Samuel Gilman

Hearing aid having a liquid transmission means communicative with the cochlea and method of use thereof

A hearing aid (100) is provided for surgically implanting in the ear of a subject. A liquid filled tube (142) is positioned between an orifice of the cochlea and a subcutaneous amplifier (200). A microphone (122) converts sound waves outside the subject into electrical signals which are amplified by the amplifier and are converted back into amplified mechanical motion by a transducer means (124). The amplified mechanical motion is transmitted through the tube by the liquid to the cochlea bypassing the outer and middle ears. The liquid and dimensions of the tube are selected to substantially match the acoustic impedance of the cochlea at the distal end of the tube.

Processor controlled ear responsive hearing aid and method

A processor controlled ear responsive hearing aid for the ear of a hearing impaired individual and method for operating a hearing aid. The input from the microphone is amplified and split into a plurality of band-pass channels each having a frequency range of approximately one-third octave. Each channel has an amplifier that is controlled by the processor. The processor receives control signals from a feedback microphone located in the ear canal and uses the control signals to develop a spectrum of the actual sound pressure levels by frequency at the eardrum. The processor compares averages of the actual sound pressure levels to the desired levels for each channel and for the overall output according to a predetermined set of instructions and controls the channel amplifiers and an output amplifier to produce the desired sound pressure levels for each frequency in the ear canal.

Acoustics of ear canal measurement of eardrum SPL in simulators

The effect of standing waves on the ear canal measurement of eardrum sound pressure level (SPL) was determined by both calculation and measurement. Transmission line calculations of the standing wave were made using the dimensions of the ANSI S3.25-1979 ear simulator and three different eardrum impedances. Standing wave curves have been obtained for the standard eardrum impedance at 1-kHz intervals in the range of 1-8 kHz. The changes in standing wave position due to each of the three eardrum impedances and their effects on ear canal measurements of SPL were computed for each of the eardrum impedances. Ear canal SPL measurements conducted on simulators modified to correspond to the eardrum impedances used in the calculations were compared to the computed values. Differences between eardrum SPLs and those measured at different locations in the ear canal approached a standing wave ratio (SWR) of 10-12 dB as the position of the measuring probe approached the standing wave minimum at each frequency. These maximum differences compared favorably with data developed by other investigators from real ears. Differences due to the eardrum impedance were found to be significant only in the frequency region of 2-5 kHz. Calibration of probes in a standard or modified ANSI simulator at the same distance from the eardrum as in the real ear reduces the eardrum SPL measurement errors to those resulting from differences in eardrum impedance.

Optical method for measurement of ear canal length

A noninvasive optical method using an operating microscope was developed to measure the length of an ear canal under both open and occluded conditions. The method is based on the optical measurement of the distance between a reference point at the eardrum and a second point on the lateral aspect of an earmold-occluded ear canal. To estimate the occluded canal length, the length of the earmold is then subtracted from results of the previous measurement. The method was also used to determine the open ear canal length (the lateral reference point was the ear canal entrance), and averaged results agreed closely with previously reported data.

Temporal integration at the ’’threshold’’ of the acoustic reflex

Investigation of the temporal integration of the acoustic reflex may be complicated by the operating characteristics of the instrumentation used to record the reflex. Several experiments were conducted to determine the operating characteristics of two impedance measuring systems (Madsen, model Z0−70 and Zwislocki Bridge (Grason Stadler, model 3), and to measure selected characteristics of the acoustic reflex, including (1) ’’threshold’’, (2) reflex intensity‐growth functions, and (3) temporal integration functions at ’’threshold’’ for several stimulus frequencies. Results indicate (1) a smaller impedance change may be identified with a Madsen Z0−70 due primarily to the higher S/N (signal‐to‐noise) ratio in that instrument; (2) differences in temporal integration functions obtained between the two instruments were partially accounted for by differences in the operating characteristics of the two measuring systems; (3) the slope of the growth‐intensity function decreases as signal duration decreases; and (4...

The effect of occluded ear impedances on the eardrum SPL produced by hearing aids

Experiments were designed to measure the effect of eardrum impedance on the SPL response at the eardrum for several earmold and hearing aid‐receiver arrangements. Three ear simulators were used representing the eardrum impedances of the 10th, 50th, and 90th percentile of the population with normal middle ear function. Data from five commercially available hearing aid receivers were obtained using eardrum SPL and receiver input phrase responses as criteria. In addition to differences in SPL due to simulator impedances, there were significant variations due to interaction between receivers and simulators at the receiver resonant frequencies. Effects as large as 10 dB were measured at receiver resonances within the range of simulator and earmold impedances tested. Receiver input phase resonances of the simulators were compared to the responses from three equivalent real ears. Real ear data corresponded generally with the simulator data in interaction effects.

Properties of Acoustic Reflex Adaptation

The dynamic behavior of the acoustic reflex to continuous sinusoidal stimuli was investigated. The major purpose was to determine the temporal characteristics of reflex adaptation as frequency (0.5, 1.0, 2.0, 3.0, 4.0 kHz) and suprathreshold level (6, +12, +18 dB re reflex threshold) were systematically varied. Repeated measurements were made with an impedance bridge on six normal listeners. Both relative and absolute impedance changes were analyzed. The results revealed large intersubject variability. Four general conclusions were reached regarding the effect of stimulus frequency and suprathreshold level on adaptation: 1) as the stimulus frequency increases, the rate of adaptation increases; 2) the adaptation curves appear to form distinct groups, at the low frequencies adaptation rates are significantly slower than those at 2.0 kHz and above; 3) the onset of adaptation occurs at an earlier time for the higher frequencies; and 4) the rate of adaptation was found to be independent of suprathreshold level. The changes in adaptation with frequency of the stimulus may be expressed by an equation involving inter-related time constants for the growth and adaptation portions of the reflex curve in accordance with a descriptive model suggested by Tietze.

An anechoic chamber and point source design for audiological measurement

A point source in a 6‐ft cubed anechoic space was designed to provide predictable audio sound fields at 1 m without near‐field effects. The chamber was acoustically isolated to permit measurement down to 25 dB SPL in an 812 × 9 × 11foot o.d. enclosure. A control microphone 20 cm from the source maintained a constant SPL at 1 m over the entire frequency range. The presence of a full size human manikin did not affect the sound field at the control microphone. SPL followed inverse square law (± 1 dB) from 10 cm to 1 m from the source over a 200 Hz to l0 kHz frequency range. Eight loudspeakers, mounted behind the upper edge wedges could develop 70 dB SPL quasi‐diffuse noise at the working location.

Exploring azimuth effects with an anthropometric manikin

In these experiments, the effects of sound direction on the eardrum response of an anthropometric manikin (the KEMAR manikin) were investigated. Pure tones and pink noise (analyzed in 1/3-octave bandwidths) over a wide frequency range were used as signals as the manikin rotated 360 degrees with respect to a point source in a anechoic chamber. The simulated eardrum SPL was compared with the averaged human field-to-eardrum data reported by Shaw [J. Acoust. Soc. Am. 56, 1848--1861 (1974)]. It was concluded that the KEMAR manikin can be used up to frequencies of approximately 8.0 kHz, with (1) 1/3-octave pink noise signals to measure a response equivalent to tht obtained by averaging over a number of humans, and (2) pure-tone signals to measure the response equivalent to that of a single human having average head and ear dimensions.

Measurement of head movement during auditory localization

Head movement can have a significant effect on the ability to locate the direction of a sound source. A system has been designed to track the head movement in response to sound originating at different azimuth locations with respect to the head. A videotape record is made of a light approximating a point source carried on a lightweight “beanie” mounted on the listener’s head. Movement of the light is monitored by the video camera and recorded on tape, along with the sound stimulus and information concerning loudspeaker location and time. The horizontal and vertical coordinates of the light-spot image are determined in relation to the video synch pulses defining the field borders. Synch signals are available from a video monitor either in real-time or from tape replay to define each TV frame and horizontal scan line. The circuitry interfaces to a computer programmed to take the information, apply a calibration, and process the data into records of time-varying head position and velocity. Examples of both digital and graphic printouts of head movement are given. The system is capable of expansion to three-axis operation.