Metacognitive Confidence Increases with,but Does Not Determine,Visual Perceptual Learning

While perceptual learning increases objective sensitivity, the effects on the constant interaction of the process of perception and its metacognitive evaluation have been rarely investigated. Visual perception has been described as a process of probabilistic inference featuring metacognitive evaluations of choice certainty. For visual motion perception in healthy, naive human subjects here we show that perceptual sensitivity and confidence in it increased with training. The metacognitive sensitivity–estimated from certainty ratings by a bias-free signal detection theoretic approach–in contrast, did not. Concomitant 3Hz transcranial alternating current stimulation (tACS) was applied in compliance with previous findings on effective high-low cross-frequency coupling subserving signal detection. While perceptual accuracy and confidence in it improved with training, there were no statistically significant tACS effects. Neither metacognitive sensitivity in distinguishing between their own correct and incorrect stimulus classifications, nor decision confidence itself determined the subjects’ visual perceptual learning. Improvements of objective performance and the metacognitive confidence in it were rather determined by the perceptual sensitivity at the outset of the experiment. Post-decision certainty in visual perceptual learning was neither independent of objective performance, nor requisite for changes in sensitivity, but rather covaried with objective performance. The exact functional role of metacognitive confidence in human visual perception has yet to be determined.     

Certainty in Categorical Judgment of Size

The certainty of judgment (or self-confidence) has been traditionally studied in relation with the accuracy. However, from an observer''s viewpoint, certainty may be more closely related to the consistency of judgment than to its accuracy: consistent judgments are objectively certain in the sense that any external observer can rely on these judgments to happen. The regions of certain vs. uncertain judgment were determined in a categorical rating experiment. The participants rated the size of visual objects on a 5-point scale. There was no feedback so that there were no constraints of accuracy. Individual data was examined, and the ratings were characterized by their frequency distributions (or categories). The main result was that the individual categories always presented a core of certainty where judgment was totally consistent, and large peripheries where judgment was inconsistent. In addition, the geometry of cores and boundaries exhibited several phenomena compatible with the literature on visual categorical judgment. The ubiquitous presence of cores in absence of accuracy constraints provided insights about objective certainty that may complement the literature on subjective certainty (self-confidence) and the accuracy of judgment.     

A Quantitative Electroencephalographic Correlate of Sustained Attention Processing

The objective of the present investigation was to develop a quantitative electroencephalographic measure (qEEG) that is sensitive and specific to changes in sustained human performance. A principal components analysis (PCA) was performed on the qEEG obtained from participants during a continuous performance test. Measures of sensitivity (proportion of correctly identified correct responses, or hits) and specificity (proportion of correctly identified incorrect responses, or misses) were calculated to assess the classification accuracy of each newly derived component. PCA solutions produced a right hemisphere component comprised of beta-wave activity measured from four unipolar sites (F8, C6a, C6, and T4) that appeared to be sensitive and specific to changes in human performance. Results provide evidence for the validity of a right hemisphere qEEG measure that is sensitive and specific to changes in sustained human performance. Consistent with the findings of previous research, the present findings implicate the right cerebral hemisphere in the sustained attention process.     

The neurophysiological basis of the marijuana experience

Experiments were done with 75 healthy young adults to explore the neurophysiological basis of the acute marijuana intoxication state. Tests included recording the scalp EEG, visual and auditory cerebral evoked-potentials, the CNV, cerebral slow potentials related to certainty of response correctness in auditory discrimination tasks, heart rate, respiration and the galvanic skin response. All variables were recorded over 45 minutes before and 45 minutes after smoking a marijuana cigarette containing either 4.8, 9.1 or less than 0.01 mg. Δ⁹-THC.High doses of marijuana induced a significant decrease in the peak power of the alpha rhythm and an increase in auditory evoked-response latency. The CNV increased in ampiitude after smoking marijuana in low doses and sequential CNVs showed changes consistent with sustained attention but decreased certainty about performance following either low or high dose. Marijuana interfered significantly with performance of the discrimination task itself.     

Long Term Effects of Aversive Reinforcement on Colour Discrimination Learning in Free-Flying Bumblebees

The results of behavioural experiments provide important information about the structure and information-processing abilities of the visual system. Nevertheless, if we want to infer from behavioural data how the visual system operates, it is important to know how different learning protocols affect performance and to devise protocols that minimise noise in the response of experimental subjects. The purpose of this work was to investigate how reinforcement schedule and individual variability affect the learning process in a colour discrimination task. Free-flying bumblebees were trained to discriminate between two perceptually similar colours. The target colour was associated with sucrose solution, and the distractor could be associated with water or quinine solution throughout the experiment, or with one substance during the first half of the experiment and the other during the second half. Both acquisition and final performance of the discrimination task (measured as proportion of correct choices) were determined by the choice of reinforcer during the first half of the experiment: regardless of whether bees were trained with water or quinine during the second half of the experiment, bees trained with quinine during the first half learned the task faster and performed better during the whole experiment. Our results confirm that the choice of stimuli used during training affects the rate at which colour discrimination tasks are acquired and show that early contact with a strongly aversive stimulus can be sufficient to maintain high levels of attention during several hours. On the other hand, bees which took more time to decide on which flower to alight were more likely to make correct choices than bees which made fast decisions. This result supports the existence of a trade-off between foraging speed and accuracy, and highlights the importance of measuring choice latencies during behavioural experiments focusing on cognitive abilities.     

Attention to uninformative features expressed by pigeons in a duration matching-to-sample task

Pigeons were trained on a matching-to-sample task in which they had to respond to a different choice stimulus following the same durations (2 or 10 s) of two different signals. The duration signals consisted of a white light presented from the ceiling and a red light presented from the front wall. Subsequent test performance indicated that matching accuracy declined (1) when the set of choice stimuli following a duration signal differed from the set presented during training, and (2) when the color or location of the duration signal was changed from values used during training. These results are discussed in terms of attention to uninformative features of a visual stimulus.     

Using Manifold Learning for Atlas Selection in Multi-Atlas Segmentation

Multi-atlas segmentation has been widely used to segment various anatomical structures. The success of this technique partly relies on the selection of atlases that are best mapped to a new target image after registration. Recently, manifold learning has been proposed as a method for atlas selection. Each manifold learning technique seeks to optimize a unique objective function. Therefore, different techniques produce different embeddings even when applied to the same data set. Previous studies used a single technique in their method and gave no reason for the choice of the manifold learning technique employed nor the theoretical grounds for the choice of the manifold parameters. In this study, we compare side-by-side the results given by 3 manifold learning techniques (Isomap, Laplacian Eigenmaps and Locally Linear Embedding) on the same data set. We assess the ability of those 3 different techniques to select the best atlases to combine in the framework of multi-atlas segmentation. First, a leave-one-out experiment is used to optimize our method on a set of 110 manually segmented atlases of hippocampi and find the manifold learning technique and associated manifold parameters that give the best segmentation accuracy. Then, the optimal parameters are used to automatically segment 30 subjects from the Alzheimer’s Disease Neuroimaging Initiative (ADNI). For our dataset, the selection of atlases with Locally Linear Embedding gives the best results. Our findings show that selection of atlases with manifold learning leads to segmentation accuracy close to or significantly higher than the state-of-the-art method and that accuracy can be increased by fine tuning the manifold learning process.     

基于氨基酸序列预测蛋白质功能性点突变位点

突变是研究蛋白质结构和功能的重要方法。点突变实验中,突变位点的选择随机性大,若能对突变后蛋白质功能是否发生变化做出预测,将大大减少实验的盲目性。为此,作者设计了一个基于信号处理的单点替换突变预测模型,对序列上每个位点所有可能的氨基酸替换的效果进行估计。使用蛋白质突变数据库(Protein Mutant Database,PMD)里的11个蛋白共2600多个点突变的数据集,对以上模型进行了验证。结果表明正确率高达81.2%,并且推荐出的替换选择位点仅占所有可能替换突变的3.1%。在体外定点突变实验中,使用本模型推荐的高可能性功能突变位点将有助于提高实验的成功率。该模型使用蛋白质的氨基酸序列信息,特别是对未知结构的蛋白质同样适用。然而,由于缺乏足够的突变实验数据,本模型的应用仍需进一步完善和验证。     

A Continuous Labour Supply Model in Microsimulation: A Life-Cycle Modelling Approach with Heterogeneity and Uncertainty Extension

This paper advances a structural inter-temporal model of labour supply that is able to simulate the dynamics of labour supply in a continuous setting and addresses two main drawbacks of most existing models. The first limitation is the inability to incorporate individual heterogeneity as every agent is sharing the same parameters of the utility function. The second one is the strong assumption that individuals make decisions in a world of perfect certainty. Essentially, this paper offers an extension of marginal-utility-of-wealth-constant labour supply functions known as “Frisch functions” under certainty and uncertainty with homogenous and heterogeneous preferences. The lifetime models based on the fixed effect vector decomposition yield the most stable simulation results, under both certain and uncertain future wage assumptions. Due to its improved accuracy and stability, this lifetime labour supply model is particularly suitable for enhancing the performance of the life cycle simulation models, thus providing a better reference for policymaking.     

The use of first vertebrae in separating, and estimating the size of, trout (Salmo trutta) and salmon (Salmo salar) in bone remains

A method is described in which a single bone, the first vertebra, is used to distinguish bone remains of juvenile salmon ( Salmo salar ) and trout ( Salmo trutta ) with 90% certainty. A single regression of salmon and trout first vertebra-width versus fish-length of fish predicted the latter with an accuracy of ±<10 mm (95% confidence limits) for salmonids of 45–150 mm fish-length. First vertebrae were assigned to salmon or trout based on three visual characters with 89%,–90% certainty. Salmon are more variable than trout for the three characters. Of first vertebrae, 6.5% were not readily identifiable as either salmon or trout, and a further 3.0%) were misclassified using our criteria.     

Accuracy of ultrasonography for pregnancy diagnosis on days 10 to 22 in heifers

Two operators independently conducted ultrasonic pregnancy examinations on nulliparous Holstein heifers on Days 10, 12, 14, 16, 18, 20 and 22, and assigned a diagnosis (pregnant or nonpregnant) and a score for degree of certainty in the diagnosis (1, 2 or 3 for low, intermediate or high, respectively). Pregnancy was retrospectively confirmed by the ultrasonographic detection of an embryo proper and embryonic heartbeat on Day 24 in 20 25 bred heifers; the five nonpregnant heifers were excluded from the analyses. Eleven nonbred heifers were included as an unequivocal source of nonpregnant heifers. Accuracy was not significantly greater than a guess (50%) before Day 18, but reached 100% on Days 20 and 22. Mean accuracy was higher (P<0.005) for nonpregnant (65 77 , 84%) than pregnant heifers (91.5 140 , 65%). For certainty score, there were main effects of day (P<0.0001), reproductive status (pregnant or nonpregnant, P<0.003), and an interaction of day and reproductive status (P<0.0001). The certainty score increased in all heifers among days and was higher (P<0.05) in pregnant than nonpregnant heifers on Days 16 to 20. For luteal area (area of corpus luteum, excluding area of fluid filled center, if present), there were significant main effects of day, reproductive status and a day by status interaction (P<0.0001 for each). Luteal area was approximately constant in pregnant heifers, but in nonpregnant heifers it was lower (P<0.05) on Days 16 to 22 than on Days 10 to 14. Uterine echotexture was scored on a scale of 1 to 3, characteristic of a diestrus, intermediate and estrus uterus, respectively. There were main effects of day and reproductive status (P<0.0001 for each) and an interaction of day and reproductive status (P<0.025). Uterine echotexture was approximately constant in pregnant heifers, but in nonpregnant heifers it was higher (P<0.05) on Days 16 to 22 than on Days 10 to 14. Pregnancy diagnosis on Days 10 to 14 was based on detection of the conceptus; however, detection of the conceptus was not accurate prior to visualization of the embryo proper (mean Day 22, range Days 20 to 24). In nonpregnant heifers, a correct diagnosis with high certainty was made when a small corpus luteum and uterine echotexture characteristic of estrus were detected. In the absence of these changes on Days 18 to 22, a diagnosis of pregnancy was made with high accuracy and intermediate or high certainty.     

Parts per million mass accuracy on an Orbitrap mass spectrometer via lock mass injection into a C-trap

Mass accuracy is a key parameter of mass spectrometric performance. TOF instruments can reach low parts per million, and FT-ICR instruments are capable of even greater accuracy provided ion numbers are well controlled. Here we demonstrate sub-ppm mass accuracy on a linear ion trap coupled via a radio frequency-only storage trap (C-trap) to the orbitrap mass spectrometer (LTQ Orbitrap). Prior to acquisition of a spectrum, a background ion originating from ambient air is first transferred to the C-trap. Ions forming the MS or MS(n) spectrum are then added to this species, and all ions are injected into the orbitrap for analysis. Real time recalibration on the "lock mass" by corrections of mass shift removes mass error associated with calibration of the mass scale. The remaining mass error is mainly due to imperfect peaks caused by weak signals and is addressed by averaging the mass measurement over the LC peak, weighted by signal intensity. For peptide database searches in proteomics, we introduce a variable mass tolerance and achieve average absolute mass deviations of 0.48 ppm (standard deviation 0.38 ppm) and maximal deviations of less than 2 ppm. For tandem mass spectra we demonstrate similarly high mass accuracy and discuss its impact on database searching. High and routine mass accuracy in a compact instrument will dramatically improve certainty of peptide and small molecule identification.     

Feature ranking and rank aggregation for automatic sleep stage classification: a comparative study

Background

Nowadays, sleep quality is one of the most important measures of healthy life, especially considering the huge number of sleep-related disorders. Identifying sleep stages using polysomnographic (PSG) signals is the traditional way of assessing sleep quality. However, the manual process of sleep stage classification is time-consuming, subjective and costly. Therefore, in order to improve the accuracy and efficiency of the sleep stage classification, researchers have been trying to develop automatic classification algorithms. Automatic sleep stage classification mainly consists of three steps: pre-processing, feature extraction and classification. Since classification accuracy is deeply affected by the extracted features, a poor feature vector will adversely affect the classifier and eventually lead to low classification accuracy. Therefore, special attention should be given to the feature extraction and selection process.

Methods

In this paper the performance of seven feature selection methods, as well as two feature rank aggregation methods, were compared. Pz-Oz EEG, horizontal EOG and submental chin EMG recordings of 22 healthy males and females were used. A comprehensive feature set including 49 features was extracted from these recordings. The extracted features are among the most common and effective features used in sleep stage classification from temporal, spectral, entropy-based and nonlinear categories. The feature selection methods were evaluated and compared using three criteria: classification accuracy, stability, and similarity.

Results

Simulation results show that MRMR-MID achieves the highest classification performance while Fisher method provides the most stable ranking. In our simulations, the performance of the aggregation methods was in the average level, although they are known to generate more stable results and better accuracy.

Conclusions

The Borda and RRA rank aggregation methods could not outperform significantly the conventional feature ranking methods. Among conventional methods, some of them slightly performed better than others, although the choice of a suitable technique is dependent on the computational complexity and accuracy requirements of the user.

     

Communication during aggressive interactions with particular reference to variation in choice of behaviour

Communication during aggressive interactions is discussed and defined primarily on the basis of functional considerations. A distinction is made between communication due to choice of action and communication due to performance of a given choice of action. Most attention is directed to choice of behaviour. Two models are developed to show that there are no arguments of general validity against communication through choice of behaviour or signalling as has been claimed. The first model is built on variation in fighting ability only and shows that choice of signal can carry information both about intentions (use of local strategy) and fighting ability. The second model which is based on the war of attrition with random rewards instead considers variation in subjective resource value. It shows that signalling of local strategy can be stable. It is concluded that evolutionary stability of communication through choice of behaviour is due to variation among animals in the utility of showing different behaviour patterns whereas communication by performance is due to a not easily removed relationship between the performance of a certain behaviour pattern and the factor communicated.     

Have Genetic Trade-Offs in Host Use been Overlooked in Arthropods?

A popular hypothesis to explain the high degree of host specialisation observed among mites and insects is the existence of host-associated fitness trade-offs. According to this theory, adaptation to a host results in a relatively poorer performance on alternative hosts due to the antagonistic pleiotropic action of one or more genes. Evidence in favour of the genetic trade-off hypothesis is however scarce. Recent ecological work has shown that the optimisation of adult performance drives the evolution of host choice in at least some phytophagous insects. Yet, most ecological and evolutionary studies on host choice assume that females maximise their fitness by optimising offspring performance. In this paper, we investigate whether a general lack of attention for the role of adult performance in host choice may have diminished the chance of detecting genetic trade-offs. We reviewed the literature on genetic trade-offs and showed that most studies neglected host specific variation in adult performance. Moreover, studies that considered both adult and offspring performance had a higher chance of detecting genetic fitness trade-offs. Our results also suggested that studies on asexual reproducing species tend to detect trade-offs more often than studies on obligate sexual reproducing species. We argue that future studies on genetic trade-offs should take all fitness parameters into account in order to be conclusive. This approach may reveal (i) that genetic trade-offs are more common than hitherto reported and/or (ii) that genetic trade-offs are more common, or more easily detected among asexual reproducing species like mites and aphids. Co-ordinating editor: Dr. F. Stuefer     

Discriminant function implementation of a minimum risk classifier

The paper discusses the possibility of implementing a minimum risk classifier using the learning machine approach. Necessary conditions on the choice of pairwise classification costs are imposed so that the minimum risk classifier can be implemented using pairwise class separating functions. Parameters of these functions are obtained using a two stage algorithm which minimizes a modified least squares criterion of class separation. In comparison to normal least squares objective function, this criterion increases the sensitivity of the learning scheme near the class separating surface and, consequently, allows for an improvement in the performance of the discriminant function decision making processor. Simplicity of the design procedure is achieved by partitioning the multimodal classes into unimodal subsets, since discriminant functions of unimodal classes can usually be implemented simply and with sufficient accuracy as low order polynomials. The proposed design approach is tested experimentally on an artificial pattern recognition problem.     

Assessment of thyroid function: towards an integrated laboratory--clinical approach

Laboratory assessment of thyroid function is now often initiated with a low pre-test probability, by clinicians who may not have a detailed knowledge of current methodology or testing strategies. Skilled laboratory staff can significantly enhance the choice of appropriate tests and the accuracy of clinical response; such involvement requires both appropriate training and relevant information from the clinician. Measurement of the serum thyroid stimulating hormone (TSH) concentration with an assay of adequate sensitivity is now the cornerstone of thyroid function testing; for untreated populations at risk of primary thyroid dysfunction, a normal TSH concentration rules out an abnormality with a high degree of certainty. However, in several important situations, most notably pituitary abnormalities and early treatment of thyroid dysfunction, serum TSH can give a misleading indication of thyroid status. An abnormal TSH concentration alone is never an adequate basis for initiation of treatment, which should be based on the typical relationship between trophic and target gland hormones, based on serum TSH and an estimate of serum free thyroxine (T4). Six basic assumptions, some clinical, some laboratory-based, need to be considered, together with the relevant limiting conditions, for reliable use of this relationship. Current methods of free T4 estimation remain imperfect, especially during critical illness. Diagnostic approach differs significantly between initial diagnosis and follow-up of treated thyroid dysfunction. In some situations, serum triiodothyronine (T3) is also required, but serum T3 lacks sensitivity for diagnosis of hypothyroidism, and has poor specificity during non-thyroidal illness. Where assay results are anomalous, most atypical findings can be resolved by attention to the clinical context, without further investigation.     

Fast noninertial shifts of attention

It was suggested that some discrimination tasks (e.g. discrimination between the letters T and L) require serial search by scrutinizing each letter (target) with a small aperture of focal attention. Here we examine the effect of intertarget distance on discrimination performance, using two targets. We find reduction in performance at short distances, in agreement with masking studies, but constant performance independent of distance outside this masking region. This constant performance is still lower than expected from masking effects and might reflect attentive process. Sequential presentation of the targets with delays up to 30-40 ms, while reducing available processing time, does not cause reduction in performance, thus supporting the suggestion that discrimination of the two targets is a serial process. The independence of performance on distance suggests fast noninertial shifts of attention.     

Study of the role of different types of glutamate receptors in spatial memory in rats]

A comparative study was performed to assess effects of different antagonists of glutamate receptors on spatial discrimination of rats in 8-arm radial and water mazes. Noncompetitive NMDA receptor blocker MK-801 in the dose 0.10 mg/kg and higher impaired the accuracy of performance in radial maze, whereas in the doses 0.05--0.30 mg/kg in water maze. Quisqualate IAMPA- and 2-amino-4-phosphonobutyrate (2-APB) I antagonists glutamate diethyl ester (250--500 mg/kg) and 2-APB (50--100 mg/kg), respectively, only increased time to complete radial maze performance and failed to alter choice accuracy. Both antagonists at the same doses did not affect performance of water maze task. The involvement of each type of glutamate receptors in different stages of spatial discrimination process in rats was discussed.     

Neurobehavioural disturbances in workers engaged in high-pressure spray painting

A battery of neurobehavioural tests consisting of reaction time (simple and choice), tweezer dexterity, hand precision, and memory (forward and backward) were administered to a group of painters before and after their work schedule to provide a quantitative assessment of the possible behavioural changes. Their responses on five affective measures, e.g., headache, mental freshness, forgetfulness, sleepiness, and general good health were also collected on visual analogue scales. Analysis of variance indicated significant deterioration of performance on reaction time (choice), tweezer dexterity (accuracy), hand precision (accuracy), and memory (backward) in the painters by the end of their work-shift. Significant deleterious effects were also noted on headache, mental freshness, and sleepiness. The degree of deterioration of their performance on these tests as also of the affective measures were found to be associated with the duration of exposure.