Advanced Hearing Aids Research Articles

Cochlear implants in children.

In recent years, notable progress has been made in the rehabilitation of children with mild to moderate-severe hearing impairment using new and advanced hearing aids. The major problem which remained was the lack of availability of treatment options for those with severe-to-profound sensorineural hearing loss who received little or no benefit from conventional amplification. The purpose of the cochlear implant is to provide these children with direct electrical stimulation of the auditory nerve. A hearing aid amplifies incoming stimuli while a cochlear implant attempts to replace a function lost by the cochlea. In a normal hearing ear, the hair cells within the cochlea act as a transducer of mechanical energy of sound vibration to energy capable of enervating the eighth nerve. The consequence of a decrease in the number of hair cells is the loss of ability of the cochlea to perform the functions, which result in eighth nerve stimulation. The implant replaces the task of the lost hair cells by converting mechanical energy into the electrical energy necessary to excite the remaining cochlear neurons. In order to truly appreciate the application and unfolding of cochlear implants as applied to the pediatric population, it is important to summarize the development of the devices in general.

Modeling of acoustics of hearing aid earmold systems

The earmold system of hearing aids guides an amplified and compressed sound into the ear canal. The description of the propagation of acoustical waves in this system is complex because of the fact that the auditory tube is not straight and the eardrum does not form a perfectly flat end. In more advanced hearing aids, the earmolds are acoustically fitted, according to the patient’s needs. However, this is done experimentally during the fitting process. Modeling of earmolds with irregular shapes can be based on the approach widely used in speech acoustic and in digital sound synthesis, namely the physical modeling of acoustical waveguides. The elaborated model uses fragments of tubes of different diameters and lengths. The difference in acoustic impedance at the boundaries of each two fragments is described by the reflection coefficient. The acoustic wave propagation is modeled using a pair of delays. The model enables the finding of a spectral response characteristic of a hearing aid earmold system in the process of its matching to the patients needs. The details of the proposed approach and some results will be presented in the paper. [Work supported by KBN, Poland, Grant No. 8 T 11E 03415.]

A programmable sound processor for advanced hearing aid research.

A portable sound processor has been developed to facilitate research on advanced hearing aids. Because it is based on a digital signal processing integrated circuit (Motorola DSP56001), it can readily be programmed to execute novel algorithms. Furthermore, the parameters of these algorithms can be adjusted quickly and easily to suit the specific hearing characteristics of users. In the processor, microphone signals are digitized to a precision of 12 bits at a sampling rate of approximately 12 kHz for input to the DSP device. Subsequently, processed samples are delivered to the earphone by a novel, fully-digital class-D driver. This driver provides the advantages of a conventional class-D amplifier (high maximum output, low power consumption, low distortion) without some of the disadvantages (such as the need for precise analog circuitry). In addition, a cochlear implant driver is provided so that the processor is suitable for hearing-impaired people who use an implant and an acoustic hearing aid together. To reduce the computational demands on the DSP device, and therefore the power consumption, a running spectral analysis of incoming signals is provided by a custom-designed switched-capacitor integrated circuit incorporating 20 bandpass filters. The complete processor is pocket-sized and powered by batteries. An example is described of its use in providing frequency-shaped amplification for aid users with severe hearing impairment. Speech perception tests confirmed that the processor performed significantly better than the subjects' own hearing aids, probably because the digital filter provided a frequency response generally closer to the optimum for each user than the simpler analog aids.

Hearing aids: New (and improved) answers for your patients

Educational objectives: To answer patient questions about amplification with updated, accurate information and to understand new concepts in selection and fitting of technologically advanced hearing aids.

A portable programmable digital sound processor for cochlear implant research

A programmable sound processor which utilizes digital signal processing has been developed for hearing prosthesis research. It incorporates a Motorola DSP56001 integrated circuit, 32 K words of memory, a 12 b analog-to-digital converter, and a data formatter and transmitter which conveys control codes to the receiver-stimulator of a cochlear implant. The processor is pocket-sized and battery powered. It has been programmed to emulate the Spectral Maxima Sound Processor for the University of Melbourne/Nucleus 22 electrode implant, and is currently being used by several implantees. In continuing research, speech processing programs are being improved, and other applications, including signal processing for binaural implants and advanced hearing aids, are being developed. >