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PubMed1999

Do P-glycoprotein and major vault protein (MVP/LRP) expression correlate with in vitro daunorubicin resistance in acute myeloid leukemia?

Two proteins that have been correlated with the occurrence of multidrug resistance in acute myeloid leukemia (AML) are P-glycoprotein (Pgp) and the major vault protein (Mvp/LRP). With the purpose of further quantifying the potential contributions of Pgp-mediated drug efflux and Mvp/LRP to drug resistance in AML we have investigated whether the transport function of Pgp and the expression of Mvp/LRP correlated with the accumulation of daunorubicin (DNR) and the in vitro resistance to DNR cytotoxicity (LC50 by MTT assay) in AML cells. In de novo adult AML, the steady-state DNR accumulation (in pmol/10(6) cells) correlated with Pgp activity or expression, whereas the LC50 for DNR did not correlate with Pgp activity (measured as the modulation of rhodamine 123 or DNR accumulation by the Pgp inhibitor PSC833) or Pgp expression (measured by flow cytometry with the MRK-16 antibody). The contribution of MRP1 expression to a reduced DNR accumulation seems minor compared to Pgp. In addition, the modulation of the DNR LC50 by PSC833 did not correlate with Pgp protein or activity. The steady-state DNR accumulation showed no correlation with the DNR LC50. The Mvp/LRP expression (immunocytochemical staining) did neither correlate with DNR accumulation nor with the DNR LC50. A significant negative correlation was seen between the Mvp/LRP immunocytochemical staining and Pgp activity, indicating that both markers define (partially) different populations. In conclusion, it is shown that Pgp function, but not Mvp/LRP or MRP1 expression correlate with a low steady-state DNR accumulation in de novo AML. The Pgp activity does, however, not predict the DNR sensitivity in AML measured as in vitro DNR LC50 with an MTT-based assay. The reason for that seems to be that a low DNR accumulation may not be the most important factor in determining the LC50. While the clinical usefulness of these drug resistance tests remains to be proven they do not seem to provide as yet a straightforward explanation for the major cause(s) of clinical chemotherapy failure.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2005

Two-dimensional (2D) correlation coefficient analyses of heavily overlapped near-infrared spectra.

Two-dimensional (2D) correlation coefficient analysis is employed to classify and characterize spectral variations among heavily overlapped near-infrared spectra of pellets and films of three kinds of polyethylene (PE), high-density (HD), low density (LD), and linear low-density (LLD) polyethylene, and five kinds of ivory signature seals. The sample-sample (SS) 2D correlation maps are used for classification while the wavenumber-wavenumber (WW) 2D correlation maps are used for determining spectral variation among the above materials. Both correlation maps are obtained by multiplying the original data with themselves. It is found that the NIR spectra of pellets and films of HD PE are clearly different from those of LD PE and LLD PE, while the NIR spectra of five kinds of ivory seals yield easily discernable squares in the SS correlation maps. The background variation is thought to be behind the differentiation of the PE samples because the WW correlation maps do not indicate appearance of new bands. The correlation results are compared with those of principal component analysis (PCA). This study is a novel application of 2D correlation coefficient analysis which reveals that a comprehensive description of demanding spectral systems is achievable by utterly simple mathematical means because 2D correlation maps are obtained via a single mathematical operation.

Animals↗

PubMed2003

[Determination of Reliability of Psychometric Tests in Psychiatry Using Canonical Correlation]

Test results (raw scores) are composed of an unknown true score and an error term. The error term can be estimated by means of test reliability which is defined by the ratio of true variance and obtained variance. Different estimates of reliability either based on single measurements (e. g. Cronbach's coefficient, split half reliability, Kuder Richardson method) or two measurements (test/retest, inter- or intrarater reliability) are available. Parallel test reliability depends on the correlation of two different tests obtained in one session. Canonical correlation methods allow an extension of the parallel test situation and split half technique. Two or more tests are performed in a sample of subjects. Randomized subsets are correlated using canonical correlation technique. The objective of this study is to estimate the homogeneity of test batteries. 94 patients (64 f, 30 m; age: 54 - 89 ys.) supposed to have dementia were tested using the clocktest (CT, scores: 1 - 5), MMSE (mini mental state examination) and SKT (Syndrom Kurztest). Four (i, j: 1 - 4) subsets of 20 patients each were determined by random and the following characteristics were calculated: Empiric correlation coefficient for n = 94 (R), canonical correlation coefficient (Rcan), eigenvalues (EV) and redundancy (Rnd) of corresponding variable sets. The results of canonical analysis showed canonical correlation coefficients in order of 0.8 to 0.9 (p-values < 0,001). This high internal consistency can be interpreted as a measure of reliability of the test batteries. In conclusion, canonical correlation based on parallel tests splitted in subsets gives information on consistency, i. e. reliability, of test batteries in addition to conventional correlation methods.

Journal Article↗

PubMed2005

Effect of the one-body potential on interelectronic correlation in two-electron systems.

The correlation energies of the helium isoelectronic sequence (IS) and of Hooke's IS are very similar and are both weakly increasing upon increasing the nuclear charge/force constant, respectively. However, their separation into radial and angular correlations shows interesting differences. First, for intermediate (and high) values of the force constant radial correlation in Hooke's IS is surprisingly low. Second, both systems exhibit a decrease in the relative contribution of radial versus angular correlation upon strengthening the one-body attractive potential; however, unlike the helium IS, in Hooke's IS the radial correlation energy increases in absolute value upon strengthening the attractive one-body potential. The contribution of radial correlation to the Coulomb hole is examined and the asymptotic behavior at both strong and weak attractive potentials is considered. Radial correlation in Hooke's IS is found to constitute about 9.3% of the total correlation energy when the spring constant approaches the limit k-->infinity, but 100% of the total correlation energy for k-->0. Our results highlight both the similarities and the differences between the helium and Hooke's ISs.

Journal Article↗

PubMed2006

Combining explicitly correlated R12 and Gaussian geminal electronic structure theories.

Explicitly correlated R12 methods using a single short-range correlation factor (also known as F12 methods) have dramatically smaller basis set errors compared to the standard wave function counterparts, even when used with small basis sets. Correlations on several length scales, however, may not be described efficiently with one correlation factor. Here the authors explore a more general MP2-R12 method in which each electron pair uses a set of (contracted) Gaussian-type geminals (GTGs) with fixed exponents, whose coefficients are optimized linearly. The following features distinguish the current method from related explicitly correlated approaches published in the literature: (1) only two-electron integrals are needed, (2) the only approximations are the resolution of the identity and the generalized Brillouin condition, (3) only linear parameters are optimized, and (4) an arbitrary number of (non-)contracted GTGs can appear. The present method using only three GTGs and a double-zeta quality basis computed valence correlation energies for a set of 20 small molecules only 2.2% removed from the basis set limit. The average basis set error reduces to 1.2% using a near-complete set of seven GTGs with the double-zeta basis set. The conventional MP2 energies computed with much larger quadruple, quintuple, and sextuple basis sets all had larger average errors: 4.6%, 2.4%, and 1.5%, respectively. The new method compares well to the published MP2-R12 method using a single Slater-type geminal (STG) correlation factor. For example, the average basis set error in the absolute MP2-R12 energy obtained with the exp(-r12) correlation factor is 1.7%. Correlation contribution to atomization energies evaluated with the present method and with the STG-based method only required a double-zeta basis set to exceed the precision of the conventional sextuple-zeta result. The new method is shown to always be numerically stable if linear dependencies are removed from the two-particle basis and the zeroth-order Hamiltonian matrix is made positive definite.

Journal Article↗

PubMed2000

Spatial correlation analysis of atrial activation patterns during sustained atrial fibrillation in conscious goats.

In this study we applied both linear and nonlinear spatial correlation measures to characterize epicardial activation patterns of sustained atrial fibrillation in instrumented conscious goats. It was investigated if nonlinearity was involved in the spatial coupling of atrial regions and to what extent fibrillation was organized in the experimental model of sustained atrial fibrillation (AF) in instrumented goats. Data were collected in five goats during experiments to convert AF by continuous infusion of cibenzoline. Spatial organization during AF was quantified with the linear spatial cross correlation function and the nonlinear spatial cross redundancy which was calculated using the Grassberger-Procaccia correlation integral. Two different types of correlation were evaluated to distinguish simultaneous interaction from non-simultaneous interaction, for instance resulting from propagation of fibrillation waves. The nonlinear association length and the linear correlation length were estimated along the principal axes of iso-correlation contours in two-dimensional correlation maps of the nonlinear spatial redundancy and the linear spatial correlation function, respectively. To quantitatively assess the degree of nonlinearity, the association length was also estimated from the linearized spatial redundancy using multivariate surrogate data. The differences between the nonlinear and linearized association lengths indicated that a nonlinear component in the spatial organization of AF predominantly existed in the right atrium. The degree of organization characterized by association length along the short principal axis was higher in the right atrium (15 +/- 7 mm) than in the left atrium (8 +/- 4 mm). The spatial extension of coherent atrial patches was estimated from a surface of association equal to the area spanned by the principal axes of iso-correlation contours from the redundancy, including the effects from non-simultaneous interaction. Interpreting this area as the spatial domain of a fibrillation wavelet, the results suggest that the mapped region was activated on average by two wavelets in the left atrium and by one wavelet in the right atrium. Therefore, the activation pattern of sustained AF in goats was relatively organized, consistent with type II of AF. It is suggested that the surface of association is a measure of the number of independent wavelets present in the atria during sustained AF, and that larger association lengths result from fewer and larger reentrant circuits.

Animals↗

PubMed2003

A cautionary tale of two statistics: partial correlation and standardized partial regression.

Partial correlation and standardized partial regression are widely used to control for other variables in cross-sectional and longitudinal studies. Two aspects of these statistics can radically alter the interpretation of data and so deserve attention. First, their sign will be opposite to that of the original zero-order correlation when this correlation is of the same sign as and smaller than the product of the other 2 correlations. Second, their size will be considerably larger than a weak zero-order correlation when either that correlation is positive and the product of the other 2 correlations is negative or that correlation is negative and the product of the other 2 correlations is positive. The first aspect is illustrated with data from J. M. Gottman and L. J. Krokoff (1989) on initial conflict behavior and initial and later marital satisfaction, and the 2nd aspect is illustrated with data from C. L. Heavey, C. Layne, and A. Christensen (1993) on the same issue. Their interpretation of their findings is questioned.

Conflict, Psychological↗

PubMedDate not supplied

Familial correlations for serial measurements of recumbent length and stature.

Familial correlation coefficients were calculated for recumbent length or stature measured serially on participants in the Fels Longitudinal Growth Study and for short-term serial or cross-sectional measurements on relatives of participants. Pairs of relatives are compared at the same chronological ages from 1 to 18 years in 1-year increments and again in adulthood. First-degree relatives are more similar than second- or third-degree relatives at all ages. Sibling correlations are consistently higher than parent-offspring correlations, except after age 15, when they become very similar. For the most part, these results agree with those of cross-sectional studies finding higher sibling than parent-offspring correlations. Familial correlations tend to decrease during adolescence, perhaps due to differences among relatives in timing of growth spurts. Trends observed in bivariate plots of correlations over age are confirmed by multivariate analysis of correlations for different types of relatives at different ages. The largest amount of variation in familial correlations is due to the degree of relationship, although the amount of genetic similarity is difficult to separate from the effects of common family environment and generational differences. Age, sex and generation also play a role in multivariate prediction of the magnitude of familial correlations.

Adolescent↗

PubMed2004

Correlated evolution in fig pollination.

This is the first comparative study of correlated evolution between figs (Ficus species, Moraceae) and their pollinators (Hymenoptera: Agaoninae) based on molecular phylogenies of both lineages. Fig relationships based on the internal transcribed spacer region (ITS) of nuclear ribosomal DNA and pollinator relationships inferred from mitochondrial cytochrome oxidase I (COI) sequences enabled the study of correlated evolution based on molecular phylogenies for the largest set of interacting species ever compared. Comparative methods have been applied to tests of adaptation, but the application of these methods in tests of coadaptation, defined as reciprocal evolutionary change in interacting lineages, has received less attention. I have extended tests of correlated evolution between two traits along a phylogeny to the case of interacting lineages, where two traits may or may not share a common phylogenetic history. Independent contrasts and phylogenetic autocorrelation rejected the null hypothesis that trait correlations within lineages are stronger than trait correlations between interacting lineages. Fig style lengths and pollinator ovipositor lengths, for example, were more highly correlated than were pollinator body size and ovipositor length. Mutualistic interactions between figs and their pollinators illustrate the novel ways in which phylogenies and comparative methods can detect patterns of correlated evolution. The most outstanding evidence of correlated evolution between these obligate mutualists is that interacting trait correlations are stronger than within-lineage allometric relationships.

Adaptation, Biological↗

PubMed1998

Correlation between two clinical balance measures in older adults: functional mobility and sensory organization test.

BACKGROUND: Functional mobility of older adults has been shown to correlate with stance stability to various extents. This variability could be due to the difference in the way sensory information is processed in these two types of balance tests. Correlations between functional mobility and stance stability under altered sensory conditions, such as those in the Sensory Organization Test (SOT), are needed to test this possibility. The present study investigated the correlation between the performance of older adults on a newly developed Sensory-Oriented Mobility Assessment Instrument (SOMAI) and on the various sensory conditions of the SOT. METHODS: Twenty-seven community-dwelling older adults (76 +/- 7 years) underwent tests of the six SOT conditions and 10 SOMAI mobility maneuvers performed under normal- and focal-vision (peripheral vision eliminated) conditions. Behavioral performance in the two SOMAI conditions and the amounts of postural sway in the six SOT conditions were ranked among the subjects. Correlations of performance rankings on these two tests were analyzed. RESULTS: Performance on the two SOMAI conditions significantly correlated with that on the SOT conditions in which accurate visual, vestibular, and somatosensory inputs were all present (p < .05). Performance on the focal-vision SOMAI condition was also significantly correlated with that on the SOT condition in which somatosensory input was unreliable for orientation while visual and vestibular inputs were reliable (p < .05). There were no correlations between the SOMAI performance and performance on the no-vision or unreliable-vision SOT conditions. CONCLUSIONS: The ability to use all visual, somatosensory, and vestibular inputs for balance was correlated with functional mobility. The moderate correlations between the performance on the normal-sensory SOT condition and the SOMAI conditions suggest that body systems other than balance senses also contribute to mobility performance.

Aged↗

PubMed2026

Consistent and idiosyncratic pleiotropy in shaping genetic correlations.

Pleiotropy, the phenomenon where a single mutation influences multiple phenotypic traits, creates genetic correlations that can constrain evolutionary trajectories. Yet genetic correlations differ in their persistence: some remain stable over long evolutionary timescales, whereas others change rapidly across generations or environments. One explanation is that similar values of genetic correlation, rG, can arise from different pleiotropic architectures: broadly aligned effects across many loci, or disproportionate covariance contributions from a few large effect loci. Motivated by the distinction between vertical and horizontal pleiotropy, here, we develop a bivariate marker effect framework for recombinant mapping populations that separates candidate large covariance contributors from the polygenic background correlation, rD. We define rD as the correlation among marker effects after trimming markers with unusually large covariance contributions. rD is a trait-pair summary of how consistently small and moderate effect markers align across the genome; high rD is expected when many perturbations propagate through shared developmental, physiological, causal, or geometric structure. Applying this framework to high-dimensional yeast single-cell morphology, we show that trait pairs with similar rG can differ substantially in rD, and that a small number of candidate outlier regions can strongly influence some marker effect correlations. We then test whether rD predicts the environmental stability of genetic correlations under geldanamycin-mediated Hsp90 perturbation. Trait pairs with stronger rD show smaller absolute changes in rG. These results suggest that genetic correlations supported by a strong polygenic marker effect background are more environmentally stable than correlations shaped primarily by a few large covariance contributors.

Genetic Pleiotropy↗

PubMed1988

Interval estimates for correlation coefficients corrected for within-person variation: implications for study design and hypothesis testing.

It is well known that random measurement error can attenuate the correlation coefficient between two variables. One possible solution to this problem is to estimate the correlation coefficient based on an average of a large number of replicates for each individual. As an alternative, several authors have proposed an unattenuated (or corrected) correlation coefficient which is an estimate of the true correlation between two variables after removing the effect of random measurement error. In this paper, the authors obtain an estimate of the standard error for the corrected correlation coefficient and an associated 100% x (1-alpha) confidence interval. The standard error takes into account the variability of the observed correlation coefficient as well as the estimated intraclass correlation coefficient between replicates for one or both variables. The standard error is useful in hypothesis testing for comparisons of correlation coefficients based on data with different degrees of random error. In addition, the standard error can be used to evaluate the relative efficiency of different study designs. Specifically, an investigator often has the option of obtaining either a few replicates on a large number of individuals, or many replicates on a small number of individuals. If one establishes the criterion of minimizing the standard error of the corrected coefficient while fixing the total number of measurements obtained, in almost all instances it is optimal to obtain no more than five replicates per individual. If the intraclass correlation is greater than or equal to 0.5, it is usually optimal to obtain no more than two replicates per individual.

Biometry↗

PubMed2003

MRI measurements of the cervical spine and their correlation to Pavlov's ratio.

STUDY DESIGN: Pavlov's ratio from plain radiographs in patients with neck pain but no radicular symptoms was compared with the areas of the cervical spinal cord and cerebrospinal fluid column on magnetic resonance scans. SUMMARY OF BACKGROUND DATA: The area of the cervical canal or cord obviously depends on both the sagittal and transverse diameters. Although the pathology in stenosis of the cervical spine is mainly in the sagittal plane, narrowing only in the sagittal diameter may not indicate significant reduction in the area of the canal. The transverse area of the cord has been shown to correlate well with the pathologic changes of the cord in cervical myelopathy. We correlated Pavlov's ratio on the plain radiographs to the area of the cerebrospinal fluid column and the area of the cord on the magnetic resonance scan. METHODS: We examined the lateral radiographs and axial and sagittal T2-weighted magnetic resonance scans in the neutral position of the cervical spine (C4-C7) of 87 patients with 332 levels with neck pain but no radicular symptoms and normal magnetic resonance scans. On the magnetic resonance images, the sagittal diameters of the cerebrospinal fluid column and the cord were measured at the midvertebra level on T2 sagittal images from C4 to C7. From the T2 axial images, the area of the cord and the area of the cerebrospinal fluid column were measured at the same levels. RESULTS: The correlation between Pavlov's ratio and the area of cerebrospinal fluid column was moderate, with the highest value of 0.31 at C5. The sagittal diameter of the cerebrospinal fluid column showed variable correlation with the area of the cerebrospinal fluid column. The highest correlation was 0.68 between the sagittal diameter and the area of the cerebrospinal fluid column at C7. The correlation between Pavlov's ratio and the area of the cord is around zero, with the highest correlation of 0.21 at C4. The sagittal diameter of the cord showed a moderate correlation with the area of the cord. CONCLUSION: This study shows a poor correlation between Pavlov's ratio and the space available for the cord. Therefore, this ratio cannot be solely relied upon to predict the area changes in that plane of the cervical spinal canal.

Adult↗

PubMed2001

Numerical study of Lyapunov exponents for products of correlated random matrices.

We numerically study Lyapunov spectra and the maximal Lyapunov exponent (MLE) in products of real symplectic correlated random matrices, each of which is generated by a modified Bernoulli map. We can systematically investigate the influence of the correlation on the Lyapunov exponents because the statistical properties of the sequence generated by the map, whose correlation function shows power-law decay, have been well investigated. It is shown that the form of the scaled Lyapunov spectra does not change much even if the correlation of the sequence increases in the stationary region, and in the nonstationary region the forms are quite different from those obtained in the delta-correlated purely random case. The fluctuation strength dependence of the MLE changes with increasing correlation, and a different scaling law from that of the delta-correlated case can be observed in the nonstationary region. Moreover, the statistical properties of the probability distribution of the local Lyapunov exponents are quite different from those obtained from delta-correlated random matrices. Slower convergence that does not obey the central-limit theorem is observed for increasing correlation.

Journal Article↗

PubMed1996

On the validity of estimating EEG correlation dimension from a spatial embedding.

We demonstrate by using simulations that spatial embedding of single-variable time series data does not reliably reconstruct state-space dynamics. Instead, correlation dimension estimated from spatially embedded data is largely a measure of linear cross-correlation in the data set. For actual electroencephalographic (EEG) data, we demonstrate a high negative correlation between spatial correlation dimension and the average amount of lag-zero cross-correlation between "nearest-neighbor" embedding channels (the greater the cross-correlation, the lower the dimension). We also show that the essential results obtained from spatially embedding EEG data are also obtained when one spatially embeds across a set of highly cross-correlated stochastic (second-order autoregressive) processes. Although, with appropriate surrogate data, correlation dimension estimated from spatially embedded data detects nonlinearity, its use is not recommended because correlation dimension estimated from temporally embedded data both reconstructs state-space dynamics and, with appropriate surrogate data, detects nonlinearity as well.

Algorithms↗

PubMed1993

Correlation of primate red nucleus discharge with muscle activity during free-form arm movements.

1. We recorded from 239 neurons located in the magnocellular division of the red nucleus of four alert macaque monkeys. At the same time, we recorded electromyographic (EMG) signals from as many as twenty electrodes chronically implanted on muscles of the shoulder, arm, forearm and hand. We recorded EMG signals for periods ranging from several months to a year. 2. The monkeys were trained to perform three free-form food retrieval tasks, each of which activated all of the recorded muscles and most of the neurons. The 'prehension' task required simply that the monkey grasp a piece of food from a fixed point in space. The 'barrier' task required the monkey to reach around a small barrier to obtain the food, and the 'Kluver' task required that food be removed from small holes. During the prehension task, we found approximately equal numbers of neurons that were strongly active while the hand was being moved toward the target (70% of units), and while the food was being grasped (60%). Relatively few units were active as the hand was returned to the mouth (15%). 3. Data files of 1-2 min duration were collected while the monkey performed a single behavioural task. Whenever possible, we recorded files for all three tasks from each neuron. For each file we calculated long time-span analog cross-correlations (+/- 1.28 s) between instantaneous neuronal firing rate and each of the full-wave rectified, low-pass filtered EMG signals. We used the peak correlation and the time of the peak as two summary measures of the functional relation between modulation of neuronal activity and EMG. 4. The magnitude of the strongest correlations was between 0.4 and 0.5 (normalized to a perfect correlation of +/- 1.0). Distal muscles were the most frequently correlated, and extensors were more frequently correlated than flexors. For all monkeys, the lags for well correlated muscles were distributed broadly about a uni-modal value near 0 ms. Eighty five per cent of the correlations larger than or equal to 0.25 had peaks between -150 and 200 ms. 5. The activity of each neuron was represented in a muscle co-ordinate system by an n-dimensional 'functional linkage vector', each element of which was the peak correlation with one of n muscles. The vector for any given neuron points in a particular direction in muscle space, depending on the similarity between the activity of the neuron and the activity of each muscle.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed2001

Interaural correlation sensitivity.

Sensitivity to differences in interaural correlation was measured for 1.3-ERB-wide bands of noise using a 2IFC task at six frequencies: 250, 500, 750, 1000, 1250, and 1500 Hz. The sensitivity index, d', was measured for discriminations between a number of fixed pairs of correlation values. Cumulative d' functions were derived for each frequency and condition. The d' for discriminating any two values of correlation may be recovered from the cumulative d' function by the difference between cumulative d''s for these values. Two conditions were employed: the noisebands were either presented in isolation (narrow-band condition) or in the context of broad, contiguous flanking bands of correlated noise (fringed condition). The cumulative d' functions showed greater sensitivity to differences in correlation close to 1 than close to 0 at low frequencies, but this difference was less pronounced in the fringed condition. Also, a more linear relationship was observed when cumulative d' was plotted as a function of the equivalent signal-to-noise ratio (SNR) in dB for each correlation value, rather than directly against correlation. The equivalent SNR was the SNR at which the interaural correlation in an NoS(pi) stimulus would equal the interaural correlation of the noise used in the experiment. The maximum cumulative d' declined above 750 Hz. This decline was steeper for the fringed than for the narrow-band condition. For the narrow-band condition, the total cumulative d' was variable across listeners. All cumulative d' functions were closely fitted using a simple two-parameter function. The complete data sets, averaged across listeners, from the fringed and narrow-band conditions were fitted using functions to describe the changes in these parameters over frequency, in order to produce an interpolated family of curves that describe sensitivity at frequencies between those tested. These curves predict the spectra recovered by the binaural system when complex sounds, such as speech, are masked by noise.

Attention↗

PubMed1998

Correlated amplitude fluctuations of spontaneous otoacoustic emissions.

The frequency spectrum of a spontaneous otoacoustic emission (SOAE) recording may contain multiple narrow peaks. These peaks correspond to multiple SOAEs emitted by the inner ear. The individual SOAEs exhibit small amplitude fluctuations. The correlation between the amplitude fluctuations of multiple SOAEs in an individual ear was studied in 19 SOAE recordings from humans. For 424 pairs of SOAEs, the normalized amplitude cross-correlation function was computed. Significant correlation was found in 63 pairs (15%): 34 pairs showed positive and 29 pairs showed negative correlation. Some SOAE pairs were part of an equally spaced triplet of emission peaks, with one SOAE apparently generated as a distortion product of the other two "primary" SOAEs. The occurrence of correlation between a distortion product SOAE and a "primary" SOAE was 56%. This is significantly higher than the occurrence of correlation for the entire set of SOAE pairs. In addition, the spectral width of the distortion product SOAE was correlated with the spectral width of the "primary" SOAEs (R = 0.87, p < 10(-6)). For 79% of the correlated SOAE pairs, the cross-correlation function peaked at positive time delay. This indicates that for these pairs the fluctuation of the lower frequency emission lagged the fluctuation of the higher frequency emission. The average peak delay was 11.0 ms (s.d. 22.1 ms). The results demonstrate that interactions between SOAEs in an individual ear frequently occur and are asymmetrical.

Cochlea↗