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PubMed2005

Temporally nonadjacent nonlinguistic sounds affect speech categorization.

Speech perception is an ecologically important example of the highly context-dependent nature of perception; adjacent speech, and even nonspeech, sounds influence how listeners categorize speech. Some theories emphasize linguistic or articulation-based processes in speech-elicited context effects and peripheral (cochlear) auditory perceptual interactions in non-speech-elicited context effects. The present studies challenge this division. Results of three experiments indicate that acoustic histories composed of sine-wave tones drawn from spectral distributions with different mean frequencies robustly affect speech categorization. These context effects were observed even when the acoustic context temporally adjacent to the speech stimulus was held constant and when more than a second of silence or multiple intervening sounds separated the nonlinguistic acoustic context and speech targets. These experiments indicate that speech categorization is sensitive to statistical distributions of spectral information, even if the distributions are composed of nonlinguistic elements. Acoustic context need be neither linguistic nor local to influence speech perception.

Adult↗

PubMed1980

The random character of protein evolution and its effects on the reliability of phylogenetic information deduced from amino acid sequences and compositions.

Because evolution occurs by random events, the actual number of substitutions that occur in any period is not exactly equal to the number expected from the mean rate of substitution, but is statistically distributed about it. In consequence, even if rates of evolution are constant in different lineages, 'trees' deduced from descendant protein sequences contain random errors. When there are fewer than about eight differences between the sequences of the most distantly related pair from a set of proteins, this random effect is very large. It can then render trivial the statistical disadvantage inherent in using a crude measure of protein difference, such as amino acid composition or immunological cross-reactivity, in preference to a measure based the sequences of the most distantly related pair from a set of proteins, this random effect is very large. It can then render trivial the statistical disadvantage inherent in using a crude measure of protein difference, such as amino acid composition or immunological cross-reactivity, in preference to a measure based the sequences of the most distantly related pair from a set of proteins, this random effect is very large. It can then render trivial the statistical disadvantage inherent in using a crude measure of protein difference, such as amino acid composition or immunological cross-reactivity, in preference to a measure based on amino acid sequence. In some cases, such as classification of mammals on the basis of cytochrome c structure, it appears to make little difference to the reliability of the results whether the sequences of the protein concerned are known or not. It may also be possible to obtain more reliable phylogenetic information from composition measurements on several kinds of protein than one could obtain from sequence measurements on a single kind of protein.

Amino Acid Sequence↗

PubMed1990

The distribution of physical, chemical and conformational properties in signal and nascent peptides.

Signal peptides play a major role in an as-yet-undefined way in the translocation of proteins across membranes. The sequential arrangement of the chemical, physical and conformational properties of the signal and nascent amino acid sequences of the translocated proteins has been compiled and analysed in the present study. The sequence data of 126 signal peptides of length between 18 and 21 residues form the basis of this study. The statistical distribution of the following properties was studied hydrophobicity, Mr, bulkiness, chromatographic index and preference for adopting alpha-helical, beta-sheet and turn structures. The contribution of each property to the sequence arrangement was derived. A hydrophobic core sequence was found in all signal peptides investigated. The structural arrangement of the cleavage site was also clearly revealed by this study. Most of the physical properties of the individual sequences correlated (correlation coefficient approximately 0.4) very well with the average distribution. The preferred occupancy of amino acid residues in the signal and nascent sequences was also calculated and correlated with their property distribution. The periodic behaviour of the signal and nascent chains was revealed by calculating their hydrophobic moments for various repetitive conformations. A graphical analysis of average hydrophobic moments versus average hydrophobicity of peptides revealed the transmembrane characteristics of signal peptides and globular characteristics of the nascent peptides.

Amino Acid Sequence↗

PubMed2002

Spatial distribution and sampling plans for Mesoplatys ochroptera (Coleoptera: Chrysomelidae) on sesbania.

With the widespread introduction of the nitrogen-fixing legume sesbania, Sesbania sesban (L.) Merril, in agroforestry systems, the defoliating beetle Mesoplatys ochroptera Stål has become a serious pest of the trees in Africa. To determine within-field and within-plant spatial distribution of M. ochroptera on both seedlings and trees of sesbania, distribution statistics were computed using Iwao's mean crowding regression model. In 1- to 3-mo-old seedlings, the model accounted for 29.8, 32.2, and 61.0% of the variation observed in mean crowding to mean relationships in egg masses, larvae and adults, respectively. The model slopes of the regression were greater than unity for all stages indicating aggregated spatial distribution. Values of the intercept were greater than zero for egg masses, larvae and adults indicating that the basic components of the population are groups of individuals. The highest density (>80%) of mating and feeding adults was found in the upper third of 1- to 2-mo-old seedlings, while most of the egg masses were found in the lower half of seedlings. In trees, >60% of the individuals of all stages were found in the lower third of the foliage canopy, while <10% were found in the upper third. Sampling adults was found to be easier and gave better density estimates of M. ochroptera population than egg masses and larvae. Therefore, sampling plans useful for population studies and decision-making in pest management were developed for adults.

Animals↗

PubMed2001

Induction policy and missed post-term pregnancies: a mathematical model.

The aim of this study was to compare the clinical performance of ultrasound dates and ultrasound dates combined with menstrual dates for the detection of post-maturity. A computer model was designed which uses the statistical distributions of the duration of normal pregnancy, day of ovulation in relation to the menstrual cycle and ultrasound error for estimating gestational age. The clinical performance of the different dating methods was then analysed from these variables, on simulations of 30,000 cases. The efficacy of different dating methods for detecting post-maturity was determined by generating receiver-operator characteristics (ROC) curves. The proportion of post-term pregnancies (294 days and over) predicted by the model (3.5%) agrees with published values. There is a steep rise in missed cases if induction is delayed beyond 10 days from the expected date of delivery, reaching 20% on day 294. Elective delivery on day 290 will detect 98.9% of cases destined to deliver post-term, with an induction rate of 10%; the respective figures for induction on day 294 are 79% and 3.8%. The ROC curves for the detection of post-maturity suggest that use of the mid-trimester biparietal diameter (BPD) is better than a 7-day or 10-day rule. Timing of elective delivery is the most important variable affecting the detection rate for post-maturity There is no advantage in using menstrual dates when ultrasound biometry is available.

Bias↗

PubMed1980

[Effects of molecular parameters of galacturonan substrate on the activity of a polygalacturonase from tomatoes].

The activity of a major form of the tomato polygalacturonase (EC 3.2.1.15) depends of the origin of the galacturonan substrates (apple, citrus) as well as upon the molecular mass, the degree of esterification and the distribution of the ester methoxyl groups. Optimal substrates are citrus pectic acids with a degree of esterification < 1% and a molecular mass corresponding to a viscosity number [eta] = 90 ml/g galacturonan. In the [eta] range from 16 to 474 ml/g, the Km values decrease to constant amount of 15.6 mM galacturonic acid units, which corresponds to 0.27% galacturonan. In a statistical distribution of the ester methoxyl groups, the activity reaches zero in the range of the degree of esterification from 80 to 90%. Enzymatically de-esterified pectins with a degree of esterification < 32% and a block-like distribution of the ester methoxyl groups behave as comparable pectic acids. In summary, there is a good agreement between these enzymesubstrate interactions and those of endopolygalacturonases from Aspergillus spec. Differentiations manifested themselves only in the transition range between macromolecular galacturonan substrates and oligomeric substrates below the established critical molecular mass.

Glycoside Hydrolases↗

PubMed1998

Predicting the distribution of synaptic strengths and cell firing correlations in a self-organizing, sequence prediction model.

This article investigates the synaptic weight distribution of a self-supervised, sparse, and randomly connected recurrent network inspired by hippocampal region CA3. This network solves nontrivial sequence prediction problems by creating, on a neuron-by-neuron basis, special patterns of cell firing called local context units. These specialized patterns of cell firing--possibly an analog of hippocampal place cells--allow accurate prediction of the statistical distribution of synaptic weights, and this distribution is not at all gaussian. Aside from the majority of synapses that are, at least functionally, lost due to synaptic depression, the distribution is approximately uniform. Unexpectedly, this result is relatively independent of the input environment, and the uniform distribution of synaptic weights can be approximately parameterized based solely on the average activity level. Next, the results are generalized to other cell firing types (frequency codes and stochastic firing) and place cell-like firing distributions. Finally, we note that our predictions concerning the synaptic strength distribution can be extended to the distribution of correlated cell firings. Recent published neurophysiological results are consistent with this extension.

Electrophysiology↗

PubMed2006

Topology of pseudoknotted homopolymers.

We consider the folding of a self-avoiding homopolymer on a lattice, with saturating hydrogen bond interactions. Our goal is to numerically evaluate the statistical distribution of the topological genus of pseudoknotted configurations. The genus has been recently proposed for classifying pseudoknots (and their topological complexity) in the context of RNA folding. We compare our results on the distribution of the genus of pseudoknots, with the theoretical predictions of an existing combinatorial model for an infinitely flexible and stretchable homopolymer. We thus obtain that steric and geometric constraints considerably limit the topological complexity of pseudoknotted configurations, as it occurs for instance in real RNA molecules. We also analyze the scaling properties at large homopolymer length, and the genus distributions above and below the critical temperature between the swollen phase and the compact-globule phase, both in two and three dimensions.

Binding Sites↗

PubMed2002

Ab initio direct dynamics study of cyclopropyl radical ring-opening.

Quasiclassical direct dynamics simulations, at the CASSCF(3,3)/6-31G(d) level of theory, are used to study the stereochemistry of the electrocyclic ring-opening reaction of the cyclopropyl radical. The trajectories are initiated at the reaction's transition state (TS), with their initial conditions sampled from the TS's 174 degrees C Boltzmann distribution. Intrinsic reaction coordinate calculations predict the overall reaction to have disrotatory stereochemistry. Though this is the preferred initial reaction stereochemistry in the trajectories, 43% of the trajectories follow the conrotatory path. Four unique trajectory types are observed during 200 fs dynamics of the product allyl radical. Intramolecular vibrational energy redistribution and internal rotation are incomplete on this time scale, and a statistical distribution of the allyl isomers is not observed.

Journal Article↗

PubMed1972

Statistical analysis of the bioassay of continuous carcinogens.

In an experiment consisting of the continuous constant application of various carcinogenic regimens to a pure strain of experimental animals for a long period, the cancer incidence rates so caused may be studied and compared by the fit of an appropriate class of statistical distributions. In this paper we show that a Weibull distribution in which the age-specific cancer incidence rate rises as a power of time since first risk is more appropriate than a lognormal distribution. If the Weibull family of distributions is used, more information can be extracted from the data, and differences of toxicity between various regimens will not bias the comparison of their carcinogenic forces.

Animals↗

PubMed1998

[Evaluation of a linear TEOAE protocol in hearing screening of neonates: feasibility study].

The audiological screening of newborns based on recording TEOAEs--the expression of anatomical-functional integrity of the cochlea--has unanimously gained importance. The prevalence of severe of genetic or congenital hearing loss in the healthy infant population and in the population at risk for audiological disorders, as well as the consequent psycholinguist and socialization problems such children have to deal with, have led the authors to set up a preliminary protocol for the audiological screening of neonates. The purpose of this protocol is to improve the feasibility of applying such a program. To this purpose, the preliminary protocol called for the recording of the TEOAE in both non linear (NL) and linear (L) modes. Examination was performed in 347 newborns (30% of all the children born during 1997) the second day of life and during spontaneous sleep. The ILO 92 was used for the screening. The results obtained with the two methods were statistically compared using the 9 parameters considered response indicators. Using the linear method of a function-window and improving the signal-to-noise ratio, the study showed a significant difference in the quality of the TEOAE using the linear method as compared with the non linear method, although this did not modify response reliability. This lead to the definition, through free distribution statistical analysis, of broader than normal criteria by which to evaluate the responses evoked with the L method. All this is aimed at increasing system specificity and reducing the number of false positives which feeds family anxiety.

Acoustic Stimulation↗

PubMed2001

Computer-assisted image analysis-derived intermediate endpoints.

The development of prostatic lesions undergoes a slow progression. To establish efficacy of chemopreventive intervention it is therefore necessary to define surrogate endpoint biomarkers. Such biomarkers should be sensitive in their ability to indicate response. They should be objective, ie, the result of measurement, and numerically defined so that a statistical validation of response is possible. They should be able to indicate not only a halt of progression of a lesion, but also a reversal of progression. The spatial and statistical distribution of nuclear chromatin in the secretory and luminal cells in prostatic intraepithelial neoplastic lesions has been shown to be well defined. It can be represented by a set of features. These have been used to define a progression curve along which progression or regression of a lesion can be assessed. One could define a fixed endpoint, or one might choose to accept a statistically significant regression along the progression curve as criterion for chemopreventive efficacy. Expected difficulties could arise from lesion heterogeneity, as it would affect the sampling, and from multifocal lesions of differing progressions. Lesion heterogeneity thus limits the precision with which regression could be detected. These problems might be partially overcome by observations taken in histologically normal appearing regions of the prostate. The nuclear chromatin pattern of secretory cell nuclei measured in such tissue regions from prostates harboring intraepithelial or malignant lesions has been shown to exhibit distinctive changes from the chromatin pattern seen in secretory cell nuclei from prostates free from any such lesions. These changes appear to be expressed in the tissue up to a substantial distance from a lesion. The expression of changes in the nuclear chromatin suggests the existence of an intraepithelial preneoplastic lesion that can be detected by biomarkers, but which is not apparent from visual microscopic inspection. Since chemoprevention might be expected to be most effective at the earliest stages of lesion development, the assessment of such early alterations is seen as highly relevant to efforts to validate the efficacy of chemopreventive intervention.

Biomarkers, Tumor↗

PubMed1986

[Statistical patterns of the anomalous staining of 5-bromodeoxyuridine-substituted chromosomes].

Five large chromosome segments showing sometimes an abnormal staining were found in the genome of Chinese hamster (clone 237). Three types of abnormal staining were recorded. After one round of replication in the presence of BrdUrd these segments showed a hetero-staining, whereas after two rounds of replication the same segments showed iso-dark or iso-light staining. Pulse labeling with 3H-thymidine showed that all these segments were the late-replicating ones. The labeling proceeded according to all-or-none principle; in a given cell all five segments showed either presence or absence of the label. On the contrary, the abnormal staining was statistically distributed among these segments. These results are in disagreement with the current view that the abnormal staining is associated with asymmetrical distribution of thymine among two strands of DNA duplex. The above regularities are considered as an argument for the two-stranded model of chromosome.

Animals↗

PubMed1997

NMR analysis of main-chain conformational preferences in an unfolded fibronectin-binding protein.

A 130-residue fragment of the Staphylococcus aureus fibronectin-binding protein has been found to exist in a highly unfolded conformation at neutral pH. Measurement of experimental NMR 3JHNalpha coupling constants provides evidence for individual residues having distinct main-chain conformational preferences that are dependent both on the amino acid concerned and on neighbouring residues in the sequence. Analysis shows that these variations in the populations of individual residues can be explained in detail in terms of statistical distributions of conformational states derived from the protein data base. In particular, when the preceding residue has a beta-branched or aromatic side-chain, a significant increase occurs in the population of the less sterically restricted b region of phi,psi space. The results indicate that the local structure of the fibronectin binding protein in solution, under conditions where it displays full activity, approximates very closely to a statistical random coil structure. This may be an important feature in the biological role of this and other polypeptides involved in protein-protein interactions.

Adhesins, Bacterial↗

PubMed2002

Effective time averaging of multiplexed measurements: a critical analysis.

Multiplexing and time averaging of signal are effective noise reduction protocols applied in many analytical measurement systems. The efficacy of these protocols may be reduced by random occurrences of high-magnitude noise that do not conform to the statistical distribution of noise for all other measurements in the data set. This high-magnitude noise, which may have an insignificant probability of occurrence for a single measurement, almost certainly affects data collected in a multichannel, multiplexed modality, such as Fourier transform infrared (FT-IR) spectroscopic imaging employing focal plane array detectors. To recover time-averaging advantages in these cases, we present a general coaddition method that uses two statistical measures, the mean and median of the ensemble of measurements of a signal, to obtain a better estimate of the true signal than that estimated by time averaging alone. This method, termed median filtered time averaging, is shown to be an effective noise removal procedure for FT-IR imaging data. The effects of noise removal on time averaging and multiplexing are examined theoretically and are demonstrated for hyperspectral infrared microspectroscopic imaging data obtained from human skin biopsies by using a rapid data acquisition procedure.

Spectroscopy, Fourier Transform Infrared↗

PubMed1984

Estimation of cumulative exposures to ethylene oxide associated with hospital sterilizer operation.

The statistical distribution of exposures to ethylene oxide was estimated for a task involving transfer of materials from a hospital sterilizer. The exposure data are consistent with either a normal or log-normal distribution. It is shown how the single-task distribution and the number of task repetitions can be used to determine the minimum differences in task repetitions necessary to distinguish for epidemiological purposes between worker groups on the basis of cumulative exposure.

Environmental Exposure↗

PubMed1998

Evaluation of bioequivalence of highly variable drugs using clinical trial simulations. II: Comparison of single and multiple-dose trials using AUC and Cmax.

PURPOSE: Evaluating of the effects of high intrasubject variability in clearance (CL) and volume of distribution (V), on 90% confidence intervals (CIs) for AUC (Area Under the concentration Curve) in single and multiple-dose bioequivalence studies. The main methodology was Monte Carlo simulation, and we also used deterministic simulation, and examination of clinical trials. The results are compared with those previously observed for Cmax (maximum concentration.) METHODS: The time course of drug concentration in plasma was simulated using a one-compartment model with log-normal statistical distributions of intersubject and intrasubject variabilities in the pharmacokinetic parameters. Both immediate-release and prolonged-release products were simulated using several levels of intrasubject variability in single-dose and multiple-dose studies. Simulations of 2000 clinical bioequivalence trials per condition (138 conditions) with 30 subjects in each crossover trial were carried out. Simulated data were compared with data from actual bioequivalence trials. RESULTS: The current simulations for AUC show similar probabilities of failure for single-dose and multiple-dose bioequivalence studies, even with differences in the rate of absorption or fraction absorbed. AUC values from prolonged-release scenario studies are more sensitive to changes in the first order absorption rate constant ka, and to variability in CL and V than AUC from studies of immediate-release studies. CONCLUSIONS: We showed that multiple-dose designs for highly variable drugs do not always reduce intrasubject variability in either AUC or Cmax, although the behavior of AUC differs from Cmax. Single dose AUC to the last quantifiable concentration was more reliable than either single dose AUC extrapolated to infinity, or multiple dose AUC during a steady-state interval. Multiple-dose designs may not be the best solution for assessing bioequivalence of highly variable drugs.

Area Under Curve↗

PubMed1994

A statistical analysis of side-chain conformations in proteins: comparison with ECEPP predictions.

A comparison of the statistical distributions of side-chain conformations of 17 amino acids (Gly, Ala, and Pro excluded), observed in 63 nonhomologous globular proteins (covering 10,832 residues), is made with similar distributions calculated from the low-energy conformational states for the same amino acids (blocked with acetyl and N-methylamide groups at the N- and C-termini, respectively) obtained by Vásquez et al. [(1983), Macromolecules 16, 1043-1049] using the ECEPP/2 force field. Those residues (i) with linear side chains (Arg, Lys, Met, Cys, Ser), or those that are unbranched through the gamma-carbon atom (Glu, Gln) show good agreement, whereas (ii) those with side chains that are branched at C beta or C gamma show poor agreement with ECEPP calculations. A possible explanation for this is shown to be the greater tendency for side-chain atoms in class (ii) to interact with the backbone and/or adjacent side chains. Accordingly, ECEPP/3 calculations, carried out after elongating the backbone chain of the model peptide unit (by adding three Ala residues on each side of the central residue, and then blocking the termini as before), result in distributions that are often closer to the observed side-chain distributions. The implications of these results for the relative importance of short-range versus long-range interactions in determining protein structure are discussed.

Amino Acids↗