Von Békésy and cochlear mechanics.

Georg Békésy laid the foundation for cochlear mechanics, foremost by demonstrating the traveling wave that is the substrate for mammalian cochlear mechanical processing. He made mechanical measurements and physical models in order to understand that fundamental cochlear response. In this tribute to Békésy we make a bridge between modern traveling wave observations and those of Békésy, discuss the mechanical properties and measurements that he considered to be so important, and touch on the range of computational traveling wave models.

Decreased BOLD responses in audiovisual processing.

Audiovisual processing was studied in a functional magnetic resonance imaging study using the McGurk effect. Perceptual responses and the brain activity patterns were measured as a function of audiovisual delay. In several cortical and subcortical brain areas, BOLD responses correlated negatively with the perception of the McGurk effect.

Shaping and timing gradient pulses to reduce MRI acoustic noise.

A method to reduce the acoustic noise generated by gradient systems in MRI has been recently proposed; such a method is based on the linear response theory. Since the physical cause of MRI acoustic noise is the time derivative of the gradient current, a common trapezoid current shape produces an acoustic gradient coil response mainly during the rising and falling edge. In the falling edge, the coil acoustic response presents a 180 degrees phase difference compared to the rising edge.

Acoustic FMRI noise: linear time-invariant system model.

Functional magnetic resonance imaging (fMRI) enables sites of brain activation to be localized in human subjects. For auditory system studies, however, the acoustic noise generated by the scanner tends to interfere with the assessments of this activation. Understanding and modeling fMRI acoustic noise is a useful step to its reduction.

Design and implementation of gradient vector flow snake to detect a reference object in pelvic x-rays for preoperative total hip arthroplasty planning application.

The main interest of this research project is to promote automation in performing preoperative planning for hip joint replacement surgery using a special medical image viewing software, ViewPro. Preoperative planning is performed to carefully prepare the surgery and to accurately select the hip implants. The first step of preoperative planning is to calibrate the x-ray image to adjust the magnification factor.

Distortion product otoacoustic emissions: a time domain analysis.

Distortion product otoacoustic emissions (DPOAEs) provide relatively easily accessible external information about internal properties of the inner ear. A primary result is that the detection of normal DPOAE components is a strong indicator of normal functioning of the cochlear mechanics. The details of amplitude and phase behavior of the DPOAEs, and the development over time (DPOAE delay) are not fully understood and subject of some debate.

Automated correction of spin-history related motion artefacts in fMRI: simulated and phantom data.

This paper concerns the problem of correcting spin-history artefacts in fMRI data. We focus on the influence of through-plane motion on the history of magnetization. A change in object position will disrupt the tissue's steady-state magnetization.

Spatial periodicity in the cochlea: the result of interaction of spontaneous emissions?

In this study the results of simulations with a nonlinear macromechanical model of the human cochlea are presented. In this model it is possible to investigate the interactions between large numbers of spontaneous emissions. The focus of this study is on the effect of a local maximum in emission strength on its direct surroundings.

Numerical methods for solving one-dimensional cochlear models in the time domain.

In this article, a robust numerical solution method for one-dimensional (1-D) cochlear models in the time domain is presented. The method has been designed particularly for models with a cochlear partition having nonlinear and active mechanical properties. The model equations are discretized with respect to the spatial variable by means of the principle of Galerkin to yield a system of ordinary differential equations in the time variable.

Measurement of pitch in speech: an implementation of Goldstein's theory of pitch perception.

Recent developments in hearing theory have resulted in the rather general acceptance of the idea that the perception of pitch of complex sounds is the result of the psychological pattern recognition process. The pitch is supposedly mediated by the fundamental of the harmonic spectrum which fits the spectrum of the complex sound optimally. The problem of finding the pitch is then equivalent to finding the best harmonic match.

Masking and partial masking in listeners with a high-frequency hearing loss.

3 listeners with sensorineural hearing loss ranging from moderate to moderate-severe starting at frequencies higher than 1 kHz participated in two masking experiments and a partial masking experiment. In the first masking experiment, fM = 1 KHz and LM = 50 dB SPL, higher than normal masked thresholds were obtained for listeners whose hearing was impaired in the frequency region of clear hearing loss as well as in the region of near-normal absolute thresholds. The second masking experiment showed that for hearing-impaired listeners the elevation of the masked thresholds, in decibels, in this frequency region of "near-normal' absolute thresholds was equal to the elevation of the absolute thresholds, in decibels.

Mechanics and nonlinearity of hair cell stimulation.

Many nonlinear auditory phenomena are described with a BPNL model, which consists of a nonlinear element preceded and followed by a linear filter. We aim at identifying these elements with cochlear processes. The directional sensitivity of the hair cell is assumed to provide a basis for the second filter.

Level effects in psychophysical two-tone suppression.

Measurements of psychophysical two-tone suppression in a number of subjects are described. Levels of the stimulus components (suppressee, L1, and suppressor, L2) were the primary experimental variables. In all experiments the pulsation threshold was used with the probe frequency fr fixed at the suppressee frequency f1.