Nonlinear time-domain cochlear model for transient stimulation and human otoacoustic emission

This paper describes the implementation and performance of a nonlinear time-domain model of the cochlea for transient stimulation and human otoacoustic emission generation. The nonlinearity simulates compressive growth of measured basilar-membrane impulse responses. The model accounts for reflection and distortion-source otoacoustic emissions (OAEs) and simulates spontaneous OAEs through manipulation of the middle-ear reflectance. The model was calibrated using human psychoacoustical and otoacoustic tuning parameters. It can be used to investigate time-dependent properties of cochlear mechanics and the generator mechanisms of otoacoustic emissions. Furthermore, the model provides a suitable preprocessor for human auditory perception models where realistic cochlear excitation patterns are desired

Central auditory masking by an illusory tone

Many natural sounds fluctuate over time. The detectability of sounds in a sequence can be reduced by prior stimulation in a process known as forward masking. Forward masking is thought to reflect neural adaptation or neural persistence in the auditory nervous system, but it has been unclear where in the auditory pathway this processing occurs. To address this issue, the present study used a "Huggins pitch" stimulus, the perceptual effects of which depend on central auditory processing. Huggins pitch is an illusory tonal sensation produced when the same noise is presented to the two ears except for a narrow frequency band that is different (decorrelated) between the ears. The pitch sensation depends on the combination of the inputs to the two ears, a process that first occurs at the level of the superior olivary complex in the brainstem. Here it is shown that a Huggins pitch stimulus produces more forward masking in the frequency region of the decorrelation than a noise stimulus identical to the Huggins-pitch stimulus except with perfect correlation between the ears. This stimulus has a peripheral neural representation that is identical to that of the Huggins-pitch stimulus. The results show that processing in, or central to, the superior olivary complex can contribute to forward masking in human listeners

Polymorphisms in beta and kappa-casein are not associated with milk production in two highly technifield populations of holstein cattle in Mexico

The purpose of this study was to identify genotype variants in the beta-casein (CSN2) and kappa-case (CSN3) genes using the PCR-RFLP method in a population of 202 Holstein cattle from two highly technified farms in the state of Jalisco, Mexico. We further assessed the association of these variants with milk production during a second lactation period. In the first population (n = 102), the genotypic frequencies for CSN2 were A1 = 0.387 and A2 = 0.613, while for CSN3, they were A = 0.829 and B = 0.172. In the second population (n = 100), the genotypic frequencies for CSN2 were A1 = 0.430 and A2 = 0.570, while for CSN3, they were A = 0.795 and B = 0.205. No differences in frequency distribution were noted in either population, and both genes were in Hardy-Weinberg equilibrium. There was greater genetic diversity for the CSN2 gene (0.477 and 0.493) than for the CSN3 gene (0.286 and 0.328) in both populations, with no significant differences between them. The fixation index was low for both genes, suggesting that there was no significant decrease in heterozygosity. The same genetic changes occur in both genes, and give their high similarity index (0.99 and 0.99). The statistical association analysis between genotypes of both genes and milk production revealed there were no significant differences between populations. Furthermore, no significant additive or dominant effects of both casein genes on milk production were identified within our population samples.El propósito de este estudio fue identificar variantes de genotipos en los genes de la beta-caseína (CSN2) y kappa-case (CSN3) utilizando el método PCR-RFLP en una población de 202 vacas Holstein de dos granjas altamente tecnificadas en el estado de Jalisco, Méjico. Además evaluamos la asociación de estas variantes con la producción de leche durante un segundo período de lactancia. En la primera población (n = 102), las frecuencias genotípicas para CSN2 fueron A1 = 0.387 y A2 = 0.613, mientras que para CSN3, fueron A = 0.829 y B = 0.172. En la segunda población (n = 100), las frecuencias genotípicas para CSN2 fueron A1 = 0,430 y A2 = 0,570, mientras que para CSN3, fueron A = 0,795 y B = 0,205. No se observaron diferencias en la distribución de frecuencias en ninguna de las poblaciones, y ambos fueron en equilibrio de Hardy-Weinberg. Hubo mayor diversidad genética para el gen CSN2 (0,477 y 0,493) que para el gen CSN3 (0,286 y 0,328) en ambas poblaciones, sin diferencias significativas entre ellos. El índice de fijación fue bajo para ambos genes, lo que sugiere que no hubo una disminución significativa en la heterocigosidad. Los mismos cambios genéticos ocurren en ambos genes, y dan su alto índice de similitud (0,99 y 0,99). El análisis de asociación estadística entre los genotipos de ambos genes y la producción de leche reveló que no había diferencias significativas entre las poblaciones. Además, no se identificaron efectos aditivos o dominantes significativos de ambos genes de caseína en la producción de leche dentro de nuestras muestras de población