Role of the Auditory Efferent System in Auditory Perceptual Learning

The goal of this study is to determine the impact of an auditory training program on the function of the inner ear and auditory brainstem. In normal-hearing individuals, the medial olivocochlear (MOC) branch of the auditory efferent system appears to aid with hearing signals in noise. A previous study in young normal-hearing adults found that auditory training strengthened the function of the MOC system in some participants in a way that coincided with their improvements in perceiving speech sounds in background noise. The MOC function measured at baseline also predicted the amount of success from the auditory training. Although these results are promising, it is not known if they generalize to populations that often have hearing-in-noise problems such as older and hearing-impaired adults.

This study will examine how an auditory training program impacts MOC activity in a group of older adults with normal hearing or mild hearing loss. This is a prospective study utilizing a repeated-measures design. Participants will participate in a computerized auditory training program taking place over 15 weeks. Transient-evoked otoacoustic emissions (TEOAEs) will be used to measure the strength of MOC activity at each visit. Performance on untrained stimuli (words and sentences) will also be measured. A control group (no auditory training) will also be used to establish test-retest reliability for TEOAE measurements and performance on the word and sentence testing. The results of this study may contribute to the improved diagnosis and treatment of hearing-in-noise problems in Veterans and in the civilian population.

This is a single-site study that will take place at the Auditory Research Laboratory, located at the VA Loma Linda Healthcare System (VALLHS) in Loma Linda, California. Veterans and non-Veterans, both males and females, between the ages of 35 and 89 with either normal hearing or mild sensorineural hearing loss will participate. Women and minorities will be encouraged to participate. Up to 200 volunteers will be enrolled in the study. Each eligible participant will participate in a maximum of 14 study visits.

Participants will be randomly assigned a priori to either the experimental group (auditory training) or Control group (no auditory training) using simple random assignment. Because this study will detect whether or not significant changes in MOC activity and speech perception across time occurred as a result of auditory training, the Control group is needed to establish the test-retest reliability of our outcome measures in the absence of any training.

Preliminary analyses of the data showed an association between a measure of speech perception and the strength of the efferent system. To increase statistical power in examination of this association, an additional group (Speech Group) is incorporated that includes subjects that only participate in one session, with only the measurements of speech recognition and medial olivocochlear reflex activity. The Speech Group will be assigned by the investigators.

This study consists of one experiment that will last 3 years total. Each participant in the Experimental and Control groups will participate in 12 study visits, ideally over a 15-week period. However, we will allow for the visits to take place across a 1-year period to account for participants needing to miss or reschedule some visits. We will also allow 2 additional make-up visits for each participant (for a total of 14 visits), should they need to end an experimental session early. All study visits will last between 2-3 hours. Thus, the maximum amount of participation for each participant is 52 hours (14 visits x 3 hours per visit) across a 1-year period.

Standard-of-care screenings and experimental testing will be carried out in a double-walled sound-isolated audiometric chamber adjoined to a single-walled room in the Auditory Research Laboratory, located at the VALLHS. Initial audiometric testing using standard-of-care procedures will be conducted to verify eligibility for the study and will be carried out using standard clinical equipment.

Experimental tests will consist of Transient Evoked Otoacoustic Emissions (TEOAE) testing, word/sentence recognition testing, and an auditory training program (only participants in the Experimental group will undergo the auditory training). For TEOAE testing, the basic task of the participants is similar to TEOAE procedures used clinically to evaluate hearing function objectively. Testing involves listening to sounds presented through earphones while seated comfortably in a sound-treated booth, and remaining alert but quiet in order to successfully measure responses from the cochlea and brainstem. All stimuli will be presented at moderate volumes that are well below sound levels considered hazardous by Occupational Safety and Health Adminstration (OSHA) and NIOSH standards. TEOAE measurements consist of waveforms, which are changes in sound amplitude across time.

Word/sentence testing involves listening to words and sentences presented through earphones while seated in the sound-treated booth. Speech stimuli will be presented in the presence of background noise. Participants make a response about the word(s) they heard. Sounds will be presented at safe and comfortable levels.

For the auditory training program, listeners will be seated comfortably in the sound booth at a workstation with a computer screen, keyboard, and mouse. Sounds will be presented to the participants through insert earphones. Participants will make their responses concerning what they heard by mouse click or keyboard entry. The auditory training program consists of a curriculum of word and sentence presentations in various noise levels, and performance on repeated measurements are tracked throughout the subject's participation in the program.

This is a minimal risk study. The participants will all be healthy adults (other than mild hearing loss in some participants). There are no foreseeable risks involved in these studies beyond those associated with routine audiological practice, such as boredom or fatigue during testing. All sound levels to be used in the study fall below the Damage Risk Criteria established by OSHA for intensity-duration interaction.

Participants will be provided with as many breaks during testing as they or the experimenter feel are helpful to minimize mental fatigue and boredom. Loudness levels of stimuli are carefully controlled, with frequent calibration and monitoring of laboratory equipment. Participant confidentially will be protected by using only participant codes (three numbers) to label data collection sheets and computer data files. All data records will be stored on password-protected computers or as hard copy in locked offices or laboratories. Participant safety and comfort and data collection will be constantly monitored for each participant by the research team member collecting the data for that participant. Overall data collection will be monitored by the Principal Investigator. Following completion of the study, all data will be maintained in accordance with Veterans Health Administration guidelines.

Regarding potential benefits of participating, all participants will receive an up-to-date hearing screening and a further understanding of their own hearing. Participants in the Experimental group may or may not notice an improved ability to hear sounds in background noise after undergoing auditory training. The knowledge gained from this study may also benefit individuals with hearing-in-noise problems by contributing to improved diagnosis and treatment of hearing-in-noise problems in Veterans and in the civilian population.