Noise Exposure and NIL

Noise Exposure - Unprotected Ears:

Using AFI 48-127 Table 1, every subject will be exposed, open ear, to continuous broadband
noise up to 25% of the allowable daily dose of noise. Ear-specific threshold measurements as
well as OAEs will be collected before and after the noise exposure sessions to measure the
auditory system's response to the noise. Based on the broadband noise used in the experiment,
the maximum effect on human thresholds can be observed at 3000, 4000, and 6000 Hz. Subjects
who do not reach audiometric threshold changes of 10 dB HL or greater at any test frequency
measured approximately 2 minutes post a noise dose will not be qualified to participate in
the experiment. This is to ensure all subjects have similar sensitivities to noise. Any
subject who reached an audiometric threshold change greater than 20 dB HL 2 minutes
post-noise will be removed from the study. A complete post-test audiogram with individual ear
responses will be accomplished before the end of each session. If hearing thresholds are not
within ±5 dB HL of the baseline after 60 minutes of testing, the subject will be told to have
minimal noise exposure overnight and to return the next day for another hearing test.
Sessions involving noise exposure will be separated by at least 72 hours.

Test of Auditory Function and Performance:

Auditory function measurements will be completed using standard audiological tests and
procedures that include: otoscopy, tympanometry, air conduction threshold measurements
(hearing test), and OAE measurements. All measurements will be performed only during subject
qualification, with the exception of the hearing tests and OAE measurements which will
continue to be collected before and after exposures to noise and NIR light. Measurements of
auditory processing will be collected using established batteries that can evaluate processes
such as: loudness scaling and matching, sound lateralization, auditory discrimination,
temporal aspects, auditory performance with competing acoustic signals, and auditory
performance with degraded signals. These types of batteries are administered under headphones
or by loud speakers at comfortable listening levels, similar to average conversational level
and require a behavioral response from the subject (typically, repeating or selecting what
was heard, or answering a question about the signals). The presentation is recorded voice on
a disc or MP3 file, which is presented through a diagnostic audiometer or tablet. These
measurements will be collected pre, during, and post noise exposure.

NIR Light Exposure:

Only subjects in the experimental group will receive exposure to NIR light therapy. The
control group will have a powered-down device placed in the ears for a duration of 180
seconds. NIR light-therapy exposures are administered to each ear individually, for a
duration of 180 seconds per ear. The 180 second NIR light-therapy exposures occur in each of
the 4 sessions. To allow for maximum effectiveness, NIR light exposures will be administered
on a schedule that provides adequate, but not excessive, separation between sessions. Table 2
illustrates the schedule that will be utilized in this study to accommodate the necessary
administration requirements.

Table 2. NIR Exposure Schedule Session Minimum and Maximum Time Allowed Between Exposures

1. First exposure

2. 3-7 days after session 1

3. 18-24 days after session 2

4. 18-24 days after session 3

Inclusion Criteria:

- 18-45 years old, male or female

- Pass hearing exam with a threshold of 15 dB hearing or less, for each ear, at 3000 Hz,
4000 Hz, and 6000 Hz

- Frequencies from 250 Hz to 3 kHz, as well as 8 kHz, must have a threshold of 25 dB HL
or less for each ear

- Normal otoscopic exam, OAEs, and middle ear function as demonstrated by a normal
tympanogram

- Completion of a hearing history questionnaire

Exclusion Criteria:

- Screening hearing test failure

- Pregnant females

- Adults unable to provide consent

- History of significant ear surgery