Speech Processors for Auditory Prostheses

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Principal Investigator	Affiliation	Contract Number	Link
Blake Wilson	RTI	N01-DC8-2105	http://www.rti.org/capr/
Bob Shannon	House Ear Inst.	N01 DC9-2100

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Project Title: Speech Processors for Auditory Prostheses,.August 1997

STATEMENT OF WORK FOR SOLICITATION PURPOSES

1. Background

Research and development on auditory prostheses for deaf individuals is supported by the National Institute on Deafness and Other Communication Disorders (NIDCD). An essential component of all auditory prostheses is the speech processor whose function is to convert the wide bandwidth, large dynamic range electrical signal from a microphone to a signal or set of signals for driving the individual electrical implant stimulators in a manner to optimize recognition of speech and environmental sounds by the implant user.

Considerable progress has been made in understanding the information that is being conveyed to the remaining auditory nerve fibers and the cochlear nucleus during electrical stimulation with electrodes in the scala tympani and on the surface of the cochlear nucleus. Based in part on these findings, there have been significant improvements in speech processors and consequently in speech recognition by deaf implant users. It has been found that many, but not all, multichannel implant patients benefit from non-simultaneous application of stimuli to their different electrodes. Also, some subjects demonstrate improved understanding of speech when activation of their electrodes is accomplished by cycling through them at a high rate, i.e. faster than individual auditory nerve fibers can follow. Another important factor appears to be the loudness growth transfer function in the speech processor. The test score results from many of these research subjects have shown significant increases over scores achieved with their conventional commercial processors even though they have had only a few hours of practice with the experimental processors. In addition, portable digital speech processors have been designed and are being evaluated using some of the new speech processing strategies.

There are several different types of single and multichannel auditory prostheses being used in human subjects. These include both unilateral and bilateral cochlear implants as well as cochlear nucleus implants. Each of these is based on different design philosophies and each has certain advantages/limitations. Since optimal speech processor design depends, among other things, upon both the implanted electrode design and the remaining auditory nervous system of the subject, it is important in designing speech processors to do so for specific implant designs and to test them with a representative cross section of users. At the present time, NIDCD is supporting two different speech processor research contracts to assure access to a sufficient number of subjects with each of the major auditory prosthesis implant designs. Most of this evaluation has been done in low background noise environments. This work needs to be further extended to permit the testing and evaluation of additional speech processing techniques in previously implanted patients under a range of signal-to-noise conditions with emphasis on subjects considered poor users with their commercial speech processors. Continued emphasis also needs to be placed on converting some of the software-based speech processing systems into wearable versions for evaluation of the devices under conditions of "daily living" and the effects of long-term learning.

This request for proposals represents a competitive renewal of on-going research which is being supported by NIDCD. A copy of a bibliography of publications resulting from this research and quarterly progress reports from current research contracts can be obtained, free of charge, by contacting the Neural Prosthesis Program (N.I.H, Federal Bldg., Rm. 8A13, Bethesda, MD, 20892).

2. Objectives

The object of this contract is to design, develop and evaluate both laboratory based and wearable speech processors for use in auditory prostheses.

3. Work to be Performed

Independently, and not as an agent of the Government, the Contractor shall furnish all the necessary services, qualified personnel, material, equipment and facilities, not otherwise provided by the Government as needed to perform the statement of work. The Contractor shall design and implement speech processors and evaluate them in deaf humans with implanted auditory prostheses.

A. Obtain, if not already available, a software controlled, laboratory based, speech processor emulator that can:

1. Control both analog and pulsatile stimulators.

2. Specify stimulus parameters for at least 8 channels for patients with unilateral implants and can simultaneously provide signals to two auditory implants of at least eight channels each for subjects with bilateral auditory prostheses. Such bilateral processing should be able to utilize possible advantages of the extra number of channels and the theoretical reduction in stimulus interaction permitted by bilateral implants.

3. Permit an exploration, in a systematic manner, of a subject's comprehension of presently available auditory test materials with differing stimulus parameters (parametric space).

4. Emulate essentially all of the commercial and experimental speech processing schemes which have been published for use with human subjects.

5. Allow the implementation of new speech processing schemes.

6. Add noise and provide adjustable signal-to-noise ratios with both wide band "white" noise and noise simulating the spectral characteristics of normal environmental noises including human speech babel.

B. Devise and implement speech processing techniques and evaluate them on human subjects with previously implanted auditory prostheses. The subjects chosen should cover the range of speech recognition abilities from poor to outstanding, with emphasis on the poor users, as determined with their commercial speech processors. They should include minorities and women in addition to men. If patients with bilateral implants become available, investigate possible advantages of simultaneous use of bilateral auditory input.

1. Utilize psychophysical and, if appropriate, neurophysiological tests to:

a. Study and minimize undesirable interactions between stimulus parameters.

b. Study and minimize undesirable interactions between activated electrodes.

c. Assess functional auditory system survival and relate it, if possible, to anatomical survival.

2. Under conditions of varying signal-to-noise ratios, determine the relationships between speech processing factors and speech comprehension. Use this information to design improved speech processing strategies.

3. Evaluate the improved speech processing techniques in:

a. Individual subjects compared with their commercial speech processor.

b. Different subjects with both poor and good speech recognition as determined with their commercial speech processors.

4. Attempt to measure factors that might account for variations in subject performance including, when possible, the recording of auditory nerve evoked potentials from unstimulated electrodes.

C. Design and fabricate wearable speech processors which emulate the improved speech processing techniques developed in the above research. They shall:

1. Operate in real time.

2. Be small and light enough to be comfortably carried by the deaf subjects.

3. Have safety features that prevent stimulus levels from reaching harmful levels.

D. Study the effects of learning by utilizing the above developed wearable speech processors in previously implanted subjects and by testing the subjects' speech comprehension periodically over at least a six month period.

E. In the performance of this contract, the Contractor shall coordinate its experimental program through the Project Officer with results of experimental findings developed by other collaborators in the Neural Prosthesis Program. Adjustments and changes so indicated shall be approved in advance by the Project Officer and if necessary, by the Contracting Officer.