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PubMedDate not supplied

Weekly alcohol consumption, brain atrophy, and white matter hyperintensities in a community-based sample aged 60 to 64 years.

OBJECTIVE: The objective of this study was to determine the association between weekly alcohol consumption and brain atrophy in adults aged 60 to 64 years. METHODS: Brain magnetic resonance imaging scans from 385 adults recruited through a community survey were analyzed. Automated segmentation and manual tracing methods were used to obtain brain subvolumes and automated methods were used to obtain quantification and localization of white matter hyperintensities. Visual measures of cortical atrophy were obtained as were data on health and lifestyle factors. Alcohol consumption was assessed with the Alcohol Use Disorders Identification Test. RESULTS: In men, weekly alcohol consumption had a positive linear association with ventricular volume and gray matter and a negative linear association with white matter. In women, weekly alcohol consumption had a nonlinear relationship with cerebrospinal fluid and white matter. Alcohol consumption was not associated with white matter hyperintensities, corpus callosum size, hippocampal or amygdala volumes in analyses adjusting for confounding variables. CONCLUSION: An association between alcohol consumption and brain atrophy is evident at the population level. In women, detrimental effects of alcohol on the brain appear to occur at lower levels of consumption. It remains possible that low levels of alcohol consumption have neuroprotective benefits but is clear that high levels of consumption are detrimental.

Alcohol Drinking↗

PubMed2004

Reexamining the effects of gestational age, fetal growth, and maternal smoking on neonatal mortality.

BACKGROUND: Low birth weight (<2,500 g) is a strong predictor of infant mortality. Yet low birth weight, in isolation, is uninformative since it is comprised of two intertwined components: preterm delivery and reduced fetal growth. Through nonparametric logistic regression models, we examine the effects of gestational age, fetal growth, and maternal smoking on neonatal mortality. METHODS: We derived data on over 10 million singleton live births delivered at >/= 24 weeks from the 1998-2000 U.S. natality data files. Nonparametric multivariable logistic regression based on generalized additive models was used to examine neonatal mortality (deaths within the first 28 days) in relation to fetal growth (gestational age-specific standardized birth weight), gestational age, and number of cigarettes smoked per day. All analyses were further adjusted for the confounding effects due to maternal age and gravidity. RESULTS: The relationship between standardized birth weight and neonatal mortality is nonlinear; mortality is high at low z-score birth weights, drops precipitously with increasing z-score birth weight, and begins to flatten for heavier infants. Gestational age is also strongly associated with mortality, with patterns similar to those of z-score birth weight. Although the direct effect of smoking on neonatal mortality is weak, its effects (on mortality) appear to be largely mediated through reduced fetal growth and, to a lesser extent, through shortened gestation. In fact, the association between smoking and reduced fetal growth gets stronger as pregnancies approach term. CONCLUSIONS: Our study provides important insights regarding the combined effects of fetal growth, gestational age, and smoking on neonatal mortality. The findings suggest that the effect of maternal smoking on neonatal mortality is largely mediated through reduced fetal growth.

Journal Article↗

PubMed1990

Wave motions in a collapsible tube conveying fluid.

This paper presents a refinement of the authors' previous analysis and additional numerical results. In order to study self-excited oscillation of a finite-length collapsible tube, a simple two-dimensional channel model analysis has been proposed using an existing one-dimensional flow theory which may account for the pressure loss due to flow separation. A flexible part of the channel consists of two elastic membranes supported by distributed nonlinear springs from the outsides. The analysis includes the effect of longitudinal membrane tensions caused by an initial stretching and membrane deflection. According to numerical analyses, an initially stretched membrane channel may have a wide region of the flow separation at the downstream of the channel throat located in the neighborhood of the middle point of the channel. The induced oscillations become large and chaotic. Some details of wave motions of membrane deflection, flow velocity and pressure are given.

Blood Flow Velocity↗

PubMed1983

[Effect of total hormone concentration on the determination of amount of binding in the hormone/receptor interaction between erythrocytes and insulin].

The interaction of erythrocytes and [125I]insulin/insulin were studied up to a total insulin concentration of 409 mumol/l. Assuming a single class receptor model the evaluation of receptor affinity Ka and concentration R0 may be performed either by non-linear regression analyses with iteration procedures of R0, Ka and U (nonspecific binding), or by a linear regression analysis of the initial part of the Scatchard plot. Nonlinear fitting of data to a two class receptor model gives results that are reliable only for the high affinity receptor site. The non-definable step of R0 determination leads to uncertainties in results determined by the negative cooperativity model. From the results of this investigation and from considerations of signal modulation by receptor occupancy, some recommendations have been formulated for the evaluation of binding parameters; these should contribute to an improvement in the comparability of studies on the interactions of erythrocytes and insulin.

Erythrocytes↗

PubMed1996

Characterization and localization of [125I]RTI-55-labeled cocaine binding sites in fetal and adult rat brain.

The present studies examined the characteristics of fetal (gestational day 20) and adult rat brain cocaine recognition sites labeled with the potent cocaine congener [125I]RTI-55 [3 beta-(4-iodophenyl)-tropane-2 beta-carboxylic acid methyl ester]. Saturation analyses of [125I]RTI-55 binding to membrane fractions from both fetal and adult whole-brain yielded curvilinear Scatchard plots that were resolved by nonlinear curve-fitting into high- and low-affinity components. Mean Kd values were 0.13 nM and 12 nM for fetal brain high- and low-affinity sites, respectively, compared to 0.26 and 18 nM for adult brain. The Kd for high-affinity binding was significantly different between the groups, suggesting a possible developmental change in the properties of [125I]RTI-55 binding sites. Drug displacement studies with various monoamine uptake inhibitors indicated that at a 10 pM concentration of [125I]RTI-55, almost all binding to fetal brain membranes could be accounted for by interaction with the serotonin (5-HT) and (to a lesser extent) dopamine (DA) transporters. This conclusion was supported by autoradiographic studies of both adult and fetal brain, demonstrating a predominance of [125I]RTI-55 binding in areas with high densities of 5-HT and/or DA uptake sites. The present results are in accordance with our previous demonstration of [3H]cocaine binding sites in fetal brain (Meyer et al., 1993) and further suggest that [125I]RTI-55 should be a useful ligand for assessing the effects of prenatal cocaine exposure on the subsequent development of cocaine recognition sites on the DA and 5-HT transporters.

Animals↗

PubMed1996

Effects of dietary protein restriction on the progression of moderate renal disease in the Modification of Diet in Renal Disease Study.

The Modification of Diet in Renal Disease (MDRD) Study consisted of two randomized controlled trials to determine the effects of dietary protein restriction and strict blood pressure control. In 255 patients with advanced renal disease (baseline GFR, 13 to 24 mL/min per 1.73 m2; Study B), secondary analyses demonstrated a correlation between achieved protein intake and rate of decline in GFR, consistent with a beneficial effect of a low-protein diet. In 585 patients with moderate renal disease (baseline GFR, 25 to 55 mL/min per 1.73 m2; Study A), the primary analysis of the effect of the low-protein diet was inconclusive because of a nonlinear GFR decline and limited duration of follow-up. A meta-analysis of recent controlled trials, including MDRD Study A, demonstrated a beneficial effect of a low-protein diet on the incidence of renal failure. The objective of these secondary analyses is to explore further the effect of dietary protein restriction in Study A. In these analyses, a total of 585 patients were randomly assigned to follow either a low-protein diet (0.58 g/kg per day) or a usual-protein diet (1.3 g/kg day). Outcomes included the rate of GFR decline, incidence of renal failure or death, and change in urine protein excretion. Analyses included comparisons of randomized groups and correlations of outcomes with achieved protein intake. The comparisons of randomized groups revealed a faster GFR decline during the first 4 months after assignment to the low-protein diet but no difference in the variability in GFR decline between the diet groups, indicating a uniform short-term effect of the low-protein diet on GFR, probably as a result of hemodynamic adjustments. After 4 months, the mean decline in GFR in the low-protein diet group was slower, and the variability of the rate of decline was smaller, than in the usual-protein diet group (ratio of standard deviations, 0.73; 95% confidence interval, 0.55 to 0.91; P < 0.01). This suggests a greater beneficial effect of the low-protein diet in patients with a more rapid GFR decline. The net effect of the low-protein diet on GFR decline over 3 yr was no significant change in mean GFR decline, but reduced variability of the decline (ratio of standard deviations, 0.76; 95% confidence interval, 0.60 to 0.92; P < 0.01). Correlational analyses revealed trends similar to the comparisons of randomized groups. During the first 4 months, patients with a greater decline in protein intake (irrespective of diet group) had a greater decline in GFR; thereafter, patients with a lower protein intake had a slower GFR decline. Over 3 yr, there was no significant correlation between GFR decline and achieved protein intake. The correlation of protein intake with GFR decline after 4 months was less strong than observed in Study B. The relative risk of death or renal failure was 0.65 (95% confidence interval, 0.38 to 1.10; P = 0.10) in patients assigned to the low-protein diet group compared with the usual-protein diet group, which is similar to that observed in the meta-analysis. During follow-up, the increase in urine protein excretion was delayed in the low-protein diet group (P = 0.008) and in patients with lower achieved protein intake (P = 0.005). In summary, the absence of a significant difference between the diet groups in the mean change in GFR from baseline to 3 yr precludes a definitive conclusion of a beneficial effect of the diet intervention based solely on MDRD Study A. However, these secondary analyses are consistent with a beneficial effect of the low-protein diet to slow the GFR decline in patients with the most rapidly declining GFR and to reduce urine protein excretion. These results, together with the results of the recent meta-analysis (including MDRD Study A), provide some support for the hypothesis that dietary protein restriction slows the progression of moderate renal disease.

Adolescent↗

PubMed2005

Cross-sectional and longitudinal relationships between alcohol consumption and lipids, blood pressure and body weight indices.

OBJECTIVE: Serum lipids, blood pressure and body mass may mediate the U-shaped relationship of alcohol consumption with type 2 diabetes mellitus and coronary heart disease. This study examines the cross-sectional and long-term longitudinal relationships of (changes in) alcohol consumption with (changes in) serum lipids, blood pressure and body mass indices. METHOD: In this prospective, observational cohort study, two measurements of alcohol consumption, serum total and high-density lipoprotein cholesterol, triglycerides, blood pressure, body weight, the thickness of four skinfolds and waist circumference were performed 4 years apart in healthy volunteers (143 men and 174 women, 32 years old at the first measurement). Alcohol consumption from beer, wine and distilled spirits was assessed using an extensive dietary history interview. Linear regression analyses were performed to study the cross-sectional relationships between the amount of alcohol consumed at the age of 32 years and the levels of the lipids, blood pressure and body weight indices, and to study the longitudinal relationships between the changes in the amount of alcohol consumed over the 4 years of follow-up and the concurrent changes in the lipids, blood pressure and body weight indices. Nonlinearity was investigated for the cross-sectional relationships. RESULTS: A 10-g/day difference in alcohol consumption was positively related with a 0.05 mmol/L (1.9 mg/dl) difference in high-density lipoprotein cholesterol in both cross-sectional (p = .004), and longitudinal (p < .0001) analyses. This relationship did not differ for men and women or for the consumption of beer, wine or distilled spirits. Relationships with changes in total cholesterol, triglycerides, systolic, diastolic, and pulse pressure, body weight and the sum of four skinfolds were not significant. A borderline significant inverse longitudinal relationship was found with waist circumference. The other lifestyle behaviors (tobacco smoking, physical activity and dietary habits) were major confounders of most cross-sectional relationships between alcohol and serum lipids, blood pressure and body mass indices. The longitudinal relationships, however, were not confounded by changes in the other lifestyle behaviors. A significant nonlinear relationship was found for systolic blood pressure, in which drinkers of about 30 g/day had the lowest values. CONCLUSIONS: Moderate alcohol consumption and moderate long-term changes in alcohol consumption are positively related with the levels and changes in high-density lipoprotein cholesterol in healthy adult men and women. A moderate inverse association between alcohol and waist circumference may be expected. No relationships were found with triglycerides, blood pressure, body weight and the sum of the thickness of four skinfolds. Other lifestyle behaviors confound the cross-sectional, but not the longitudinal, relationships between alcohol consumption and serum lipids, blood pressure and body mass indices. Gender and type of beverage do not modify the relationships between alcohol consumption and these indices.

Adult↗

PubMed1990

Distinguishing error from chaos in ecological time series.

Over the years, there has been much discussion about the relative importance of environmental and biological factors in regulating natural populations. Often it is thought that environmental factors are associated with stochastic fluctuations in population density, and biological ones with deterministic regulation. We revisit these ideas in the light of recent work on chaos and nonlinear systems. We show that completely deterministic regulatory factors can lead to apparently random fluctuations in population density, and we then develop a new method (that can be applied to limited data sets) to make practical distinctions between apparently noisy dynamics produced by low-dimensional chaos and population variation that in fact derives from random (high-dimensional) noise, such as environmental stochasticity or sampling error. To show its practical use, the method is first applied to models where the dynamics are known. We then apply the method to several sets of real data, including newly analysed data on the incidence of measles in the United Kingdom. Here the additional problems of secular trends and spatial effects are explored. In particular, we find that on a city-by-city scale measles exhibits low-dimensional chaos (as has previously been found for measles in New York City), whereas on a larger, country-wide scale the dynamics appear as a noisy two-year cycle. In addition to shedding light on the basic dynamics of some nonlinear biological systems, this work dramatizes how the scale on which data is collected and analysed can affect the conclusions drawn.

Chickenpox↗

PubMed1999

A kinetic distribution model of evaporation, biosorption and biodegradation of polychlorinated biphenyls (PCBs) in the suspension of Pseudomonas stutzeri.

Kinetics of distribution of PCBs in an active bacterial suspension of Pseudomonas stutzeri was studied by monitoring the evaporated amounts and the concentration remaining in the liquid medium with the biomass. To determine the biodegradation rate constants of the individual congeners of the PCB formulation Delor 103, a model considering biosorption, evaporation, and primary biodegradation constructed previously was used. Rate constants of biodegradation imply that biodegradation of individual congeners is structure-dependent process. Biodegradability decreases with increasing number of chlorine substituents in the molecule, especially if they are in the ortho and para positions. On the other hand, the increasing number of free ortho and meta positions in the biphenyl molecule leads to better biodegradability. For a simple empirical determination of the influence of the chlorine substitution pattern on biodegradability, the di- and trichlorobiphenyl rate constants of biodegradation were analysed.

Adsorption↗

PubMed2004

Nonlinear dynamic analysis of voices before and after surgical excision of vocal polyps.

Phase space reconstruction, correlation dimension, and second-order entropy, methods from nonlinear dynamics, are used to analyze sustained vowels generated by patients before and after surgical excision of vocal polyps. Two conventional acoustic perturbation parameters, jitter and shimmer, are also employed to analyze voices before and after surgery. Presurgical and postsurgical analyses of jitter, shimmer, correlation dimension, and second-order entropy are statistically compared. Correlation dimension and second-order entropy show a statistically significant decrease after surgery, indicating reduced complexity and higher predictability of postsurgical voice dynamics. There is not a significant postsurgical difference in shimmer, although jitter shows a significant postsurgical decrease. The results suggest that jitter and shimmer should be applied to analyze disordered voices with caution; however, nonlinear dynamic methods may be useful for analyzing abnormal vocal function and quantitatively evaluating the effects of surgical excision of vocal polyps.

Adult↗

PubMedDate not supplied

[Ventricular fibrillation: the current methods for analysing the degree of irregularity of the process].

Ventricular fibrillation has traditionally been described as "chaotic" and in recent years there has been discussions that fibrillation may be an instance of deterministic chaos in the context of nonlinear dynamical systems theory. The current paper summarizes modern methods of mathematical analysis of the degree of electrical irregularities of the heart during VF. The traditional methods of Fourier analysis of electrocardiographic data as well as concepts of chaos theory--fractal dimension, entropy, reconstruction of attractors and some new methods such as spatial coherence have been considered. The results are discussed in context of mathematical models and hypothesis of mechanisms of VF.

Animals↗

PubMed2000

Pharmacodynamics of beta-blocker modulation of aqueous humor production.

A conscious rabbit model with microdialysis sampling of endogenous aqueous humor ascorbate was developed in order to assess the pharmacodynamics of beta-blocker modulation of aqueous humor production. CMA/20 microdialysis probes were implanted in the anterior chamber of each eye of rabbits (n = 6). After a 2 week recovery period, an i.v. bolus of 14C-ascorbate (20 microCi) was administered. Blood samples and aqueous humor microdialysis probe effluent were collected and analysed for endogenous and 14C-ascorbate to estimate the basal rate of ascorbate blood to aqueous humor secretion (Ro). After a 1 hr washout, each rabbit received a series of three doses of 3H-propranolol (750-3000 microg, 16.5 microCi mg(-1)) every 60 min into the lower cul-de-sac of each eye. Probe effluent was analysed for endogenous ascorbate and 3H-propranolol; ascorbate and propranolol in the iris/ciliary body, vitreous and aqueous was determined at the end of the experiment. Nonlinear least-squares regression analysis of the concentration-time profiles for aqueous humor ascorbate was performed to estimate the change in aqueous humor flow. The average basal aqueous humor ascorbate secretion rate was approximately 48/microg hr(-1). Propranolol (1500 microg) produced significant increases in aqueous humor ascorbate, this observation is consistent with a reduction in aqueous humor production (approximately 47%). Analysis of intraocular tissue ascorbate indicated that propranolol inhibited ascorbate secretion at the 3000 microg dose, the highest dose examined in this study; this inhibition was not observed at the 750 microg or 1500 microg doses. Changes in aqueous humor production precipitated by the administration of beta-adrenergic antagonists can be estimated by measuring changes in aqueous humor ascorbate concentrations in the conscious rabbit. Microdialysis sampling of aqueous humor for endogenous ascorbate provides a relevant analytic tool to estimate modulatory effects of anti-glaucoma drugs on aqueous humor production.

Acetazolamide↗

PubMed1984

Extended least squares nonlinear regression: a possible solution to the "choice of weights" problem in analysis of individual pharmacokinetic data.

It is often difficult to specify weights for weighted least squares nonlinear regression analysis of pharmacokinetic data. Improper choice of weights may lead to inaccurate and/or imprecise estimates of pharmacokinetic parameters. Extended least squares nonlinear regression provides a possible solution to this problem by allowing the incorporation of a general parametric variance model. Weighted least squares and extended least squares analyses of data from a simulated pharmacokinetic experiment were compared. Weighted least squares analysis of the simulated data, using commonly used weighting schemes, yielded estimates of pharmacokinetic parameters that were significantly biased, whereas extended least squares estimates were unbiased. Extended least squares estimates were often significantly more precise than were weighted least squares estimates. It is suggested that extended least squares regression should be further investigated for individual pharmacokinetic data analysis.

Computers↗

PubMed1999

The dynamics of goal-directed rhythmical aiming.

Based on the kinematics of goal-directed aiming movements in a reciprocal Fitts' task, a minimal limit cycle model is proposed that is capable of producing the behavior observed at levels of task difficulty ranging from 3 to 7. From graphical and statistical analyses of the phase planes, Hooke's planes and velocity profiles, we concluded that the minimal terms to be included in the model were (i) a nonlinear damping in the form of a self-sustaining, velocity-driven Rayleigh oscillator and (ii) a nonlinear stiffness in the form of a softening spring Duffing term. The model reproduced the kinematic patterns experimentally observed in rhythmical precision aiming, accounting for 95% of the variance. The coefficients in the model changed in a systematic way when distance and precision constraints were varied, and the meaning of these changes is discussed in the framework of the dynamical patterns approach.

Adult↗

PubMed1990

Trends of mechanical consequences and modeling of a fibrous membrane around femoral hip prostheses.

In the present study, the effects of a fibrous membrane between cement and bone in a femoral total hip replacement were investigated. The study involved the problem of modeling this fibrous membrane in finite-element analyses, and its global consequences for the load-transfer mechanism and its resulting stress patterns. A finite-element model was developed, suitable to describe nonlinear contact conditions in combination with nonlinear material properties of the fibrous membrane. The fibrous tissue layer was described as a highly compliant material with little resistance against tension and shear. The analysis showed that the load transfer mechanism from stem to bone changes drastically when such a membrane is present. These effects are predominantly caused by tensile loosening and slip at the interface, and are enhanced by the nonlinear membrane characteristics. Using parametric analysis, it was shown that these effects on the load-transfer mechanism cannot be described satisfactorily with linear elastic models. Most importantly, the fibrous tissue interposition causes excessive stress concentrations in bone and cement, and relatively high relative displacements between these materials.

Biomechanical Phenomena↗

PubMed1983

Fluctuation and linear analysis of Na-current kinetics in squid axon.

The power spectrum of current fluctuations and the complex admittance of squid axon were determined in the frequency range 12.5 to 5,000 Hx during membrane voltage clamps to the same potentials in the same axon during internal perfusion with cesium. The complex admittance was determined rapidly and with high resolution by a fast Fourier transform computation of the current response, acquired after a steady state was attained, to a synthesized signal with predetermined spectral characteristics superposed as a continuous, repetitive, small perturbation on step voltage clamps. Linear conduction parameters were estimated directly from admittance data by fitting an admittance model, derived from the linearized Hodgkin-Huxley equations modified by replacing the membrane capacitance with a "constant-phase-angle" capacitance, to the data. The constant phase angle obtained was approximately 80 degrees. At depolarizations the phase of the admittance was 180 degrees, and the real part of the impedance locus was in the left-half complex plane for frequencies below 1 kHz, which indicates a steady-state negative Na conductance. The fits also yielded estimates of the natural frequencies of Na "activation" and "inactivation" processes. By fitting Na-current noise spectra with a double Lorentzian function, a lower and an upper corner frequency were obtained; these were compared with the two natural frequencies determined from admittance analysis at the corresponding potentials. The frequencies from fluctuation analyses ranged from 1.0 to 10.3 times higher than those from linear (admittance) analysis. This discrepancy is consistent with the concept that the fluctuations reflect a nonlinear rate process that cannot be fully characterized by linear perturbation analysis. Comparison of the real part of the admittance and the current noise spectrum shows that the Nyquist relation, which generally applies to equilibrium conductors, does not hold for the Na process in squid axon. The Na-channel conductance, gamma Na, was found to increase monotonically from 0.1 to 4.8 pS for depolarizations up to 50 mV from a holding potential of -60 mV, with no indication of a maximum value.

Animals↗

PubMed2003

Immature human osteoblastic MG63 cells predominantly express a subtype 1-like CGRP receptor that inactivates extracellular signal response kinase by a cAMP-dependent mechanism.

Although accumulated data suggest that calcitonin gene-related peptide (CGRP) produces anabolic effects in skeletal tissue by directly acting on osteogenic cells, neither the distribution of CGRP receptor subtypes nor the associated cellular signaling pathways are well understood. In this study, we have pharmacologically and biochemically characterized CGRP-binding sites in immature human osteoblastic MG63 cells. In a [125I]CGRP whole-cell-binding assay, nonlinear regression curve-fitting analysis demonstrated a single binding site (K(D)=405+/-29 pM; 13,100+/-223 sites per cell). Immunocytochemical and Western blot analyses demonstrated that 48-, 52-, and 120-kDa forms of the calcitonin receptor-like receptor (CRLR) and a 15-kDa form of the receptor-activity-modifying protein-1 (RAMP-1) was expressed on the plasma membrane. CGRP strongly stimulated cellular cAMP production and this effect was antagonized not only by an antagonist of the subtype-1 CGRP (CGRP(1)) receptor, CGRP-(8-37), but by an agonist of the putative subtype-2 CGRP (CGRP(2)) receptor, [Cys(Acm)(2,7)]-CGRP, that also itself acted as a weak agonist. In contrast to published data, CGRP dose- and time-dependently dephosphorylated and inactivated extracellular signal response kinase (ERK). This action was blocked by CGRP-(8-37), by an inhibitor of cAMP-dependent protein kinase (H-89), or by an inhibitor of protein phosphatases (vanadate). Prolonged CGRP treatments significantly suppressed DNA synthesis at 27 h, but up-regulated type I collagen. Both these actions were blocked by CGRP-(8-37) and mimicked by a specific inhibitor of ERK (PD98059). In summary, our data suggest that the CGRP receptors in MG63 cells meet many, but not all, of the classical criteria used to define CGRP(1) receptors. These receptors that functioned in a pharmacologically distinct manner could inhibit cell proliferation, and were substantially more sensitive to a CGRP(2) receptor agonist than are typical CGRP(1) receptors. These receptor proteins were not exactly matched with the known components of a CGRP(1) receptor that have been reported. Therefore, it is possible that the CGRP receptors expressed in immature osteoblastic human MG63 cells represent a variation of the known CGRP(1) receptor.

Animals↗

PubMed1993

Nonlinear processes in visual pattern discrimination.

Visual performance on many simple pattern discrimination tasks can be accurately predicted by quasi-linear models composed of oriented linear filters followed by simple contrast nonlinearities. However, many complex discrimination tasks require highly nonlinear processes for their explanation. Evidence is provided for two nonlinear processes in pattern discrimination: (i) one process involves a sequence of filtering, rectification, and subsequent filtering to extract texture boundaries; (ii) the second process results from contrast gain-control processes. It is suggested that quasi-linear processes and nonlinear texture-boundary processes, each with an appropriate contrast gain control, may operate in parallel to provide the basis for all higher-level visual analyses.

Discrimination, Psychological↗