Temporal discrimination learning by pigeons

Memory for time by animals appears to undergo a systematic shortening. This so-called choose-short effect can be seen in a conditional temporal discrimination when a delay is inserted between the sample and comparison stimuli. We have proposed that this temporal shortening may result from a procedural artifact in which the delay appears similar to the intertrial interval and thus, produces an inadvertent ambiguity or 'instructional failure'. When this ambiguity is avoided by distinguishing the intertrial interval from the delay, as well as the samples from the delay, the temporal shortening effect and other asymmetries often disappear. By avoiding artifacts that can lead to a misinterpretation of results, we may understand better how animals represent time. An alternative procedure for studying temporal discriminations is with the psychophysical bisection procedure in which following conditional discrimination training, intermediate durations are presented and the point of subjective equality is determined. Research using the bisection procedure has shown that pigeons represent temporal durations not only as their absolute value but also relative to durations from which they must be discriminated. Using this procedure, we have also found that time passes subjectively slower when animals are required to respond to the to-be-timed stimulus.     

Ethics, ambiguity aversion, and the review of complex translational clinical trials

Clinical trials of novel agents often present several layers of ethical challenge. Because time and resources for ethical and safety review are limited, how investigators, IRBs, and regulators allocate attention to a trial's various safety dimensions itself represents a critical ethical question. In what follows, I use the example of a Parkinson's disease gene transfer trial to show how risks involving unknown probabilities or outcomes (ambiguity), might sometimes draw attention away from risks that involve known probabilities or outcomes. This potentially undermines the goal of 'systematic and nonarbitrary analysis of risk' during ethical review. To counteract the possible effects of such attention biases, I propose that reviewers develop 'cognitive aids' like lists and, where appropriate, set aside time to discuss non-ambiguous risks. I also propose further research for addressing and understanding how attention allocation, emotion, and ambiguity influence ethical decision-making.     

Conditional likelihood methods for haplotype-based association analysis using matched case-control data

Genetic epidemiologists routinely assess disease susceptibility in relation to haplotypes, that is, combinations of alleles on a single chromosome. We study statistical methods for inferring haplotype-related disease risk using single nucleotide polymorphism (SNP) genotype data from matched case-control studies, where controls are individually matched to cases on some selected factors. Assuming a logistic regression model for haplotype-disease association, we propose two conditional likelihood approaches that address the issue that haplotypes cannot be inferred with certainty from SNP genotype data (phase ambiguity). One approach is based on the likelihood of disease status conditioned on the total number of cases, genotypes, and other covariates within each matching stratum, and the other is based on the joint likelihood of disease status and genotypes conditioned only on the total number of cases and other covariates. The joint-likelihood approach is generally more efficient, particularly for assessing haplotype-environment interactions. Simulation studies demonstrated that the first approach was more robust to model assumptions on the diplotype distribution conditioned on environmental risk variables and matching factors in the control population. We applied the two methods to analyze a matched case-control study of prostate cancer.     

Systematization of ambiguous genitalia

Sex assignment in newborns depends on the anatomy of the external genitalia, despite this stage being the final in embryogenesis. According to the current view, the genital tubercle is the embryonic precursor of penis and clitoris. It originates from mesenchymal tissue, but mesenchymal cells are arranged across the embryonal body and do not have specific androgen receptors. The nature of the signal that initiates early derivation of the indifferent genital tubercle is unknown at present. The aims of this article are to improve surgical management of intersex disorders and investigate the development of the genital tubercle. Clinical examination of 114 females with various forms of DSD revealed ambiguous (bisexual) external genitalia in 73 patients, and 51 of them underwent feminizing surgery. Intersexuality (ambiguity) in 46,XY patients results from disruptors in the pathways of sex steroid hormones or receptors; in 46,XX females arises from excessive levels of androgens. Systematization of intersex disorders distinguishes the karyotype, gonadal morphology, and genital anatomy to provide a differential diagnosis and guide appropriate surgical management. Modified feminizing clitoroplasty with preservation of the dorsal and ventral neurovascular bundles to retain erogenous sensitivity was performed in females with severe virilization (Prader degree III-V). The outgrowth of the genital tubercle and the fusion of the urethral fold proceed in an ordered fashion; but in some cases of ambiguity, there was discordance due to different pathways. Speculation about the derivation of the genital tubercle have discussed with a literature review. The genital tubercle derives from the following 3 layers: the ectodermal glans of the tubercle, the mesodermal corpora cavernosa and the endodermal urogenital groove. According to the new hypothesis, during the indifferent stages, the 5 sacral somites have to recede from their segmentation and disintegrate: the sclerotomes form the pelvic bones, the fused myotomes follow with their genuine neurotomes and the angiotomes join to the corpora cavernosa of the genital tubercle. Sexual differentiation of external genitalia is final in gender embryogenesis, but surprisingly derivation of the indifferent genital tubercle from 5 somites occurs before gonadal and internal organs development.     

The ionic environment determines ribozyme cleavage rate by modulation of nucleobase pK a

Several small ribozymes employ general acid–base catalysis as a mechanism to enhance site-specific RNA cleavage, even though the functional groups on the ribonucleoside building blocks of RNA have pK_a values far removed from physiological pH. The rate of the cleavage reaction is strongly affected by the identity of the metal cation present in the reaction solution; however, the mechanism(s) by which different cations contribute to rate enhancement has not been determined. Using the Neurospora VS ribozyme, we provide evidence that different cations confer particular shifts in the apparent pK_a values of the catalytic nucleobases, which in turn determines the fraction of RNA in the protonation state competent for general acid–base catalysis at a given pH, which determines the observed rate of the cleavage reaction. Despite large differences in observed rates of cleavage in different cations, mathematical models of general acid–base catalysis indicate that k₁, the intrinsic rate of the bond-breaking step, is essentially constant irrespective of the identity of the cation(s) in the reaction solution. Thus, in contrast to models that invoke unique roles for metal ions in ribozyme chemical mechanisms, we find that most, and possibly all, of the ion-specific rate enhancement in the VS ribozyme can be explained solely by the effect of the ions on nucleobase pK_a. The inference that k₁ is essentially constant suggests a resolution of the problem of kinetic ambiguity in favor of a model in which the lower pK_a is that of the general acid and the higher pK_a is that of the general base.     

Understanding Food Scares: The Role of Ambiguity Aversion and Analogical Reasoning

Why do individuals exhibit similar reactions to manifestly different food scares? This article examines the hypothesis of analogical reasoning, a cognitive shortcut whereby individuals anchor their risk judgements in other similar previous risky events present in their memories explains together with known determinants of risks perceptions such as risk attitudes and ambiguity aversion. Considering the distribution of risk perceptions related to three food scares that people in Europe remember, namely dioxins, genetically modified food (GMF), and bovine spongiform encephalopathy (BSE). Furthermore, the article explores whether intrinsic individual attitudes toward risk (risk aversion) or a common human reaction to lack of information, namely ambiguity aversion, are associated with perceptions of risk. The findings suggest that perceptions of the three food scares appear to be statically distributed in almost the same way, consistently with the presence of analogical reasoning. Results show that although risk perceptions were affected by a degree of ambiguity aversion, the intensity of risk perceptions is mainly explained by individual-specific risk attitudes.