The extinction context enables extinction performance after a change in context

One experiment with human participants determined the extent to which recovery of extinguished responding with a context switch was due to a failure to retrieve contextually controlled learning, or some other process such as participants learning that context changes signal reversals in the meaning of stimulus-outcome relationships. In a video game, participants learned to suppress mouse clicking in the presence of a stimulus that predicted an attack. Then, that stimulus underwent extinction in a different context (environment within the game). Following extinction, suppression was recovered and then extinguished again during testing in the conditioning context. In a final test, participants that were tested in the context where extinction first took place showed less of a recovery than those tested in a neutral context, but they showed a recovery of suppression nevertheless. A change in context tended to cause a change in the meaning of the stimulus, leading to recovery in both the neutral and extinction contexts. The extinction context attenuated that recovery, perhaps by enabling retrieval of the learning that took place in extinction. Recovery outside an extinction context is due to a failure of the context to enable the learning acquired during extinction, but only in part.     

The effect of context change upon long-term memory of CS duration

An experiment with rats investigated forgetting of inhibition of delay in the conditioned suppression paradigm. The combined effects of contextual change and retention interval were tested. After a reliable temporal discrimination was reached, half of the rats received a test in the training context after a retention interval of 3 or 20 days. The other half received it in a different but equally familiar context at either retention interval. The longest retention interval flattened the temporal discrimination gradient and increased suppression to the CS. A similar but weaker pattern was found with the change of context; this effect was independent of the retention interval. The implications for retrieval and interference theory [Bouton, M.E., 1993. Psychol. Bull., 114: 80–99] and hypotheses concerning the forgetting of specific features of stimuli over time [Riccio, D.C., Richardson, R. and Ebner, D.L., 1984. Psychol. Bull., 96: 152–165] are discussed.     

Bisexual branching processes in a genetic context: the extinction problem for Y-linked genes

In this paper the inheritance of a Y-linked gene with alleles R and r in a population with both females and males is modelled using a two-type bisexual branching process. It is assumed that the reproductive distribution associated with the R allele can differ from the associated with the r allele and that females prefer to mate with a male having the R allele rather than with a male with the r allele. Under these assumptions, we provide some conditions for the extinction and/or survival of both alleles in the population. These conditions depend on the magnitudes of the average number of females and males per mating unit. Moreover, the almost sure extinction of the r allele is independent of the behaviour of the R allele. On the other hand, the survival of the R allele with positive probability may depend strongly on the reproductive behaviour of the other allele. Theoretical results are illustrated by means of simulated examples and some open problems are proposed to the reader as conjectures.     

A comparison of explicitly unpaired treatment and extinction: recovery of sign-tracking within a context renewal design

The present experiment compared the effectiveness of explicitly unpaired treatment and extinction in preventing the recovery of sign-tracking within a context renewal design. Three groups of rats were first trained on a sign-tracking procedure in Context A where insertions of a retractable lever were paired with food. In a second phase, the sign-tracking response was eliminated. One group received standard extinction of the CS in Context B, while another group received explicitly unpaired treatment in Context B where food was presented only during inter-trial intervals (and not paired with the lever). A third group received this explicitly unpaired treatment in Context A. After the sign-tracking response was eliminated, all groups received a test session in Context A where the lever was presented alone and no food was delivered at any time. Significantly more responding occurred in the group that received explicitly unpaired treatment in Context B than in either of the other groups. This demonstrates that there are situations where explicitly unpaired treatment is less effective than extinction in preventing the reappearance of previously eliminated responding.     

Technical note: PCR analysis of minimum target amount of ancient DNA

The study of ancient DNA plays an important role in archaeological and palaeontological research as well as in pathology and forensics. Here, we present a new tool for ancient DNA analysis, which overcomes contamination problems, DNA degradation, and the negative effects of PCR inhibitors while reducing the amount of starting target material in the picogram range. Ancient bone samples from four Egyptian mummies were examined by combining laser microdissection, conventional DNA extraction, and low‐volume PCR. Initially, several bone particles (osteons) in the micrometer range were extracted by laser microdissection. Subsequently, ancient DNA amplification was performed to verify our extraction method. Amelogenin and β‐actin gene specific fragments were amplified via low‐volume PCR in a total reaction volume of 1 μl. Results of microdissected mummy DNA samples were compared to mummy DNA, which was extracted using a standard DNA extraction method based on pulverization of bone material. Our results highlight the combination of laser microdissection and low‐volume PCR as a promising new technique in ancient DNA analysis. Am J Phys Anthropol, 2010. © 2010 Wiley‐Liss, Inc.     

A revaluation of lake-phosphorus loading models using a Bayesian hierarchical framework

We revisit the phosphorus-retention and nutrient-loading models in limnology using a Bayesian hierarchical framework. This methodological tool relaxes a basic assumption of regression models fitted to data sets consisting of observations from multiple systems, i.e., the systems are assumed to be identical in behavior, and therefore the models have a single common set of parameters for all systems. Under the hierarchical structure, the models are dissected into levels (hierarchies) that explicitly account for the role of significant sources of variability (e.g., morphometry, mixing regime, geographical location, land-use patterns, trophic status), thereby allowing for intersystem parameter differences. Thus, the proposed approach is a compromise between site-specific (where limited local data is a problem) and globally common (where heterogeneous systems in wide geographical areas are assumed to be identical) parameter estimates. In this study, we used critical values of the mean lake depth $ \left( {\bar{z} = 10.3\,{\text{m}}} \right) $ and the hydraulic residence time (τ _w = 2.6 years) to specify the hierarchical levels of the models. Our analysis demonstrates that the hierarchical configuration led to an improvement of the performance of six out of the seven hypothesized relationships used to predict lake-phosphorus concentrations. We also highlight the differences in the posterior moments of the group-specific parameter distributions, although the inference regarding the importance of different predictors (e.g., inflow-weighted total phosphorus input concentration, and hydraulic retention time) of lake phosphorus or the relative predictability of the models examined are not markedly different from an earlier study by Brett and Benjamin. The best fit to the observed data was obtained by the model that considers the first-order rate coefficient for total phosphorus loss from the lake as an inverse function of the lake hydraulic retention time. Finally, our analysis also demonstrates how the Bayesian hierarchical framework can be used for assessing the exceedance frequency and confidence of compliance of water-quality standards. We conclude that the proposed methodological framework will be very useful in the policy-making process and can optimize environmental management actions in space and time.     

Effects of an extinguished CS on competition with another CS

Three experiments were conducted using a conditioned taste aversion procedure with rats to examine the effect of nonreinforced presentations of a conditioned stimulus (CS) on its ability to compete with a target stimulus for manifest conditioned responding. Two CSs (A and B) were presented in a serial compound and then paired with the unconditioned stimulus. CS A was first paired with the US and then presented without the US (i.e., extinction) prior to reinforced presentation of the AB compound. Experiment 1 showed that A was poor at competing with B for conditioned responding when given conditioning and extinction prior to reinforcement of AB relative to a group that received both A and B for the first time during compound conditioning. That is, an extinguished A stimulus allowed greater manifest acquisition to B. Experiment 2 found that extinction treatment produced a poor CR to the pretrained and extinguished CS itself following compound conditioning. Experiment 3 found that interposing a retention interval after extinction of A and prior to compound conditioning enhanced A's ability to compete with B. The results of these experiments are discussed with regard to different theories of extinction and associative competition.     

Effect of parasitic sex-ratio distorters on host gene frequencies in a mainland-island context

It was previously argued that infection by parasitic sex-ratio distorters can enhance both random genetic drift and genetic influx from outside the population. However, these two enhancement effects have been studied independently. Here, we study the equilibrium frequencies of alleles (neutral and selected) in a mainland-island scenario where both genetic drift and genetic influx are enhanced due to infection by a cytoplasmic feminizing element. Interestingly, our model reveals that at neutral loci, the two effects almost exactly cancel each other out, such that infection has only a very minor effect on the equilibrium frequency distributions of alleles. At selected loci, in contrast, the two effects are unbalanced and infection has conspicuous effects. Despite the cryptic effects of infection at neutral loci, we demonstrate that temporally spaced data can be used to evaluate the effect of infection on genetic drift and that on gene flow separately.