Some psychophysical determinants of discrete Moiré patterns

In a series of experiments we have investigated the perception of Moiré patterns as a function of spatial density, rotation and temporal display parameters. Results indicate that the local correlation extraction process involved in the perception of these patterns is not feature specific, yet is driven by excitatory (correlated) and inhibitory (uncorrelated) information under a form of spatial summation. These results are comparable with recent results on texture discrimination where texture interpoint distance distributions (dipole statistics) have also been discovered to have excitatory and inhibitory components.     

Moiré patterns: an accurate technique for determination of the locus of the centres of rotation

This study describes an accurate technique for the determination of the centre of rotation of small angles. The moiré fringe method localizes the centre of rotation by defining two primary fringes, each of which is found by the intersection of three lines. The primary fringes intersect at the centre of rotation at 90 degrees to each other, the angle least likely to produce an error in measurement. By utilizing joints with known centres of rotation, we have found that the method is extremely accurate and reproducible to within 2 mm of the real centre for angular changes as small as 3 degrees. This technique is useful in evaluating whether a joint is a simple hinge, i.e. rotating about a single axis of rotation or whether the joint moves about a changing axis of rotation referred to as a locus or centrode.     

Energy levels of Moiré patterns: relation to human perception

Quantitative analyses were undertaken to obtain a priori information regarding the energy levels of the random-dot display or Moiré patterns as a function of the angle of rotation θ by employing classical Newtonian mechanics. The energy profiles for these patterns were found to be similar for 10°<θ <350° in which the energies exhibited a maxima. For 10°≥ θ ≥ 350°, the profiles were found to be dramatically different, especially for the focus pattern where the profile exhibited a downward spike. Specifically, it was found that the minimum energy levels correspond to the angles of rotation where the profiles are perceived by humans. These results may provide insights into the underlying mechanism responsible for the perception of these patterns and information processing in the brain, specifically in the cerebral cortex.     

Blood feeding patterns of mosquitoes: random or structured?

Background

During the non-breeding period, many birds migrate to milder areas, found closer to the equator than their breeding sites. Opposite movements are very rare. In the Southern Ocean, the abundance of ¹³C declines markedly with more southern latitude, providing a characteristic ¹³C isoscape. This can be used as a tracer for the movement of seabirds between breeding and inter-breeding areas, by comparing stable isotope ratios of feathers grown at different times of the year.

Results

We studied seasonal movements of Thin-billed prions (Aves, Procellariiformes), breeding at the Subantarctic Falkland/Malvinas Islands, compared with those of Wilson's storm-petrels breeding in the Antarctic South Shetland Islands. The two species showed opposite migratory movements. While Wilson's storm-petrels moved to warmer waters north of the Drake Passage in winter, Thin-billed prions showed a reversed movement towards more polar waters. Carbon stable isotope ratios in recent and historical feathers indicated that poleward winter movements of Thin-billed prions were less common historically (45% in 1913-1915), and have only recently become dominant (92% in 2003-2005), apparently in response to warming sea temperatures.

Conclusions

This study shows that pelagic seabirds can rapidly change migration strategies within populations, including migration towards more poleward waters in winter.     

Can environmental constraints determine random patterns of plant species co-occurrence?

Plant community ecologists use the null model approach to infer assembly processes from observed patterns of species co‐occurrence. In about a third of published studies, the null hypothesis of random assembly cannot be rejected. When this occurs, plant ecologists interpret that the observed random pattern is not environmentally constrained – but probably generated by stochastic processes. The null model approach (using the C‐score and the discrepancy index) was used to test for random assembly under two simulation algorithms. Logistic regression, distance‐based redundancy analysis, and constrained ordination were used to test for environmental determinism (species segregation along environmental gradients or turnover and species aggregation). This article introduces an environmentally determined community of alpine hydrophytes that presents itself as randomly assembled. The pathway through which the random pattern arises in this community is suggested to be as follows: Two simultaneous environmental processes, one leading to species aggregation and the other leading to species segregation, concurrently generate the observed pattern, which results to be neither aggregated nor segregated – but random. A simulation study supports this suggestion. Although apparently simple, the null model approach seems to assume that a single ecological factor prevails or that if several factors decisively influence the community, then they all exert their influence in the same direction, generating either aggregation or segregation. As these assumptions are unlikely to hold in most cases and assembly processes cannot be inferred from random patterns, we would like to propose plant ecologists to investigate specifically the ecological processes responsible for observed random patterns, instead of trying to infer processes from patterns.     

Symmetries,non-Euclidean metrics,and patterns in a Swift–Hohenberg model of the visual cortex

The aim of this work is to investigate the effect of the shift-twist symmetry on pattern formation processes in the visual cortex. First, we describe a generic set of Riemannian metrics of the feature space of orientation preference that obeys properties of the shift-twist, translation, and reflection symmetries. Second, these metrics are embedded in a modified Swift-Hohenberg model. As a result we get a pattern formation process that resembles the pattern formation process in the visual cortex. We focus on the final stable patterns that are regular and periodic. In a third step we analyze the influences on pattern formation using weakly nonlinear theory and mode analysis. We compare the results of the present approach with earlier models.     

On the salinity tolerance of eggs and young larvae of Phryganea grandis Linné (Trichoptera)

Summary The salinity tolerance of eggs and recently hatched larvae of Phryganea grandis Linné (Trichoptera) from brackish-water in the Baltic Sea was investigated. Freshly deposited eggs will not develop to hatching in salinities above 7 More mature eggs will hatch even in 20 \% but the larvae die soon after emerging. Larvae have the same tolerance range as freshly deposited eggs (distilled water to 7 \%) in accordance with the actual distribution of the species. The high tolerance of mature eggs is probably due to changes in the egg-membranes or in the jelly of the egg-masses.Case building becomes abnormal in salinities above 10

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Résumé La tolérance de sel des oeufs et des larves récemment écloses de Phryganea grandis Linné (Trichoptera) de l'eau saumâtre de la Baltique a été examinée. Des oeufs nouvellement pondus ne se développeront pas jusqu'à éclosion dans une salinité de 7 Des oeufs plus mûrs sortiront de l'oeuf même dans une salinité de 20 \%, mais les larves meurent bientôt. Les larves ont la même limite de tolérance que des oeufs nouvellement pondus (de l'eau distillee de 7 \%), conformément à la distribution actuelle des espèces. La haute tolérance des oeufs mûrs est probablement conditionnée par des changements dans les membranes des oeufs ou dans la gelèe des masses d'oeufs. La construction des fourreaux devient anormale dans des salinités au-dessus de 10

     

How random is the toss of a coin?

Background

The toss of a coin has been a method used to determine random outcomes for centuries. It is still used in some research studies as a method of randomization, although it has largely been discredited as a valid randomization method. We sought to provide evidence that the toss of a coin can be manipulated.

Methods

We performed a prospective experiment involving otolaryngology residents in Vancouver, Canada. The main outcome was the proportion of “heads” coin tosses achieved (out of 300 attempts) by each participant. Each of the participants attempted to flip the coin so as to achieve a heads result.

Results

All participants achieved more heads than tails results, with 7 of the 13 participants having significantly more heads results (p ≤ 0.05). The highest proportion of heads achieved was 0.68 (95% confidence interval 0.62–0.73, p < 0.001).

Interpretation

Certain people are able to successfully manipulate the toss of a coin. This throws into doubt the validity of using a coin toss to determine a chance result.The toss or flip of a coin to randomly assign a decision traditionally involves throwing a coin into the air and seeing which side lands facing up. This method may be used to resolve a dispute, see who goes first in a game or determine which type of treatment a patient receives in a clinical trial. There are only 2 possible outcomes, “heads” or “tails,” although, in theory, landing on an edge is possible. (Research suggests that when the coin is allowed to fall onto a hard surface, the chance of this happening is in the order of 1 in 6000 tosses.¹)When a coin is flipped into the air, it is supposedly made to rotate about an axis parallel to its flat surfaces. The coin is initially placed on a bent forefinger, and the thumb is released from under the coin surface, where it has been held under tension. The thumbnail strikes the part of the coin unsupported by the index finger, sending it rotating upward. All this is done with an upward movement of the hand and forearm. The coin may be allowed to fall to the floor or other surface or it may be caught by the “tosser” and sometimes turned onto the back of the opposite hand and then revealed. The catching method should not matter, provided it is consistent for each toss. The opponent often calls the toss when the coin is airborne, although in the case of randomization for clinical trials, this is unnecessary because one is simply looking for an outcome.Open in a separate windowThe appeal of the coin toss that it is a simple, seemingly unbiased, method of deciding between 2 options. Although the outcome of a coin toss should be at even odds, the outcome may well not be. Historically, the toss of a coin before a duel reputedly decided which person had his back to the sun — an obvious advantage when taking aim! In medical trials, a simple statistical manipulation can have a dramatic effect on the treatment a patient receives. Our hypothesis is that with minimal training, the outcome of the toss can be weighted heavily to the call of the tosser, thus abolishing the 50:50 chance result that is expected and allowing for manipulation of an apparently random event.     

On the structure and ecology of the micro-fauna in the Central Amazonian forest stream ‘Igarapé da Cachoeira’

A method was developed to sample the microfauna in open stream water and to observe its food habits over long periods in the laboratory. Evaluation of the material leads to the following conclusions:

1. The microfauna is primarily associated with submerged leaf litter. Its density in the open water is a function of water current and hence, of rainfall,
2. A considerable quantity of living and detritus-biomass is swept down-stream with each heavy rain,
3. The foodweb starts essentially with decomposing fungi and detritus, and to a much lesser extent with algae and bacteria. Protozoa and Rhabdocoela are an insignificant input into the foodweb of higher invertebrates, but their role for maintenance of water quality may be important. Prey of fishes and shrimps depends primarily on ‘primary input’, i.e. on detritus, fungi and to some extent on algae and bacteria. The role of biomass transport from forest streams into larger rivers is discussed in relation to the fauna of the periodically inundated forest (igapó).

     

On the Mechanism of Metabolism of (−)-Epicatechin

(?)-Epicatechin was administered orally to rabbits and vanillic acid, 3-hydroxybenzoic acid, protocatechuic acid, and three kinds of neutral substances were found to be excreted in the urine. The three kinds of neutral substances were identified as 1-δ-(3-methoxy-4-hydroxyphenyl)-, 1-δ-(3-hydroxyphenyl)-, and 1-δ-(3,4-dihydroxyphenyl)-γ-valerolactones, which are optical isomers of the three kinds of neutral substances excreted after administration of (+)-catechin. From the presence of these intermediate metabolites, it was verified that (?)-epicatechin is metabolized by the same mechanism as (+)-catechin described earlier.     

Evolution of the genetic machinery of the visual cycle: a novelty of the vertebrate eye?

The discovery in invertebrates of ciliary photoreceptor cells and ciliary (c)-opsins established that at least two of the three elements that characterize the vertebrate photoreceptor system were already present before vertebrate evolution. However, the origin of the third element, a series of biochemical reactions known as the "retinoid cycle," remained uncertain. To understand the evolution of the retinoid cycle, I have searched for the genetic machinery of the cycle in invertebrate genomes, with special emphasis on the cephalochordate amphioxus. Amphioxus is closely related to vertebrates, has a fairly prototypical genome, and possesses ciliary photoreceptor cells and c-opsins. Phylogenetic and structural analyses of the amphioxus sequences related with the vertebrate machinery do not support a function of amphioxus proteins in chromophore regeneration but suggest that the genetic machinery of the retinoid cycle arose in vertebrates due to duplications of ancestral nonvisual genes. These results favor the hypothesis that the retinoid cycle machinery was a functional innovation of the primitive vertebrate eye.     

A texture-processing model of the ‘visual sense of number’

It has been suggested that numerosity is an elementary quality of perception, similar to colour. If so (and despite considerable investigation), its mechanism remains unknown. Here, we show that observers require on average a massive difference of approximately 40% to detect a change in the number of objects that vary irrelevantly in blur, contrast and spatial separation, and that some naive observers require even more than this. We suggest that relative numerosity is a type of texture discrimination and that a simple model computing the contrast energy at fine spatial scales in the image can perform at least as well as human observers. Like some human observers, this mechanism finds it harder to discriminate relative numerosity in two patterns with different degrees of blur, but it still outpaces the human. We propose energy discrimination as a benchmark model against which more complex models and new data can be tested.     

Fixed or random? On the reliability of mixed‐effects models for a small number of levels in grouping variables

Biological data are often intrinsically hierarchical (e.g., species from different genera, plants within different mountain regions), which made mixed‐effects models a common analysis tool in ecology and evolution because they can account for the non‐independence. Many questions around their practical applications are solved but one is still debated: Should we treat a grouping variable with a low number of levels as a random or fixed effect? In such situations, the variance estimate of the random effect can be imprecise, but it is unknown if this affects statistical power and type I error rates of the fixed effects of interest. Here, we analyzed the consequences of treating a grouping variable with 2–8 levels as fixed or random effect in correctly specified and alternative models (under‐ or overparametrized models). We calculated type I error rates and statistical power for all‐model specifications and quantified the influences of study design on these quantities. We found no influence of model choice on type I error rate and power on the population‐level effect (slope) for random intercept‐only models. However, with varying intercepts and slopes in the data‐generating process, using a random slope and intercept model, and switching to a fixed‐effects model, in case of a singular fit, avoids overconfidence in the results. Additionally, the number and difference between levels strongly influences power and type I error. We conclude that inferring the correct random‐effect structure is of great importance to obtain correct type I error rates. We encourage to start with a mixed‐effects model independent of the number of levels in the grouping variable and switch to a fixed‐effects model only in case of a singular fit. With these recommendations, we allow for more informative choices about study design and data analysis and make ecological inference with mixed‐effects models more robust for small number of levels.     

Is the development of orientation selectivity instructed by activity?

Is the development of orientation selectivity in visual cortex instructed by the patterns of neural activity of input neurons? We review evidence as to the role of activity, review models of activity-instructed development, and discuss how these models can be tested. The models can explain the normal development of simple cells with binocularly matched orientation preferences, the effects of monocular deprivation and reverse suture on the orientation map, and the development of a full intracortical circuit sufficient to explain mature response properties including the contrast-invariance of orientation tuning. Existing experiments are consistent with the models, in that (a) selective blockade of ON-center ganglion cells, which will degrade or eliminate the information predicted to drive development of orientation selectivity, in fact prevents development of orientation selectivity; and (b) the spontaneous activities of inputs serving the two eyes are correlated in the lateral geniculate nucleus at appropriate developmental times, as was predicted to be required to achieve binocular matching of preferred orientations. However, definitive tests remain to be done to firmly establish the instructive rather than simply permissive role of activity and determine whether the retinotopically and center type-specific patterns of activity predicted by the models actually exist. We conclude by critically examining alternative scenarios for the development of orientation selectivity and maps, including the idea that maps are genetically prespecified.     

On the Wholesomeness of γ-Irradiated Potatoes

Fattening pigs and pigs for breeding have been fed γ-irradiated and non-irradiated control potatoes. The irradiation dose was 14–15 kilorad at the rates 175 r/sec. and 625 r/hr. Rats (Wistar) were also fed irradiated and control potatoes, but in this case the tubers were given a dose of about 200 kilorad. No unfavourable effects have been observed from the feeding with irradiated potatoes. All the facts indicate that the nutritional adequacy of the irradiated and the control tubers is equal. In some cases, the animals have even shown an improvement after feeding on irradiated potatoes which was not apparent after feeding on non-irradiated potatoes; for example there was a more rapid growth, somewhat higher fertility, and increased haemoglobin values. However, current experiments with larger groups of animals will provide more definite evidence in these questions.