Relation between Belief and Performance in Perceptual Decision Making

In an uncertain and ambiguous world, effective decision making requires that subjects form and maintain a belief about the correctness of their choices, a process called meta-cognition. Prediction of future outcomes and self-monitoring are only effective if belief closely matches behavioral performance. Equality between belief and performance is also critical for experimentalists to gain insight into the subjects'' belief by simply measuring their performance. Assuming that the decision maker holds the correct model of the world, one might indeed expect that belief and performance should go hand in hand. Unfortunately, we show here that this is rarely the case when performance is defined as the percentage of correct responses for a fixed stimulus, a standard definition in psychophysics. In this case, belief equals performance only for a very narrow family of tasks, whereas in others they will only be very weakly correlated. As we will see it is possible to restore this equality in specific circumstances but this remedy is only effective for a decision-maker, not for an experimenter. We furthermore show that belief and performance do not match when conditioned on task difficulty – as is common practice when plotting the psychometric curve – highlighting common pitfalls in previous neuroscience work. Finally, we demonstrate that miscalibration and the hard-easy effect observed in humans'' and other animals'' certainty judgments could be explained by a mismatch between the experimenter''s and decision maker''s expected distribution of task difficulties. These results have important implications for experimental design and are of relevance for theories that aim to unravel the nature of meta-cognition.     

Atypicalities in Perceptual Adaptation in Autism Do Not Extend to Perceptual Causality

A recent study showed that adaptation to causal events (collisions) in adults caused subsequent events to be less likely perceived as causal. In this study, we examined if a similar negative adaptation effect for perceptual causality occurs in children, both typically developing and with autism. Previous studies have reported diminished adaptation for face identity, facial configuration and gaze direction in children with autism. To test whether diminished adaptive coding extends beyond high-level social stimuli (such as faces) and could be a general property of autistic perception, we developed a child-friendly paradigm for adaptation of perceptual causality. We compared the performance of 22 children with autism with 22 typically developing children, individually matched on age and ability (IQ scores). We found significant and equally robust adaptation aftereffects for perceptual causality in both groups. There were also no differences between the two groups in their attention, as revealed by reaction times and accuracy in a change-detection task. These findings suggest that adaptation to perceptual causality in autism is largely similar to typical development and, further, that diminished adaptive coding might not be a general characteristic of autism at low levels of the perceptual hierarchy, constraining existing theories of adaptation in autism.     

Heuristics and Biases in Evolutionary Biology

Approaching science by considering the epistemological virtues which scientists see as constitutive of good science, and the way these virtues trade-off against one another, makes it possible to capture action that may be lost by approaches which focus on either the theoretical or institutional level. Following Wimsatt (1984) I use the notion of heuristics and biases to help explore a case study from the history of biology. Early in the 20th century, mutation theorists and natural historians fought over the role that isolation plays in evolution. This debate was principally about whether replication was the central scientific virtue (and hence the ultimate goal of science to replace non-experimental evidence with experimental evidence) or whether consilience of inductions was the central virtue (and hence, as many kinds of evidence as possible should be pursued).     

Biases in prevalent cohorts

Several natural history studies of the Acquired Immunodeficiency Syndrome (AIDS) have been based on the follow-up of individuals infected with the AIDS virus prior to enrollment. The natural time scale for studying the preclinical course of AIDS is the time since first infection; however, in these studies the time at infection was a random unknown quantity. The biases inherent in using follow-up time instead of time from infection are investigated for estimation of both the cumulative distribution function and the hazard ratio for proportional hazards models with both fixed and time-dependent covariates. Although the magnitudes of the biases depend on the shape of the epidemic curve, a number of bounds on the biases are established. These results are useful for interpreting prevalent cohort studies and then comparing them with studies on newly infected individuals in order to assess consistency of results across studies.     

Redefining Rationality: Paranormal Investigators' Humour in England

In contemporary England, amateur paranormal investigators are actively engaged in attempts to produce objective knowledge about the ghostly and paranormal. Their project requires them to balance subjective, personal encounters with objective, technologically mediated ones. In doing so, they struggle to align their project with dominant understandings of rationality. Drawing on an ethnographic study of knowledge production among paranormal investigators, I explore paranormal investigators' use of humour and argue that they rely on humorous performances to align themselves with a powerful, hegemonic notion of rationality. Through their humour, they do not contest the scope of rationality; rather, they locate themselves as central to it.     

Using Multiple Control Groups and Matching to Address Unobserved Biases in Comparative Effectiveness Research

Studies of large policy interventions typically do not involve randomization. Adjustments, such as matching, can remove the bias due to observed covariates, but residual confounding remains a concern. In this paper we introduce two analytical strategies to bolster inferences of the effectiveness of policy interventions based on observational data. First, we identify how study groups may differ and then select a second comparison group on this source of difference. Second, we match subjects using a strategy that finely balances the distributions of key categorical covariates and stochastically balances on other covariates. An observational study of the effect of parity on the severely ill subjects enrolled in the Federal Employees Health Benefits (FEHB) Program illustrates our methods.     

Biases induced by using geography and environment to guide ex situ conservation

Ex situ germplasm collections seek to conserve maximum genetic diversity in a small number of samples. Geographic and environmental information have long been treated as surrogate measures of genetic diversity, proposed to be useful for increasing allelic diversity of collections. We examine the effect of maximizing geographic and environmental diversity on the retention of distinct haplotype blocks in germplasm subsets, using three species with extensive genomewide genotypic data. We show that maximizing diversity in the surrogate measures produces subsets with uneven representation of haplotypic diversity across the genome. Some regions are well-conserved, exhibiting high haplotypic diversity, while others are poorly-conserved and contain significantly less haplotypic diversity than would be obtained via random sampling. In two of three species, poorly-conserved genomic regions were enriched in regulatory genes which, as a class, contribute to phenotypic variation. The specific genes affected varied by species but, overall, haplotypic diversity was poorly-conserved at genes controlling?~?10% of major molecular functions and biological processes. While this study was limited to three exemplar species, we find little evidence to support continued use of geographic or environmental surrogates for ex situ conservation activities attempting to capture maximum genomewide allelic diversity. Although geographic and environmental diversity have proven to be reliable predictors of allele frequency differences and ecotypic differentiation across species ranges, they appear to be poor predictors of allelic diversity per se, offering little opportunity to enrich collections for haplotypic diversity overall, and ample opportunity to bias the conservation of important functional genetic variation. We propose a bioinformatic bridge between haplotypic diversity and the potential phenotypic diversity residing in collections using the Gene Ontology.     

Biomass and Abundance Biases in European Standard Gillnet Sampling

The European Standard EN 14757 recommends gillnet mesh sizes that range from 5 to 55mm (knot-to-knot) for the standard monitoring of fish assemblages and suggests adding gillnets with larger mesh sizes if necessary. Our research showed that the recommended range of mesh sizes did not provide a representative picture of fish sizes for larger species that commonly occur in continental Europe. We developed a novel, large mesh gillnet which consists of mesh sizes 70, 90, 110 and 135mm (knot to knot, 10m panels) and assessed its added value for monitoring purposes. From selectivity curves obtained by sampling with single mesh size gillnets (11 mesh sizes 6 – 55mm) and large mesh gillnets, we identified the threshold length of bream (Abramis brama) above which this widespread large species was underestimated by European standard gillnet catches. We tested the European Standard gillnet by comparing its size composition with that obtained during concurrent pelagic trawling and purse seining in a cyprinid-dominated reservoir and found that the European Standard underestimated fish larger than 292mm by 26 times. The inclusion of large mesh gillnets in the sampling design removed this underestimation. We analysed the length-age relationship of bream in the Římov Reservoir, and concluded that catches of bream larger than 292mm and older than five years were seriously underrepresented in European Standard gillnet catches. The Římov Reservoir is a typical cyprinid-dominated water body where the biomass of bream > 292mm formed 70% of the pelagic trawl and purse seine catch. The species-specific relationships between the large mesh gillnet catch and European Standard catch suggested that the presence of carp (Cyprinus carpio), European catfish (Silurus glanis), tench (Tinca tinca) or bream warrants the use of both gillnet types. We suggest extending the gillnet series in the European Standard to avoid misinterpretation of fish community biomass estimates.     

Measuring Attentional Biases for Threat in Children and Adults

Investigators have long been interested in the human propensity for the rapid detection of threatening stimuli. However, until recently, research in this domain has focused almost exclusively on adult participants, completely ignoring the topic of threat detection over the course of development. One of the biggest reasons for the lack of developmental work in this area is likely the absence of a reliable paradigm that can measure perceptual biases for threat in children. To address this issue, we recently designed a modified visual search paradigm similar to the standard adult paradigm that is appropriate for studying threat detection in preschool-aged participants. Here we describe this new procedure. In the general paradigm, we present participants with matrices of color photographs, and ask them to find and touch a target on the screen. Latency to touch the target is recorded. Using a touch-screen monitor makes the procedure simple and easy, allowing us to collect data in participants ranging from 3 years of age to adults. Thus far, the paradigm has consistently shown that both adults and children detect threatening stimuli (e.g., snakes, spiders, angry/fearful faces) more quickly than neutral stimuli (e.g., flowers, mushrooms, happy/neutral faces). Altogether, this procedure provides an important new tool for researchers interested in studying the development of attentional biases for threat.     

Bird to Human Transmission Biases and Vaccine Escape Mutants in H5N1 Infections

Background

The avian influenza A H5N1 virus occasionally infects humans, with high mortality rates. Although all current human infections are from avian-to-human transmission, it has been shown that H5N1 can be evolved to transmit between mammals, and is therefore a pandemic threat. For H5N1 surveillance, it is of interest to identify the avian isolates most likely to infect humans. In this study, we develop a method to identify mutations significantly associated with avian to human transmission.

Method

Using protein sequences for the surface glycoprotein hemagglutinin from avian and human H5N1 isolates in China, Egypt, and Indonesia from the years 1996–2011, we used Principle Component Analysis and a Maximum Likelihood Multinomial method to identify mutations associated with avian to human transmission. In each geographic region, transmission bias residues were identified using two signatures: a) significantly different amino-acid frequencies in human isolates compared to avian isolates from the same year, and b) significantly low probability of neutral evolution of the human isolates from the avian viral pool of the previous year.

Results

In each geographic region, we find specific transmission bias mutations associated with human infections. These mutations are located in antigenic regions and receptor binding, glycosylation and polybasic cleavage sites of HA. We show that human isolates derive from a limited, subset of the avian pool characterized by geography specific mutations. In Egypt, two of three PCA clusters have very few human isolates but are highly enriched in mutations associated with a vaccine escape mutant H5N1 avian sub-clade that is known to be resistant to the Mexican H5N2 vaccine Furthermore, at these transmission bias associated residues, the mutations characteristic of these two clusters are distinct from those associated with the cluster enriched in human isolates, suggesting that vaccine resistant avian strains are unable to infect humans. Our results are relevant for surveillance and vaccination strategies for human H5N1 infections.     

Biases in the assays of steroids and their binding proteins

Many immunoassays exhibit a bias. In such assays, the results are inaccurate, i.e. they deviate from the true value. The biases are mostly due to interfering compounds originating from the biological material assayed and/or from reagents. Sometimes systematic errors in calculation are also involved. The magnitude of the bias should be determined for every assay method, in order to make possible an assessment of reliability of the method. Biases frequently occur also in the measurements of steroid binding proteins, such as receptors, sex hormone binding globulin, corticosteroid binding globulin, etc. These biases are mostly due to the assumption that the measurements are performed under saturation conditions. These biases can be avoided by conducting the measurements at several concentrations of the ligand and by an appropriate correction for non-specific (low affinity) binding. In the assays of "free" steroids, biases are frequently encountered because of the disturbance of equilibrium in the course of the measurement proper. These biases can be minimized by a careful choice of experimental conditions.     

Perceptual differences in trail-following leaf-cutting ants relate to body size

Leaf-cutting ants of the genus Atta have highly size-polymorphic workers, and size is related to division of labor. We studied trail-following behavior of different-sized workers in a laboratory colony of Atta vollenweideri. For small and large workers, we measured responsiveness and preference to artificial conspecific and heterospecific pheromone trails made from poison gland extracts of A. vollenweideri and A. sexdens. Responsiveness was measured as the probability of trail-following, and preference was measured by testing the discrimination between one conspecific and one heterospecific trail. Minute amounts of the releaser component methyl-4-methylpyrrole-2-carboxylate (0.4pg/1m), present in both, conspecific and heterospecific trails, suffice to elicit trail-following behavior. Workers followed heterospecific trails, and these trails (after normalizing their concentration) were as effective as conspecific trails. Small workers were less likely to follow a trail of a given concentration than large workers. In the discrimination test, small workers preferred the conspecific trail over the heterospecific trail, whereas large workers showed no significant preference. It is suggested that large workers primarily respond to the releaser component present in both trails, whereas small workers focus more on the conspecific traits provided by the blend of components contained in the trail pheromone.     

A Contribution to the Problem of Perceptual Constancy

The problem of the psychological nature of perceptual constancy is, as we know, among the most pressing and as yet unresolved problems of modern psychology. Despite the fact that the past decade has seen large-scale experimental investigation of the problem, the study of the psychological mechanism of this phenomenon has hardly gone beyond the advancement of a number of theories hypothetical in nature.     

Direction Specific Biases in Human Visual and Vestibular Heading Perception

Heading direction is determined from visual and vestibular cues. Both sensory modalities have been shown to have better direction discrimination for headings near straight ahead. Previous studies of visual heading estimation have not used the full range of stimuli, and vestibular heading estimation has not previously been reported. The current experiments measure human heading estimation in the horizontal plane to vestibular, visual, and spoken stimuli. The vestibular and visual tasks involved 16 cm of platform or visual motion. The spoken stimulus was a voice command speaking a heading angle. All conditions demonstrated direction dependent biases in perceived headings such that biases increased with headings further from the fore-aft axis. The bias was larger with the visual stimulus when compared with the vestibular stimulus in all 10 subjects. For the visual and vestibular tasks precision was best for headings near fore-aft. The spoken headings had the least bias, and the variation in precision was less dependent on direction. In a separate experiment when headings were limited to ±45°, the biases were much less, demonstrating the range of headings influences perception. There was a strong and highly significant correlation between the bias curves for visual and spoken stimuli in every subject. The correlation between visual-vestibular and vestibular-spoken biases were weaker but remained significant. The observed biases in both visual and vestibular heading perception qualitatively resembled predictions of a recent population vector decoder model (Gu et al., 2010) based on the known distribution of neuronal sensitivities.     

Perceptual Adaptation to the Correction of Natural Astigmatism

Background

The visual system adjusts to changes in the environment, as well as to changes within the observer, adapting continuously to maintain a match between visual coding and visual environment. We evaluated whether the perception of oriented blur is biased by the native astigmatism, and studied the time course of the after-effects following spectacle correction of astigmatism in habitually non-corrected astigmats.

Methods and Findings

We tested potential shifts of the perceptual judgments of blur orientation in 21 subjects. The psychophysical test consisted on a single interval orientation identification task in order to measure the perceived isotropic point (astigmatism level for which the image did not appear oriented to the subject) from images artificially blurred with constant blur strength (B = 1.5 D), while modifying the orientation of the blur according to the axis of natural astigmatism of the subjects. Measurements were performed after neutral (gray field) adaptation on naked eyes under full correction of low and high order aberrations. Longitudinal measurements (up to 6 months) were performed in three groups of subjects: non-astigmats and corrected and uncorrected astigmats. Uncorrected astigmats were provided with proper astigmatic correction immediately after the first session. Non-astigmats did not show significant bias in their perceived neutral point, while in astigmatic subjects the perceived neutral point was significantly biased, typically towards their axis of natural astigmatism. Previously uncorrected astigmats shifted significantly their perceived neutral point towards more isotropic images shortly (2 hours) after astigmatic correction wear, and, once stabilized, remained constant after 6 months. The shift of the perceived neutral point after correction of astigmatism was highly correlated with the amount of natural astigmatism.

Conclusions

Non-corrected astigmats appear to be naturally adapted to their astigmatism, and astigmatic correction significantly changes their perception of their neutral point, even after a brief period of adaptation.     

考古动物群中的偏移现象——埋藏学的视角

考古动物群是由古代生物群经过死亡群、埋藏群、化石群的逐次"过滤"而形成的一个"采集群"[1]。在这一漫长而复杂的地质历史过程中,不同来源、不同规模、不同作用方式的多种埋藏学因素都在其中打上了自己的深刻"烙印",并在各自的层面上改变了考古动物群的最终面貌,从而导致了化石记录与原始生物群之间的客观偏移。因此,在对考古遗址发掘出土的大量动物化石进行合理解释之前,有必要了解和研究那些可能影响考古动物群最终组成的埋藏学过程或动因。本文以东亚地区的几项埋藏学研究为例,重点阐释了一些可能导致考古动物群偏移的埋藏学过程。