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PubMed2005

Is image steganography natural?

Steganography is the art of secret communication. Its purpose is to hide the presence of information, using, for example, images as covers. We experimentally investigate if stego-images, bearing a secret message, are statistically "natural." For this purpose, we use recent results on the statistics of natural images and investigate the effect of some popular steganography techniques. We found that these fundamental statistics of natural images are, in fact, generally altered by the hidden "nonnatural" information. Frequently, the change is consistently biased in a given direction. However, for the class of natural images considered, the change generally falls within the intrinsic variability of the statistics, and, thus, does not allow for reliable detection, unless knowledge of the data hiding process is taken into account. In the latter case, significant levels of detection are demonstrated.

Algorithms↗
PubMed1986

The evolution of electrophoretic mobility of proteins.

A model was constructed that predicts the electric charge of a protein and its isoelectric point from its primary and quaternary structures. By using two different patterns of mutation and purifying selection, four schemes of nucleotide substitution were simulated. In the absence of selection for a specific value of pI, proteins are expected to evolve toward a mildly basic pI. Thus, the selection for maintaining extreme values of pI must be stringent, and proteins with extreme pI's will evolve very slowly. This prediction is consistent with observations on the evolution of histones and ubiquitin. The mean charge change is expected to be about 0.005 units pI per nucleotide substitution. The amount of electrophoretically hidden variation is expected to be considerable even for large degrees of divergence at the nucleotide and amino acid levels. Electrophoretic detectability depends on the size of the protein. The longer the protein the larger the amount of variation at the amino acid level that is undetectable by isoelectric focusing. This property may be partially responsible for the imperfect correlation between molecular weight and gene diversity observed for electrophoretic data. Very basic and very acidic proteins are expected to generate less electrophoretic variability than proteins with intermediate pI's. Unequal rates of mutation between nucleotides and asymmetrical patterns of purifying selection have almost no effect on the equilibrium pI of proteins, but affect the rates of change in pI, and increase the amount of electrophoretically hidden variation in comparison to the expectations derived from random patterns of mutation and constant selection. Comparison of detectability of protein differences among four electrophoretical techniques suggests that the best performance is obtained by the sequential electrophoresis method.

Amino Acid Sequence↗
PubMed2003

Hidden messages in the nef gene of human immunodeficiency virus type 1 suggest a novel RNA secondary structure.

The coexistence of multiple codes in the genome of human immunodeficiency virus type 1 (HIV-1) was analyzed. We explored factors constraining the variability of the virus genome primarily in relation to conserved RNA secondary structures overlapping coding sequences, and used a simple combination of algorithms for RNA secondary structure prediction based on the nearest-neighbor thermodynamic rules and a statistical approach. In our previous study, we applied this combination to a non- redundant data set of env nucleotide sequences, confirmed the conservative secondary structure of the rev-responsive element (RRE) and found a new RNA structure in the first conserved (C1) region of the env gene. In this study, we analyzed the variability of putative RNA secondary structures inside the nef gene of HIV-1 by applying these algorithms to a non-redundant data set of 104 nef sequences retrieved from the Los Alamos HIV database, and predicted the existence of a novel functional RNA secondary structure in the beta3/beta4 regions of nef. The predicted RNA fold in the beta3/beta4 region of nef appears in two forms with different loop sizes. The loop of the first fold consists of seven nucleotides (positions 494-500), with consensus UCAAGCU appearing in 79% of sequences. The other has a five-base loop (positions 495-499) with consensus CAAGC. The difference in size between these two loops may reflect the difference between respective counterparts in the hairpin recognition. This may also have an adaptive biological significance.

Algorithms↗
PubMed1998

Use of neural networks to model complex immunogenetic associations of disease: human leukocyte antigen impact on the progression of human immunodeficiency virus infection.

Complex immunogenetic associations of disease involving a large number of gene products are difficult to evaluate with traditional statistical methods and may require complex modeling. The authors evaluated the performance of feed-forward backpropagation neural networks in predicting rapid progression to acquired immunodeficiency syndrome (AIDS) for patients with human immunodeficiency virus (HIV) infection on the basis of major histocompatibility complex variables. Networks were trained on data from patients from the Multicenter AIDS Cohort Study (n = 139) and then validated on patients from the DC Gay cohort (n = 102). The outcome of interest was rapid disease progression, defined as progression to AIDS in <6 years from seroconversion. Human leukocyte antigen (HLA) variables were selected as network inputs with multivariate regression and a previously described algorithm selecting markers with extreme point estimates for progression risk. Network performance was compared with that of logistic regression. Networks with 15 HLA inputs and a single hidden layer of five nodes achieved a sensitivity of 87.5% and specificity of 95.6% in the training set, vs. 77.0% and 76.9%, respectively, achieved by logistic regression. When validated on the DC Gay cohort, networks averaged a sensitivity of 59.1% and specificity of 74.3%, vs. 53.1% and 61.4%, respectively, for logistic regression. Neural networks offer further support to the notion that HIV disease progression may be dependent on complex interactions between different class I and class II alleles and transporters associated with antigen processing variants. The effect in the current models is of moderate magnitude, and more data as well as other host and pathogen variables may need to be considered to improve the performance of the models. Artificial intelligence methods may complement linear statistical methods for evaluating immunogenetic associations of disease.

Acquired Immunodeficiency Syndrome↗
PubMed2006

Variance estimation, design effects, and sample size calculations for respondent-driven sampling.

Hidden populations, such as injection drug users and sex workers, are central to a number of public health problems. However, because of the nature of these groups, it is difficult to collect accurate information about them, and this difficulty complicates disease prevention efforts. A recently developed statistical approach called respondent-driven sampling improves our ability to study hidden populations by allowing researchers to make unbiased estimates of the prevalence of certain traits in these populations. Yet, not enough is known about the sample-to-sample variability of these prevalence estimates. In this paper, we present a bootstrap method for constructing confidence intervals around respondent-driven sampling estimates and demonstrate in simulations that it outperforms the naive method currently in use. We also use simulations and real data to estimate the design effects for respondent-driven sampling in a number of situations. We conclude with practical advice about the power calculations that are needed to determine the appropriate sample size for a study using respondent-driven sampling. In general, we recommend a sample size twice as large as would be needed under simple random sampling.

Analysis of Variance↗
PubMed2006

A computationally efficient approach to the estimation of two- and three-dimensional hidden Markov models.

Statistical modeling methods are becoming indispensable in today's large-scale image analysis. In this paper, we explore a computationally efficient parameter estimation algorithm for two-dimensional (2-D) and three-dimensional (3-D) hidden Markov models (HMMs) and show applications to satellite image segmentation. The proposed parameter estimation algorithm is compared with the first proposed algorithm for 2-D HMMs based on variable state Viterbi. We also propose a 3-D HMM for volume image modeling and apply it to volume image segmentation using a large number of synthetic images with ground truth. Experiments have demonstrated the computational efficiency of the proposed parameter estimation technique for 2-D HMMs and a potential of 3-D HMM as a stochastic modeling tool for volume images.

Algorithms↗
PubMed2001

Postal surveys in primary care: the hidden burden.

OBJECTIVE: To investigate and analyse concerns raised by unsolicited mailing of a health survey to a community sample of older people. DESIGN: Observation and monitoring of all telephone calls received throughout a 6-week survey mailing period. SETTING AND PARTICIPANTS: A total sample of all those aged over 50 years registered with three general practices in North Staffordshire (n=8995). MAIN VARIABLE STUDIED: The frequency of telephone contact following the receipt of a postal questionnaire, and the nature of any associated distress. RESULTS AND CONCLUSIONS: Individuals who receive unsolicited postal surveys may experience anxiety because of the actual receipt of the questionnaire, concerns about taking part or not taking part, personal issues, anger, worthiness or frustration with NHS services. Anxiety may also be triggered because of administrative issues, for example lost mail or overlap between mailing periods. Researchers can adopt measures both to reduce the potential anxiety and often hidden burden of postal surveys, and to facilitate individuals' positive participation in research.

Aged↗
PubMed1996

Informational properties of neural nets performing algorithmic and logical tasks.

It is argued that the genetic information necessary to encode an algorithmic neural processor tutoring an otherwise randomly connected biological neural net is represented by the entropy of the analogous minimal Turing machine. Such a near-minimal machine is constructed performing the whole range of bivalent propositional logic in n variables. Neural nets computing the same task are presented; their informational entropy can be gauged with reference to the analogous Turing machine. It is also shown that nets with one hidden layer can be trained to perform algorithms solving propositional logic by error back-propagation.

Algorithms↗
PubMed1979

Smooth pursuit eye movements and optokinetic nystagmus elicited by intermittently illuminated stationary patterns.

Stationary periodic visual patterns (row of equally spaced dots or black-white stripes) of the period Ps illuminated stroboscopically with a flash frequency fs induce an apparent movement perception (sigma-movement) when slow eye movements are performed across the periodic pattern. The movement appears in the direction of the eye movements when the angular speed VE of the eyes corresponds to the following condition: Ve = k . Ps . fs [deg . s-1] (1) k is a constant and equals 1 (or exceptionally 2 or 3). The sigma-movement induces a sigma-OKN with an average angular speed of its slow phases corresponding to Eq.(1). sigma-OKN can be elicited when identical foveal or identical extrafoveal stimulus patterns are applied from flash to flash. A considerable random variability of the flash sequence does not interrupt the sigma-movement and the sigma-OKN. Both phenomena can also be elicited by a stimulus pattern with its periodicity hidden in spatial noise and this periodic pattern only becomes visible during the eye movements. It is argued that the sigma-phenomena are caused by efference copy signals of the gaze control system, which interact with the afferent signals (displacement of visual stimuli on the retina) at different levels of the afferent visual system. One interaction is supposed at a cortical level where the extrapersonal visual space is represented.

Adult↗
PubMed1989

Genetic influences on spatial ability: transmission in an extended kindred.

Transmission of six spatial tests, Card Rotations, Cube Comparisons, Group Embedded Figures, Hidden Patterns, Mental Rotations, and portable Rod and Frame, is examined among 73 members in four generations of an extended kindred. Nonadditive genetic variance is substantial for one of the six tests, Card Rotations. Whether this nonadditive genetic variance is due to a major autosomal gene is equivocal based on results from segregation and linkage analysis. There is no evidence for genetic variance for Mental Rotations or Hidden Patterns, in contrast to previous findings suggesting major gene involvement (Ashton et al., 1979). If spatial ability is due, in part, to an autosomal major gene, the gene has variable expression (reflected in different tests) or genetic heterogeneity is pronounced.

Adolescent↗
PubMed2006

Prediction for human motion tracking failures.

We propose a new and effective method of predicting tracking failures and apply it to the robust analysis of gait and human motion. We define a tracking failure as an event and describe its temporal characteristics using a hidden Markov model (HMM). We represent the human body using a three-dimensional, multicomponent structural model, where each component is designed to independently allow the extraction of certain gait variables. To enable a fault-tolerant tracking and feature extraction system, we introduce a single HMM for each element of the structural model, trained on previous examples of tracking failures. The algorithm derives vector observations for each Markov model using the time-varying noise covariance matrices of the structural model parameters. When transformed with a logarithmic function, the conditional output probability of each HMM is shown to have a causal relationship with imminent tracking failures. We demonstrate the effectiveness of the proposed approach on a variety of multiview video sequences of complex human motion.

Algorithms↗
PubMed2006

[The utility of artificial neural networks in the prediction of prostate cancer on transrectal biopsy].

OBJECTIVE: To determine whether the development of an artificial neural network (ANN) made up of clinical variables allows for the prediction of prostate biopsy (PB) outcome. MATERIALS AND METHODS: Patients (n=953) underwent PB at the Arquitecto Marcide Hospital in Ferrol (Spain), between january 2000 and june 2005. The variables studied were age, PSA, digital rectal examination (DRE) and prostate volume, data for all of which were available in 843 cases. In order to determine factors related to prostate cancer (PC) diagnosis, a logistic regression analysis and a feed-forward neural network were developed, including three hidden layer nodes and an output node, representing the probability of PC. Both models were constructed from a random sample of n=643 patients (derivation set). The predictive capacity was assessed with the remaining 200 patients (validation set), by means of ROC curves and the area under the curve (AUC). RESULTS: PC was detected in 500 (59.3%) cases. Adjusting for age, PSA, digital rectal examination and prostate volume, in a multivariate logistic regression model it was observed that all the variables were independent predictors of PC. The AUC were 0.693 for PSA, 0.707 for prostate volume, 0.815 for logistic regression and 0.819 for ANN. The predictive capacity of the ANN was significantly higher than that of the PSA (p=0.002) and prostate volume (p<0,001) and similar to that of logistic regression (p=0.760). CONCLUSIONS: The ANN shows a PC prediction capacity that is significantly higher than unimodal diagnosis methods, and similar to that of logistic regression.

Aged↗
PubMed2002

[Cystocele].

A cystocele is a bladder hernia through the anterior wall of the vagina. It is common in elderly women. There is no clinico-anatomical correlation, but the functional disturbance, although both variable and variably experienced, remains a major factor in the indication of eventual surgery. Methodologic clinical examination should be made to seek anomalies of pelvic stasis associated with a more or less hidden urinary incontinence. The surgical technique should be chosen according to the age and the classification of the patient, determined by complementary examinations that range from simple to highly technical (echography, cystography and sometimes study of urinary dynamics and MRI). The surgeon should chose the technique of perineal support and clearly explain the possibility of failure or recurrence. Confidence between the patient and the surgeon remains the best guarantee of a good result of management. Such surgery can be proposed to women to request it for physical comfort, whereas the surgeon should be very cautious with regard to those who do not want to undergo surgery (but also with those who strongly insist on surgery).

Adult↗
PubMed1989

Methodology and overt and hidden bias in reports of 196 double-blind trials of nonsteroidal antiinflammatory drugs in rheumatoid arthritis.

Important design aspects were decreasingly reported in NSAID trials over the years, whereas the quality of statistical analysis improved. In half of the trials, the effect variables in the methods and results sections were not the same, and the interpretation of the erythrocyte sedimentation rate in the reports seemed to depend on whether a significant difference was found. Statistically significant results appeared in 93 reports (47%). In 73 trials they favored only the new drug, and in 8 only the active control. All 39 trials with a significant difference in side effects favored the new drug. Choice of dose, multiple comparisons, wrong calculation, subgroup and within-groups analyses, wrong sampling units (in 63% of trials for effect variables, in 23% for side effects), change in measurement scale before analysis, baseline difference, and selective reporting of significant results were some of the verified or possible causes for the large proportion of results that favored the new drug. Doubtful or invalid statements were found in 76% of the conclusions or abstracts. Bias consistently favored the new drug in 81 trials, and the control in only one trial. It is not obvious how a reliable meta-analysis could be done in these trials.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2002

Assessing the economic impact of stress--the modern day hidden epidemic.

This article examines the economic effects of all forms of stress-work-related stress, home stress, and post-traumatic stress disorder (PTSD)-as health hazards. Such an approach inherently broadens the analysis from a few well-defined, quantitative variables, such as those most commonly studied by economists who traditionally examine job stress alone. It also enables us to draw conclusions regarding the socioeconomic factors and the psychology of stress and helps in understanding the larger question of the economic cost of stress in today's global environment. Stress and its related comorbid diseases are responsible for a large proportion of disability worldwide. The World Health Organization (WHO) Global Burden of Disease Survey estimates that mental disease, including stress-related disorders, will be the second leading cause of disabilities by the year 2020. Although the term "stress" is used in a wide variety of contexts, it has consistently been demonstrated that individuals with stress and related disorders experience impaired physical and mental functioning, more work days lost, increased impairment at work, and a high use of health care services. The disability caused by stress is just as great as the disability caused by workplace accidents or other common medical conditions such as hypertension, diabetes, and arthritis. We present evidence that calls for early recognition of workplace stress and for businesses to allocate more resources to stress management in the workplace.

Absenteeism↗
PubMed1999

Social stress of variable intensity: physiological and behavioral consequences.

Stress effects in humans depend on stress type, intensity, and duration. Animal models of social stress serve as good ways to mimic stress experienced in humans. However, the available stress paradigms pay little attention to the relationship between the intensity and the type of social stressors. The aim of the present work is to study behavioral and endocrinological consequences of social stress by varying the intensity and type of agonistic social contacts. Subjects were exposed to the attacks of an experienced fighter resident rat once a day for 4 consecutive days. Mild versus strong effects were studied by varying the length of daily confrontations (30 min vs. 4 h). The type of social confrontations was varied by ceasing or maintaining sensory contacts among contestants between encounters. Endocrinological variables were measured on the 5th day. Anxiety was assessed by means of the elevated plus-maze. The stress state depended on the length of daily encounters: 30-min encounters did not, whereas 4-h encounters did result in weight loss and chronic elevation of plasma corticosterone. The type of contacts between subjects and dominants also affected the resulting stress state: adrenal hypertrophy was obtained only when contacts between contestants were maintained between encounters. Although the mildest stress procedure (30-min encounters on 4 consecutive days) did not affect endocrinological variables, it resulted in subtle behavioral modifications that changed the anxiety-related effects of additional acute stressors. Thus, anxiety-related behavioral changes resulting from repeated mild stressors may be hidden factors that can have long-term consequences on the development of anxiety-like behavioral deficits. Results outline the necessity of studying the effects of social stressors of different intensities and different types.

Adrenal Glands↗
PubMed1997

Three Methods to Speed up the Training of Feedforward and Feedback Perceptrons.

Training of artificial neural networks is normally a time consuming task due to iterative search imposed by the implicit nonlinearity of the network behaviour. In this work, three improvements to "batch-mode" offline training methods, gradient-based or gradient-free, are proposed. For nonlinear multilayer perceptrons (NMLP) with linear output layers, a method based on linear regression in the output layer is presented. For arbitrary NMLPs, an algorithm is developed for detecting "saturated" hidden nodes and re-activating them while transferring their contribution onto the bias node in the same layer. For state-feedback NMLPs with incomplete learning data in the state variables, a method is shown that interpolates the unknown state values to form an intermediate training set used for finding good initial weights for the final training with only the original training set. In addition, three conventional gradient-based training methods-steepest-descent gradient search, conjugate gradient, and Gauss-Newton-are compared mutually and with the above improvements on the same two example problems. Where conventional methods get stuck in bad local minima, saturation avoidance leads to satisfactory results, and the speed-up achieved by the two other improvements is about two orders of magnitude.

Journal Article↗
PubMed1999

Amplitudes and latencies of single-trial ERP's estimated by a maximum-likelihood method.

The common approach in research on event-related electroencephalogram (EEG) potentials is to assume that the trigger-related signal is always the same and can be extracted from EEG background activity by simple averaging. To check the validity of this approach and to provide more exact results, latencies and amplitudes of components have to be estimated in single trials. Pham et al. applied a maximum-likelihood approach to solve the more general model which assumes that the signal hidden in EEG background activity has the same shape and amplitude but may vary in its latency from trial to trial. Extending their method we present a solution in which amplitude variability is also allowed. The utility of the solution to estimate the P3 component in single trials was investigated both by extensive pseudoreal simulations and in an application to real data. The simulations showed some advantage of the method over two other methods (Woody's method and peak-picking) commonly used in event-related potentials research. Application to real data provided a plausible description of single-trial sequential effects on the amplitude of the P3 component.

Artifacts↗