation with short CSs and in mediated extinction with long CSs. These results highlight the role of the duration of the stimulus in behavioral control. Moreover, these results illuminate one cause (the CS duration) of whether retrospective revaluation or mediated extinction will be observed.     

Overshadowing of geometric cues by a beacon in a spatial navigation task

In three experiments, we examined whether overshadowing of geometric cues by a discrete landmark (beacon) is due to the relative saliences of the cues. Using a virtual water maze task, human participants were required to locate a platform marked by a beacon in a distinctively shaped pool. In Experiment 1, the beacon overshadowed geometric cues in a trapezium, but not in an isosceles triangle. The longer escape latencies during acquisition in the trapezium control group with no beacon suggest that the geometric cues in the trapezium were less salient than those in the triangle. In Experiment 2, we evaluated whether generalization decrement, caused by the removal of the beacon at test, could account for overshadowing. An additional beacon was placed in an alternative corner. For the control groups, the beacons were identical; for the overshadow groups, they were visually unique. Overshadowing was again found in the trapezium. In Experiment 3, we tested whether the absence of overshadowing in the triangle was due to the geometric cues being more salient than the beacon. Following training, the beacon was relocated to a different corner. Participants approached the beacon rather than the trained platform corner, suggesting that the beacon was more salient. These results suggest that associative processes do not fully explain cue competition in the spatial domain.     

Development of excitatory backward associations during the establishment of forward associations in a delayed conditional discrimination by pigeons

The development of excitatory backward associations in pigeons was demonstrated in three experiments involving conditional discriminations with differential outcomes. In Phase 1 of all three experiments, correct comparison choices following one sample were followed by food, whereas correct comparison choices following the other sample were followed by presentation of an empty feeder. In Phase 2, the food and no-food events that served as outcomes in Phase 1 replaced the samples. When the associations tested in Phase 2 were consistent with the comparison-outcome associations developed in Phase 1, transfer performance was significantly better than when the Phase 2 associations were inconsistent with the Phase 1 associations. In Experiment 1, an identity matching-to-sample task was used with red and green samples and red and green comparisons. In Experiment 2, a symbolic matching task was used with shape samples and hue comparisons, and it was shown that the backward associations formed were between the trial outcome (food or no food) and the correct comparison. In Experiment 3, it was determined that the transfer effects observed in these experiments did not depend on either the similarity of behavior directed toward the samples in the training and test phases, or the similarity of food and no-foodexpectancies generated by the samples in Phase 1 to food and no-foodevents presented as samples in Phase 2.     

Attenuation by contextual cues of retroactive interference of a conditional discrimination in rats

We investigated the effect of associating unique contextual cues with an interpolated learning task on retroactive interference in long-term memory. Rats were originally trained in a two-bar operant chamber with an auditory conditional discrimination stimulus. During interpolated learning, which occurred in either the original or a new context, some rats were trained on a probability learning task that did not include the auditory stimuli present during original learning. Subsequent retraining on the original conditional discrimination task in the original context showed that (1) significant retroactive interference occurs in rats, and (2) the presence of unique contextual cues during interpolated learning significantly reduces this interference. These results extend the conditions under which the susceptibility to retroactive interference can be altered by contextual cues.     

Time-course of control by specific stimulus features and relational cues during same-different discrimination training

We trained 7 pigeons to discriminate visual displays of 16same items from displays of 16different items. The specific stimulus features of the items and the relations among the items could serve as discriminative stimuli. Unlike in most studies of same-different discrimination behavior, we gave a small number of probe tests during each session of acquisition to measure the time-course of control by the learning of specific stimulus features and relational cues. Both the specific stimulus features and relational cues exerted reliable stimulus control, with the specific stimulus features exerting more control during the final three fourths of same-different learning. These findings replicate research suggesting that pigeons encode both the specific stimulus features and relational cues, and for the first time document the time-course of control by each kind of cue.     

Efficient design of rotary traveling wave oscillator array via geometric programming

This paper presents an efficient method for globally optimizing and automating component sizing for rotary traveling wave oscillator arrays. The lumped equivalent model of transmission lines loaded by inverter pairs is evaluated and posynomial functions for oscillation frequency, power dissipation, phase noise, etc. are formulated using transmission line theory. The re- sulting design problem can be posed as a geometric programJning problem, which can be efficiently solved with a convex opti- mization solver. The proposed method can compute the global optima more efficiently than the traditional iterative scheme and various design problems can be solved with the same circuit model. The globally optimal trade-off curves between competing objectives are also computed to carry out robust designs and quickly explore the design space.     

Peer-based discrimination and adolescent emotional and sleep health: A daily examination of direct and buffering associations

Using 10-day daily diary data collected in 2019 from 10th grade students in southern U.S. (N = 161, 57% Latina/x/o, 21% Biracial, 10% Asian, 9% White, 4% Black; 55% female, M_age = 15.51), this study examined various forms of peer-based discrimination in adolescents’ everyday lives. Results showed that personally experienced discrimination, peer racial teasing, and vicarious discrimination were frequent and impactful events. Results also provided strong evidence for the protective role of psychological resilience and some evidence for the protective-reactive roles of peer support and school climate in moderating the link between peer-based discrimination and daily well-being. The findings highlight the necessity to eliminate peer-based discrimination and shed light on interventions to reduce the harmful effects of peer-based discrimination on adolescents’ daily well-being.     

Conditioned reinforcement and complex discrimination: Can conditioned reinforcing value be specific to a complex of three cues?

The present experiment is concerned with the nature of the cues that might acquire conditioned reinforcing value, and the ways in which such cues might interact with one another. Red and green colored keylights were differentially paired with food dependent upon the houselight context (A or B) and the trial type (training or choice/forced). The duration of the colored keylights was varied between groups in an attempt to manipulate the effectiveness of the short-term memory of trial-type cues at the trial’s end. The red and green stimuli were of 30 sec duration for Group 30 and of 3 sec duration for Group 3. The results indicated that the choices of the pigeons in Group 30 were influenced by the houselight context present and by the keylight color. The choices of the pigeons in Group 3 seemed to be influenced by the houselight context present, the keylight color, and the memory of trial-type cues. Memory cues for trial antecedents were not overshadowed by presumably more salient external houselight stimuli for the pigeons in Group 3. Two alternative explanations for the results are discussed, and determined to be unlikely based on the results of an earlier experiment. The present results are related to a model of the conditioned reinforcing value of momentary stimuli and of transmission of conditioned reinforcing value.     

Sevoflurane postconditioning reduces myocardial reperfusion injury in rat isolated hearts via activation of PI3K/Akt signaling and modulation of Bcl-2 family proteins

Sevoflurane postconditioning reduces myocardial infarct size.The objective of this study was to examine the role of the phosphatidylinositol-3-kinase(PI3K)/Akt pathway in anesthetic postconditioning and to determine whether PI3K/Akt signaling modulates the expression of pro-and antiapoptotic proteins in sevoflurane postconditioning.Isolated and perfused rat hearts were prepared first,and then randomly assigned to the following groups:Sham-operation(Sham),ischemia/reperfusion(Con),sevoflurane postconditioning(SPC),Sham plus 100 nmol/L wortmannin(Sham+Wort),Con+Wort,SPC+Wort,and Con+dimethylsulphoxide(DMSO).Sevoflurane postconditioning was induced by administration of sevoflurane(2.5%,v/v) for 10 min from the onset of reperfusion.Left ventricular developed pressure(LVDP),left ventricular end-diastolic pressure(LVEDP),maximum increase in rate of LVDP(+dP/dt),maximum decrease in rate of LVDP(?dP/dt),heart rate(HR),and coronary flow(CF) were measured at baseline,R30 min(30 min of reperfusion),R60 min,R90 min,and R120 min.Creatine kinase(CK) and lactate dehydrogenase(LDH) were measured after 5 min and 10 min reperfusion.Infarct size was determined by triphenyltetrazolium chloride staining at the end of reperfusion.Total Akt and phosphorylated Akt(phospho-Akt),Bax,Bcl-2,Bad,and phospho-Bad were determined by Western blot analysis.Analysis of variance(ANOVA) and Student-Newman-Keuls' test were used to investigate the significance of differences between groups.The LVDP,±dP/dt,and CF were higher and LVEDP was lower in the SPC group than in the Con group at all points of reperfusion(P0.05).The SPC group had significantly reduced CK and LDH release and decreased infarct size compared with the Con group [(22.9±8)% vs.(42.4±9.4)%,respectively;P0.05].The SPC group also had increased the expression of phospho-Akt,Bcl-2,and phospho-Bad,and decreased the expression of Bax.Wortmannin abolished the cardioprotection of sevoflurane postconditioning.Sevoflurane postconditioning may protect the isolated rat heart.Activation of PI3K and modulation of the expression of pro-and antiapoptotic proteins may play an important role in sevoflurane-induced myocardial protection.