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PubMed2004

Sodium fraction excretion rate in nocturnal enuresis correlates with nocturnal polyuria and osmolality.

PURPOSE: We verify the sodium fraction excretion rate (FE Na) and potassium fraction excretion (FE K) rates in monosymptomatic nocturnal enuresis. We also correlate FE Na and FE K to urinary osmolality, nocturnal polyuria and vasopressin in the same population. MATERIALS AND METHODS: A total of 438 children 6 to 15 years old (mean age 9.7) presenting with monosymptomatic nocturnal enuresis were recruited from different centers. Inclusion criteria were 3 or greater wet nights a week, no daytime incontinence and no treatment in the previous 2 months. Exclusion criteria were cardiopathy, endocrinopathy, psychiatric problems and urinary tract abnormalities. Micturition chart, diurnal (8 am to 8 pm) and nocturnal (8 pm to 8 am) urine collection, including separate diuresis volumes, (Na, K and Ca) electrolytes and osmolality were evaluated, as well as serum electrolytes, creatinine and nocturnal (4 am) vasopressin. Diurnal and nocturnal FE K and FE Na were calculated. ANOVA test, chi-square test, Student's t test and Pearson correlation test were used for statistical analysis. RESULTS: : Nocturnal polyuria (diurnal to nocturnal diuresis ratio less than 1) was found in 273 children (62.3%, group 1 and nocturnal urine volumes were normal in 165 with enuresis (37.7%, group 2). Nocturnal FE Na was abnormal in 179 children (40.8%), including 118 in group 1 (43.2%) and 61 in group 2 (36.9%) (chi-square not significant). FE Na was also increased in nocturnal versus daytime diuresis (Student's t test p <0.001). In group 1 nocturnal FE Na correlated with nocturnal diuresis (Pearson correlation p = 0.003, r = +0.175), while daytime FE Na and nocturnal FE Na correlated with diurnal diuresis (Pearson correlation p = 0.001, r = +0.225 and Pearson correlation p = 0.001, r = +0.209, respectively). In group 2 nocturnal FE Na did not correlate with diuresis (Pearson correlation p = 0.103, r = +0.128) but correlated with vasopressin values (Pearson correlation p = 0.042, r = -0.205). Urine osmolality was reduced in 140 children (31.9%) and correlated with nocturnal diuresis (Pearson correlation p = 0.003, r = -0.321). Vasopressin was decreased in 332 children (75.8%, 62.6% in group 1 and 13.2% in group 2). No significant difference was found between sexes and age of enuretic subgroups. CONCLUSIONS: Nocturnal FE Na correlates with nocturnal diuresis, whereas daytime FE Na does not. FE K in daytime and nighttime diuresis does not statistically differ in nocturnal polyuric and nonpolyuric enuretic groups. Osmolality correlates with nocturnal diuresis, and vasopressin at 4 am was lower in the nocturnal polyuric group. The hypothesis of a subset of enuretic patients presenting with nocturnal polyuria associated with high nocturnal natriuria and low vasopressin values has been confirmed.

Adolescent↗

PubMed2006

Generalized correlation for biomolecular dynamics.

Correlated motions in biomolecules are often essential for their function, e.g., allosteric signal transduction or mechanical/thermodynamic energy transport. Because correlated motions in biomolecules remain difficult to access experimentally, molecular dynamics (MD) simulations are particular useful for their analysis. The established method to quantify correlations from MD simulations via calculation of the covariance matrix, however, is restricted to linear correlations and therefore misses part of the correlations in the atomic fluctuations. Herein, we propose a general statistical mechanics approach to detect and quantify any correlated motion from MD trajectories. This generalized correlation measure is contrasted with correlations obtained from covariance matrices for the B1 domain of protein G and T4 lysozyme. The new method successfully quantifies correlations and provides a valuable global overview over the functionally relevant collective motions of lysozyme. In particular, correlated motions of helix 1 together with the two main lobes of lysozyme are detected, which are not seen by the conventional covariance matrix. Overall, the established method misses more than 50% of the correlation. This failure is attributed to both, an interfering and unnecessary dependence on mutual orientations of the atomic fluctuations and, to a lesser extent, attributed to nonlinear correlations. Our generalized correlation measure overcomes these problems and, moreover, allows for an improved understanding of the conformational dynamics by separating linear and nonlinear contributions of the correlation.

Bacteriophage T4↗

PubMed1990

Effect of self-correlation on the relation between QT interval and cardiac cycle length.

The electrocardiographic QT interval, with a wide variety of practical and theoretic applications in medicine, pharmacology, and cardiology, is critically dependent on heart rate as expressed by cycle length (RR). To account for this and permit intraindividual and interindividual comparisons of changing QT intervals, a wide variety of formulas have been offered as single rate-correcting expressions over the range of heart rates. Yet as rate rises, the QT interval occupies more and more of the cycle length, until at the highest heart rates almost the entire cycle length is QT interval, and the QT-RR correlations become largely self-correlation. To elucidate this we investigated 150 consecutive patients divided into high, mid, and low rate terciles. For the entire group, and in each tercile, we determined the level of correlation between the QT interval and cycle length (RR interval). To remove the self-correlation, we repeated the calculations, correlating QT interval with RR interval minus QT interval. For the group, correlation (r) of QT with RR was 0.65. For the high, mid, and low rate terciles, correlation fell sharply, respectively: 0.58 to 0.36 to 0.25. When the self-correlation was removed by subtracting QT from cycle length (RR-QT), all correlations were even further sharply reduced for each tercile, respectively: 0.35, 0.16, and 0.03 (the latter being virtually no correlation). We conclude that at low heart rates, when it is not being correlated with itself, the correlation between QT and RR is low; at high heart rates the higher correlation is spurious because it is mainly self-correlation.

Electrocardiography↗

PubMed1991

A meta-analysis of reported correlations between prognostic factors in breast cancer: does axillary lymph node metastasis represent biology or chronology?

A statistical overview of published results on correlations between various prognostic factors in breast cancer was undertaken. A distinction was made between clinical (or anatomical) prognostic factors--namely, axillary lymph node status and tumour size--and eight different biological prognostic factors. The latter included: tumour grade, oestrogen and progesterone receptor status, thymidine labelling index, DNA ploidy, S-phase fraction, epidermal growth factor receptor expression and c-erbB-2 gene amplification (or overexpression). 139 articles were eligible for review which reported a total of 432 individual correlations. A simple form of meta-analysis was employed: the counting method, in which the number of studies achieving a statistically significant correlation or not were counted. For each possible correlation examined, the proportion of studies showing a statistically significant correlation was calculated and an exact binomial 99% confidence interval determined for that proportion. If the 99% confidence interval included 5% (the proportion of correlations that would be expected to be statistically significant if the null hypothesis was true), it was taken as failing to exclude the null hypothesis of a zero correlation, while if it excluded 5% it was taken as rejecting the null hypothesis of a zero correlation. A broad agreement was found among published reports on the existence of a statistically significant correlation between the various biological prognostic factors in breast cancer. Of the 20 correlations examined, 18 had a 99% confidence interval excluding 5%, thus rejecting the null hypothesis of a zero correlation. On the other hand, a completely different result was obtained when reports on possible correlations between lymph node status and tumour size on the one hand and the eight biological prognostic factors on the other were analysed. Of the 16 correlations examined, 13 had a 99% confidence interval including 5%, failing to reject the null hypothesis of a zero correlation. These observations suggest the hypothesis that the prognostic influence of node status and tumour size cannot be explained by an analysis of the biology of breast cancer; and is compatible with the contention that axillary node status is merely a reflection of the relative chronological age of breast cancer.

Breast Neoplasms↗

PubMed2003

Correlations of amino acids in proteins.

A correlation analysis among 20 amino acids is performed for four protein structural classes (alpha, beta, alpha/beta, and alpha+beta) in a total of 204 proteins. The correlation relationships among amino acids can be classified into the following four types: (1) strong positive correlation, (2) strong negative correlation, (3) weak correlation, and (4) no correlation. The correlation relationships are different for different proteins and are correlated with the features of their structural classes. The amino acids with the weak correlation relationship can be treated as the independent basis functions for the space where proteins are defined. The amino acids with large correlation coefficients are linear correlative with each other and they are not independent. The strong correlation among amino acids reflects their mutual constrained relationship, as exhibited by their relevant structural features. The information obtained through the correlation analysis is used for predicting protein structural classes and a better prediction quality is obtained than that by the simple geometry distance methods without taking into account the correlation effects.

Amino Acids↗

PubMed1999

Correlations between neural discharges are related to receptive field properties in cat primary auditory cortex.

The functional role of correlated neural activity in auditory cortex for the processing of sounds was explored by investigating whether and how cross-correlation parameters are related to receptive field similarities of neurons. Multi-unit activity was recorded simultaneously from several sites of isofrequency domains in primary auditory cortex. At each site various receptive field properties were determined. From the discharges of pairs of clusters, normalized cross-correlation histograms (CCH) were calculated for extended periods of spontaneous activity and for periods with noise-burst stimulation. In both conditions, most CCHs exhibited a symmetrical positivity near the origin of the CCH, a few to several tens of milliseconds wide. Cross-correlation histograms were characterized with two parameters: the correlation strength, which was estimated from the peak correlation, and the correlation width, i.e. the time period of correlated firing, which was measured as the width of the positivity at half height. It was found that correlation strength increased and correlation width narrowed with increasing similarity of the receptive fields of two clusters. These relationships were observed both in the acoustically-driven and spontaneous conditions. Specifically, correlation strength was most strongly associated with similarity in binaural interaction and in temporal response properties such as response onset, response offset and the temporal pattern of the response. Correlation width was predominantly associated with similarity in characteristic frequency, bandwidth and intensity threshold. Results suggest that correlated activity, reflecting potential mechanisms involved in the neural computation in auditory cortex, provides a means to evaluate the properties of the functional organization of auditory cortex. Systematic relationships were found between correlation properties and the receptive field-based organization of cortical processing, suggesting that similar general mechanisms are utilized in many parts of the sensory cortex. In particular, the magnitude and/or the time period of synchronized firing of neurons is increased if the receptive field properties of the involved neurons are similar.

Acoustic Stimulation↗

PubMed2004

Correlated measurement error--implications for nutritional epidemiology.

BACKGROUND: In nutritional epidemiology, it is common to fit models in which several dietary variables are included. However, with standard instruments for dietary assessment, not only are the intakes of many nutrients often highly correlated, but the errors in the estimation of the intake of different nutrients are also correlated. The effect of this error correlation on the results of observational studies has been little investigated. This paper describes the effect on multivariate regression coefficients of different levels of correlation, both between the variables themselves and between the errors of estimation of these variables. METHODS: Using a simple model for the multivariate error structure, we examine the effect on the estimates of bivariate linear regression coefficients of (1) differential precision of measurement of the two independent variables, (2) differing levels of correlation between the true values of the two variables, and (3) differing levels of correlation between the errors of measurement of the two variables. As an example, the prediction of plasma vitamin C levels by dietary intake variables is considered, using data from the European Prospective Investigation of Cancer (EPIC) Norfolk study in which dietary intake was estimated using both a food frequency questionnaire (FFQ) and a 7-day diary (7DD). The dietary variables considered are vitamin C, fat, and energy, with different approaches taken to energy adjustment. RESULTS: When the error correlation is zero, the estimates of the bivariate regression coefficients reflect the precision of measurement of the two variables and mutual confounding. The sum of the observed regression coefficients is biased towards the null as in univariate regression. When the error correlation is non-zero but below about 0.7, the effect is minor. However, as the error correlation increases beyond 0.8 the effect becomes large and highly dependent on the relative precision with which the two variables are measured. At the extreme, the bivariate estimates can become indefinitely large. In the example, the error correlation between fat and energy using the FFQ appears to be over 0.9, the corresponding value for the 7DD being approximately 0.85. The error correlation between vitamin C and fat, and vitamin C and energy, appears to be below 0.5 and smaller for the 7DD than for the FFQ. The impact of these error correlations on bivariate regression coefficients is large. The effect of energy adjustment differs widely between vitamin C and fat. CONCLUSION: High levels of error correlation can have a large effect on bivariate regression estimates, varying widely depending on which two variables are considered. In particular, the effect of energy adjustment will vary widely. For vitamin C, the effect of energy adjustment appears negligible, whereas for fat the effect is large indicating that error correlation close to one can partially remove regression dilution due to measurement error. If, for fat intake, energy adjustment is performed by using energy density, the partial removal of regression dilution is achieved at the expense of substantial reduction in the true variance.

Ascorbic Acid↗

PubMed1989

[Ultrastructural study of left ventricular myocardium in mitral regurgitation--correlations with postoperative cardiac functions].

Light and electron microscopic examination was carried out in tissue samples which were obtained from the left ventricular free wall in 21 patients with mitral regurgitation during open-heart surgery. Their correlations with postoperative cardiac functions were also studied. The area of the interstitial fibrosis (%fib) was calculated from the light microscopic examination of the tissue samples, and changes of intracellular structures were expressed in scores by means of electron microscopy (EM-SCORE). Postoperative hemodynamics were studied with echocardiography before and after exercise. The hemodynamic parameters consisted of SVI, CI, EF, FS, mVcf and percent changes of these parameters before and after exercise. 1. EM-scores correlated with EF, FS and mVcf at rest with correlation coefficient of -0.653, -0.629 and -0.712 respectively and their significant levels were all less than 0.005. They also correlated with EF, FS and mVcf after exercise with correlation coefficient of -0.665 and -0.708 respectively and their significant levels were all less than 0.005. They also correlated with %delta EF, %delta FS and %delta Vcf with correlation coefficient of -0.79, -0.76 and -0.811 respectively and their significant levels were all less than 0.005. 2. Percent fibrosis did not correlated with the hemodynamics at rest. But they correlated with EF, FS after exercise with correlation coefficient of -0.577 and -0.599 respectively and their significant level reached less than 0.01. They also correlated with %delta EF, %delta FS and %delta mVcf with correlation coefficient of -0.584, -0.599 and -0.571 respectively and their significant levels were all less than 0.01. 3. There were no correlations between EM-score and %fib. 4. There were significant correlations between left ventricular function and myocardial morphology, in patients with mitral regurgitation. The patients with EM-score over 7 and %fib. over 14% showed poor left ventricular function and poor cardiac reserve postoperatively.

Adult↗

PubMed2004

Correlation of bone marrow lipid water content with bone mineral density on the lumbar spine.

STUDY DESIGN: Prospective study. OBJECTIVES: To assess the proton MR spectroscopy (1H MRS) of vertebral bone marrow and correlate the lipid water ratio (LWR) and spectral line width (LW) with bone mineral density (BMD) in female subjects. SUMMARY OF BACKGROUND DATA: The mechanism of bone marrow fat accumulation and bone mineral content is poorly understood. Proton MR spectroscopy was used to demonstrate the lipid and water spectra in the bone marrow. We try to assess the possible interaction between the bone marrow lipid content, aging, and BMD. METHODS: Proton MRS and BMD of the lumbar spine were performed in 52 female subjects (mean age, 58 years; SD, 10 years). They were 13 premenopausal and 39 postmenopausal women. The BMD (g/cm2) was measured using dual energy radiograph absorptiometry at the lumbar spine. Single voxel 1H MRS was measured at L3 vertebral body by stimulated echo-acquisition mode (STEAM) sequence and demonstrated two major peaks (lipid and water). Comparisons of the differences between the two subgroups were made. Pearson's correlation was also calculated to explore the association of 1H MRS measurements with age and BMD. Partial correlation was further conducted when controlling the variable such as age or BMD. RESULTS: BMD and LWR had statistically significant difference between the pre- and postmenopausal subgroups (P < 0.001), while lipid LW had a borderline difference and water LW had no difference. LWR was positively correlated with age (r = 0.52 and P < 0.0001) and negatively correlated with BMD (r = -0.40 and P = 0.003) for all the subjects. Lipid LW was negatively correlated with age (r = -0.32 and P = 0.0197) and positively correlated with BMD (r = 0.67 and P < 0.0001). When controlling for BMD effect, only LWR is statistically correlated with age (partial r = 0.39, P = 0.0045), while only the lipid LW is statistically correlated with BMD when controlling for age (partial r = 0.63, P < 0.0001). None of the correlations between water LW and age or BMD was significant. In the subgroups, only the lipid LW is significantly correlated with BMD (r = 0.78, P = 0.0016 in premenopausal women; r = 0.62, P < 0.0001 in postmenopausal women). CONCLUSION: The LWR had a positive correlation with the age, while the lipid LW had a positive correlation with BMD, even after controlling the age factor. The bone marrow lipid water content and metabolism acted as important roles in the internal environment of bone and influenced bone mineralization.

Absorptiometry, Photon↗

PubMedDate not supplied

Determining extreme parameter correlation in ground water models.

In ground water flow system models with hydraulic-head observations but without significant imposed or observed flows, extreme parameter correlation generally exists. As a result, hydraulic conductivity and recharge parameters cannot be uniquely estimated. In complicated problems, such correlation can go undetected even by experienced modelers. Extreme parameter correlation can be detected using parameter correlation coefficients, but their utility depends on the presence of sufficient, but not excessive, numerical imprecision of the sensitivities, such as round-off error. This work investigates the information that can be obtained from parameter correlation coefficients in the presence of different levels of numerical imprecision, and compares it to the information provided by an alternative method called the singular value decomposition (SVD). Results suggest that (1) calculated correlation coefficients with absolute values that round to 1.00 were good indicators of extreme parameter correlation, but smaller values were not necessarily good indicators of lack of correlation and resulting unique parameter estimates; (2) the SVD may be more difficult to interpret than parameter correlation coefficients, but it required sensitivities that were one to two significant digits less accurate than those that required using parameter correlation coefficients; and (3) both the SVD and parameter correlation coefficients identified extremely correlated parameters better when the parameters were more equally sensitive. When the statistical measures fail, parameter correlation can be identified only by the tedious process of executing regression using different sets of starting values, or, in some circumstances, through graphs of the objective function.

Models, Theoretical↗

PubMed2002

Detection of static and dynamic changes in interaural correlation.

This study examines the relation between a static and a dynamic measure of interaural correlation discrimination: (1) the just noticeable difference (JND) in interaural correlation and (2) the minimum detectable duration of a fixed interaural correlation change embedded within a single noise-burst of a given reference correlation. For the first task, JNDs were obtained from reference interaural correlations of + 1, -1, and from 0 interaural correlation in either the positive or negative direction. For the dynamic task, duration thresholds were obtained for a brief target noise of +1, -1, and 0 interaural correlation embedded in reference marker noise of +1, -1, and 0 interaural correlation. Performance with a reference interaural correlation of +1 was significantly better than with a reference correlation of -1. Similarly, when the reference noise was interaurally uncorrelated, discrimination was significantly better for a target correlation change towards +1 than towards -1. Thus, for both static and dynamic tasks, interaural correlation discrimination in the positive range was significantly better than in the negative range. Using the two measures, the length of a binaural temporal window was estimated. Its equivalent rectangular duration (ERD) was approximately 86 ms and independent of the interaural correlation configuration.

Adult↗

PubMedDate not supplied

Correlates of low bone density in females with anorexia nervosa.

UNLABELLED: The objectives were to delineate those factors which correlate with low bone density in patients with anorexia nervosa and in turn to predict those at greatest risk for osteopenia. DESIGN: Bone density was evaluated by dual energy x-ray absorptiometry in 28 postmenarchal females with anorexia nervosa who had never received hormonal therapy. Bone density results were correlated with specific historical and physical factors utilizing descriptive statistics, scatter plots, and the Spearman correlation coefficient. RESULTS: Mean age was 18.6 years, mean age at menarche was 12.9 yrs, mean length of illness was 19.8 months and mean duration of amenorrhea was 13.4 months. Mean % ideal body weight was 84% at the time of bone density, 75% at minimum weight and 100% at maximum weight. Mean lumbar spine bone density was -1.69 standard deviations from the norm; mean lateral spine bone density was -1.45 standard deviations from the norm; mean femoral neck of the hip bone density was -1.18 standard deviations from the norm. There was a strong negative correlation between duration of amenorrhea and bone density at the lumbar spine (r = -0.50, p < .01) and a mild correlation at the lateral spine (r = -0.49, p < 0.05) and femoral neck (r = -0.41, p < 0.05). There was also a strong negative correlation between length of illness and bone density at the lumbar spine (r = -0.53, p < 0.01) and lateral spine (r = -0.77, p < 0.0001), and a mild correlation with the femoral neck (r = -0.48, p < 0.05). Scatter plots of lumbar bone density versus duration of amenorrhea, and versus length of illness clearly showed not only that longer duration of amenorrhea and longer length illness correlated to bone loss, but also strikingly that within a short time of being ill and amenorrheic, significant bone loss was seen. Age, and age at menarche correlated mildly with osteopenia at the lateral spine; age correlated mildly with osteopenia at the femoral neck as well. There was a trend for minimum BMI to correlate with osteopenia at the lateral spine. There were no correlations of bone density with % IBW at bone density, minimum % IBW, maximum % IBW, change in % IBW, BMI at the time of the bone density, maximum BMI or change in BMI. CONCLUSIONS: Low bone density, especially in the lumbar spine, correlated with both a longer duration of amenorrhea and longer length of illness, but not with other factors, in our patients with anorexia nervosa. As many of these patients, even those with a short duration of illness and amenorrhea, were osteopenic, it is advisable to continue to perform bone density studies in all patients with anorexia nervosa, on both a clinical and research basis.

Adolescent↗

PubMed1985

Estimates of genetic correlations between testicular measurements and female reproductive traits in cattle.

Data from 528 male and 645 female progeny of 63 sires were used to estimate genetic correlations between female and male reproductive traits. Data were from two Hereford herds involved in a long-term selection program of the North Carolina Agricultural Experiment Service. Testicular measurements of circumference, diameter, length and volume were obtained on bulls at 205 and 365 d. Testicular growth measures were defined as differences between 205-and 365-d measurements. Heifers were placed in the breeding herd as yearlings and given two breeding seasons to produce a calf. Traits utilized from females were three age-at-first-breeding traits, two age-at-first-calving traits, two pregnancy rate traits, rebreeding interval and calving interval. Genetic correlations were estimated from half-sib and from sire-daughter analyses. Seventy-five percent or more of the correlations of testicular measurements with pregnancy rats, age at first breeding and age at first calving were in the favorable direction. Average correlations were .62, -.55 and -.66, respectively. For each of the remaining female traits, approximately 50% of the correlations were favorable and the average correlations were small. Correlations were summarized by testicular measurement with favorable correlations given a negative sign. Testicular diameter had more favorable correlations (80%) than length, volume or circumference (70%). However, average correlations were similar (-.31, -.30, -.34 and -.26, respectively). Testicular measurements taken at either 205 or 365 d had the same percentage of favorable correlations (72%), while testicular growth measurements had a slightly higher percentage of favorable correlations (78%). Average correlations of 365-d measures were higher (-.38) than either 205-d or growth measures (-.25 and -.28, respectively). Heritabilities for testicular measurements tended to be moderate to high, while those for female reproduction tended to be low to moderate. These results suggest that selection for increased testicular size would lead to improvement in female reproduction, particularly an increase in calving rate and a decrease in age at first breeding.

Animals↗

PubMedDate not supplied

In vitro/in vivo correlations: scientific implications and standardisation.

In vitro/in vivo correlations and the parameters that should be correlated have now been well defined in the USP and FDA working group proposals. Among the three levels of correlation defined, Level A is the most interesting one. In this paper, the Level A correlation is studied from a mathematical and a biopharmaceutical point of view. The conditions that must be met before attempting to establish correlations and the place of in vitro/in vivo correlation in modified release drug dosage form development are discussed. To establish in vitro/in vivo correlations requires a strict development methodology in order to obtain them in the most favourable conditions. In vitro/in vivo correlations should be sought as early as possible during the dosage form development (a priori correlations). If the formulation has been undertaken first and correlations sought on the finished product from subsequent in vitro tests, the predictive power of these correlations (a posteriori correlations) is thus limited and they require additional validation.

Animals↗

PubMed1995

Sibling correlations of coronary heart disease risk factors in a sample of Israeli offspring with parental history of myocardial infarction.

Sibling correlations for coronary heart disease risk factors were analyzed in 731 pairs of siblings whose parents experienced a first myocardial infarction. Sibling correlations for lipids, lipoproteins and apolipoproteins ranged from 0.29 to 0.48, with limited changes on adjustment for sex, age, education and body mass index. For most lipid variables brother-brother correlation coefficients were highest and sister-brother correlation coefficients were lowest. Sib-sib correlation coefficients for lipids, lipoproteins, blood pressure and body mass index were similar to those estimated from a random sample of Jewish families. The sibling correlations were relatively low for waist to hip ratio, triceps and suprailiac skinfolds, moderate for subscapular skinfolds and body circumference measurements and high for number of cigarettes smoked by the siblings. The sibling correlations for lipid variables showed a moderate dependency on the apolipoprotein B XbaI genotypes. Siblings living in the same household tended to have higher correlation coefficients for HDL-C, apolipoprotein B and apolipoprotein AI than those living apart. The correlation coefficients for number of cigarettes and anthropometric variables tended to be heterogeneous due to the higher correlations among siblings living apart. A clear trend of decline in sib-sib correlations for apolipoprotein AI, glucose, cigarette smoking, body mass index and circumference measurements with increased spacing between sibling's ages was indicated. This temporal trend in sibling correlations for coronary heart disease risk factors suggests that genetic and/or environmental factors may have different influences at different ages.

Adult↗

PubMed2006

Detection of interaural correlation by neurons in the superior olivary complex, inferior colliculus and auditory cortex of the unanesthetized rabbit.

A critical binaural cue important for sound localization and detection of signals in noise is the interaural time difference (ITD), or difference in the time of arrival of sounds at each ear. The ITD can be determined by cross-correlating the sounds at the two ears and finding the ITD where the correlation is maximal. The amount of interaural correlation is affected by properties of spaces and can therefore be used to assess spatial attributes. To examine the neural basis for sensitivity to the overall level of the interaural correlation, we identified subcollicular neurons and neurons in the inferior colliculus (IC) and auditory cortex of unanesthetized rabbits that were sensitive to ITDs and examined their responses as the interaural correlation was varied. Neurons at each brain level could show linear or non-linear responses to changes in interaural correlation. The direction of the non-linearities in most neurons was to increase the slope of the response change for correlations near 1.0. The proportion of neurons with non-linear responses was similar in subcollicular and IC neurons but increased in the auditory cortex. Non-linear response functions to interaural correlation were not related to the type of response as determined by the tuning to ITDs across frequencies. The responses to interaural correlation were also not related to the frequency tuning of the neuron, unlike the responses to ITD, which broadens for neurons tuned to lower frequencies. The neural discriminibility of the ITD using frozen noise in the best neurons was similar to the behavioral acuity in humans at a reference correlation of 1.0. However, for other reference ITDs the neural discriminibility was more linear and generally better than the human discriminibility of the interaural correlation, suggesting that stimulus rather than neural variability is the basis for the decline in human performance at lower levels of interaural correlation.

Animals↗

PubMed2004

Wavefront analysis in post-LASIK eyes and its correlation with visual symptoms, refraction, and topography.

PURPOSE: To evaluate the information assessed with the LADARWave wavefront measurement device and correlate it with visual symptoms, refraction, and corneal topography in previously LASIK-treated eyes. PARTICIPANTS: One hundred five eyes (58 patients) of individuals who underwent LASIK surgery were evaluated. DESIGN: Retrospective, noncomparative case series. MAIN OUTCOME MEASURES: Complete ophthalmologic examination, corneal topography, and wavefront measurements were performed. Correlations were made between the examinations and symptoms. METHODS: Wavefront measurements were assessed with the LADARWave device. Manifest, cycloplegic refraction, and topographic data were compared with wavefront refraction and higher order aberrations. Visual symptoms were correlated to higher order aberrations in 3 different pupil sizes (5-mm, 7-mm, and scotopic pupil size). Pearson's correlation coefficient and generalized estimating equations were used for statistical analysis. RESULTS: In post-LASIK eyes, wavefront refraction components were poorly correlated to manifest and cycloplegic components. The comparison between manifest, cycloplegic, and wavefront refraction with total amount of higher order aberrations showed no strong correlation. The comparison between topography and manifest, cycloplegic, and wavefront refraction did not show strong correlation. Visual symptoms analysis showed correlation of double vision with total coma and with horizontal coma for the 5-mm and 7-mm pupil size; correlation between starburst and total coma for the 7-mm pupil size; and correlation of double vision with horizontal coma, glare with spherical aberrations and with total aberrations, and starburst with spherical aberrations for the scotopic pupil size. Scotopic pupil size had a positive association with starburst and a negative association with double vision. CONCLUSIONS: The LADARWave wavefront measurement device is a valuable diagnostic tool in measuring refractive error with ocular aberrations in post-LASIK eyes. A strong correlation between visual symptoms and ocular aberrations, such as monocular diplopia with coma and starburst and glare with spherical aberration, suggest this device is valuable in diagnosing symptomatic LASIK-induced aberrations. Horizontal coma was correlated with double vision, whereas vertical coma was not.

Adult↗

PubMed2004

Binocular correlation does not improve coherence detection for fronto-parallel motion.

We studied the low-level interactions between motion coherence detection and binocular correlation detection. It is well-established that e.g. depth information from motion parallax and from binocular disparities is effectively integrated. The question we aimed to answer is whether such interactions also exist at the very first correlation level that both mechanisms might have in common. First we quantitatively compared motion coherence detection and binocular correlation detection using similar stimuli (random pixels arrays, RPAs) and the same noise masking paradigm (luminance signal to noise ratio, LSNR). This showed that human observers are much more sensitive to motion than to binocular correlation. Adding noise therefore has a much stronger effect on binocular correlation than on motion detection. Next we manipulated the shape of the stimulus aperture to equalize LSNR thresholds for motion and binocular correlation. Motion sensitivity could be progressively reduced by shortening the length of the motion path, while keeping the aperture area constant. Changing the shape of the aperture did not affect binocular correlation sensitivity. A 'balanced' stimulus, one with equal strengths of motion and binocular correlation signals was then used to study the mutual interactions. In accordance with previous results, motion was found to greatly facilitate binocular correlation. Binocular correlation, however did not facilitate motion detection. We conclude that interactions are asymmetrical; fronto-parallel motion is primarily detected monocularly and this information can then be used to facilitate binocular correlation, but binocular correlation cannot improve motion sensitivity.

Adult↗